AutoQuiz is edited by Joel Don, ISA's social media community manager.
This automation industry quiz question comes from the ISA Certified Control Systems Technician (CCST) program. Certified Control System Technicians calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables. Click this link for more information about the CCST program.
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
e) none of the above
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.
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.”
Reference: Goettsche, L.D. (Editor), Maintenance of Instruments and Systems, 2nd Edition
About the Editor
Joel Don is the community manager for ISA and is an independent content marketing, social media and public relations consultant. Prior to his work in marketing and PR, Joel served as an editor for regional newspapers and national magazines throughout the U.S. He earned a master's degree from the Medill School at Northwestern University with a focus on science, engineering and biomedical marketing communications, and a bachelor of science degree from UC San Diego.