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this alarm will be indicated and the output switch will pulse ON and OFF to limit the average
power output to a value approximately equal to the
MAXIMUM POWER setting
3.8.22 SWITCH LIMITING STATUS (SSR ONLY)
Purpose: The switch limiting feature is always enabled when using an
SSR output switch and
provides protection for the output switch. Enabling this alarm will only inform the user that
switch limiting is currently active and an excessively high current condition is present. The con-
troller pulses its output switch for a small number of cycles and reads the resulting current. If
the measured current exceeds the
SWITCH RATING setting, the duty cycle of its output switch will
be varied so that an average current not exceeding the
SWITCH RATING setting is maintained.
Alarm Mask: ENABLE or DISABLE
Procedure: Adjust the SWITCH CURRENT RATING setting to the actual current rating of the SSR.
Enable or disable the alarm as required. The
SWITCH LIMITING ALARM need not be enabled to
adjust the
SWITCH CURRENT rating setting.
Notes:
• This is a non-latching alarm.
• This alarm is normally enabled. Currents in this range cannot be considered normal and
should be investigated.
3.8.23 CONTACTOR COUNT ALARM (V3.11 AND UP)
Purpose: Generates an alarm if the number of off-to-on transitions of a contactor reaches or
exceeds the
CONTACTOR COUNT ALARM setting. This serves as a method to perform preventative
maintenance on the contactor before a failure is likely to occur.
Alarm Mask:
ENABLE or DISABLE
Range: 0 to 999999 off-to-on transitions
Procedure: Adjust the CONTACTOR ALARM setting to the desired value. The CONTACTOR ALARM
must be enabled to adjust the
CONTACTOR ALARM setting.
Note: The CONTACTOR ALARM is only available if the SWITCH CONTROL MODE is set to either DEAD-
BAND
or PROPORTIONAL AMBIENT CONTACTOR.
3.8.24 EEROM DATA FAILURE ALARM
Purpose: The
EEROM DATA FAILURE ALARM indicates that the controller has detected a failure in
its nonvolatile memory.
Alarm Mask:
ENABLE or DISABLE
Procedure: Enable or disable alarming of a nonvolatile memory failure as desired.
Note: The EEROM DATA FAILURE ALARM should always be enabled. This memory stores all of the
controller’s configuration and calibration settings and the alarm will only be generated if the
microprocessor cannot bypass the failed area of its memory. This indicates an internal problem,
and the control module should be replaced and returned to Tyco Thermal Controls for repair.
3.9 Communications Setup
The following section describes the setup parameters that relate to the way the controller com-
municates with another device. If the optional communications interface is not installed in the
920 control module, these parameters need not be configured. All these parameters are com-
mon for both of the two control points—Point A and Point B, except the
HTCBUS™ ADDRESS,
MODBUS™ ADDRESS, and MODBUS™ SUB ADDRESS settings, as
applicable.
3.9.1 PROTOCOL
Purpose: Defines the communications language used by the controller to communicate with
other devices.
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