CIRO Process Control & Instrumentation 2

Question 1

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?

Accepted Answer

Modbus RTU/TCP or Ethernet/IP

Answer

Modbus RTU/TCP and Ethernet/IP are the dominant industrial communication protocols for SCADA integration with PLCs and field devices in refrigeration plant automation.

Question 2

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?

Accepted Answer

Manual reset is required after the fault condition has been corrected

Answer

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.

Question 3

What is the purpose of a suction pressure regulator (SPR) valve in a multi-evaporator refrigeration system?

Accepted Answer

To maintain a minimum evaporator pressure regardless of compressor suction pressure, preventing the evaporator from freezing product

Answer

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.

Question 4

When calibrating a temperature sensor in an ammonia refrigeration system, which reference standard is most appropriate for verifying accuracy near -20°F?

Accepted Answer

NIST-traceable calibrated reference thermometer and dry block calibrator

Answer

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.

Question 5

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:

Accepted Answer

Open the valve wider to increase refrigerant flow to the evaporator

Answer

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.

CIRO - Certified Industrial Refrigeration Operator Practice Test

CIRO - Certified Industrial Refrigeration Operator Practice Test

CIRO Process Control & Instrumentation 2