nvent 910 Series Installation, Operating And Maintenance Instructions page 27

5.2.3 SWITCH CONTROL MODE
Purpose: This allows selection of the type of algorithm to be used by the HTC to maintain the
CONTROL SETPOINT temperature. There are four different control algorithms available in the
HTC—proportional, proportional ambient SSR, proportional ambient contactor, and deadband. See
Section 7.2 for a complete explanation of these controlling techniques as implemented in the HTC.
Setting: PROPORTIONAL, PROPORTIONAL AMBIENT SSR, PROPORTIONAL AMBIENT
CONTACTOR, or DEADBAND
Procedure: Select the desired control technique. Note that deadband control and proportional
ambient contactor should be selected when using contactors or when precise control and
advanced current handling functions are not required.
IMPORTANT: If deadband is selected, a DEADBAND setting will be available in the HTC
configuration menu; otherwise, a PROPORTIONAL BAND setting will be available. No
MAXIMUM POWER, SWITCH CURRENT RATING, or CIRCUIT BREAKER CURRENT RATING
settings are available when the controller is set to operate in either contactor mode. If
proportional ambient contactor is selected, the CYCLE TIME setting will also be available.
5.2.4 PROPORTIONAL BAND SETTING
(For use with the three proportional control modes only).
Purpose: When an HTC equipped with SSRs is used to control a heating circuit, proportional or
proportional ambient SSR modes are normally used, allowing for more precise tem- perature
control. When using contactors, the proportional ambient contactor mode should be selected.
This programmable proportional band acts to vary the on to off time of the output based
on the 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 PROPORTIONAL BAND setting to the desired differential from the
CONTROL SETPOINT temperature.
IMPORTANT:
• See Section 7.2 of this manual for an explanation of how the three proportional modes use
the PROPORTIONAL BAND setting.
• When using Series-type, constant wattage, or self-regulating tracers in an ambient tem-
perature control application, significant energy savings may be realized by setting the
PROPORTIONAL BAND to match the expected range of operating ambient temperatures.
Tracer design is normally done assuming worst-case conditions, where 100% of the design
output power is required to maintain the desired minimum temperature. When the ambient
temperature is above the design minimum, but some heat is still required, adjusting the
PROPORTIONAL BAND width accordingly will allow only the amount of power required by the
application to be consumed, while maintaining the minimum required temperature.
Example: A water line must be protected from freezing when the ambient temperature falls
below 10°C. Either the proportional ambient SSR or proportional ambient contactor mode is
selected as the control method (depending on the type of switch being used). The heater and
insulation combination are chosen to impart enough heat to the line to keep it from freezing at a
worst-case ambient temperature of –40°C. At 10°C, the heater should be completely off, since no
heat is required at this temperature to guarantee that the product will not freeze. It follows that
the amount of heat required by the water line decreases as the ambient temperature increases
from –40°C to 10°C (theoretically, at –15°C the heater output should be approximately 50%).
Setting 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.
5.2.5 DEADBAND SETTING
(Deadband control mode only)
Purpose: When an HTC equipped with a contactor is used to control a heating circuit, it is
necessary 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.
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