Plant Operator Selection System Test Process Control and Instrumentation 3

Question 1

The term 'turndown ratio' for a flow meter describes:

Accepted Answer

The ratio of the maximum to minimum measurable flow with acceptable accuracy

Answer

Turndown ratio defines the usable measurement range of a flow meter; a 10:1 turndown means it reads accurately from 100% down to 10% of full scale.

Question 2

In a heat exchanger control scheme, the coolant flow is increased when the process outlet temperature rises above setpoint. This is an example of:

Accepted Answer

Feedback control

Answer

Feedback control measures the process output (temperature), compares it to the setpoint, and adjusts the manipulated variable (coolant flow) to correct the deviation.

Question 3

What is the purpose of an interlock in a process plant?

Accepted Answer

To automatically prevent or stop an operation when an unsafe condition is detected

Answer

Interlocks enforce safe operating limits by automatically triggering actions (closing valves, tripping pumps) when process parameters reach dangerous levels.

Question 4

A pressure transmitter has a range of 0-100 psig and a 4-20 mA output. What current signal corresponds to 50 psig?

Accepted Answer

12 mA

Answer

50 psig is 50% of span; 50% of the 16 mA span (4 to 20 mA) is 8 mA, added to the zero of 4 mA gives 12 mA.

Question 5

Control valve hysteresis is best described as:

Accepted Answer

The difference in valve position between increasing and decreasing signal strokes

Answer

Hysteresis causes a valve to reach different positions for the same signal depending on whether it is traveling upward or downward, degrading control precision.

Plant Operator Selection System Test Practice Test

Plant Operator Selection System Test Practice Test

Plant Operator Selection System Test Process Control and Instrumentation 3