instrumentation control process
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Instrumentation & Control
Registration No: - 10D2-113031
Program: - B-Tech (Pass) Electronics
What is instrument ?
Instrument is a devices which is used to measure,
monitor, display etc. of a process variable.
What are the process Variable ?
The process Variable are :
A process of ( liquid, gas, or electricity) move steadily and
continuously in a current or stream.
What is Flow ?
go from one place to another in a steady stream, typically in
large numbers. .
Flow can be measured in a variety of ways. Positive-
displacement flow meters accumulate a fixed volume of fluid
and then count the number of times the volume is filled to
What is pressure ?
Pressure is force per unit area applied in a direction perpendicular to the surface of an object .
Pressure is the ratio of force applied per area covered
P = F/A he unit of pressure is the Pascal
Pa = N = kg m/s2 =kg The Pascal is also a unit of stress and the topics of pressure and
stress are connected.
Bed of nails (not really pressure but shear strain?)
Finger bones are flat on the gripping side to increase surface area in
contact and thus reduce compress ional stresses .
What is Temperature ?
In a qualitative manner, we can describe the temperature of an object as that which determines the sensation of warmth or coldness felt from contact with it.
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.
A temperature is a numerical measure of hot or cold. Its measurement is by detection of heat radiation or particle velocity or kinetic energy, or by the bulk behavior of a thermometric material. It may be calibrated in any of various temperature , Celsius, Fahrenheit, Kelvin, etc. The fundamental physical definition of temperature is provided by thermodynamic .
What is Level ?
A device for establishing a horizontal line or plane by means of a
bubble in a liquid that shows adjustment to the horizontal by
movement to the center of a slightly bowed glass tube
A measurement of the difference of altitude of two points by
means of a level .
Horizontal condition; especially : equilibrium of a fluid
marked by a horizontal surface of even altitude
The magnitude of a quantity considered in relation to an
arbitrary reference value; broadly : magnitude, intensity
What is meaning of Loop in instrumentation ?
In computer programming, a loop is a sequence of instructions that is continually repeated until a certain condition is reached. Typically, a certain process is done, such as getting an item of data and changing it, and then some condition is checked such as whether a counter has reached a prescribed number. If it hasn't, the next instruction in the sequence is an instruction to return to the first instruction in the sequence and repeat the sequence. If the condition has been reached, the next instruction "falls through" to the next sequential instruction or branches outside the loop. A loop is a fundamental programming idea that is commonly used in writing programs. An infinite loop is one that lacks a functioning exit routine . The result is that the loop repeats continually until the operating system senses it and terminates the program with an error or until some other event occurs (such as having the program automatically terminate after a certain duration of time).
Define the types of loop control ?
Open loop control system .
Close loop control system .
Cascade loop control system .
What is open loop system ?
An open-loop controller, also called a non-feedback controller, is a type
of controller that computes its input into a system using only the current
state and its model of the system.
A characteristic of the open-loop controller is that it does not use feedback
to determine if its output has achieved the desired goal of the input. This
means that the system does not observe the output of the processes that it is
controlling. Consequently, a true open-loop system can not engage in
machine learning and also cannot correct any errors that it could make. It
also may not compensate for disturbances in the system.
An open-loop controller is often used in simple processes because of its
simplicity and low cost, especially in systems where feedback is not critical.
A typical example would be a conventional washing machine .
Open loop control system Diagram
What is close loop system ?
Closed loop control systems are those that provide feedback of the actual state of the
system and compare it to the desired state of the system in order to adjust the system.
The closed loop control system is a system where the actual behavior of the system is
sensed and then fed back to the controller and mixed with the reference or desired
state of the system to adjust the system to its desired state. The objective of the
control system is to calculate solutions for the proper corrective action to the system
so that it can hold the set point (reference) and not oscillate around it.
When a scale out triggering event occurs, the input parameter that triggers the event
is monitored around its set point. The system increases and decreases capacity on
demand to stay as close as possible to the set point for the triggering parameter.
With closed loop systems, you can evaluate the system near the set point using a PID
control algorithm or similar control scheme. A simpler approach, such as hysteretic,
can be very effective and can be implemented with less complexity and tuning.
Close loop system diagram .
Close loop Block diagram
What is Cascade loop control system ?
A cascade control system is a multiple-loop system where the primary variable is
controlled by adjusting the set point of a related secondary variable controller. The
secondary variable then affects the primary variable through the process.
The primary objective in cascade control is to divide an otherwise difficult to control
process into two portions, whereby a secondary control loop is formed around a
major disturbances thus leaving only minor disturbances to be controlled by the
The use of cascade control is described in many texts on process control
Cascade control is most advantageous on applications where the secondary closed
loop can include the major disturbance and second order lag and the major lag is
included in only the primary loop. The secondary loop should be established in an
area where the major disturbance occurs.
Cascade loop control system Diagram.
Pressure measurements .
Pressure is the force exerted per unit area
Pressure is the action of one force against another force. Pressure is force applied to, or
distributed over, a surface. The pressure P of a force F distributed over an area A is
defined as P = F/A
TOTAL VACUUM - 0 PSIA
NOM. 14.7 PSIA
Pressure Measurement Terms.
Measured above total vacuum or zero absolute. Zero absolute represents total lack of pressure.
The pressure exerted by the earths atmosphere. Atmospheric pressure at sea level is 14.696 PSI. The value of atmospheric pressure decreases with increasing altitude.
Same as atmospheric pressure.
The pressure above atmospheric pressure. Represents positive difference between measured pressure and existing atmospheric pressure. Can be converted to absolute by adding actual atmospheric pressure value.
The difference in magnitude between some pressure value and some reference pressure. In a sense, absolute pressure could be considered as a differential pressure with total vacuum or zero absolute as the reference. Likewise, gauge pressure (defined above) could be considered as Differential Pressure with atmospheric pressure as the reference.
mm of Hg 5171
mm of WC 70358
in of WC 2770
Types of Pressure Instruments
Pressure Gauges (Vacuum, Compound, Absolute, Gauge)
Differential Pressure Gauge
Pressure Switch (Vacuum, Absolute, Gauge)
Differential Pressure Switch
Pressure Transmitter (Vacuum, Absolute, Gauge)
Differential Pressure Transmitter
PRESSURE SWITCH DIFFERENTIALPRESSURE
A Pressure Gauge is used for measuring the pressure of a gas or liquid.
A Vacuum Gauge is used to measure the pressure in a vacuum.
A Compound Gauge is used for measuring both Vacuum and Pressure.