SPiCESchool of Process instrumentation & Control EducationFrom Indias leading Process Control Enterprise

Yokogawa

GRADUATE TRAINING PROGRAMPROCESS MEASUREMENT AND CONTROL APPLICATION

INTRODUCTION TO YOKOGAWA PCI PRODUCTS FIELDBUS ENGINEERING

YIL TRAINING CENTER

PROCESS MEASUREMENT AND CONTROL APPLICATIONOBJECTIVE DURATION : This course enables participants to learn the terminologies of Instrumentation, measurement techniques and concepts of control system. : 6 Days

COURSE CURRICULUM :

DAY 1 2 3 4 5 6

CONTENTINTRODUCTION & BASICS OF MEASUREMENT CALIBRATION & CONVERSION TABLES LEVEL MEASUREMENT FLOW MEASUREMENT PRESSURE MEASUREMENT TEMPERATURE MEASUREMENT FEEDBACK ,FEED FORWARD AND CASCADE CONTROL TUNING OF CONTROLLER

INTRODUCTION TO YOKOGAWA PCI PRODUCTSOBJECTIVE : This course enables the participant to understand the latest sensor technology for industrial measurement including the recent advances in process instrumentation. : 5 Days

DURATION

COURSE CURRICULUM :

DAY

CONTENTINTRODUCTION TO FIELD INSTRUMENTS

1

EVOLUTION OF PCI PRODUCTS (YOKOGAWA) TRANSMITTERS - EJA , EJX , YTA FLOW METERS VORTEX

2

ULTRASONIC FLOW METERS MAGNETIC FLOW METERS MASS FLOW METERS

3 4 5

RECORDERS / DAQWORKS CONTROLLERS (YS170 / UT SERIES) CONTROLLERS - US1000

FIELDBUS ENGINEERINGOBJECTIVE DURATION : This course is designed to provide participants an overall understanding of Fieldbus Technology and the Asset Management tool. : 4 Days

COURSE CURRICULUM :

DAY1 OFFLINE ENGINEERING ONLINE ENGINEERING 2 DEVICE REGISTRATION

CONTENTINTRODUCTION TO FIELD BUS CONCEPT

OPERATION OF FF SHADOW BLOCKS

3 4

PRM INSTALLATION PRM FEATURES & OPERATION

PROCESS MEASUREMENT AND CONTROL APPLICATION

o INTRODUCTION o CALIBRATION TECHNIQUE o LEVEL MEASUREMENT o FLOW MEASUREMENT o PRESSURE MEASUREMENT o TEMPERATURE MEASUREMENT o CONTROL LOOPS AND TUNING o ALARM ANNUNCIATORS

INTRODUCTION TO INSTRUMENTATIONAUTOMATION: You are well aware that the different Industrial sectors like Information technology, Telecom, Automobiles, Textiles all play a major role in our life. Likewise, Automation is another important core sector, which is virtually controlling our life. Today, automation solutions are required right from agriculture to space technology and Plant Automation has become absolute necessity for the manufacturing / process industries to survive in todays global market. Automation is simply the delegation of human control function to process equipments for increasing productivity, Quality, Cost reduction, Plant equipment safety A CONTROL SYSTEM, which takes cares the various operations involved in a process, in an automated way with minimal human intervention, is generally known as AUTOMATION. CONTROL SYSTEM: A Control system is a combination of various devices that are integrated as a system used to sense, measure, indicate and control the process variables, which in turn controls the process to achieve the desired results. PROCESS CONTROL INSTRUMENTATION As part of a control system various measurements and controls are generally involved in a process, to achieve the desired process conditions. PROCESS CONTROL INSTRUMENTATION

MEASUREMENT When we want to quantify something, Measurement is required. Examples: At what SPEED the train is going?. What is the TEMPERATURE in the furnace? What is the PRESSURE exerted by the System? What is the WEIGHT of the parcel? What is the water LEVEL in the tank? How much water is FLOW ing through the pipe?

CONTROL

Now, these parameters like Pressure, Tempeature, Flow, Level which are measured are called PROCESS VARIABLES

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PROCESS VARIABLES: The most commonly used measurements (Process variables) are: Pressure Temperature Flow Level Speed Weight Humidity Density Vibration Conductivity Ph Current Voltage Power Torque Position

MEASUREMENT

INDICATION What is INDICATION? When the measured value is presented in a readable form, we call that the value of the parameter is INDICATED. As the value changes the indication changes and the earlier readings are lost.

RECORDING What is RECORDING? When the measured value is RECORDED in a readable form, we call that the value of the parameter is RECORDED. As the value changes since the earlier readings are recorded we can refer the previous readings.

MEASUREMENTS: Measurements are made available either in Local OR in RemoteLOCAL

Examples:

PI 18

When it is required to know the Pressure in the pipeline or level in the tank, one has to go to that place of installation (local) to know the values. These types of measurement are known as LOCAL MEASUREMENT.

LI 24 24

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REMOTE: The Parameter to be measured is sensed in the field area and the signal is transmitted to a remote place. (Central Control Room) for readable & control purpose and this type of measurement is known as REMOTE MEASUREMENT. Sitting in Control room, one can know the values. Fig 1 & 2 represents Remote measurement. Examples: FIELD AREA CONTROL ROOM

PS H

FIG. 1ReceiverFT 13FIC 13

Transmitter Primary (sensing) elementFE 13

FIG. 2

Two types of Signals: DIGITAL & ANALOG DIGITAL: ANALOG: The output represents anyone of the two states, that is 0 or 1, ON/OFF, OPEN / CLOSE (FIG. 1) The output is continuous, representing 0 to 100% value of the Measurement (FIG. 2).

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The Plant Instrumentation can be divided as FIELD IINSTRUMENTATION and Control room INSTRUMENTATIION. PLANT INSTRUMENTATION

FIELD

CONTROL ROOM DCS PLC SCADA Industrial PCs Marshalling Racks UPS Control Panel

INSTRUMENTSSensors Pressure Instruments Temperature Instruments Flow Instruments Level Instruments Speed Instruments Density Instruments Weight Instruments Analytical Instruments Control Valves Actuators

OTHER ITEMSLocal Panels Junction Boxes Cable trays Cable duct Cables Impulse Lines SS / Copper tubes

BASICS ON MEASUREMENTUNITS:The measurements made to quantify any thing has to be expressed in UNITS. Example: The The The The The The The SPEED of the train : kilometers per hour. TEMPERATURE in the furnace: Deg. C PRESSURE : psi WEIGHT of the parcel: kgs. LEVEL in the tank: meters AREA of the plot: Sq. Feet FLOW of water in the pipeline: lts/hr.(LPH)

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INDICATION / READING: Examples : Measurements are generally expressed in Percentage (%) Example: The pressure in a chamber is between 0 and 200 psi. psi 0% 10 % 20 % 0 20 40

100%

-

200 TRANSMITTER

PNEUMATIC Output 3 to 15 psi 0.2 to 1 kg/cm2 XR Output 3 psi 6 psi 9 psi 12 psi 15 psi % 0 25 50 75 100L PH

ELECTRONIC Output 4 to 20 mA XR Output 4 mA 8mA 12 mA 16 mA 20 mA % 0 25 50 75 100 Kg/cm2 0 100 200 300 400

0 50 100 150 200

LINEAR AND SQUARE ROOT SCALES: Recorder charts for Pressure, Temperature, Level, Specific Gravity, etc. generally have a linear scale whereas flow charts have a square root scale. This is because the rate of flow is proportional to the sq. Root of the differential head. Whereas linear charts have a uniform calibration, Sq.root charts have a sq. root calibration as shown in the figure below. It will be noted that 50% of the flow is actually marked on 25% of the linear chart, 70% of the flow near the 50% of linear scale and 90% of the flow very near 80% of the linear scale.

0

1

2

3

LINEAR SCALE

4

5

6

7

8

9

10

02

3

4

5

SQ. ROOT SCALE

6

7

8

9

10 Page 5 of 11

Consequently flow scales are cramped at the bottom (near zero) and expanded near maximum. Accuracy of flow meter reading against such a scale can be had only above 25% of the linear scale. LINEAR AND SQUARE ROOT CALIBRATION TABLE: TRANSMITTER OUTPUT mA psi Kg/ cm2 0.2 0.4 0.6 0.8 1 READING LINEAR SCALE SQUARE ROOT SCALE 0% 50% 70.71% 86.60% 100% MEASURED VALUE FLOW (m3 / Hr.)

4 8 12 16 20

3 6 9 12 15

0% 25% 50% 75% 100%

0 100 200 300 400

BASIC DELINITIONS

ELEVATED ZERO: A range where the zero value of the measured signal is greater than the lower range value. Zero lies between LRV and URV Range: (-) 25 to 100

(-)25 LRVSUPPRESSED ZERO:

0

100 URV

A range where the zero value of the measured signal is less than the lower range value. Zero does not appear in the scale. Page 6 of 11

Example: 20 to 100

20Typical Ranges Name Range Lower Range Value

100Upper range Value +100 +100 Span

ILLUSTRATIONS OF THE USE OF RANGE AND SPAN TERMINOLOGY:

0 20

+100 +100

Suppressed Zero Range

0 to 100 0 20 to 100 20

100 80

-25

0

+100 Elevated Zero -25 to Range +100 0

-25

+100

125

-100

Elevated Zero -100 to 0 -100 Range

0

100

ILLUSTRATIONS OF THE USE OF TERMS MEASURED VARIABLE & MEASURED SIGNAL: TYPICAL RANGES THERMOCOUPLE 0 2000 F TYPE K T/C -0.68 +44.91mV TYPE OF RANGE RANGE Measured 0 to Variable 2000F Measured -0.68 to Signal +44.91mV LOWER RANGE VALUE 0 F -0.68mV UPPER RANGE VALUE 2000 F SPAN 2000 F

+44.91mV 45.59mV 10,000Ib/h 100in H2O 500 rpm 5V 10,000 Ib/h 100in H2O 500 rpm 5V

FLOWMETER 0 10,000Ib/h 0 100in H2O

Measured 0 to 0 Ib/h Variable 10,000Ib/h Measured 0 to 100 0in H2O Signal in H2O Measured 0 to Variable rpm Measured 0 Signal 500 0 rpm 0V

TACHOMETER 0 500 rpm 0 5V

to 5V

is defined as the closeness with which the reading approaches an ACCURACY accepted standard value or true value. Accuracy is often quoted as a percentage of the full scale value. Ex : accuracy : +/- 1 % fsd ERROR - The algebraic difference between the indicated and the true value of the measured signal.

