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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