ISA CAP Control Systems & Instrumentation 2

Question 1

In a cascade control system, the output of the primary (master) controller becomes the:

Accepted Answer

Setpoint of the secondary (slave) controller

Answer

In cascade control, the primary controller's output sets the setpoint for the secondary controller, allowing faster disturbance rejection.

Question 2

A thermocouple produces an EMF based on the Seebeck effect. What is the purpose of cold junction compensation?

Accepted Answer

To correct for the reference junction temperature not being at 0°C

Answer

Cold junction compensation accounts for the actual reference junction temperature so the measured EMF accurately represents the process temperature.

Question 3

What does the term 'rangeability' refer to in a control valve?

Accepted Answer

The ratio of maximum to minimum controllable flow

Answer

Rangeability is the ratio of the maximum to minimum flow that the valve can control while maintaining its specified flow characteristic.

Question 4

In process control, what is 'offset' in the context of proportional-only control?

Accepted Answer

A sustained steady-state error between setpoint and process variable

Answer

Proportional-only controllers have inherent offset because a nonzero error is required to produce a nonzero control output.

Question 5

A 4-20 mA transmitter is configured for a 0-100 psi range. What process pressure corresponds to a signal of 12 mA?

Accepted Answer

50 psi

Answer

12 mA is the midpoint of the 4-20 mA span (16 mA range), representing 50% of the 0-100 psi range, which equals 50 psi.

(ISA CAP) ISA Certified Automation Professional Practice Test