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.
What type of switch is designed to detect the end of travel of a valve?
a) a limit switch
b) a terminator
c) a solenoid
d) Form C contacts
e) none of the above
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Answer B is not correct; a terminator is an electrical device that is placed at the end of a fieldbus trunk line to prevent reflections of electrical signals back through the cable.
Answer C is not correct; a solenoid is an electrical inductive device that converts energy into linear motion.
Answer D is not correct; Form C contacts refer to a type of electrical contact that is composed of a normally closed and a normally open contact operated by the same device, with a common electrical connection.
The correct answer is A, “a limit switch.” Limit switch is a general term to describe the class of devices that are used to detect the end of travel of a valve, louver, or any other item that may be in motion. Limit switches are now also commonly used to detect jams in conveyor systems or to prove the position of a device or component (such as a gate or lane rail).
Reference: Goettsche, L.D. (Editor), Maintenance of Instruments and Systems, 2nd Edition