300+ Instrumentation Engineering Interview Questions – Part 5

1. What is the definition of a gas’s thermal conductivity?

The quantity of heat (in calories) transferred in unit time (seconds) in a gas between two surfaces 1 cm2 in area when the temperature difference between the surfaces is 1oC is defined as thermal conductivity.

2. Define the term “humidity”

It is the amount of water vapour retained by a gas or the moisture content of the air.

3. Define the term “viscosity”

It is a measure of the system’s fluidity. When shearing stress is applied to many fluids, they undergo continuous deformation.

4. What is Pitot tube?

A pitot tube (pitot probe) measures the velocity of fluid flow. It is widely used in industry to calculate the airspeed of aircraft, the waterspeed of boats, and the flow velocity of liquids, air, and gases.

5. Pitot tube advantages

1). Low cost

2). Do not have any moving components; this reduces frictional loss.

3). Simple to install

4). It can introduce fluid flow without stopping it because of its small size.

5). Pressure loss is really little.

6). Can be simply installed in environments with harsh circumstances, including high temperatures and pressure.

7). Some types are also simple to take out of the pipeline.

6. What are the drawbacks of pitot tubes?

They can become clogged with sediment, and the pressure difference detected may be insufficient to provide the desired accuracy for the flow rate under consideration.

7. List the benefits of the orifice plate.

1).Used in a variety of pipe sizes

2). Used in conjunction with a pressure differential device.

3). There are numerous materials available.

8. Applications of pitot tube

In utility streams where great accuracy is not required, the pitot tube is employed. The air duct and pipe system uses it. Air flow velocity is measured using it in aeroplanes. They are utilised to map the flow profile in a duct or channel.

9. List the orifice plate’s drawbacks.

1). Significant permanent pressure loss

2). Reduces slurry service usage

3). The accuracy is determined by the care taken during installation.

4). It possesses square root properties.

10. What are the benefits of an electromagnetic flow meter?

1). It is capable of handling slurries and corrosive fluids.

2). It has a small pressure drop.

3). It can function as a bidirectional meter.

4). Large pipe sizes and capacities are available.

11. Explain the turbine flow metre principle.

When liquid enters through the inlet, the shaft rotates, cutting the magnetic pickup and producing voltage proportional to the inflow of water.

12. List the drawbacks of glass Rotameter.

1). Breakage is possible.

2). It must be installed vertically and is limited to low temperatures.

3). Less precision

4). If the pressure exceeds 35 kg/cm3, the tube will be damaged.

13. Explain the vortex flow meter principle.

It is based on vortex shedding, which occurs when a gas or liquid flows around an object that is not stream lined. When fluid flows pass an obstacle, boundary layers of slow moving fluid form along the outer surface of the obstacle, preventing the flow from following contours of the obstacle on its downstream side.

14. Why do we need mathematical process modelling?

The physical equipment needed to control the chemical process has not yet been built. As a result, we can’t experiment to see how the process reacts to different inputs, and thus can’t design an appropriate control system. If the process equipment must be replaced,

The procedure is expensive and open to experimentation. As a result, we require a simple description of how the process responds to various inputs, which mathematical models can provide to the control designer.

15. Define continuous processes.

A continuous process is one in which materials or work flow more or less continuously through a plant apparatus while being treated. The problem with continuous processes is caused by changes in load.

16. Define batch processes.

A batch process is one in which the materials or work are stationary at one physical location while being treated.

17. Explain proportional band.

The proportional band is defined as the change in input required by the proportional controller mode to produce a full-scale change in output.

18. Explain offset?

It is the steady-state deviation (error) caused by a change in the value of the load variable.

19. What does integral (reset) windup mean?

Overcharging occurs when there is a continuous error in the integral capacitor, which must discharge via a long time constant discharge path, preventing a quick return to the desired control point.

20. How will air be vented in the D.P. cell? What happens if seal pots are used?

Opening the vent plugs on a liquid service transmitter allows air to escape. When using seal pots, isolate the primary isolation valves and open the vent valves. Using a pump, fill the line from the transmitter drain plug.

