CCST Calibration & Testing of Control Instruments

Question 1

What is the standard live zero signal range for a 4-20mA transmitter used in industrial process control?

Accepted Answer

4-20 mA

Answer

The 4-20mA range is the industry-standard signal range, where 4mA represents 0% of span and 20mA represents 100% of span, with the live zero at 4mA allowing detection of broken wire conditions.

Question 2

What does 'zero suppression' mean when calibrating a differential pressure transmitter for level measurement?

Accepted Answer

Setting the zero point below the actual process zero to account for a static head offset

Answer

Zero suppression shifts the transmitter's zero point downward to compensate for a positive static head caused by wet legs or elevated mounting, so the transmitter reads correctly across the true measurement span.

Question 3

During a 5-point calibration of a pressure transmitter, at what percentages of span should calibration points typically be checked?

Accepted Answer

0%, 25%, 50%, 75%, 100%

Answer

A standard 5-point calibration uses 0%, 25%, 50%, 75%, and 100% of span to adequately characterize linearity and identify any non-linear errors across the full range.

Question 4

What is 'as-found' data in the context of instrument calibration records?

Accepted Answer

The calibration data recorded before any adjustments are made during a calibration event

Answer

As-found data captures the instrument's actual performance at the time of calibration before any corrections or adjustments, providing a record of instrument drift and compliance history.

Question 5

A loop calibrator is used primarily to:

Accepted Answer

Source and measure 4-20mA signals to test and calibrate transmitters and I/P converters

Answer

A loop calibrator can source a precise 4-20mA signal to simulate a transmitter output and also measure the milliamp signal produced by an actual transmitter, making it the primary tool for analog loop calibration.

(CCST) Certified Control Systems Technician Practice Test

(CCST) Certified Control Systems Technician Practice Test

CCST Calibration & Testing of Control Instruments