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

All of the following instrumentation bus networks can be implemented with a single pair of wires, except for?

A. Foundation Fieldbus
B. DeviceNet
C. AS-i

CCST Answer

The correct answer is B, "DeviceNet." Foundation Fieldbus (FFB), Actuator-Sensor Interface (AS-i), and Highway-Addressable Remote Transducer (HART) instrument bus networks all operate over a single pair of wires. The power for the transmitter and the communication signal are both carried over that single pair of wires.

DeviceNet requires a separate pair of wires for power and signal, with an additional shield/ground wire. DeviceNet, then, typically requires five conductors (two pairs and a shield/ground).

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

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