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

RS-232 serial point-to-point

Answer

HDMI

Answer

USB 3.0

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

The switch resets automatically when pressure drops below the cutout point

Answer

The PLC automatically restarts the compressor after a 30-second delay

Answer

Refrigerant must be fully evacuated before restart

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

To boost suction pressure above the compressor's minimum operating range

Answer

To regulate oil pressure in the compressor crankcase

Answer

To control condenser head pressure during low ambient conditions

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

Ice water bath at 32°F

Answer

Boiling water at 212°F

Answer

Room temperature dry-bulb thermometer

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

Close the valve further to reduce refrigerant flow

Answer

Increase compressor speed to lower suction pressure

Answer

Activate the hot gas defrost cycle

Question 6

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?

Accepted Answer

Coriolis mass flow meter

Answer

Turbine flow meter

Answer

Rotameter (variable area meter)

Answer

Bucket-and-stopwatch method

Question 7

In a programmable logic controller (PLC) ladder logic program for refrigeration control, a normally-closed (NC) contact associated with a high-temperature alarm will:

Accepted Answer

Pass current (be conductive) during normal operation and open (stop current) when the alarm activates

Answer

Block current during normal operation and close when the alarm activates

Answer

Always remain conductive regardless of input state

Answer

Only conduct during manual override mode