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ERROR = Indicated (measured) value True value. LAG : When the quantity being measured changes, a certain time might have elapsed before the measuring instrument responds to the change. It is said to show LAG.

DEAD SPACE / THRESHOLD: When the quantity being measured is gradually increased from zero, a certain minimum level might have reached before the instrument responds and gives a detectable reading. This is called the threshold. It is just a dead space that happens to occur when the Instrument is used from a zero value. For example, a pressure gauge might not respond until the pressure has risen to some value. This may be due to friction and other factors of the gauge. . REPEATABILITY: The repeatability of an instrument is its ability to display the same reading for repeated applications of the same value of the quantity being measured. OR The closeness of agreement among a number of consecutive measurements of the output for the same value of the input under the same operating approaching from the same direction, for full range traverses. SENSITIVITY: The ratio of a change in output magnitude to the change of input which causes it after the steady state has been reached. RESOLUTION : The least interval between two adjacent discrete details, which can be distinguished one from the other.

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BASIS ON CONTROLMANUAL PERCEPTION & CONTROL

MANUAL FEEDBACK CONTROL WITH SENSOR & INDICATOR

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SKETCH FOR AUTOMATIC CLOSED LOOP FEEDBACK CONTROL

MEASUREMENTS & CONTROLS:

A control loop can broadly be divided into four functional categories: to sense or detect the variable to be measured transforms the detected ( sensed )signal to an interpretable stage where it can either be read or used for further control applications . to compare the measured signal with the desired conditions and perform the necessary. Carries out the corrections required so that the variable is controlled within the specified limits.

1 2

Primary Element

Secondary Element Manipulating Element gPrimary Final Control

3

4

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CONTROLLER: What is Control? The Process of achieving the actual measurement at a predetermined DESIRED VALUE is known as the CONTROL of that variable. Example: The flow of water through a pipe line has to be controlled at a particular flow, say - 40 litres / hr; We know that we want to control the flow at a specific value. (SET POINT) We have to know how much water is flowing. So, we have to measure the flow (MEASUREMENT). The difference is known as Error. Based on the error, a suitable OUTPUT from the controller goes to the valve to regulate in such a way to get the desired flow.

CONTROLLER BLOCK DIAGRAM: SET POINT OUTPUT

FEED FORWARD CONTROL & FEEDBACK CONTROL Feed forward control involves making an estimate of the quantity of action necessary to accomplish a desired objective. Its basis is in prediction. There is NO feedback. Eg : Washing Machine In Feedback control, measurement (MV) of the variable to be controlled is compared with a reference point (SP). If the difference or error exits between the actual measurement and the set point, the automatic controller takes the necessary action by sending the Increased / decreased output (O/P) to the final control element to achieve the desired control.

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CALIBRATION PROCEDURES FOR CONTROL & INSTRUMENTATIONCALIBRATION Calibration refers to the process of determining the relation between the output (or response) of a measuring instrument and the value of the input quantity or attribute, a measurement standard. Calibration is often regarded as the process of adjusting the output or indication on a measurement instrument to agree with value of the applied standard, within a specified accuracy " GENERAL INSTRUCTIONS FOR CALIBRATION Before calibrating the instrument, o Check for any Physical Damage to the Instrument o Check whether the Instrument is working or not in the following manner For Digital Instruments, switch on the power. For Analog Instruments, see the pointer deflection. o Clean the switch contacts, Potentiometers, if any, by cleaning agent. o Give at least half an hour warm-up time for all Power-On Instruments and for Regulated Power Supply before starting Calibration. o For Analog Instruments ensure Mechanical zero before starting the Calibration. o Parallax error is to be avoided. o Instruments used, as masters for Calibration must be calibrated from Govt. approved Laboratory. " ENVIRONMENTAL CONDITIONS For Mechanical Instruments For Electrical Instruments " CALIBRATION POINTS o o o o The instruments should be Calibrated for all ranges. Ranges which cannot be Calibrated or for which accuracy of the instrument is not as per requirement must be indicated on the instrument itself as well in records. For Analog Instruments, Calibration of an Instrument should be performed at 25%, 50%, 75% and 100% of the range being calibrated, Readings should be recorded at same point while increasing and decreasing. For Digital Instruments, Calibration should be performed at 25%, 50%, 75%, 90% of the range being calibrated. 20 +/- 2.5C 25 +/- 2.5CTEMPERATURE RELATIVE HUMIDITY

35 to 65 % 35 to 65 %

Calibration area should be adequately free from dust, shocks and vibrations

" TABLE FOR SELECTION OF MASTER (REFERENCE STANDARD) FOR CALIBRATION BASED ON ACCURACY DESIREDDESIRED % ACCURACY OF THE INSTRUMENT RANGE TO BE CALIBRATED MIN. RECOMMENDED ACCURACY OF REFERENCE STANDARD

0.05% 0.01% 0.1% 0.02% 0.2% 0.04% 0.5% 0.1% 1.0% 0.2% 2.5% 0.3% Accuracy of Master Instrument required for Calibrating Mechanical Instruments is recommended to be 10 times higher than the accuracy desired Accuracy. Page 1 of 9

" TRACEABLITY CHAINNPL NPL National Physical Laboratory DGSTQC Directorate General of Standardization, Testing and Quality Certification

DGSTQC

GOVT. APPROVED

INDUSTRY /USER

" TECHNICAL INFORMATION 1. DESCRIPTION OF THE MEASUREMENT PROCESS Standards used along with traceability information. Brief Description of measurement method (could include measurement scheme, measurement time frame etc.) State the number of measurement made. Explain how the data were analyzed to obtain measured values Include an explanation of equations, algorithms or formula used. Definition of acronyms used in report. 2. REPORTING MEASUREMENT RESULTS Report the measured values for the measurement. Where item is found to be out of tolerance, both the incoming and outgoing data should be reported. Measurement uncertainties Influence quantities - Quantities which are not the subject of measurement but which influences the measured values Example 1.Frequency of AC Voltage 2. Temperature & Resistance 3. Temperature & length

3. TEST CONDITIONS LABORATORY ENVIRONMENTAL CONDITIONS Temperature Humidity Pressure ABNORMAL CONDITIONS Stability Erratic readings Excessive wear Noticeable physical change Repairs performed on the calibrated item

4. PRESENTING THE DATA Units of measurement should be stated along with associated measured values Units of Uncertainty Uncertainty stated in the same units as the measured value 0.1% * 1000 PPM USE % 0.01% * 100 PPM USE% 0.001% * 10 PPM USE PPM 0.0001% * 1 PPM USE PPM Tables Graphs

Page 2 of 9

5. TRACEABILITY CONTENTS OF CERTIFICATE OF CALIBRATION 1. Calibration Organization. 2. Certificate Title 3. Item Identification 4. Requester 5. Calibration Due 6. Due Date 7. Certificate Number 8. Signature 6. MAINTAINING RECORDS FOR THE EQUIPMENTS Make Type Serial Number or other ID Measurement Capability Calibration Certificates Date of Calibration Calibration Results After and, if necessary, before Recalibration Date Identification of Calibration Procedure Limits of permissible error Source of Calibration Traceability Environmental conditions during Calibration Uncertainties Details of servicing, Adjustment, repairs or modifications Any limitations in use Persons performing Calibration Persons responsible for ensuring correctness Unique ID of Calibration Report / certificate Retain Records

7. NON CONFORMING MEASURING Suffered Damage. Mishandled or Overloaded. Shows Malfunction. Calibration Overdue. Such Equipment shall not returned to service until reasons for nonconformity have been eliminated and again calibrated Calibration Level Intervals of Calibration

8. SEALING FOR INTEGRITY Access to Adjustable Devices on Measuring Equipment whose setting affects the performance shall be sealed to prevent tampering by unauthorized personnel. Sub-Contracting or use of outside products and services Storage and Handling

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9. CALIBRATION LAB EVALUATION MAJOR POINTS Adequate Records Adequate Recall system Proper Cal. Intervals Proper Labeling Proper Procedures Traceability Adequacy of Standards Cal. Quantity Adequate Environmental Control 10. LABELLING Label shall include Date or Usage time due for Recal ID of the Person who performed the cal ID of the Agency Visibility Cal labels 11. CERTIFICATE OF CALIBRATION Identifies the item being Calibrated and the specification used for Calibration, includes a Traceability statement, and certifies that the calibration was performed. " CALIBRATION PROCEDURE FOR PRESSURE INSTRUMENTS LIKE PRESSURE & DP TRANSMITTERS, PRESSURE GAUGES, TRANSMITTERS, ETC. VISUAL INSPECTION For any type of Physical Damage LEAK TEST Apply full-scale pressure and check the leakage if any in the external lines and fittings. EXERCISE MOVEMENT Three pressure cycles should be applied to the uuc to exercise the movement DATA RECORDING Appropriate pressure will be applied to the UUC and readings will be recorded. Calibrate by starting at zero and continue applying appropriate pressure increments to full range and back to zero. " CALIBRATION PROCEDURE FOR RTD/ T/ C Read the temp. Range and select the set temp. at 10%, 50% & 90% of FS. Adjust the temp. Control in the oil bath at the temp. Corresponding to 10% of FS Allow the oil bath to stabilize for 30 minutes. Dip the RTD Thermocouple into the oil bath and connect it to the multimeter. Record the corresponding temp. The measured value as indicated value and set temp. In the oil bath as true value. Repeat the steps no.2 to no.5 for other set temp. LEVEL

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" CALIBRATION PROCEDURE FOR TEMP. INDICATORS & TRANSDUCERS Feed 0 mV to the UUC (IUC) and observe the display. Find out the corresponding mV from IPTS chart for the observed temperature (RT) Select the temperature at 10%, 50% and 90% of FS and take the corresponding mV. Subtract the mV as taken in step 2 from the mV taken from step 3 Feed the mV (obtained from step 4) and observe the temp. In the indicator. Record the display in the temp. Indicator as indicated value and the selected temperature as the true value. UUC IUC IPTS UNIT UNDER CALIBRATION INSTRUMENT UNDER CALIBRATION INTERNATIONAL PRACTICAL TEMP. SCALE.

