CCST Calibration & Testing of Control Instruments 2

Question 1

What is the key difference between accuracy and precision in instrument measurement?

Accepted Answer

Accuracy is how close a measurement is to the true value; precision is how repeatable measurements are

Answer

Accuracy describes closeness to the true or accepted value, while precision describes the repeatability or reproducibility of measurements regardless of how close they are to the true value.

Question 2

What is 'hysteresis' in a control instrument?

Accepted Answer

The difference in output readings when approaching the same input value from increasing versus decreasing directions

Answer

Hysteresis is the phenomenon where an instrument gives different output readings for the same input value depending on whether the input is increasing or decreasing, caused by mechanical friction, backlash, or magnetic effects.

Question 3

Why must calibration standards used in the field be NIST-traceable?

Accepted Answer

To ensure measurements are linked through an unbroken chain of comparisons to national measurement standards, ensuring accuracy validity

Answer

NIST traceability provides an unbroken documented chain of calibrations from the working standard back to NIST's primary standards, ensuring the reference standard's accuracy is known and defensible.

Question 4

An RTD (Resistance Temperature Detector) operates on what principle?

Accepted Answer

The predictable change in electrical resistance of a metal with temperature

Answer

RTDs exploit the well-characterized positive temperature coefficient of resistance in pure metals like platinum, where resistance increases predictably and repeatably with temperature according to known equations.

Question 5

What is 'deadband' in a control instrument or controller?

Accepted Answer

A range of input values over which no change in output occurs, used to prevent unnecessary control action

Answer

Deadband is an intentional or inherent zone around a setpoint or threshold within which no output change occurs, reducing wear on final control elements and preventing control system hunting.

(CCST) Certified Control Systems Technician Practice Test

(CCST) Certified Control Systems Technician Practice Test

CCST Calibration & Testing of Control Instruments 2