Process Control & Instrumentation Flashcards
7 cards from real CIRO practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Process Control & Instrumentation flashcards as text
In SCADA systems used for industrial refrigeration plants, which communication protocol is most commonly used for reading data from PLCs and remote I/O devices?
Answer: Modbus RTU/TCP or Ethernet/IP
Modbus RTU/TCP and Ethernet/IP are the dominant industrial communication protocols for SCADA integration with PLCs and field devices in refrigeration plant automation.
A high-pressure cutout switch in an industrial ammonia system trips the compressor when discharge pressure exceeds the setpoint. What is the typical action required before the compressor can restart?
Answer: Manual reset is required after the fault condition has been corrected
High-pressure cutouts are typically manual-reset safety devices; an operator must investigate and correct the cause of high pressure before physically resetting the switch to restart the compressor.
What is the purpose of a suction pressure regulator (SPR) valve in a multi-evaporator refrigeration system?
Answer: To maintain a minimum evaporator pressure regardless of compressor suction pressure, preventing the evaporator from freezing product
An SPR valve holds the evaporator pressure at or above a set minimum, preventing the temperature from dropping too low and freezing sensitive products while the compressor handles lower-pressure loads from other evaporators.
When calibrating a temperature sensor in an ammonia refrigeration system, which reference standard is most appropriate for verifying accuracy near -20°F?
Answer: NIST-traceable calibrated reference thermometer and dry block calibrator
A NIST-traceable reference thermometer combined with a dry block calibrator allows accurate calibration at the actual operating temperature range of the sensor, ensuring reliable process control.
An electronic expansion valve (EEV) in an industrial refrigeration system is controlled by a superheat controller. If the measured superheat is too high, the controller will:
Answer: Open the valve wider to increase refrigerant flow to the evaporator
High superheat indicates insufficient refrigerant in the evaporator; the controller opens the EEV wider to admit more liquid refrigerant and reduce superheat back to the setpoint.
Which type of flow meter is most suitable for measuring liquid ammonia flow in a large industrial refrigeration system due to its accuracy and lack of moving parts?
Answer: Coriolis mass flow meter
Coriolis mass flow meters measure mass flow directly with no moving parts, are highly accurate with ammonia, and are unaffected by fluid density variations, making them ideal for industrial refrigeration applications.
In a programmable logic controller (PLC) ladder logic program for refrigeration control, a normally-closed (NC) contact associated with a high-temperature alarm will:
Answer: Pass current (be conductive) during normal operation and open (stop current) when the alarm activates
In PLC ladder logic, a NC contact is conductive (passing power) when the associated input coil is de-energized (normal state) and opens to stop current flow when the alarm input energizes, matching real-world NC relay behavior.