NOTE:

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CALIBRATIONCONVERSION : (GENERAL ENGG. UNITS)

Refer and use the conversion table Examples: 1) Convert 1000 mm into inches Ans: 1000 x 0.03937 = 39.37 inches 2) Convert 500 litres into gallons (UK) Ans: 500 x 0.22009 = 110.045 gallons (UK) 3) Convert 75 pounds into kilograms Ans: 75 x .4536 = 34.02 kgs 4) Convert 150 kgs into lbs Ans: 150 x 2.20462 = 330.693 lbs 5) Convert 175 Cubicfeet into Cubic mtrs. Ans: 175 x 0.02832 = 4.956 Cubic mtrs. 6) Convert 150 Cubic inches into Cubic centimeters Ans: 150 x 16.3871 = 2458.065 Cubic cm 7) Convert 45 Kg/cm2 into psi Ans: 45 x 14.22 = 639.9 psi 8)Convert 220 inches of water column into mmHg Ans: 220 x 1.867 = 410.74 mmHg 9) Convert 175 m3/Hr into l/Hr. Ans: 175 x 1000 = 175000l/Hr. 10) Convert 120 l/Hr. into m3/min. Ans: 120 x 16.67 x 10 - 6 = 0.0020004 m3/min

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PROBLEM 1 :

Arrange the following in order from Highest to the lowest FLOW: a) 10 gpm b) 10 l/min c) 10 l/Hr d) 10 Cfh e) 10 Cfm f) 10 m3 / min g) 10 m3 / Hr.PROBLEM 2 :

Arrange the following in order from lowest to the highest PRESSURE: a) 2 Kg/cm2 b) 2 Bar c) 14.7 psig d) 500 mmHg e) 1000 in H2O f) 2000 mmH20 g) 300 in Hg ANSWERS: PROBLEM 1 : ( ANSWER ) f , e , g , a , b , d , c

Arrange the following in order from Highest to the lowest FLOW: a) 10 gpm b) 10 l/min c) 10 l/Hr d) 10 Cfh e) 10 Cfm f) 10 m3 / min g) 10 m3 / Hr 10 gpm 10 x 0.264 = 2.64 gpm 10 x 0.0044 = 0.044 gpm 10 x 0.1247 = 1.247 gpm 10 x 7.481 = 74.81 gpm 10 x 264.2 = 2642 gpm 10 x 4.403 = 44.03 gpm

PROBLEM 2 : ( ANSWER ) f , d , c , a , b , e , g Arrange the following in order from lowest to the highest PRESSURE: a) 2 Kg/cm2 2 kg / cm2 b) 2 Bar 2 x 1.02 = 2.04 kg/cm2 c) 14.7 psig 14.7 x 0.07031 = 1.033 kg/cm2 d) 500 mmHg 500 x 1.36 x 10-3 = 0.68 kg/cm2 e) 1000 in H2O 1000 x 2.538 x 10-3 = 2.538 kg/cm2 f) 2000 mmH20 2 x 0.0999 = 0.1998 kg/cm2 g) 300 in Hg 300 x 25.39998 x 1.36 x 10-3 = 10.363 kg/cm2

Page 7 of 9

Refer and use the conversion table:

Temperature conversion Fahrenheit AND CentigradeC = ( F 32 ) x 5/9 F = ( C x 9/5 ) + 32 Examples: Convert 176 deg F into deg C C = ( 149 32 ) x 5/9 = 117x 5/9 = 65 Convert 46 deg C into deg F F = ( 46 x 9/5 ) +32 = ( 9.2 x 9 ) + 32 = 82.8 + 32 = 114.8

Refer and use the conversion table: PAGE 5 OF 33 F 338 * C 640.4 170.44

Temperature Conversion

( Thermocouple )

T / C - TYPE K ( Ni Cr / Ni Al ) ( Chromel Alumel ) Consider the room temp as 32 0 C Use the table For 320C . 1.285 mV Assume you are measuring the temp. of the bath and the indicator shows 100 0 C. But when you measure directly the mV across the T / C head, you will get 2.810 mV Use the table For 1000 C. 4.095 2.810 + 1.285 4.095

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TEMPERATURE CONVERSION ( THERMOCOUPLE ) T / C - TYPE K ( Ni Cr / Ni Al ) ( Chromel Alumel )0

Consider the room temp as 32

C

Assume you are measuring the temp. of the bath and the indicator shows 150 0 C. But when you measure directly the mV across the T / C head, How much it will show ? Ans : 6.137 1.285 4.852 TEMPERATURE CONVERSION ( R T D ) Pt 100 .. The Resistance is 100 OHMS for 0 Use the table Find out the resistance value for 65 Ans : 125.15 or 125.16 Find out the temperature if the resistance value is 112.735 Ans : 330 0 0

C

C

C

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LEVEL MEASUREMENTINDUSTRIAL LEVEL MEASUREMENTThe Vast amount of water used by industry, let alone all the solvents, chemicals, and other liquids that are necessary for material processing, make the measurement of liquid level essential to modern manufacturing. There are two ways of measuring level: directly by using the varying level of the liquid as a means of obtaining the measurement; and indirectly, by using a variable, which change with the liquid level, to actuate the measuring mechanism.INDUSTRIAL LEVEL MEASUREMENTS

MEASUREMENT METHODS

DIRECT METHOD

INDIRECT METHOD

VISUAL LEVEL SENSOR

FLOAT TYPE LEVEL SENSOR

BUOYANT FORCE LEVEL MEASUREMENT

HEAD PRESSURE MEASUREMENT

ELECTRICAL LEVEL MEASUREMENT

DIP STICK SIGHT GLASS GAUGE GLASS

DISPLACEMENT TYPE LEVEL SENSOR

1. GUAGE PRESSURE MEASUREMENT 2. AIR BUBBLE PURGE SYSTEM 3. DIFFERENTIAL PRESSURE MEASUREMENT

1. CAPACITANCE 2. CONDUCTIVITY 3. SONIC/ ULTRASONIC 4. RADAR

DIRECT LIQUID LEVEL MEASUREMENT

FIG -1 A bob weight and measuring tape provide measurement The most simple and direct method of measuring liquid level

Dip stick level

BOB AND TAPE The simplest of the direct devices for liquid level measurement is the bob and tape (fig.1). All you need is a bob (or weight) suspended from a tape marked in feet and inches. The bob is lowered to the bottom of the vessel containing the liquid, and the level is determined by noting the point on the tape reached by the liquid. The actual reading is made after the tape is removed from the vessel. Obviously this method isnt suited to continuous measurement.

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HIGH PRESSURE GAUGE GLASS (REFLEX GLASS)SIGHT GLASS Another direct means of liquid level measurement is the sight glass (Fig 2). This consists of a graduated glass Tube mounted on the side of the vessel. As the level of the liquid in the vessel changes, so does the level of the liquid in the glass tube. Measurement is a simple matter of reading the position of liquid level on the scale of the sight glass tube.

FIG -2 As the level of the liquid in the vessel rises or falls, so does the level of the liquid in the sight glass.GROOVES

REFLUX GLASS

FLOATS There are many kinds of float-operated mechanisms for continuous direct liquid level measurement. The Primary device is a float that by reason of its buoyancy will follow the changing level of the liquid, and a mechanism that will transfer the float action to a pointer (Fig 3). The float most familiar to you is the hollow metal sphere; but cylinder-shaped ceramic floats and disc-shaped floats of synthetic materials are also used. The float is usually attached to a cable, which around a pulley or drum to which the indicating pointer is attached. The movement of the float is thus transferred to the pointer, which indicates the liquid level on an appropriate scale.

FIG -3 The buoyancy of the float permits it to be immersed in the liquid, and its movement is transmitted to the indicator as it follows the changing liquid level.

In another kind of float-operated instrument, the float is attached to a shaft, which transfers the motion of the float to an indicator (Fig. 4). This type doesnt permit a wide range of level measurement, but it does have mechanical advantages that make it excellent for control and transmitter application.

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FIG -4 When the level of the liquid is low, the ball float will be at position A. As the tank fills, the flow rises with the level of the liquid to position B and its movement rotates the shaft which operates the pointer.

FIG- 5 Float cable weight level indicator arrangement

Another variation uses the float to move a magnet (Fig. 6). As this magnet moves, it attracts a following magnet connected to the indicator, thus providing a reading of liquid level measurement.FIG 6 The doughnut-shaped float with magnets in it rises and falls with the level of liquid. The follower magnet, suspended by cable in the guide tube, rises and falls to maintain a corresponding position with the float, and thus moves the cable to the indicator.

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FIG- 7 Magnetic float devices The magnetic float sensor may be used to determine the level of single material in the vessel or to determine the position of an interface between two materials of different densities. For example oil will float on top of water. If oil and water were both in this vessel the float could be constructed so that it would sink in oil and float on the water.

FIG 8 Magnetic type float Devices

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The displacer (Fig. 9) is similar in action to the buoyant float described above, with the exception that its movement is more restricted. With changes in liquid level, more or less of the displacer is covered by the liquid. The more the displacer is submerged, the greater is the force created by the displacer because of its buoyancy. This force transferred through a twisting or bending shaft to a pneumatic or Electronic system. For every new liquid level position, there is a new force on the shaft, causing it to assume a new position. The pneumatic or Electronic system is so arranged that for each new shaft position there is a new signal or indication. The displacer float has the advantage of being more sensitive to small level changes than the buoyant float and less subject to mechanical friction.

FIG 9 In The lower drawing the displacer, which weighs 5 lbs., weighs only 2 lbs. When the water level is at 7 inches, the changes in weight are converted into Torque (See upper illustration). Which operates the pneumatic system to provide readings on the indicator. (Mason- Neilan Div of Worthington Corp.)

