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the CONTROL SETPOINT temperature to 10°C, and the PROPORTIONAL BAND to 50°C, will force the
controller’s output to be 100% on at –40°C, 50% on at –15°C, and off at 10°C.
3.5.5 DEADBAND SETTING
(Deadband control mode only or if a point controls an
INHIBIT output signal)
Purpose: When an
HTC equipped with a contactor is used to control a trace circuit, it is neces-
sary to use deadband rather than proportional control. This is done to prevent the contactor
from switching on and off rapidly and being worn out prematurely. This deadband acts as an on/
off control where the decision to turn the output off or on is based upon a window of difference
between the measured control temperature and the desired
CONTROL SETPOINT temperature.
Range: 2°F to 90°F (1°C to 50°C)
Procedure: Adjust the DEADBAND setting to the desired differential from the desired CONTROL
SETPOINT
temperature. When the control temperature is above the setpoint + deadband value,
the controller will turn off the output to the tracer. If the control temperature drops down below
the setpoint, the output will be turned back on. Note that the smaller the DEADBAND setting, the
more often the contactor will cycle on and off, decreasing its operational life.
Notes:
• See section 5.2 on page 50 for an explanation of deadband control. Note that the
MAXIMUM
POWER
, SWITCH CURRENT RATING, and CIRCUIT BREAKER CURRENT RATING settings are not
available when the
HTC is set to deadband mode (typically when switching a contactor).
• The
DEADBAND parameter is also available for Point A when the EXTERNAL OUTPUT is config-
ured for use as an
INHIBIT output. See section 3.6.4 on page 30 for additional details.
3.5.6 CYCLE TIME SETTING (V3.11 AND UP)
(For proportional ambient contactor control mode only)
Purpose: This parameter determines the minimum amount of time it will take for a complete
contactor
ON-OFF-ON cycle.
Range: 10 to 255 minutes
Procedure: Adjust the
CYCLE TIME setting to yield the desired contactor ON+OFF time for a partic-
ular duty cycle. For instance, if the contactor should remain on for five minutes with a 50% duty
cycle, then the
CYCLE TIME should be 10 minutes. A new duty cycle (based on measured control
temperature,
PROPORTIONAL BAND and CONTROL SETPOINT) is calculated every time the contac-
tor is required to change state.
Notes:
• If the calculated duty cycle is 0% or 100%, then the contactor will not change state and the
duty cycle will not be calculated again for a time period =
CYCLE TIME/30.
• The minimum cycle time setting is 10 minutes, and the minimum controller output duty cycle
is 3%. This results in a minimum contactor
ON time of 18 seconds.
3.5.7 SWITCH CURRENT RATING SETTING (SSR ONLY)
Purpose: The
SWITCH CURRENT RATING setting defines the current rating of the output switch. It
is used by the controller to limit the maximum average current that will be allowed to flow to the
load before it begins to adjust the output duty cycle, limiting the amount of current to an accept-
able level.
Range: 0.3 to 100.0 amps
(
CURRENT TURNS RATIO = 1.00)
Procedure: Adjust the SWITCH CURRENT RATING setting to match the current rating of the output
device (i.e. 30.0 amps). Note that the
SWITCH CURRENT RATING setting is affected by the
CURRENT TURNS RATIO setting. The absolute maximum adjusted SWITCH CURRENT RATING setting
is 300.0 amps. The absolute minimum adjusted
SWITCH CURRENT RATING setting is 0.1 amps.
See section 3.5.22 on page 26 for more information regarding the
CURRENT TURNS RATIO
function.
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