Stand by System Changeover Procedure for Walk in Type Stability Chamber

HUMIDITY SYSTEM CHANGEOVER

The two Humidity systems are provided with 1 no. The industrial heater of 2000 watts for each system; on the failure of the regular humidity system the PLC will change over to the standby humidity system. A safety thermostat is also fitted in each humidity tank to prevent the Industrial heater so that whenever the humidity tank becomes empty due to a shortage of water and the temperature in the humidity tank exceeds 110°C then this safety thermostat will be cut off. Humidity system changeover occurs on any of the following conditions.

1. In a running condition of the chamber at any time if water level 1 goes down then the PLC will change over to a second water level if it is available and start the Standby Humidity system. If Later on the First Water Level is resumed & water level 2 goes down then PLC will again change over to a Regular Humidity system. If both the water levels are not available then the PLC will trip the main contactor with alarm & indication.
2. After the completion of the stabilization period i.e. 60 minutes (settable), if the running humidity system fails due to humidity undershooting by 5% (settable) then PLC will change over to a second humidity system with an alarm and indication if it is healthy or else trip the chamber.
3. After completion of the stabilization period; if humidity overshoot by 5% (settable) of the set value then the PLC should cut off the running humidity contactor if the humidity reaches within the range then the PLC should start that humidity contactor which was in operation; this same operation should repeat for the second time. If this condition repeats for the third time PLC should change over to another humidity system & secondary stabilization period starts but at any time other humidity systems fail then PLC should shut down the chamber.
4. In a running condition of the chamber at any time if the Humidity safety thermostat contact of a running system becomes open, then the PLC will change over to other humidity systems with alarm & indication & due to any fault if the other humidity system fails then PLC should trip the chamber.

NOTE: AT ANY GIVEN POINT IN TIME ONLY ONE HUMIDITY SYSTEM WILL BE RUNNING.

REFRIGERATION SYSTEM CHANGEOVER

The standby cooling system, which consists of a hermetically, sealed EMERSON CLIMATE TECHNOLOGIES compressor is connected to the air condenser and a capillary and is passed inside the Hydronic system.

The refrigerant gas used is R134A. Normal accessories are attached to the line for enhanced efficiency. The cooling system is tested for high-pressure nitrogen up to 300 psi and evacuated to any leakage and to free from any moisture trap in the system. Thus there are a total of 2 nos. independent refrigeration systems out of which one no. is working as another is standing by. Refrigeration system changeover occurs for any of the following conditions.

1. After completion of the stabilization period that is 60 minutes from the main start, if the running cooling system fails, a temperature rise will occur, if there is a temperature rise of 2°C above the set value for 30 sec it will be considered as temperature overshoot and then the PLC will changeover from running cooling system to other cooling systems with alarm and indication.
2. After the cooling system changeover had taken place the PLC will check for any temperature overshoot after 30 minutes of changeover. If after completion of 30 minutes of changeover, there occurs a temperature rise of 2 degrees above the set value, then the PLC will trip the Main contactor with alarm and indication.
3. Two numbers of cooling systems are provided, out of which Regular Cooling System will remain ON for Monday 10.00 am to Thursday 10.00 am and Standby Cooling System will remain ON for Thursday 10.00 am to Monday 10.00 am. If the running cooling system fails it will change over to other cooling systems through PLC and after the changeover weekly calendar plan for the cooling system will not be applicable.
4. In running conditions after the completion of the stabilization period of the chamber at any time if there is humidity overshoot by 15% (settable) of the set value for 1 minute then PLC should changeover the running cooling system to another cooling systems if the second cooling system is healthy, else wise the PLC should trip the chamber.

NOTE: AT ANY GIVEN POINT IN TIME ONLY ONE COOLING SYSTEM WILL BE RUNNING.

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