21. Define cascade control.

Cascade control is a two-loop control system in which the set point of one loop (the inner loop) is the output of the controller of the other loop (the outer loop)

22. What role does an I/P converter play in a control system?

In some process loops, the controller and final control element are both electronic. To connect these two, we need a device that converts electric current linearly into gas pressure (4-20mA to 3-15 psi). This type of device is known as I/P converter.

23. Define control valve cavitation?

When a liquid enters a valve and the static pressure at the vena contracta drops to less than the fluid vapour pressure before recovering to above the fluid vapour pressure, the vapour bubbles formed at the vena contracts implode or collapse. This is referred to as cavitation.

24. Why is instrument calibration important?

Calibration of all instruments is critical because it allows the instrument to be checked against a known standard and, as a result, errors in accuracy can be identified.

25. What is LVDT?

The linear variable differential transformer is what converts linear motion into electrical signals. It has a single primary winding and two secondary windings.

26. What is the range of LVDT?

1.25mm to250m

27. What is Controlled Mexium?

It is the process energy or material that controls a variable. The controlled variable is a property or condition of the controlled medium. For example, in a tank where the temperature is automatically controlled, the controlled variable is temperature and the controlled medium is water.

28. What is the purpose of a three-way manifold valve?

If you apply too much pressure to your differential pressure transmitter, you risk damaging it. This is referred to as over-ranging the transmitter. A three-way manifold valve prevents the instrument from becoming over-ranged. It also allows the transmitter to be isolated from the process loop.

29. What is Manipulated variable?

It is the quantity or condition that the automatic controller changes in order to affect the value of the controlled variable.

30. What exactly is a plant layout?

A proper layout is required for a good process to run smoothly. The primary goal of a plant layout should be to have a low handling cost and a short throughput time.

31. Types of plant layout

1). Plant layouts are classified into two types:

2). Product or straight-line layouts: In this, the flow from one operation to the next is minimised for any product class as machinery is located.

3). Process arrangements, also known as functional arrangements, are the grouping of similar facilities.

32. What is impedance?

The opposition to the flow of current in an AC circuit.

33. What is reactance?

Capacitance or inductance creates resistance to the flow of alternating current.

34. What is Error?

The difference between the signal’s indication and its true value.

35. What is Span Error?

It is the difference between the actual and specified spans, expressed as a percentage of the specified span.

36. What is Zero Error?

It is the error of a device operating under the specified operating conditions when the input is in the lower range.

37. Define Static gain

It is the ratio of the change in output to the change in input after the steady state has been reached.

38. What is Reset Action?

It is the movement of the value at a rate proportional to the magnitude of the deviation.

39. What is rate action?

It is defined as a continuous linear relationship between the rate of change of the controlled variable and the position of the final control element. Value motion is produced by rate action in proportion to the rate of change of actual measurement.

40. Explain repeatability?

The degree of agreement between a series of consecutive output measurements for the same value of the measured signal under the same operating conditions.

41. Explain Reproducibility?

The degree of agreement between repeated measurements of output for the same input value taken under the same operating conditions.

42. Define Response?

It is the general behaviour of a device’s output as a function of input, both in time and in space.

43. Explain proportional band

It is the set of controlled variable values that correspond to the full operating range of the final control element.

44. What is the seal liquid used for filling impulse lines on crude and viscous liquid?


45. What exactly is absolute pressure?

The total pressure in the system is referred to as absolute pressure.

Absence pressure = Gauge pressure + atmospheric pressure

46. What exactly is absolute zero pressure?

Vacuum = 760 mm Hg Absolute zero

47. What is the highest vacuum setting?

760 mm Hg is the maximum vacuum.

48. Thermistor is a _________

Digital transducer

49. Resolution of a transducer depends on

Diameter of wire

50. What exactly is vacuum?

Any pressure less than atmospheric pressure is referred to as vacuum.

300+ Instrumentation Engineering Interview Questions – Part 1

300+ Instrumentation Engineering Interview Questions – Part 2

300+ Instrumentation Engineering Interview Questions – Part 3

300+ Instrumentation Engineering Interview Questions – Part 4

300+ Instrumentation Engineering Interview Questions – Part 6

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