FIG- 10 Displacement Level Sensor

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UNDERSTANDING OF BUOYANCY AND DISPLACER FOR INDIRECT LEVEL MEASUREMENTDISPLACEMENT DEVICES The displacement type level devices are commonly used for continuous level measurement. It works on the buoyancy principle of Archimedes, which states that a body immersed in a liquid will be buoyed up a force equal to the weight of the liquid displaced. The displacer body has a cylindrical shape. As a result for each equal increment of submersion depth, an equal increment of buoyancy change will result. This gives a linear, proportional relationship, which is desirable. The effects of buoyancy are illustrated in the fig 11. Although the vessels shown are open in the atmosphere the principle desired applies to the closed tank as well. The displacer is suspended from a scale that indicates its weight at various depths of immersion. In the first figure 11 A the displacer is completely out of the liquid and the scale supports its full weight. As the scale indicates, it weighs 10 kg when suspended in air. When the level of the tank has risen to immerse about half the displacer, the weight of the displacer is approximately 6 kg. The displacers loss in weight is equal to the weight of the volume of the liquid displaced. As the water increases to fully immerse the displacer. The weight of the displacer decreases, the displacer now weighs approximately 2 kg. So, when the water level changes from 0 to 100%, the weight of the displacer also changes proportionally. BOUYANCY EFFECT ON THE DISPLACER Two important points to be considered here are: 1. When the liquid level is lowered to completely uncover the displacer, the displacer can no longer measure level. Any changes in level below the lower end of the displacer will not be measured. 2. The same is true when the liquid level rises to the top of the displacer. Then, any changes in liquid level above the top of the displacer will not be detected. The main difference between a displacer and the float operated device are: The displacer movement is very little compared to the float which rises or falls as per the level. Therefore the displacer loses weight and the float gains in height as the level rises in the tank. The displacer can also be used for interface level measurement whereas float can only be used for measuring the level of liquids. When the displacer is attached to a torque tube by linkage the equivalent torque variations due to the buoyancy effect on the displacer operates a pneumatic or Electronic Transducer / Transmitter. This is the normal transmission of level in closed process vessels, distillation columns, intermediate storage tanks etc.

FIG- 11

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INDIRECT LIQUID LEVEL MEASUREMENT

There are several types of indirect level measuring devices that are operated by Pressure. Any rise in the level causes an increase of pressure, which can be measure by the gauge. The gauge scale is marked in units of level measurement (feet or inches).FIG- 12 B Liquid naturally increases. This

FIG- 12 A As the tank fills, the pressure of the

Hydrostatic level measurement in Increase of pressure can be read on the Gauge in feet and inches of level.

an open tank

FIG- 12 C Closed tank level measurement

FIG- 12 D The pressure of air in the air trap is Expressed on the scale in units of level

If the nature of the liquid prevents its being allowed to enter the pressure gauge, a transmitting fluid (such as air, which is the cheapest and handiest) must be used between the liquid and the gauge. The air trap and the diaphragm box provide a means of accomplishing this. The air trap consists of a box, which is lowered into the liquid (Fig.12 D). As the liquid rises, the pressure on the air trapped in the box increases. This air pressure is piped through tubing to the pressure gauge, which has a scale on which the level can be read.The diaphragm box (Fig 13), like the air trap, transmits air pressure to a gauge, but in this case the air is trapped inside it by a flexible diaphragm covering the bottom of then box. As the level of the liquid rises, the pressure on the diaphragm increases. This pressure acts on the air in the closed system and is piped to the pressure gauge where a reading can be taken.FIG- 13: Deflection of the flexible diaphragm by compression, as the liquid level rises, causes the gauge to respond.

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AIR BUBBLER SYSTEM

FIG- 14 Air Bubbler System of Level Measurement

The Air bubbler system is a system of indirect level measurement especially suitable for liquids that are corrosive, viscous, or contain suspended solids. BUBBLER TYPE LEVEL MEASUREMENT

FIG- 15 The air pressure to the bubbler pipe is minutely in excess of the liquid pressure in the vessel, so that the air pressure indicated is a measure of the level in the tank

The pressure caused by the liquid column is used in the bubbler method of level measurement (Fig.15). A pipe is installed vertically in the vessel with its open end at the zero level. The other end of the pipe is connected to a regulated air supply and to a pressure gauge. To make a level measurement the air supply is adjusted so that the pressure is slightly higher than the pressure due to the height of the liquid. This is accomplished by regulating the air pressure until bubbles can be seen slowly leaving the open end of the pipe. The gauge then measures the air pressure needed to overcome the pressure of the liquid. The gauge is calibrated in feet or inches of level. The methods described above can only be used when the vessel containing the liquid is open to the atmosphere. When the liquid is in a pressure vessel, the liquid column pressure cant be used unless the vessel pressure is balanced out. This is done through the use of differential pressure meters (Fig. 16). Connections are made to the vessel at top and bottom, and to the two column of the differential pressure meter. The top connection is made to the low made to the low pressure column of the meter, and the bottom connection to the high pressure column. In this way the pressure in the vessel is balanced out, since it is fed both column of the meter. The difference in pressure detected by the meter will be due then only to the changing level of the liquid.FIG- 16 When the liquid is in a closed vessel, level can be measured using a differential pressure manometer.

--------------------------------------------------------------------------------------------------------------------Page 8 of 24

Liquid level can be measured using radioactivity or ultrasonic. For continuous level measurement by radioactivity, one or more radioactive source are placed on one side of a vessel with a pick-up on other side (Fig. 17). As the level of the liquid changes, it absorbs more or less of the radioactive energy received by the pick-up, which is a special electronic amplifier designed to produce enough electrical meter. The meter scale is marked in level units-inches or feet.

FIG- 17 Radioactive system Measurement

of

Level

The ultrasonic method operates on the sonar principle (Fig. 18). Sound waves are sent to the surface of the liquid and are reflected back to the receiving unit. Changes in level are accurately measured by detecting the time it takes for the waves to travel to the surface and back to the receiver. The longer the time required the further away is the liquid surface, providing a measurement of how much the level has changed. These systems have been described very simply here. Actually they are highly complicated in both design and installation. These systems have been described very simply here. Actually they are highly complicated in both design and installation.

FIG- 18 Sound waves reflected back from the surface of the liquid to the receiving unit can provide an accurate measurement of liquid level.

Another method of determining the level of liquid materials is to weigh the entire vessel, since the weight changes as the level of the material varies. The vessel may be weighed on mechanical scale (Fig.19); or it may be weighed electrically using load cells (Fig.20). Load Cells are Specially constructed mechanical units containing strain gauges, which provide a measurable electrical output proportional to the stress applied by the weight of the vessel on the load Cells. As the pressure on the cell due to the weight of the vessel changes, the electrical resistance of the strain gauge changes. The strain gauge is connected into a bridge circuit containing an electrical meter graduated in unit of level measurement. It should be noted that the weighing method is accurate only if the density and particle size of the substance being weighed are uniform and the moisture content remains constant. The change in weight must be due entirely to the change in level.

FIG- 19 Scale on which the vessel and its Liquid content weighed mechanically

FIG- 20 Vessel weighed electrically using load cells

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LEVEL MEASUREMENT BY D.P. TRANSMITTERS

To determine the level of a liquid in an open tank, connect the high side of the Transmitter to a tap at the bottom of the tank. Vent the low side of the transmitter to the atmosphere. The pressure represents the height of the liquid in the tank multiplied by the specific gravity of the liquid; therefore, the output of the transmitter will be proportional to the liquid level above the transmitter. If the tank is located above the transmitter, the zero must be readjusted to elevate the range. To determine the liquid level in a closed tank, steps must be taken to compensate for tank pressure generated above the top of the liquid and the top of the tank. This is accomplished by placing a tap at the top of the tank and connecting it to the low side of the transmitter. When this has been done, the differential pressure measured by the Transmitter is proportional to the height of the liquid in the tank multiplied by the specific gravity of the liquid. If the liquid has a vapor that could condense in the piping connected to the top of the tank, the piping should be filled with the measured liquid. This will exert a head pressure on the low side of the transmitter and must be zeroed out. D.P. Transmitter with process connection for clean liquids

FIG- 21 DP Transmitters

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THREE APPLICATIONS OF LIQUID LEVEL MEASUREMENT WITH DP TRANSMITTERAPPLICATION 1 LIQUID LEVEL IN OPEN TANKSPAN = H1x G1, in inches w.g. if H1 is in inches G1= specific gravity of the process liquid Lower Range Value = (H2 x G1), in inches w.g. if H2 is in inches Upper Range Value = Lower Range Value + Span

FIG -22 APPLICATION 2 LIQUID LEVEL IN CLOSED TANK WITHOUT CONDENSABLE VAPOURSSPAN = H1x G1, in inches w.g. if H1 is in inches G1= specific gravity of the process liquid Lower Range Value = (H2 x G1), in inches w.g. if H2 is in inches Upper Range Value = Lower Range Value + Span

FIG -23 APPLICATION 3 LIQUID LEVEL IN CLOSED TANK WITH CONDENSABLE VAPOURS

SPAN = H1x G1, in inches w.g. if H1 is in inches Lower Range Value = (H2 x G1) (H4 x Gw), in inches w.g. if H2 & H4 is in inches Upper Range Value = Lower Range Value + Span G1= specific gravity of the process liquid Gw= specific gravity of liquid in wet leg

FIG -24

--------------------------------------------------------------------------------------------------------------------Page 11 of 24

ZERO SUPPRESSION/ ZERO ELEVATION TECHNIQUES FOR D.P. TYPE LEVEL MEASUREMENTS1. ZERO SUPPRESSION Adjusting the Zero Output Signal to produce to desired measurement. Usually used in Level Measurement to Counteract the Zero Elevation caused by a Wet leg. 2. ZERO ELEVATION Adjusting the Zero Output Signal to raise the Zero to a higher starting point. Usually used in Level Measurement for starting measurement above the Vessel Connection Point.

