nvent 910 Series Installation, Operating And Maintenance Instructions page 31

5.2.18 AUTOCYCLE ENABLING
Purpose: The autocycle function momentarily (approximately 10 seconds) applies power to
the heating circuit at the selected interval. It is used to test the integrity of the heating circuit.
Alarms present at the time of autocycle then become latched and remain active after
the completion of the autocycle function. Autocycling effectively eliminates the need for
preventive maintenance by automatically verifying the heating circuit integrity.
Setting: ENABLE or DISABLE
Procedure: Enable or disable the autocycling feature as desired. If the feature is disabled,
you will not be prompted to enter the AUTOCYCLE INTERVAL or AUTOCYCLE UNITS.
IMPORTANT:
• Autocycling should always be enabled for normal operation. Disabling this feature should
only be required where the HTC system is monitoring a circuit exercised by some other
device or means. Although this function defeats temperature control and forces output on,
the controller will continue to adjust the output for protection purposes or power limiting
(SSR option only).
• Autocycling is inhibited if the controller is in the load shedding mode. See Section 7.3.
• If autocycling is enabled, the HTC will always autocycle for 10 seconds when power is
initially applied.
• If autocycling is enabled, and TS FAIL MODE = OFF and all the control temperature sensors
have failed, the HTC will still perform an autocycle.
• If an alarm condition with an alarm filter time greater than 0 appears during the autocycling,
then the autocycle will be extended (past the 10 seconds) until the alarm filter time has
expired.
5.2.19 AUTOCYCLE TIME INTERVAL
Purpose: AUTOCYCLE INTERVAL is the number of hours/minutes between successive heating
circuit integrity tests depending on the AUTOCYCLE UNITS specified.
Range: 1 to 240
Procedure: Set the AUTOCYCLE INTERVAL to the desired time period.
IMPORTANT:
• When using proportional ambient contactor mode, the CYCLE TIME setting should be less
than the AUTOCYCLE INTERVAL; otherwise, autocycling could affect the duty-cycle.
• If an AC ALARM becomes active during an autocycle, but the AUTOCYCLE INTERVAL expires
prior to the corresponding ALARM FILTER time, then autocycling will continue until the
ALARM FILTER time has elapsed.
• For the earliest possible alarming of heating circuit problems, the AUTOCYCLE INTERVAL
should be set to a small value.
5.2.20 AUTOCYCLE TIME UNITS
Purpose: The autocycle time units parameter allows selection of minutes or hours for the
AUTOCYCLE INTERVAL setting.
Setting: HOURS or MINUTES
Procedure: Set the AUTOCYCLE UNITS to the desired time units.
5.2.21 OVERRIDE SOURCE
Purpose: An override signal can be sent to the HTC from one of two sources. This override
signal can be used to override the controller's temperature control and force the output switch
off or on. This is especially useful when the user wishes to turn a controller or a group of
controllers off over the summer months, during maintenance, or when a line is flowing and
does not require heating.
Setting: REMOTE or EXT. INPUT
Procedure: If the override signal will be generated remotely and received by the HTC via the
optional communications interface, select REMOTE as the OVERRIDE SOURCE. If the
override signal will be received by the HTC via the external input, select EXTERNAL INPUT as
the OVERRIDE SOURCE.
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