ISA Certified Control Systems Technician (CCST) program


Certified Control System Technicians (CCSTs) calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables.

CCST question

To change a 4–20 mA analog signal from a transmitter to the signal required by a digital controller, a(n) _____ must be between the transmitter and controller in the measurement loop. 

A. I/P transducer
B. P/I transducer
C. DP transmitter 
D. A/D converter

CCST Answer

The correct answer is D, “A/D converter.” A digital controller requires a digital signal as its input. A 4–20 mA transmitter outputs an analog signal. Therefore, a device to convert an analog (A) signal to a digital (D) is required. This class of device is referred to as an “A/D converter.”
An “I/P transducer” is used to convert an analog current (I) signal to a pneumatic (P) signal, as for actuation of final control elements. A “P/I transducer” is used to convert a pneumatic signal (P) to an analog current (I) signal, as for a pneumatic transmitter in a programmable logic controller loop.
A “DP transmitter” is a differential pressure transmitter, which can output a pneumatic, an analog, or a digital signal, depending on the model of transmitter used.


Reference: Goettsche, L.D. (Editor), Maintenance of Instruments and Systems, Second Edition, ISA, 2005.


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