CALIBRATION POINTS TO BE NOTED FOR LEVEL MEASUREMENTA- VENTED / OPEN TANK B- PRESSURISED CLOSE TANK

CALIBRATION POINTS TO BE NOTED FOR LEVEL MEASUREMENT WITH DIAPHRAGM & REMOTE SEAL TYPE TRANSMITTERA- VENTED / OPEN TANK B- VENTED / OPEN TANK

CALIBRATION POINTS TO BE NOTED FOR LEVEL MEASUREMENT WITH DIAPHRAGM & REMOTE SEAL TYPE TRANSMITTERA- VENTED / OPEN TANK B- VENTED / OPEN TANK

--------------------------------------------------------------------------------------------------------------------Page 12 of 24

CALIBRATION POINTS TO BE NOTED FOR LEVEL MEASUREMENT WITH DIAPHRAGM & REMOTE SEAL TYPE TRANSMITTERA- PRESSURISED CLOSE TANK B- PRESSURISED CLOSE TANK

FIG- 31

FIG- 32

CALIBRATION POINTS TO BE NOTED FOR LEVEL MEASUREMENT WITH DIAPHRAGM & REMOTE SEAL TYPE TRANSMITTER

FIG- 33

ELECTRICAL / ELECTRONIC METHODS OF LEVEL MEASUREMENTA) CONTINUOUS LEVEL MEASUREMENT With continuous measurement the level is detected and converted into an Electronic / Pneumatic Signal. Continuous measurements can be carried for all liquid and solids. Capacitance, hydrostatic, pulse-echo (Ultrasonic Type), pulse-radar and electromechanical principles as well as pressure measuring sensors can be used. B) LEVEL DETECTION FOR LEVEL SWITCHING & OVERFILL PROTECTION. Level can be detected at fixed points and converted into switched outputs Level detection can be done for all liquids and solids. This type of level switches work on capacitance, microwave, radioactive, vibration and conductive principles. The switched output can either be used for stopping and starting filling systems (Conveyor belts, pumps, pneumatic conveyors) or for overfill protection. --------------------------------------------------------------------------------------------------------------------Page 13 of 24

SUMMARY OF BASIC ELECTRICAL / ELECTRONIC / LEVEL MEASURING PRINCIPLES 1) Capacitance Type Level Measurement. 2) Pulse-Echo or Ultrasonic Type Measurement 3) Antenna or Radar Type Level Measurement. 4) Microwave Type Detection. 5) Electro-mechanical Type Level Detection. 6) Vibration Level Switch. 7) Conductive Level Switch. 1. CAPACITANCE TYPE LEVEL MEASUREMENT # MEASURING PRINCIPLE The metal vessel wall & the measuring electrode forms a capacitor. The product acts as the dielectric and changes the capacitance as the level changes. An oscillator in the housing of the electrode converts the capacitance value into a level proportional DC current or a switched output .This universal measuring principle is used for continuous level Measurement and solids- even under arduous conditions.

A FIG- 34

B

C

D

# APPLICATIONS OF CAPACITANCE LEVEL MEASUREMENT 1. Capacitance type level measurement can be used for continuous level measurement or Hi Lo level switching for all products including solids. 2. One of the unique capabilities is to indicate the interface between two immiscible liquids, each having a different dielectric const. Oil/water interface is a common application. # LIMITATIONS 1. Calibration may be time consuming. 2. Affected by change in dielectric constant and temperature of the material and thus requires temperature compensation. 3. Conductive residue coating will affect performance. 2. PULSE-ECHO OR ULTRASONIC TYPE MEASUREMENT # MEASURING PRINCIPLE Sonic and ultrasonic sensors consist of a transmitter that converts electrical energy into acoustical energy and a receiver that converts acoustical energy into electrical energy. The transmitted and return time of sonic pulse is relayed electronically and converted to level indication. These devices are non-contacting, reliable and accurate, no moving parts, unaffected by changes in density, conductivity and composition. # LIMITATIONS 1. Cannot be used for foam as the signal may be absorbed by foam. 2. Will not work in vacuum. 3. Various factors like instrument accuracy, vapor concentration, pressure, temperature, relative humidity, and pressure of other gases/vapors may affect the performance --------------------------------------------------------------------------------------------------------------------Page 14 of 24

A

B

FIG- 35 C ULTRASONIC LEVEL MEASUREMENT IN OPEN CHANNEL FLOW MEASURING APPLICATIONS

3. ANTENNA / GUIDED WAVE RADAR TYPE LEVEL MEASUREMENT# TECHNOLOGY/ MEASURING PRINCIPLE Guided Wave Radar is based upon the technology of TDR (Time Domain Reflectometry). TDR utilizes pulses of electromagnetic energy, which are transmitted down a probe. When a pulse reaches a liquid surface that has a higher dielectric than air/vapor in which it is traveling, the pulse is reflected. An Ultra high-speed timing circuit precisely measures the transit time and provides an accurate measure of the liquid level. The measurement requires complete mapping of the inner surfaces of the vessel in empty conditions. The information is stored in the memory and reflections form protrusions, shafts, agitators etc. are compensated. Thus true level is measured. This technology is fairly new and costly. # APPLICATIONS This measuring principle provides non-contact continuous level measurement for liquids, solids and slurries with high pressures and temperatures, vacuum, dust, vapour and aggressive and toxic products

A B

DIELECTRIC ANTENNA

FIG- 36

HORN ANTENNA

--------------------------------------------------------------------------------------------------------------------Page 15 of 24

4. MICROWAVE SWITCHING

TYPE

NON-CONTACT

LEVEL

DETECTION

/

LEVEL

# MEASURING PRINCIPLE The operation of the microwave barrier is similar to a light filter. A transmitter emits microwaves with a frequency of 5.8 GHz to a receiver. If product is between transmitter and receiver, the microwaves are absorbed and a damped signal is received. The receiver signals this by a switching command. The detection principle functions with all liquids and solids, which reflect or absorb microwaves.

FIG- 37 A

B

C

# APPLICATIONS Non-Contact type level switching/detection in products like oil, coal, stones and foodstuffs. 5A. ELECTRO-MECHANICAL TYPE LEVEL DETECTION/ LEVEL SWITCHING # MEASURING PRINCIPLE The electromechanical measuring principle is ideal for many applications with its rugged construction. A weight is wound off electro-mechanically on a cable. When the weight touches the measured product, the weight is rewound to the initial position. The measured cable length is a measure of the level. # USER ADVANTAGES 1. Vessel heights up to 40 m 2. Accuracy better than 0.1% 3. Adapts to product types by choice of sensing weights. 4. Full operation even with dust formation. 5. Complete separation between cable pulley and control mechanism. 6. Easy installation.

FIG- 38

# APPLICATIONS It is suitable for level measurement of fine and coarse solids as well as liquids, but also for the measurement of solids in water. Main applications are in large vessels where solutions with other techniques are expensive or physically not possible. # TYPICAL PRODUCTS Ore, coal, stones, sinter, plastic powder, lime, cement, raw flour, cereals, sludge and sewage water. --------------------------------------------------------------------------------------------------------------------Page 16 of 24

5B. MAGNETIC TILT LEVEL SWITCH # WORKING PRINCIPLE Float mounted at one end of rigid rod moves with change in level. Magnetic capsule at other end of rod moves accordingly within fixed limits. Hermitically sealed switch contacts across the stainless steel case change accordingly.FIG- 39 Nomenclature 1. Float Assy. 2. Magnet Assy. 3. Mounting flange. 4. Housing 5. Switch Assy. 6. Terminal Assy. 7. Cable Gland 8. Cover.

# APPLICATIONS HI-LO Level signals for Alarm Annunciation, Safety Interlock circuits, Automatic Pump Control, Solenoid Valve control, Prevention of tank overflows, Pump safeguard against dry running 5C. ROTATING PADDLE LEVEL SWITCH # WORKING PRINCIPLE Operation centers around a low torque, slow speed synchronous motor. Absence of dry materials allows the motor to turn the paddle. Presence of dry material tends to stall the paddle and the motor. The resultant torque actuates a snap-action switch (es) which in turn controls audible and visual signals and/or starts and stops machinery such as conveyers, elevators, feeders, etc. Mounts on top or side of bin.

FIG- 40 Rotating paddle level switch

# APPLICATIONS

1. Eliminates bin overflow, empty bins, clogged conveyors, choked elevators and resultant damage and waste. 2. For Chemical, food, mining, plastics, ceramics and other industries.

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5D. TILT TYPE LEVEL SWITCH# WORKING PRINCIPLE Tilt switches are either of mercury or micro-switch type, mounted so as to hang from the top of the storage bin. When the tilt switch hangs freely, there is no contact between the tilt switch and control relay. As soon as the level reaches the tilt switch, the vertical angle changes, causing the contact to close. This creates a closed circuit with the control relay, which activates a solenoid valve, an alarm relay, or a motor control start/stop command.

FIG- 41 Tilt Type switches level

6A. VIBRATION TYPE LEVEL SWITCHES# MEASURING PRINCIPLE Vibration probes for solids operate with piezoelectrically generated vibration which is damped when the rod is covered by the product. The integral electronics detects this damping and triggers a switching command.

FIG- 42 Vibrating different versions. probes in mounting

# APPLICATIONS Powders and granules above a density of 0, 03 g / cm can be detected, e.g. styropore, cement, cereals, flour, plastic Granules etc.

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6B. TUNING FORK LEVEL DETECTION / LEVEL SWITCHING# MEASURING PRINCIPLE The tuning fork is energized by a piezoelectric element and vibrates at its resonant frequency of approx. 380 Hz. A second piezoelectric element detects this frequency which is than passed to the integral electronics. If the fork is covered by the product, the frequency changes, and a switching command is triggered.

FIG- 43 Installation options

7. CONDUCTIVITY TYPE LEVEL SWITCHES# MEASURING PRINCIPLE When the electrode is covered by a conductive product, a measuring circuit is closed and a switching signal is triggered. The metallic vessel itself is the reference electrode. In plastic vessels a version with integral reference electrode is used. The position of the switch point is simply determined by the electrode length. Rod and multiple rod electrodes as well as cable and multiple cable electrodes are available.

