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Instrumentation and Control Engineering Materials-Free Download
• Question 45. Can We Use A Control Valve Without Positioner?
Control valve can not be without positioner. The purpose of the positioner is to control the control valve stroke so as to keep the valve in desired position. The positioner receives signal from the controller, and send the boosted signal to the actuator to reach the desired position as and when the valve reaches the desired position the positioner cuts the boosted signal to the actuator and keeps the position.
• Question 46. Why 4-20 Ma Signal Is Preferred Over A 0-10v Signal?
Generally in a transistor some amount of voltage is required for turning it on. This voltage is the cut in voltage. Up to this voltage the exists a nonlinearity in its characteristics. Beyond this cut in voltage the char. of transistor is linear. This nonlinear region lays between 0-4ma, beyond 4ma it linear. This is why 4-20 ma range is used.
• Question 47. What Is Remote Mount With Mta Option? (in Case Of Dual Sensor Vortex Flowmeter, Rosemount Has Written In Its Catalog Drawings)?
Remote mount with MTA means MTA connector for mounting remote connection.
MTA is the Connector used for connection. Generally we called it MTA Connector.
There are many types of MTA connector such as MTA 100connectors, Mta 156 connectors etc.
• Question 48. How To Write The Program For Single Push Button By Using Ladder Diagram?
1. Create a Push button
2. Connect a Counter series to PB
3. Create a compare button
4. Initialize 1 at one end
5. Counter output in another
6. Connect the Coil which has to be energized
7. Initialize 2 at one end
8. Counter output in another
9. Connect the Coil which has to be reenergized.
1. List any four objectives of process control.
Suppressing the influence of external disturbances, Optimizing the performance, Increasing the productivity, Cost effective.
2. Define process
Any system comprised of dynamic variables usually involved in manufacturing and production operations. It is defines as a series of operations during which some materials are placed in more useful state.
3. What is manipulated variable
It is a variable which is altered by the automatic control equipment so as to change the variable under and make it conform with the desired value.
4. Define Controlled variable
It is the quantity of control system which is directly measured and controlled.
5. What do you mean by self regulation?
The output will move from one steady state to another for the sustained change in input. This means that for change in some input variable the output variable will rise until it reaches a steady state (inflow = outflow). It is the tendency of the process to adopt a specific value of controlled variable for nominal load with no control operations.
Why do we need mathematical modeling of process?
The physical equipment of the chemical process we want to control have not been constructed. Consequently we cannot experiment to determine how the process reacts to various inputs and therefore we cannot design the appropr iate control system. If the process equipment needs to be available for experimentation the procedure is costly. Therefore we need a simple description of how the process reacts to various inputs, and this is what the mathematical models can provide to the control designer.
7. Name different test inputs.
Step, Ramp, Impulse, Sinusoidal, Pulse inputs
8. Name a process giving inverse response
Drum boiler system, in which the flow rate of the cold feed water is increased by a step the total volume of the boiling water and consequently the liquid level will decreased for a short period and then it will start increasing.
9. Define interacting system and give an example.
Load changes in first process affects the second process and vise versa when both are connected in series nature is called interacting system. Eg. Two level tanks are connected in series.
10. A tank operating at 10ft head, 51pm outflow through a valve and has a cross section area of 10 sq f calculate the time constant.
11. What is meant by non-self regulation?
A system that grows without limit for a sustained change in input (constant outflow or outflow independent of inflow condition).
12. Write any two characteristics of first order process modeling
The smaller the value of time constant the steeper the initial response of the system. A first order lag proce ss is self regulating the ultimate value of the response equal to Kp (steady state gain of the process) for a unit step change in the input.
13. Distinguish between continuous process and batch process.
A process in which the materials or work flows more or less continuously through a plant apparatus while being treated is termed as continuous process. The problem of continuous process is due to load changes. (e.g.) storage vessel control.
A process in which the materials or work are stationary at one physical location while being treated is termed as batch process. (e.g.) furnace.
14. Explain the function of controller.
The element in a process control loop that evaluated error of the controlled variable and initiates corrective action by a signal to the controlling variable.
15. What is the purpose of final control element?
Components of a control system (such as valve) is used to directly regulates the flow of energy or materials to the process. It directly determines the value of manipulated variable.
16. Define Process control
It is the scheme that describes how much the manipulated variable should change inorder to bring the controlled variable back to the setpoint.
17. List the two types of process control.
Direct process control
– Controlled variable directly indicates the performance of the process Eg. Water heater system
InDirect Process control the performance of the process.
– Controlled variable indirectly indicates Eg. Annealing
18. What is Servo operation and Regulatory operation.
If the purpose of the control system is to make the process follow the changes in setpoint as quick as possible, then it is servo operation.
19. What is mathematical modeling.
Set of equations that characterize the process is termed as Mathematical Modelling.
20. Define an non-interacting system.
The dynamic behaviour one tank is affected by the other, but the reverse is not true, then it is non-interacting system. Here the liquid heads are independent of each other.
21. Define an interacting system.
The dynamic behavior one tank is affected by the other, but the reverse is also true, then it is non-interacting system. Here the liquid heads are dependent of each other.
22. Mention two drawbacks of derivative action
(i) The output of controller is zero at constant error condition.
(ii)It will amplify the noise present in the error signal.
23. What are the steps involved to design a best controller?
Define appropriate performance criterion (ISE, IAE, ITATE). Compute the value of the performance criterion using a P, PI, or PID controller with the best setting for the adjusted parameters Kp, Ti, Td. Select controller which give the best value for the performance criterion.
24. Define proportional control mode
A controller mode in which the controller output is directly proportional to the error signal P=Kpep+p0 P-controller output Kp= Propotional gain, ep=error in percent of variable range, P0-Bias.
25. Define proportional band.
Proportional band is def ined as the change in input of proportional controller mode required to produce a full-scale change in output
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