JNTU
JNTU B.Tech III PROCESS CONTROL INSTRUMENTATION Previous Question Paper (April - 2018 - R15)
Note: This question paper contains two parts A and B. Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit.
Part A
Explain the term degree of freedom of a process.
Answer
The degree of freedom of a process is defined as the minimum number of independent variables that must be specified to uniquely determine the state of the system. It is mathematically calculated as the difference between the total number of process variables and the number of independent equations relating those variables.
What is Batch process? Name the applications.
Answer
A batch process is a manufacturing method where a finite quantity of raw materials is processed through a series of steps to produce a specific amount of final product within a defined time frame. Unlike continuous processes, the system operates in discrete cycles, where the equipment is cleaned or prepared between batches, and the process parameters may vary over the duration of the cycle.
Common applications include:
- Pharmaceutical manufacturing (e.g., drug formulation and synthesis).
- Specialty chemical production (e.g., dyes, paints, and additives).
- Food and beverage processing (e.g., brewing, dairy products, and baking).
- Biotechnology (e.g., fermentation processes).
Differentiate Discontinuous and Continuous Controller modes.
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Discuss why derivative control mode cannot be used alone.
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Define Integral Square Errors (ISE).
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Differentiate SERVO problem and REGULATORY problem.
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What is “quack opening” control valve?
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A spring less pneumatic actuator has a diaphragm of 500cm2 area. Its positioner operates from 0.2 to 1 kg/cm2. The underside cushion pressure is set at 0.3 kg/cm2. What range of thrust load can be accommodated?
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List out the main advantages of Cascade control.
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Briefly discuss the purpose of ratio station in a ratio control loop.
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Part B
A Tank system having a time constant of 0.5 min and a resistance of 0.25min/m2 is operating at a steady state with an inlet flow of 2m3/min. The flow is suddenly increased to 3m3/min. Plot the response of the tank level (Assume area of cross section A = 2m2).
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With an example explain Self-regulation of a process. Write the effect of time delay in process control system.
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Obtain the mathematical modelling of Non-Interacting system.
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Discuss the effects of an integral controller on the closed loop response of first order process.
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Two first order level processes connected in cascade. Find out total transfer function and output when the input is subjected to unit step change and draw the response.
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Explain the operation of Pneumatic P+I controller with neat sketch.
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Compare PI and PID control modes used in process control.
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Design a proportional integral controller with a proportional band of 30% and an integration gain of 0.1 %. The 4-20 mA input converts to a 0.4 – 2 volt signal and the output is to be 0-10 volts. Calculate the values of Gp, Gi, R2, R1 and C respectively with reference to the figure.
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Explain controller tuning using Damped oscillation method.
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Define Integral of the time weighted Absolute Error ITAE and its dependence on time.
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For a temperature control system whose ultimate gain is 0.4 PSI/ 0C and ultimate time period is 2 minutes. Determine setting for various controllers using Z-N ultimate method.
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Find the working force resulting from 250N applied to a 1.25 cm radius forcing piston in a hydraulic actuator (i) if the working piston has a radius of 10 cm Then (ii) find the hydraulic pressure.
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Explain the construction and working of Butterfly Valves with the help of a neat figure.
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What is the function of Valve Positioner? Describe the operation of Valve Positioner for Pneumatic Spring Actuator with neat figure.
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A split range control has been designed for a cooling operation with two control valves. The controller output varies from 4-20mA. The small valve positioner has been designed to open from 0% to 100% when the controller output varies from 4 to 12 mA and remain open afterwards. The large valve positioner has been designed to operate for 10mA to 20mA from 0% to 100%. Assuming both the valves are linear and maximum flow through small valve is 10% of the maximum flow through large valve, draw controller output current Vs stem position of both valves as well as that of total flow if maxi flow through large valve is 2000m3/hr.
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Describe the dynamic characteristics of a Cascade control system with example.
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Give the designing of feedforward controllers with an example for stirred tank heater.
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