41
Note: The SWITCH FAILURE ALARM should always be enabled. A high temperature condition as a
result of a failed circuit can only be caused if the output switch fails closed. When an output
switch fails closed, the controller cannot turn the tracer power off, therefore no protection fea-
tures are available (ground-fault trip, power limiting, etc.). If a
SWITCH FAILURE ALARM is
detected, the unit should be serviced immediately.
3.8.19 HTC RESET ALARM
Purpose: The
HTC RESET ALARM is used to indicate:
1. Power to the
HTC has been interrupted and subsequently restored.
2. A transient has caused the
HTC’s microprocessor to restart.
3. An internal condition has caused the
HTC’s microprocessor to restart its program.
Alarm Mask: ENABLE or DISABLE
Procedure: Enable or disable alarming on reset as desired.
Note: Normally the
HTC RESET ALARM is left disabled since powering the controller off and on for
maintenance or troubleshooting would require the user to reset this alarm every time. If the par-
ticular installation includes a Model 780/GCC-9000, this alarm may be left enabled since resets
are not considered normal occurrences and the Model 780/GCC-9000 provides the capability to
easily log and reset alarms such as these. The difference in time between when a
COMMUNICA-
TIONS FAIL ALARM
and an HTC RESET ALARM are logged provide an indication of how long the cir-
cuit has been “
OFF.”
3.8.20 CIRCUIT BREAKER LIMITING STATUS (SSR ONLY)
Purpose: The circuit breaker limiting feature is always enabled when using an
SSR output switch
and is intended to prevent the circuit breaker immediately upstream of the controller from trip-
ping during a temporary overcurrent condition. Enabling this alarm will only inform the user that
circuit breaker limiting is currently active.
Alarm Mask:
ENABLE or DISABLE
Procedure: Adjust the CIRCUIT BREAKER CURRENT RATING setting to the heating circuit breaker
size (i.e. 15.0 or 20.0 amps). Enable or disable the alarm as required. The
CIRCUIT BREAKER
LIMITING ALARM
need not be enabled in order to adjust the CIRCUIT BREAKER CURRENT RATING
setting.
Notes:
• This is a non-latching alarm.
• This alarm is advisory. If the measured current exceeds the level that would cause the
upstream circuit breaker to release, the
HTC will begin to switch the SSR ON and OFF rapidly to
limit the average current to an acceptable level.
3.8.21 POWER-LIMITING STATUS (SSR ONLY)
Purpose: The power-limiting feature is always enabled when using an
SSR output switch and is
intended to limit the average amount of power that is applied to the trace circuit. The controller
measures the voltage and current of the trace circuit and will vary its output switch to limit the
amount of power applied to the trace to the value set by the
MAXIMUM POWER setting. Enabling
this alarm will only inform the user that power limiting is currently active.
Alarm Mask:
ENABLE or DISABLE
Procedure: Adjust the MAXIMUM POWER setting to the desired value. Enable or disable the alarm
as required. The
POWER LIMITING ALARM need not be enabled to adjust the MAXIMUM POWER set-
ting.
Notes:
• This is a non-latching alarm.
• This alarm is advisory and is normally disabled. It will be active if the
MAXIMUM POWER set-
ting is set below the power output level required for temperature maintenance. In other
words, if the circuit demands the maximum power allowed and the alarm is enabled, then
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