Level measurement interview questions

What is level?

The total quantity of substance stored in a tank or vessel.

Different types of level measurement instruments used in industries are

Gauge glass, pressure gauge -scale graduated in %of level, rope and weight, dipsticks, hydrostatic methods, purged methods, displacer methods, load cells, nuclear methods, capacitance, ultrasonic methods etc.

Explain how a leveltrol works?, Name the parts of leveltrol?

As the name indicates it is used for measuring level.The leveltrol works on the buoyancy principle .leveltrol has a float chamber which contains float submerses proportionately with a liquid level rise.The amount of submersion of displacer depends on the liquid density, which produces a torque. The amount of torque produced is measured in terms of %level.

Parts of leveltrol:

Float, float chamber, torque lever, knife edge, feedback bellows, air relay, restriction, flapper, nozzle

What type of level measuring instrument is suitable for a closed tank?

If the level measurement is required for a fixed and small height, a leveltrol is more suitable. If it is for a total height, then either static head or a differential pressure transmitter with its HP side connected to the bottom of the tank and LP side connected to the top of the tank to a gas phase.

What are zero suppression and zero elevation in level measurement?

Zero suppression: when a static head transmitter is installed below the zero liquid level the transmitter gets a positive error in level measurement. This error is corrected by a zero suppression kit.

Zero elevation: when a static head transmitter is connected above zero liquid level the transmitter gets a negative error in level measurement. This error is corrected by zero elevation kit.

What is the interface in liquid level measurement?

An interface is the separation point between the two dismissible liquids levels in a vessel, the condition arises when the liquid does not mix due to its chemical composition and difference in density.

How to calibrate a leveltrol for an interface level measurement?

Fill the leveltrol chamber 100% with the lower density liquid and adjust its zero for 4 ma output. Drain the liquid and fill the leveltrol chamber 100% with the higher density liquid and adjust its span for 20 ma output.

Why is static head level transmitter more suitable than a leveltrol in surge tank?

A leveltrol has a limitation in measuring the maximum height of liquid. Considering huge surge tank static head transmitter is more suitable.

State the difference between float and displacer?

Float is used in level switch (6 inches)

The displacer is used in the level transmitter. (14inch, 48inch, 60inch, 72inch)

Write the formula for calculating a static head in Kpa?

Static head = qgh

q=density of the liquid g =gravity h= height of the liquid column

What happens if the displacer has a hole in it, what will be the output of that leveltrol mechanism?

The output will be minimum ie 4MA.

What will be the output if the displacer fell down in online?

The output will be maximum ie 20MA.