Pentair 920 Series - Switch Control Mode and Proportional Band

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EN- Raychem920series-IM-H5687405/15
INDUSTRIAL HEAT TRACING SOLUTIONS
3.5.2 ALPHANUMERIC TAG ASSIGNMENT
Purpose: A 19-character alphanumeric TAG may be assigned to a control point to allow it to be
easily associated with a pipe, vessel, process, circuit, drawing name or number.
Setting: Any combination of 19 characters from A-Z, 0-9, /, -, ., (,) or #.
Procedure: Using the 920 Operator Console, enter the desired text. Refer to the separate
Raychem 920 Series HTC Operator Console—Installation and Operating Instructions (Pentair
Thermal Managament reference H56903) for TAG entry information.
3.5.3 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
5.2 on page 50 for a complete explanation of these controlling techniques as implemented in the HTC.
Setting: PROPORTIONAL, PROPORTIONAL AMBIENT SSR (V3.11+), PROPORTIONAL AMBIENT
CONTACTOR (V3.11+), 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, else 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.
3.5.4 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 temperature 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)
2°F to 630°F (1°C to 350°C) V3.2x and up
Procedure: Adjust the PROPORTIONAL BAND setting to the desired differential from the
CONTROL SETPOINT temperature.
IMPORTANT:
• Seesection5.2onpage50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
temperature 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
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.