TENNEY ENVIRONMENTAL
Tenney Junior Test Chambers: Models TJR and TUJR, W942, or WF4
Page 18
7.2 Watlow 942 Control Functions:
The Main Power switch 1SS must be turned ON to enable the conditioning control circuitry. 1SS will also turn
on the chamber conditioner fan.
The following descriptions detail the functions of the various outputs. Event outputs (user entered) are
provided mainly for special applications. These features are normally described in the “Options” section of
the manual.
- HEAT CONTROL -
1C - 01 - - This time proportioned output will trigger triac 1TRC to conduct and provide power to the electric
heaters.
- COOLING CONTROL -
1C - 02 - - This On/Off output will trigger triac 2TRC to conduct and energize the refrigeration system. The
high stage compressor will immediately start. The low stage compressor will start after a slight
delay from the Low Pressure Cut-In Switch PS2.
- EVENT OUTPUTS - (Optional)
1C - 03 - - This is Event No. 1, which serves as a compressor shutoff when going from a very low to a vary
high setpoint. In this scenario, any cycling of the compressors is not desired, and a heat
overshoot is tolerated. 1C-03 contacts are normally closed. They will open when the event is
turned ON to disable the Cooling Control Output.
For Model XXXX, SN xxxxx Only:
Event No. X - - Output 1C-0x:
WATLOW 942 COMPRESSOR TURN-ON LOGIC
In determining when to turn the refrigeration system On or Off, the controller’s logic will compare the
following signals and setpoints.
1. Actual Chamber Temperature 3. Hysteresis
2. Setpoint Temperature 4. Deadband
Hysteresis (HYS) and deadband (db) are parameters entered at the factory. Hysteresis is the temperature
change necessary to change the output from full ON to full OFF, and is detailed in the Setup Menu section in
the Watlow 942 Manual. Deadband is the span in which Output 1C-02 will remain ON below the controller’s
low setpoint, and is detailed in the Operation Menu section of the Watlow Manual. HYS and db are entered
in degrees Celsius. Deadband is always entered as a (-) minus. The logic is:
♦ Measured temperature rises above setpoint: Refrigeration turn-on = hysteresis minus deadband.
♦ Measured temperature falls below setpoint: Turn-on is always above setpoint.
♦ Turn-off is always below setpoint: Turn-on is always above setpoint.
Example Settings For HYS and db: See Next Page
To Next Page
Loading...
