Calibration & Testing of Control Instruments Flashcards

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

Answer: 4-20 mA

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.

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

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

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.

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

Answer: 0%, 25%, 50%, 75%, 100%

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.

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

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

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.

A loop calibrator is used primarily to:

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

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.

When performing span adjustment on a transmitter, what are you changing?

Answer: The relationship between the input signal range and the output signal range (gain)

Span adjustment sets the gain or slope of the transmitter's input-to-output transfer function, defining how much output change occurs per unit of input change across the full measurement range.

What is the primary purpose of performing a 'leak test' before calibrating a pressure or differential pressure transmitter?

Answer: To ensure there are no leaks in the calibration tubing or manifold that would cause incorrect applied pressure readings

A leak test confirms that the calibration test equipment connections and tubing are leak-free so that applied pressure is accurately delivered to the transmitter's sensing element without loss.