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 :

    1. Flow

    2. Pressure

    3. Temperature

    4. Level

  • 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

    measure flow.

  • 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

    Open loop

  • 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

    primary controller.

    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.

    Cascade loop

  • 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








    NOM. 14.7 PSIA

  • Pressure Measurement Terms.

    Absolute Pressure

    Measured above total vacuum or zero absolute. Zero absolute represents total lack of pressure.

    Atmospheric 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.

    Barometric Pressure

    Same as atmospheric pressure.

    Gauge 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.

    Differential Pressure

    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.

  • Pressure Units.

    psi 100

    bar 6.895

    mbar 6895

    mm of Hg 5171

    mm of WC 70358

    in of WC 2770

    Kg/cm2 7.032

    Pascal 689476

    kPa 689.5

    atm 6.805

  • 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





    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.