Topic covers in Unit - ITopic covers in Unit - IInstrumentation - BasicsInstrumentation - BasicsRole of InstrumentationRole of InstrumentationMeasuring of process parametersMeasuring of process parametersBasics of field InstrumentationBasics of field InstrumentationControlling of Process parametersControlling of Process parameters

PLC BasicsPLC BasicsIntroduction to PLCIntroduction to PLCPLC Fundamentals – (PLC Architecture)PLC Fundamentals – (PLC Architecture)PLC Components – Power supply, CPU, I/O and PLC Components – Power supply, CPU, I/O and

communication modulescommunication modulesTypes of Inputs and Out putsTypes of Inputs and Out putsIntroduction to the field devises attached to PLCIntroduction to the field devises attached to PLC

Measuring of process Measuring of process parametersparameters

• Measurement:

A set of operation having the object of determine the quantity, property or condition which is being measured. Sometimes referred to as the “measurand” .In other way the measurements in general are made with the objective of determining the physical characteristics of an item

• Purpose of Measuring and monitoring of process parameters

Good control requires measurements that are accurate, reliable, responsive and maintainable. These factors are influenced by the choice of principle used for the measurement, the detailed specifications and features of the instrument selected, how well the installation and maintenance.The vast majority of physical measurements are Flow, Pressure, Temperature, Level, and Weight & Position.

Terminologies use in measurement techniqueTerminologies use in measurement technique

• Range:- The region between the limits within which a quantity is measured, received or transmitted, expressed by stating the lower and upper range values

• Error:- This is the difference between the measured signal value or actual reading and the true (ideal) or desired value.

• Span:- The algebraic difference between the upper and lower range values, expressed in the same units as the range in other word Span is the difference between Maximum and minimum values. Input span is Imax - Imin and Output span is Omax – Omin.

• Accuracy: -Degree of conformity of a measured value to an accepted standard value (or) closeness of a reading

• Precision (Repeatability):-This is the maximum difference between output readings when the same input is applied consecutively. This is the closeness of agreement among consecutive measurements of an output for the same value of input under the same operating conditions, approaching from the same direction. It is usually measured as non- repeatability and expressed as a percentage of span.

CalibrationCalibration• Calibration

It defined, in general, as the process of determination / verification by measurement or comparison with a standard of greater accuracy in order to detect, correlate, report or eliminate by adjusting any deviation in accuracy; or determination of the settings of a control device that correspond to particular values of its characteristics.

Measuring parameters in an Measuring parameters in an IndustryIndustry

PressureTemperatureLevelFlowWeightVibrationsQuality ParametersSpeedPosition

PressurePressure • It is defined as the force per unit area. Pressure is generally measured in pounds per

square inches (psi) or inches of water column (WC) or in bars or Kg/Cm2

Terminologies used in Pressure Terminologies used in Pressure measurementsmeasurements

Static pressure is the pressure of a fluid at rest.

Dynamic Pressure: If the fluid is in motion, its pressure will depend on its flow velocity and it is termed as the dynamic pressure.

Absolute pressure: At sea level atmospheric pressure is 14.7 psi (Also expressed as 1 bar or 100Kpa) but it varies 0.5 psi for every 1000ft elevation. Absolute pressure is measured with respect to vacuum (Zero pressure). In other words Absolute pressure is the Pressure referenced to full vacuum ie atmospheric pressure (1 bar).

Gauge Pressure:-Pressure indicate in Gauge in other words the indicative pressure with out atmospheric pressure

Pressure measuring technique and instrumentsVariety of pressure measurements methods are used, such as manometers, bourdon tubes and bellows, and diaphragm

Pressure Measuring Pressure Measuring InstrumentsInstruments

• Pressure Gauge:• Pressure Switch:• Pressure transmitter:

Principles of Pressure Principles of Pressure MeasurementMeasurement

Pressure Switch (PS)Pressure Switch (PS)

Pressure Transmitter (PT)Pressure Transmitter (PT)

TemperatureTemperature • Temperature is a degree of hotness or coldness the can be measured using a

thermometer. It's also a measure of how fast the atoms and molecules of a substance are moving. Temperature is measured in degrees on the Fahrenheit, Celsius, and Kelvin scales

Terminologies used in Temperature Terminologies used in Temperature measurementsmeasurements

Ambient temperature:- The average or mean temperature of the atmospheric air which is surrounding a sensor or instrument.

Ambient temperature compensation:-An automatic correction which prevents the reading of a sensor or instrument from being affected by variations in ambient temperature

Temperature measuring technique and instrumentsIn general there are four types of temperature sensors based on the following physical properties, which are temperature dependent.

