PLC Practice Questions
Explain what the following PLC Practice Questions on “ladder-logic” circuit does, and identify the meaning of each symbol in the diagram: PLC Practice Questions Explain why the TSH uses a normally-open contact...
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Instrumentation Questions For You
Process Control Loop Testing
A very useful technique for testing process control loop response is to subject it to a “step-change” in controller output. In other words, the process is perturbed (the highly technical...
Identify Level Control Loop Tuning Problems
A level control loop is supposed to maintain a constant level of liquid at the bottom of the stripping tower where considerable amount of vibration exists, but it seems to have...
PLC Permissive for Motor Control
A engineer needs to write a PLC program to control a water pump driven by an electric motor. This water pump will be manually started and stopped by pushbutton switches,...
Process Control High Level Alarm Fault Analysis
An operator reports a high level alarm (LAH-12) displayed at the control room for the last 13 hours of operation, in this sour water stripping tower unit (where sulfide-laden water...
Compressor Emergency Shutdown Root Cause Analysis
The compressor emergency shutdown system (ESD) has tripped the natural gas compressor off-line three times in the past 24 hours. Each time the operator goes to reset the compressor interlock,...
Solenoid Valves Practical Problems
Suppose this valve control system has a problem. The control valve (LV-104) does not move to the full-open position as it should when the solenoid is de-energized, although it will...
Troubleshoot Allen Bradley PLC Logic
A engineer needs to write a program for an Allen-Bradley CompactLogix PLC to control a pressure relieving solenoid valve in a gas processing system. A pair of high-pressure control switches...
Liquid Flow Control Loop Controller Action
A liquid flow control loop consisting of a flow transmitter (FT) to sense liquid flow rate through the pipe and output an electronic signal corresponding to the flow. A flow...
Motor Trip Logic using PLC Programming
Programmable Logic Controller (PLC) Questions and Answers This PLC is being used to start and stop an electric motor, and also to shut it down automatically if any of three...