FIG- 44 Working Principle & Multiple rod electrode for Min./Max. Control

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A BRIEF COMPARISON OF VARIOUS LEVEL SENSORS

--------------------------------------------------------------------------------------------------------------------Page 20 of 24

GLOSSARY OF TERMS TO BE UNDERSTOOD FOR INDUSTRIAL LEVEL MEASUREMENTACCURACY The closeness of an Indication of reading of a measurement device to the actual value of the quantity being measured usually expressed as percent of full scale output or reading. ATMOSPHERIC PRESSURE The barometric reading of pressure exerted by the atmosphere. At sea level 14.7 lb per sq. in. or 29.92 in. of mercury. BUBBLE TUBE A length of pipe or tubing placed in a vessel at a specified depth. To transport a gas injected into a liquid to measure level from a hydrostatic Head. BUOYANCY The tendency of the fluid to lift any object submerged in the body of the fluid; the amount of force applied to the body equals the product of fluid density and volume of fluid displaced. DENSITY 1. The mass of a unit volume of a liquid at a specified temperature. Units shall be stated as kg / m. 2. A physical property of materials measured as mass per unit volume. DIELECTRIC CONSTANT A material characteristic expressed as the capacitance between two plates when the intervening space is filled with a given insulating material divided by the capacitance of the same plate arrangement when the space is filled with air or evacuated. DIFFERENTIAL PRESSURE TYPE LEVEL METER/ TRANSMITTER Any of several devices designed to measure the head of the liquid in a tank above some minimum level and produce an indication proportional to this value; alternately, the head below some maximum level can be measured and similarly displayed. DISPLACER TYPE LIQUID LEVEL DETECTOR A device for determining a liquid level by means of force measurements on cylindrical element partly submerged in the liquid in a vessel; as the level in the vessel rises and falls, the displacement (buoyant) force on the cylinder varies and is measured by the lever system, torque tube or other force measurement device. FLOAT Any component having positive buoyancy for example, a Hollow watertight body that rests on the surface of the liquid, partly or completely supported by buoyant forces. FLOAT CHAMBER A vessel in which a float regulates the liquid level. FOAMING Any of various methods of introducing air or gas into a liquid or solid material to produce foam. The continuous formation of bubbles which have sufficiently high surface tension to remain as bubbles beyond the disengaging surface.

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GAUGE GLASS A glass or plastic tubes for measuring liquid level in a tank or pressure vessel, usually by direct sight; it is usually connected directly to the vessel through suitable fitting and shut off valve. GAUGE PRESSURE 1. Pressure measured relative to ambient pressure. 2. The difference between the local absolute pressure of the system and the atmospheric pressure at the place of measurement. 3. Static pressure is indicated on a gauge. HYDROSTATIC HEAD The pressure created by a height of a liquid above a given point. MAGNETIC FLOAT GAUGE Any of several designs of liquid level indicator that use a magnetic float to position a pointer. PURGE 1. Increasing the sample flow above normal for the purpose of replacing current sample-line fluid or removing deposited or trapped materials. 2. To cause a liquid or gas to flow from an independent source into the impulse pipe. TORQUE A rotary force, such as that applied by a rotating shaft at any point on its axis of rotation. WET LEG The liquid-filled low-pressure side of the impulse line in a differential pressure level measuring system. ZERO ELEVATION Adjusting the zero output signals to raise the zero to a higher starting point. Usually used in level measurement for starting measurement above the vessel connection point. ZERO SUPPRESSION Adjusting the zero output signals to produce the desired Measurement. Usually used in level measurement to counteract the zero elevation caused by a wet leg.

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CALCULATION PROCEEDURESA) OPEN VESSEL BOTTOM MOUNTED TRANSMITTER & CLOSED TANK DRY LEG METHOD20

X

ZERO SUPPRESSION

Y HP

LT LP4 90 540 WC

X- VERTICAL DISTANCE BETWEEN THE MINIMUM & MAXIMUM MEASURABLE LEVEL

= 500 mmH2O = 100 mmH2O = 0.9

Y- VERTICAL DISTANCE BETWEEN TRANSMITTER DATUM LINE & MINIMUM MEASURABLE LEVEL SG - SPECIFIC GRAVIY OF THE FLUID H MAXIMUM HEAD PRESSURE TO BE MEASURED IN mmH2O E HEAD PRESSURE PRODUCED BY Y EXPRESSED IN mmH2O RANGE = E TO E+H H = X x SG = 500 x 0.9 E = Y x SG = 100 x 0.9 = 450 mmH2O = 90 mmH2O

RANGE = E TO E+H = 90 TO (90 + 450) = 90 TO 540 mmH2O NOTE IN CLOSED TANK DRY LEG METHOD, IF THE GAS ABOVE THE LIQUID DOES NOT CONDENSE & THE PIPING FOR THE LOW SIDE OF THE TRANSMITTER WILL REMAIN EMPTY. CALCULATIONS FOR DETERMINING THE RANGE WILL BE THE SAME AS SHOWN FOR OPEN VESSEL BOTTOM MOUNTED TRANSMITTER. -----------------------------------------------------------------------------------------------------------

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CALCULATION PROCEEDURESB) CLOSED TANK WET LEG METHOD20 ZERO ELEVATION

X Z Y HP LT LP- 610 WC 90 -110 4

X- VERTICAL DISTANCE BETWEEN THE MINIMUM & MAXIMUM MEASURABLE LEVEL Y- VERTICAL DISTANCE BETWEEN TRANSMITTER DATUM LINE & MINIMUM MEASURABLE LEVEL Z- VERTICAL DISTANCE BETWEEN TOP OF LIQUID IN WETLEG & TRANSMITTER DATUM LINE SG1 - SPECIFIC GRAVIY OF THE FLUID SG2 - SPECIFIC GRAVIY OF THE FLUID IN THE WET LEG H MAXIMUM HEAD PRESSURE TO BE MEASURED IN mmH2O E HEAD PRESSURE PRODUCED BY Y EXPRESSED IN mmH2O S HEAD PRESSURE PRODUCED BY Z EXPRESSED IN mmH2O RANGE = (E-S) TO (H+ (E-S)) H = X x SG1 E = Y x SG1 = = 500 x 1 50 x 1 600 x 1.1 = 500 mmH2O = 50 mmH2O = 660 mmH2O

= 500 mmH2O

= 50 mmH2O

= 600 mmH2O = 1.0 = 1.1

S = Z x SG21 =

RANGE = (E-S) TO (H+ (E-S)) = [(50-660) TO 500 + (50-660)] = [(-610) TO 500 + (-610)] = -610 TO -110 mmH2O

--------------------------------------------------------------------------------------------------------------------Page 24 of 24

FLOW MEASUREMENTFLOW MEASURMENT BASICS

Flow is another very important process variable that has to be measured and controlled. To understand the basic principles of flow measurement one should be familiar with the relationship between fluid flow and Pressure, Temperature, Viscosity, Density The two basic properties - DENSITY & VISCOSITY play an important role in flow measurement. Density applies to fluids in static phase. Viscosity applies to fluids in motion.DENSITY: In simple terms, Density is a measure of closeness of molecules in a substance.

Density is defined as Mass per unit Volume. d=m/v where d = density, m = mass, v = volumeSPECIFIC GRAVITY

d=lbs/ft3

Another term commonly used to express density of fluid is SPECIFIC GRAVITY (SG) SG of a liquid=density of liquid / density of water at standard conditions. SG of a gas = density of gas / density of air at standard conditions.VISCOSITY

Viscosity is the property that determines how freely fluids flow. The viscosity of a fluid refers to its physical resistance to flow. Fluids have various degrees of viscosity. Such variations results from internal friction between particles of the substance. A substance with a higher viscosity has a resistance to flow. For example, two substances with different viscosities are oil and water. Water pours freely while oil pours more slowly. Molasses is more viscous than water, and water much more viscous than gas. Viscosity contributes to laminar or turbulent flow characteristics. Laminar flow is highly effected by viscosity than turbulent flow. Viscosity reduces with the increase of temperature. For example, when molasses is heated its viscosity will decrease. There are several viscosity units, the most widely used being the centipoise. The Viscosity of water at 68F is 1.0 centipoise. The viscosity of kerosene at 68F is 2.0 centipoises. Viscosity () can be expressed as : -1 -1 = lb . ft .s

Also one should know and be able to define the following general flow measurement terms :Laminar flow Incompressible flow Mass flow Static pressure Working pressure Turbulent flow Transitional flow Compressible flow Steady flow Unsteady flow Pulsating flow Dynamic pressure Stagnation pressure Differential pressure Pressure loss

Page 1 of 43

VARIOUS FLOW MEASUREMENT TERMSLAMINAR FLOW :

Laminar flow is a flow characterized by the tendency of the fluid to remain in thin parallel layers. Laminar flow occurs when the average velocity is slow. The layers are fast moving in the center and become slower on the outer edges of the stream. In laminar flow fluid particles move along in parallel paths. The laminar flow appears as several streams of liquid flowing smoothly alongside each other.TURBULENT FLOW

Turbulent flow is a flow characterized by random motions of the fluid particles in the transverse as well as axial directions. Turbulent flow occurs when the average velocity is fast. The layers disappear and the velocity is more uniform across the stream.TRANSITIONAL FLOW

.

Transitional flow is the flow between laminar and turbulent. Transitional flow exhibits the characteristic of both laminar and turbulent patterns. In some cases transitional flow will oscillate between laminar and turbulent flow.Incompressible flow is fluid flow under conditions of constant density. Compressible flow is fluid flow under conditions that cause significant changes in density. Mass flow is the amount of fluid, measured in mass units, that passes a given location per unit time. Steady flow is a flow in which the flow rate in a measuring section does not vary significantly with time. Unsteady flow is a flow in which the flow rate fluctuates randomly with time and for which the mean value is not constant. Pulsating flow is a flow rate characterized by irregular or repeating variations. Static pressure is the pressure of a fluid that is independent of its kinetic energy. Stagnation pressure is a theoretical pressure that could be developed if a flowing fluid could be brought to rest without loss of energy.

