Basic Instrumentation Interview Questions and Answers
Basic Instrumentation Interview Questions and Answers are given. Download the pdf file for More interview question and Answers. Instrumentation Interview Questions and Answers pdf file attached in below.
List of Instrumentation Interview Questions and Answers
- Mention the types of orifice plates . What are their uses?
Concentric, Segmental and Eccentric are the three different types of orifice plates. Their uses are:
- Concentric plates are used for liquid, gases and steam. These plates contain Concentric holes in them.
- Segmental plates contain holes in the form of segments of the circle. They are used for measuring colloidal and sherry flows.
- Eccentric plates contain eccentric holes. They are applied to measure viscous and sherry flow.
- How can you locate an orifice in the pipeline?
After welding an orifice tab to the orifice plate, it is extended out of the line. This indicates the location of the orifice plate.
- What is the purpose of the orifice tab?
Some of the reasons for providing an orifice tab are to give an Indication of the orifice plate in a line, to mark orifice diameter, to locate the tag number of the orifice plate and to mark the inlet of the orifice.
- What is Bernoulli’s theorem and its application?
Bernoulli’s theorem affirms that the ‘total energy of a liquid flowing from one point to another remains constant’ and it is mainly true for liquids that cannot be compressed. The speed of the fluid, its dynamic pressure and its kinetic energy are directly proportional to one another. Bernoulli’s theorem is applied for measuring pressure on the wings of the aircraft and for calibrating the airspeed indicator. In carburettors, it is used to lower pressure in the venturi tubes.
- How to calibrate a D.P. transmitter?
A D.P. transmitter can be calibrated by Adjusting to zero of the Transmitter, conducting a static pressure test. This is done by applying equal pressure on both sides of the transmitter. It should be observed that Zero should not shift to either side. static alignment should be done if the zero shifts to either side. A vacuum test can be performed by giving an equal vacuum to both sides. In this condition also, the Zero should not shift. Calibration can be done by providing a 20 psi air supply to the transmitter and vent L. Then the output of the instrument should be connected to the standard test gauge. After adjusting to zero, the required pressure should be applied to the high-pressure side. Now adjust the span and calibrate.
- Explain the use of a single-seated valve?
In smaller sizes where an absolute shut off is required, a single seated valve is preferred. The use of a single-seated valve is determined by the pressure drop across the valve where it is either in the closed or almost closed position.
- What are the different parts of a pressure gauge? What is the use of hairspring in the pressure gauge?
The pressure gauge consists of components like a dial, a pointer, a hairspring, pinion and sector gears, a connecting link and a ‘C’ type bourdon tube. The purpose of a Hairspring is to control the torque. It is useful in eliminating any type of linkage.
- How can a D.P. transmitter be used in a closed tank?
The bottom of the tank in a closed tank is connected to the high-pressure side of the transmitter. The lower pressure side of the transmitter is connected to the top of the tank. This method can be used to measure the vessel pressure.
- How can a D.P. transmitter be used in an open tank?
The lower pressure side is connected to the atmosphere in the case of an open tank. The whole of the pressure is applied to the high-pressure side only. In an open tank, the vessel pressure is measured only through the high-pressure side.
- What is the working of an electronic level troll?
The level of buoyancy varies as a result of changes in the liquid level. This causes alterations in the net weight of the displacer leading to either an increase or decrease in the load on the torque arm. The changes observed are proportionate to change in the specific gravity of the liquid. The torque tube movement changes following the angular motion of the rotor in RVDT . This causes a rotor change which is proportional to the rotor displacement. This is then converted and amplified in the form of a D.C. current.
- Elaborate the working on an enraf level gauge.
The working of an Enraf level gauge is based on the servo powered null balance technique. A displacer is used for level sensing. A capacitive balance system controls the two-phased servo motor. This wind and unwinds the measuring wire till the time the tension in the weight springs equals the weight of the displaced part that is immersed in the liquid.
The sensing system in balance also measures the two capacitances. This is achieved by moving the central sensing rod provided by the two capacitor plates and the si plates.
- What are the various uses of a valve positioner?
The uses of a Valve positioner include reverse valve operations when the bench set is not standard when there are significant line pressure changes in the valve, split range, viscous liquids, valve hysteresis and when quick action is needed.
- Why are the uses of thermowell? What materials are used in thermowells?
When it is not suitable to expose a temperature sensor directly to a material, thermowells are used. They help in protecting against damage, corrosion, erosion, abrasion and other similar high-pressure processes. A thermowell also safeguards a sensor from physical damage which occurs during handling and normal operations.
- What is the method to carry out an automatic reference junction compensation in temperature recorders?
A variable nickel resistor is used in automatic reference junction compensation. Along with the temperature changes, the resistance also changes. The reference junction compensator is located in such a way that it is placed at the temperature of the reference junction. The reference junction refers to the point where the dissimilar wires of the thermocouple are rejoined. This joint is located at the terminal end of the instrument.