Siemens siemens compact universal controllers manual

Function of the controller when used for burner control

Low-fire operation	In low-fire operation, the RWF40... operates like a control thermostat or pressurestat.
	This means that it operates as a 2-position controller maintaining the required setpoint
	by switching the burner on and off. The switching differential for 2-position operation
	can be adjusted within a wide range. If the demand for heat increases, the controller
	switches to high-fire operation only when an adjustable limit is exceeded. This function
	is aimed at optimizing the burner´s switching ratio.
High-fire operation,	In that case, the RWF40... operates as a 2-position controller with adjustable switching
2-stage control	thresholds. Using the relays of the 3-position output, the RWF40... drives the actuator
	to the 1st and 2nd output stage. In this operating mode, the optional analog output
	switches between the minimum signal for the 1st stage and the maximum output signal
	for the 2nd stage.
High-fire operation,	In that case, the RWF40... operates as a PID / PI controller with a 3-position output
modulating control	without position feedback signals or, optionally, with a modulating output. By making
	use of its self-setting facility, the RWF40... is able to determine the PID / PI control
	parameters, or the parameters can be set manually.

Binary input 1 (change- over of operating mode)

Binary input 2 (setpoint shifting or setpoint changeover)

Limit comparator

Operation

Weather-dependent setpoint shifting

Using a potential-free contact, the RWF40... can be switched from the modulating mode to 2-stage operation.

In the case «setpoint shifting» is configured, the current setpoint is shifted by an adjust- able amount. Configuration of «setpoint changeover» provides changeover between 2 setpoints adjusted on the RWF40... If analog input 2 is configured for an «external set- point», changeover is provided between the setpoint adjusted on the RWF40... and an external setpoint.

Potential-free contact «K6» can be assigned a number of functions. Example: Limit value supervision

4 buttons on the unit front are used to operate and program the RWF40... During op- eration and programming, the 7-segment displays show the parameter values and pa- rameter names.

The controller´s standard configuration ex works is such that when connecting a QAC22… outside sensor, automatic changeover to weather-dependent setpoint shifting takes place.

The signal delivered by the QAC2... outside sensor must not be fed parallel to sev- eral RWF40...!

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Building Technologies	CC1N7865en
HVAC Products	01.09.2005