Page 2 of 43

Dynamic pressure is the increase in pressure above the static pressure that results from complete transformation of the kinetic energy of the fluid into potential energy. Working pressure is the maximum allowable operating pressure for an internally pressurized vessel, tank, or piping system. Differential pressure with respect to flow, is the pressure drop across a restriction Pressure loss is the decrease in pressure of a fluid as it passes through a restriction

FLUID FLOW RELATIONSHIPSOne should know the physical laws that apply to the flow of fluids and their measurement. 1. Pressure across a particular point (such as an orifice) causes a flow through the point ; the higher the pressure drop, the higher the flow. 2. Temperature can affect flow ; higher temperatures decrease viscosity. 3. Viscosity affects flow; a more viscous fluid flows less easily 4. Density affects flow. The Flow decreases as the density increases. 5. Friction affects flow ; more friction reduces flow. 6. Specific gravity affects flow in the same way as density. 7. Flow and flow rate refer to the volume of fluid that passes a given point in a pipe per unit time, as defined by the following equations : Q = AV Where : Q = flow rate A = cross-sectional area of pipe V = average fluid velocity The principle of the continuity of flow is expressed by the equation: Q= Q= A1, V1, A1V1 = A2V2 = A3V3 where flow rate A2, A3 = cross-sectional areas of pipe at different locations 1,2,3 V2, V3 = average fluid velocity at locations 1,2,3

VELOCITY

The Velocity of a flowing fluid is its speed in the direction of flow. It is an important factor in flow metering because it determines the behavior of the fluid. When the average velocity is slow, the flow is said to be laminar. This means that the fluid flows in layers with the fastest moving layers toward the center and the slowest moving layers on the outer edges of the stream. As the velocity increases, the flow becomes turbulent, with layers disappearing and the velocity across the stream being more uniform. In this discussion, the flow is assumed to be turbulent and the term velocity refers to the average velocity of a particular cross section of the stream. Rate of flow (Cubic ft. per sec) Velocity = ----------------------------------------------- = V = ft / sec Area of pipe (Sq. feet)

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BERNOULLI'S THEOREMBernoulli's theorem relates the velocity of a fluid at a point and the pressure of the fluid at that point. It is just the application of work-energy theorem. According to work energy theorem, the work done by a force acting on a system is equal to the change in kinetic energy of the system. Consider the streamlined flow of a.liquid through a pipe as shown in the figure. As the liquid flows through the pipe, depending upon the position of the liquid, there are three types of energy possessed by the liquid during its flow.KINETIC ENERGY

Let m be the mass of liquid that-flows through the pipe with a velocity v. Kinetic energy of the liquid = 1/2 mv 2 Kinetic energy per unit mass of the liquid= 1/2V2POTENTIAL ENERGY

If h is the height from the ground, then the potential energy is given by mgh. Potential energy per unit mass = ghPRESSURE ENERGY

If p is the pressure exerted on the liquid of cross sectional area a, then the force acting on the liquid surface is given by F = pa (pressure = force / area)

Under the influence of this force, the liquid is driven through a small displacement x. The work done is given by w = Fx = p.a.x w = pV ( volume V = a x ) this work done is stored as the pressure energy. pressure energy = pV = p m/ ( density p = mass / volume ) pressure energy per unit mass = p/

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The three types of energy possessed by the liquid at two different points in the pipe are as follows: at A : potential energy per unit mass = gh1 kinetic energy per unit mass = 1/2V12 pressure energy per unit mass = p1/ Total energy at A = p1/ + gh1 + 1/2V12 at B : potential energy per unit mass = gh2 kinetic energy per unit mass = 1/2V22 pressure energy per unit mass = p2/ Total energy at B = p2/ + gh2 + 1/2V22 Bernoulli's theorem states that the sum of the energies possessed by a flowing liquid at any point is constant provided the flow of liquid is steady. Total energy at A = total energy at B p1/ + gh1 + 1/2V12 = p2/ + gh2 + 1/2V22 (ie) p/ + gh + 1/2 V2 = constant This is known as Bernoullis equation. From the above, it is understood that when a fluid is in motion, the pressure within the fluid varies with the velocity of the fluid if the flow is streamlined. The pressure within a fast moving fluid is lower than that in a similar fluid moving slowly. This is known as Bernoullis principle.

REYNOLDS NUMBERIn flow metering, the nature of flow can be described by a number-the Reynolds Number, which is the average velocity x density x internal diameter of pipe divided by viscosity. In equation form, this is expressed as vD R = -------- Where, v = velocity D = inside diameter of pipe = fluid density = viscosity The Reynolds Number has no dimensions of its own. From the Reynolds Number, it can be determined whether the flow is laminar or turbulent. Reynolds Number < 2000, the flow is laminar Reynolds Number > 4000, the flow is turbulent. Between these two values, the nature of the flow is unpredictable. In most Industrial applications, the flow is turbulent. Although measurement can be made without consideration of the Reynolds Number, greater accuracy is possible when a correction based upon it is made.

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METHODS OF FLOW MEASUREMENTMany different methods are used to measure flow in a wide variety of industrial applications. These can be divided into three broad categories as follows: 1. Inferential type flow meters 2. Quantity flow meters 3. Mass flow metersINFERENTIAL FLOW MEASUREMENTS

In the inferential type of flow measuring methods, the flow rate is inferred from a characteristic effect of a related phenomenon The following are the inferential type of flow measuring methods 1. Variable head or differential flow meters 2. Variable area meters 3. Magnetic flow meters 4. Turbine meters 5. Target meters 6. Thermal flow meters 7. Vortex flow meters, 8. Ultrasonic flow meters VARIABLE HEAD OR DIFFERENTIAL FLOW METERS This is one of the oldest and most widely used methods of industrial flow measurements. The variable head flow meters operate on the principle that when a restriction (or) obstruction in the line / pipe of a flowing fluid is made ,it produces a differential pressure across the restriction element which is proportional to the flow rate. The proportionality is not a linear one but has a square root relationship because the flow rate is proportional to the square root of the differential pressure. It is simply expressed as Qh Q=Kh where h = diff .pr (or ) P h = HP LP K =constant DIFFERENTIAL PRESSURE METERS A differential flow meter basically consists of two parts : Primary Elements and Secondary Elements. The parts of the meter used to restrict the fluid flow in the pipe line in order to produce a differential pressure are known as primary elements They are : Orifice Plate Dall tubes Elbow Taps Venturi Tube Pitot tubes Weir Flow nozzles Annubar tubes Flume

Secondary elements are those which measure the differential pressure produced by the primary elements and convert them to signals. Various secondary elements are: Manometer, Bellow/ Diaphragm Meter/ Transmitters (Mechanical/ Electrical/ Electronic/ Pneumatic).

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PRIMARY ELEMENTSOrifice Plate : The simplest and the most common pipeline restriction used in DP method of flow measurement is the Orifice Plate, which is a thin, circular metal plate with a hole in it. It is held in the pipeline between two flanges called orifice flanges . It is the easiest to install and to replace. Concentric Orifice Plate : It is most widely used. It is usually made of stainless steel and its thickness varies from 3.175 to 12.70mm (1/8 to 1 /2 inch.) depending on pipe line size and flow velocity. It has a circular hole (orifice) in the middle, and is installed in the pipe line with the hole concentric to the pipe. Eccentric Orifice Plate : It is similar to the concentric plate except for the offset. It is useful for measuring fluids containing solids, oils containing water and wet steam. The eccentric orifice plate is used where liquid fluid contains a relatively high percentage of dissolved gases. Segmental Orifice Plate : This orifice plate is used for the same type of services as the eccentric orifice plate. It has a hole which is a segment of a circle. Quadrant Edge Orifice Plate : This type of orifice plate is used for flows such as heavy crudes, syrups and slurries, and viscous flows. It is constructed in such a way that the edge is rounded to form a quarter-circle. Depending on the application, it is often necessary to drill a small drain hole usually called a weep hole. This hole is located at the bottom when gases are measured to allow the condensate to pass in order to prevent its building up at the orifice plate. When the fluid is a liquid, this hole is located at the top so that gases can pass and gas pockets cannot build up.MAXIMUM FORCE IN THE ORIFICE PLATE INSTALLATION IS AT A. MINIMUM PRESSURE IS AT B. BECAUSE OF LOSS OF PRESSURE , ACROSS THE PLATE, DOWNSTREAM PRESSURE RISES ONLY AS HIGH AS POINT

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Figure gives a cross-section of a typical orifice plate installation showing the variation in pressure that occurs across the plate. Notice that the main flow stream takes the shape of the venturi tube with the narrowest path slightly downstream from the plate. This point is called the vena contracta. At this point, the pressure is at its minimum. From this point on, the fluid again begins to fill the pipe and the pressure rises. The pressure, however, does not recover completely. There is a loss of pressure across the plate. The principal consideration in selecting an orifice plate is the ratio of its opening (d) to the internal diameter of the pipe (D). This is often called the beta ratio. If the d/D ratio is too small, the loss of pressure becomes too great. If he ratio is too great the loss of pressure becomes too small to detect and too unstable. Ratios from 0.2 to 0.6 generally provide best accuracy. Several procedures have been developed for calculating the correct size of an orifice to make it suitable for measuring a particular rate of flow. The fundamental equation for all these procedures are based as Q=EA0 2gh where, Q = flow rate (volume per unit of time) E = Efficiency factor Ao = Area of orifice in square feet g = acceleration due to gravity 32 feet/sec/sec h = differential pressure across orifice in feet The efficiency factor E is required since the actual flow through an orifice is not the same as the calculated flow. Values of E have been determined by tests and are found in tables. It is different for each combination of d/D radio and Reynolds Number. The letters K or C are used to express this factor in some other equations. It may be called as flow coefficient. This factor or coefficient has no units since it is a ratio of the actual to the theoretical. As stated above, values of E are found in table or on graphs. Example : for Reynolds No. of 10,000 ratio of .6 The value of E is .678 The orifice plate, flow nozzle, and venturi tube operate on the same principle, and the same equation is used for the three. In addition to the difference in flow coefficient (E), there are other factors for each that determine which element should be used.GIVEN REYNOLDS NO. OF 10,000 AND SELECTION OF ORIFICE PLATES RATIO OF 0.6, THE GRAPH INDICATES THE VALUE OF E AS .678

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Precision Standard Orifices are used where accounting or plant efficiency tests are involved as per B.S. 1042 Code for Flow Measurement. Concentric sharp edged orifice plates should be used for, all normal applications. Eccentric or segmental orifice plates should be used for liquids containing solids. Beveled or rounded-edge orifice plates should be used for viscous fluids. Plate material for industrial fluids normally should be stainless steel or such superior material as demanded by the process conditions. Note : Orifice plates are not generally recommended for applications where :1.Wide variations in Flow-rate occurs. 2.Tolerance less than 3% is required. 3.Highly viscous fluids and slurries are to be measured 4.Piping layouts do not permit adequate straight lengths to be used. 5.System allowable pressure drop is very small. There must be a long continuous run of straight pipe leading up to any of these primary elements. Considerable information is available concerning the length of straight pipe required between such devices as elbows and valves and the primary elements. When insufficient straight pipe is not possible, the disturbances can be reduced or eliminated by the installation of straightening vanes.LENGTHS OF STRAIGHT PIPE REQUIREMENT

When the beta ratio=0.6, upstream distance A must be at least 13 pipe diameters after the elbow, tee or cross. After globe or a regulating valve upstream distance A must be at least 31 pipe diameters. In both cases downstream distance B is 5 pipe diameters. Straight run requirements become less as Beta ratio decreases. For example, when the beta ratio is 0.4, the distance A becomes 9D after elbows and 19D after valves. (not drawn to scale.)

