Specifications

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5. The microprocessor will determine the amount of drying needed to
maintain the desired set-point.
If less than the full drying capacity of the Self-Regenerating
Dehumidification System is needed, the controller will provide
pulses of power to the control valve to limit the quantity of dried air
coming into the chamber. The controller will open and close the
control valve cyclically to obtain an average input of dried air less
than the full capacity of the system.
To achieve a smooth, even dehumidification process, the humidity
microprocessor Cycle Time 2 (CYC.2) should be set to a low value.
However, a short cycle time will prematurely wear out the control
valve. As a compromise, CYC.2 should be set to 5.0 seconds.
Shorter cycle times will afford better low humidity control at the
desired set-point, but at the risk of accelerating valve wear.
3.0 MICROPROCESSOR HUMIDITY CONTROLLER
3.1 System Description
The Model 518 Microprocessor Humidity Controller with the Model 554 temperature
compensated RH sensor is capable of controlling the relative humidity in the chamber
working space by supplying a proportionally controlled power output to the
Humidification System and/or Dehumidification System.
The controller provides low voltage (6 VDC) control signals to the HEAT and COOL
solid-state relays, located on the ‘RELAY PC Board’. When the low voltage signal is
applied to the relay ‘Input’, the ‘Output’ of the relay ‘closes’ and allows AC Power to flow
to the connected device.
When the “RH” STANDBY switch on the front panel is in the ‘OFF’ (‘0’) position, AC
power is manually disconnected from the control relays and no humidification or
dehumidification can take place until the switch is placed in the ‘ON’ (‘I’) position.
All devices in the Model 518 are connected using screw terminals on the ‘Relay PC
Board’. All relays and screw terminals are labeled.