Principles of temperature Principles of temperature MeasurementMeasurement

Expansion of a substance with temperature (TG)

Change in electrical resistance with temperature (RTD)

Change in contact potential between dissimilar metals with temperature (TC)

Changes in radiated energy with temperature (Radiation Pyrometer)

Level MeasurementLevel Measurement

A device that measures the height of material–typically liquid–inside a tank or other vessel.

Principles of Level MeasurementPrinciples of Level MeasurementFloatUltrasonic and radar CapacitanceDifferential pressure

FlowFlowFlow measurement is the quantification of bulk material (fluid) movement

Volumetric flow is the commonest and is used to measure the volume of flow fluid past a given point per unit time.

Mass flow is the mass of fluid past a given point per unit time

Inferential method: - Placing an obstruction in the flow path causes the velocity to increase and the pressure to drop. This pressure difference in the pipe can be used to measure the flow rate. An orifice type is the most common one used in this technique

Velocity methods – Magnetic flow meters depends on this principle that motion between a conductor (the flowing fluid) and a magnetic field develops a voltage in the conductor that is proportional to the velocity of the fluid. Exa: Vortex, Turbine, Ultrasonic

Principles of FLOW MeasurementPrinciples of FLOW Measurement

SensorsSensors• Limit Switches

Proximity sensors

Photo electric sensors Position Sensing

Barcode reader

Actuation technologyActuation technology

Electrical motors (MOV)

Pneumatic Control Valves

Solenoid Valves

Pneumatic actuators

Basics of field instrumentationsBasics of field instrumentations & & TerminologiesTerminologies

• Transducer is a device that converts one physical quantity into another, the second being an analog representation of the physical quantity.

• Sensor: It a device which will sense the presents of physical quantity (Object, temperature etc...) in other word nothing but a transducer

• Transmitter is a signal processing device which receives signal from a sensing device (transducer) and converts it to 4 to20mA or 0 to10v for transmitting to Control or Display devices

• Digital Signals: - The signals from field / to the field have two states as ON of OFF called Digital signals. Widely used digital signals are 24V DC, 230V Ac, and 110V Ac

• Analogue signals: - An analog or analogue signal is any continuous signal for which the time varying feature (variable) of the signal is a representation of some other time varying quantity. It differs from a digital signal in that small fluctuations in the signal are meaningful. Most commonly used analogue signals are 4-20mA and 0-10V

• Protocols: - An agreed-upon format for transmitting data between two devices. The protocol determines the following:

The type of error checking to be used Data compression method, if any How the sending device will indicate that it has finished sending a message How the receiving device will indicate that it has received a message

Commonly used protocols are RS-232, RS-485, Modbus, profibus, field bus and Ethernet protocols

Field Instruments connectionField Instruments connection

PGPS

PT

Field Analogue Junction box (AJB)

Field Digital Junction box(DJB)

ON/OFFController

LinerController

Controlling of Process Controlling of Process parametersparameters

• A control system is a system of integrated elements whose function is to maintain a process variable at a desired value or within a desired range of values. The control system monitors a process variable or variables, and then causes some action to occur to maintain the desired system parameter.

• A control system is a device or set of devices to manage, command, direct or regulate the behavior of other devices or systems

Method of process controlMethod of process control• Manual: It means take necessary action by a man to control the process

parameters. In this case only process indicating instruments will be available.

• Automatic: By using a control device maintains the process parameters with in the accepted limit. Automatic process controls are implemented in four levels as follows Open loop control, Closed loop control, Sequential Controller and Logic controller

• Open loop controller: By this concepts the process parameters (PV) are measured / monitored from particular point and based on the set point - SV (Operation control point) output signal (ON/OFF -Control signal) will be generated and it will actuate / operate the controlling device

• Closed loop controlIf the PV, the objective of control, is used to determine the control action it is called closed loop control system.

Method of process control Method of process control Cont..Cont..

• Sequential ControllerAn automatic sequential control system may trigger a series of equipments in the correct sequence to perform a task. For example various electric and pneumatic transducers may fold and glue a cardboard box, fill it with product and then seal it in an automatic packaging machine.

• Logic controllerPure logic controls were historically implemented by electricians with networks of relays, and designed with a notation called ladder logic. Nowadays, most such systems are constructed with programmable logic controllers.

Logic controllers may respond to switches, light sensors, pressure switches etc and cause the machinery to perform some operation. Logic systems are used to sequence mechanical operations in many applications. Examples include elevators, washing machines and other systems with interrelated stop-go operations.

Logic systems are quite easy to design, and can handle very complex operations. Some aspects of logic system design make use of Boolean logic