Emerson E2 operation manual Walk-In Freezer Control, Fail-Safe Mode, Recoverable Sensor Failures

Clean Modes may be either fixed or timed. Fixed Clean Modes begin when the clean switch is turned ON and end when the clean switch is turned OFF. Timed Clean Modes begin when the clean switch is turned ON and ends a specific time afterwards. The user specifies how long the wash mode will last.

End of Mode Warning

To warn service personnel that wash mode is about to end, the case controller will blink the case lights for five seconds. After five seconds of blinking, the case fan will activate and refrigeration will restart.

11.4.10 Walk-In Freezer Control

The CC-100P and CCB (dual-pulse valve model) case controller is used to control walk-in boxes, since it is the only model capable of controlling two valves.

Walk-in boxes are controlled the same way as for other cases. The primary difference between walk-in boxes and other cases is the use of the door switch.

When the case controller’s door switch input is turned ON, refrigeration is suspended (all pulse valves go to 0%), the fans turn OFF, and the lights turn ON. The walk-in box remains in this state until the door switch turns OFF again.

Alarm times can be assigned to the door switch input so that an alarm can be generated when the door is left open for too long.

Also, when temperature alarm setpoints are configured for the case, the case controller will begin refrigeration if a temperature alarm trips with the door open.

11.4.11 Fail-Safe Mode

When major system malfunctions occur, the case con- troller enters a Fail-Safe Mode. The Fail-Safe Mode is designed to keep the case functioning as normally as pos- sible under system conditions that would otherwise make case control impossible.

Acase controller will enter Fail-Safe Mode whenever one of three conditions occur:

1.The superheat and/or temperature control set- point(s) are corrupted (i.e., outside of its pro- grammed minimum/maximum range).

2.The software is corrupted.

3.An unrecoverable sensor failure has occurred (see Operation with Failed Sensors, below).

Actions Taken During Fail-Safe Mode

When a case controller enters Fail-Safe Mode, each output will be set to the fail-safe state described in Table 11-7.

Output	Fail-Safe State
Pulse Valve, Stepper Valve	Controller will fix
	the position to the
	last known good out-
	put percentage
Fans	ON
Lights	ON
Defrost	OFF
Anti-Sweat	Pulse at 50%
CC-100 and CS-100 Alarm	Flashes at a rate of 2
LEDs (red)	per second
Dual Temp Output	Off
Suction Solenoid Valve	Open
Liquid Solenoid Valve	Open
Satellite Output(s)	OFF

Table 11-7- Fail-Safe States

11.4.11.1 Recoverable Sensor Failures

The CC-100 and CS-100 will be able to cope with some sensor failures without having to enter Fail-Safe Mode.

Coil In or Coil Out Failure

A coil inlet temperature or coil outlet temperature sen- sor will be considered failed if one of two conditions occur:

1.The sensor gives a value outside of its minimum and maximum temperature range (that is, below - 50°F or above 120°F) for two consecutive read- ings, or

2.The sensor value is 20°F above the control set- point for longer than ten minutes.

If the coil inlet or coil outlet temperature sensor has failed, the case controller will compensate by “guessing” the inlet or outlet temperature based on the values of the remaining functional coil sensor and the case temperature sensor(s). The case controller will continue to guess the value until the coil inlet or outlet sensor can be fixed.

If both the coil inlet and coil outlet sensors have failed, or if one coil sensor and the case temperature sensor(s) have failed, the case controller will not be able to make the required calculations, and they will go into Fail-Safe Mode.

Discharge/Return Air

If the sensor or combination of sensors supplying the case temperature to the case controller have failed (i.e., the

Case Control Circuits Software Overview • 11-15