STRAIGHTENING VANES ARE INSTALLED ABOVE THE ORIFICE TO REDUCE TURBULENCE AND MAKE ACCURATE MEASUREMENT POSSIBLE (ROBERTSON MFG. CO.)

TURBULENT FLOW OCCURS WHEN THE AVERAGE VELOCITY IS FAST. THE LAYERS DISAPPEAR AND THE VELOCITY IS MORE UNIFORM ACROSS THE STREAM.

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Advantages of Orifice Plates (i) low cost (ii) can be used in a wide range of pipe sizes (3.175 to 1828.8 mm.) (iii) can be used with differential pressure devices (iv) well-known and predictable characteristics (v) available in many materials Disadvantages and Limitations of Orifice Plates (i) cause relatively high permanent pressure loss, (ii) tend to clog, thus reducing use in slurry services (iii) have a square root characteristics (iv) accuracy dependant on care during installation (v) changing characteristics because of erosion, corrosion and scaling. VENTURI TUBE Another pipeline restriction for flow metering is the venturi tube, which is a specially shaped length of pipe resembling two funnels joined at their smaller openings. The venturi tube is used for large pipelines. It is more accurate than the orifice plate, but considerably more expensive, and more difficult to install. The Venturi tube is the most expensive but it is the most accurate primary element. High beta ratios (above 0.75) can be used with good results. The pressure recovery of the venturi tube is excellent, which means that there is little pressure drop through it. Functionally, the venturi tube is good since it does not obstruct abrasive sediment; in fact, because of its shape it resists wear effectively. A Venturi tube is used where permanent pressure loss is of prime importance, and where maximum accuracy is desired in the measurement of high viscous fluids. The pressure taps are located one-quarter to one-half pipe diameter up-stream of the inlet cone and at the middle of the throat section. The venturi tube can be used to handle a fluid which is handled by an orifice plate and fluids that contain some solids, because these venturi tubes contain no sharp corners and do not project into the fluid stream. It can be also used to handle slurries and dirty liquids. Advantages (i) causes low permanent pressure loss (ii) widely used for high flow rates (iii) available in very large pipe sizes (iv) has well known characteristics (v) more accurate over wide flow ranges than orifice plates or nozzles (vi) can be used at low and high beta ratios Disadvantages (i) high cost, (ii) generally not useful below 76.2 mm pipe size (iii) more difficult to inspect due to its construction (iv) limitation of a lower Reynolds number of 150,000, (Some data is however available down to a Reynolds number of 50,000 in some sizes)

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FLOW NOZZLE : compromise between the orifice plate and the Venturi tube is the flow nozzle, which resembles the entering half of the venturi tube .The flow nozzle is almost as accurate as the Venturi tube, and is not so expensive to buy or as difficult to install.

The flow nozzle is simpler and cheaper than the venturi tube. It is slightly less accurate and does not provide as good pressure recovery. The flow nozzle can be used with higher beta ratios (above .75), but is not quite so wear resistant as the venturi. Advantages (i) (ii) (iii) (iv) Disadvantages (i) (ii) permanent pressure loss lower than that for an orifice plate available in numerous materials for fluids containing solids that settle widely accepted for high-pressure and temperature steam flow cost is higher than orifice plate & limited to moderate pipe sizes requires more maintenance (it is necessary to remove a section of pipe to inspect or install it).

TAPPING POINTSTo obtain the pressures upstream and downstream of the primary elements requires taps on both sides of the restriction. The location of these pressure taps varies with the orifice Plate. The following methods of tappings are generally used. FLANGE TAPS, CORNER TAPS, PIPE TAPS and VENA CONTRACTA TAPSFLANGE TAPPINGS CORNER TAPPINGS

Flange taps are located on the flanges that hold the orifice plate in positionFLANGE TAPPING

The tapping holes are in the corners of the flange. The tappings will be in 45o angle to the flow direction. This type of tapping is used for pipe lines with diameter less than 2.

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PIPE TAPS

Pipe taps are located at fixed distances upstream and down-stream of the orifice plate - the upstream pipe tap is located 2 1/2 pipe diameters from the plate & the downstream pipe tap 8 pipe diameters, from the orifice plate. NOTE : Pipe tap is also called as FULL FLOW TAPSVENA CONTRACTA TAPS ( D & D / 2 TAPS )

At Vena contracta point, the velocity will be max. and the pressure will be min. The distance of vena contracta taps on the downstream side must be calculated from application data. On the upstream side it is located at one pipe diameter from the plate (1 D). Approx. the downstream point (Vena Contracta) is at a distance of 1/2 D. Hence it is also known as D & D/2 taps. The pressure taps used with the Venturi tube are located at the points of maximum and minimum pipe diameter. The pressure taps used with the flow nozzle are located at distances upstream and downstream of the nozzle as designated by the manufacturer. This location is critical and the manufacturers recommendations must be followed. Any of the differential pressure instruments can be used for rate of flow measurement with these primary flow elements. Since the desired measurement is rate of flow and not differential pressure, a conversion from differential pressure to rate of flow must be made.FIVE WAY VALVE MANIFOLD

T1, T2 1A 1B 2A 2B 3 4A 4B 5A 5B 6

TAPPING POINTS PRIMARY ISOLATION VALVE (HP) PRIMARY ISOLATION VALVE (LP) SECONDARY ISOLATION VALVE (HP) SECONDARY ISOLATION VALVE (LP) EQUALISING VALVE ISOLATION VALVE TO TX (HP) ISOLATION VALVE TO TX (LP) DRAIN VALVE (HP) DRAIN VALVE (LP) TRANSMITTER

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DALL TUBES (LO-LOSS FLOW TUBE A MODIFIED FORM OF VENTURI TUBE) The Dall Tube is a modified form of venturi tube, a cross-section of which is shown. It consists of two truncated cones, each with a relatively large cone angle. The throat is formed by a circumferential slot located between the two smaller diameters of the truncated cones. The differential pressure produced by a dall tube is much higher (about double) than that of venturi tube or nozzle having the same upstream and throat diameters with the same net head loss. Advantages i.low head loss ii.short lying length iii.available in numerous materials of construction iv.no upper line-size limit Disadvantages I.pressure difference is sensitive to up-stream disturbances II.more straight pipe required in the approach pipe length III.not considered for measuring flow of hot feed waterOVERALL PRESSURE LOSS THROUGH OVERALL PRESSURE LOSS THROUGH VARIOUS PRIMARY ELEMENTS VARIOUS PRIMARY ELEMENTS100 PRESSURE LOSS IN % OF ACTUAL DIFFERENTIAL 90 80 70 60 50 40 30 20 10VENTURI TUBE WITH 15 % RECOVERY CONE (SHORT) HERCHEL TYPE VENTURI TUBE WITH LONG CONE LOW LOSS FLOW TUBE (DALL TUBE) FLOW NOZZLE ORIFICE

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

BETA RATIO =d/D

PITOT TUBEAnother Primary flow element used to produce a differential pressure is the pitot tube. In its simplest form, the pitot tube consists of a tube with a small opening at the measuring end. This small hole faces the flowing fluid (Fig). When the fluid contacts the pitot tube, the fluid velocity is zero and the pressure is at a maximum. This small hole, or impact opening as it is called, provides the higher pressure for differential pressure measurement. While the pitot tube provides the higher pressure for differential pressure measurement, an ordinary pressure tap provides the lower pressure reading.Page 13 of 43

The Pitot tube is an economical device for providing a differential pressure readingP IT O T T U B E A S S E M B L Y IM P A C T P R E S S U R E

HO LES FO R S T A T IC P R E S S U R E

S T A T IC P R E S S U R E C O M P R E S S IO N R IN G A N D G L A N D F O R L IN E C E N T E R IN G

The pitot tube actually measures the velocity of fluid flow and not rate of flow. However, the flow rate can be determined from the velocity using the is formula : Q = KAV1 Where, Q = flow rate (cubic ft. per Sec.) A = Area of flow cross section in feet. V1 = Velocity of flowing fluid (ft.per.sec) K = flow coefficient of pitot tube (normally about 8) There is no standardization of pitot tubes as there is for orifice plates, venturi tubes and flow nozzles. Each pitot tube must be calibrated for each installation. Pitot tubes may be used where the flowing fluid is not enclosed in a pipe or duct. For instance, a pitot tube may be used to measure the flow of river water, or it may be suspended from an airplane to measure the air flow. Any of the differential pressure type instruments previously described may be used with the pitot tube. Advantages : i. no process loss ii. economical to install iii. some types can be easily removed from the pipe line Disadvantages i. Have poor accuracy ii. unsuitability for dirty or sticky fluids iii. sensitivity to upstream disturbances

ANNUBARThe Annubar is a Multiple-Ported Pitot tube that Spans the Pipe. Pressure Ports are located at mathematically defined positions based on Published axis symmetric Pipeline velocity profile. These are claimed to average the differential, thereby eliminating the need to locate average velocity point as is necessary for pitot tubes.

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Ease of installation, low cost, very low permanent pressure loss, and insertability into existing piping make these devices convenient for ducts and large line size measurements.PRINCIPLE OF OPERATION

Delta Tubes are averaging pitots designed to produce a differential pressure output having a classical square root relationship with flow rate. The multiported Delta Tube's strategically located sensing ports continually sample the impact and static pressures produced by the Delta Tube's obstruction of the flow stream profile. Within the probe, the impact and static pressures sensed by the upstream and downstream ports are continually averaged in separate plenum chamber. Secondary instruments like Switzer Differential Pressure Indicator/ Switches (or Differential Pressure Transmitter) can be used for switching monitoring or for direct measurement of the differential pressure generated by the Delta Tube.

Advantages and Disadvantages of Annubar : Advantages i. It is available for a wide range of pipe sizes ii. It is simple and economical to install iii. It provides negligible pressure drop iv. It can be placed in service under pressure v. It can be rotated while in service, for cleaning action vi. It provides long-term measurement stability. Disadvantages i. unsuitability for operating dirty or sticky fluids ii. limited operating data

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ELBOW TAPS

The flow measurement using elbow taps as a