27
5
Firing Rate Controller (optional)
5.1.6
Thermostat and Control Range
The thermostat function switches the burner on and off on the basis of the temperature and/
or pressure value, but only when burner is released by the start signal. The control range is
formed by entering the controller setpoint value and the parameters P 802 (switch-on point),
P803 (upper control range) and P 804 (burner OFF). The cut-off hysteresis is divided into 2
ranges. The first part lies above the setpoint and forms the upper control range. The second
part lies below the setpoint and forms the lower control range.
The control range may lie asymmetrically around the setpoint.
The power control unit functions within the upper and lower control range according to its set-
tings in the parameters and the default values.
If the actual value of the control unit reaches the shut-down range, the base firing rate request
is emitted. If the control unit’s setpoint exceed the shut-down range a control shut-off occurs.
This is done by internal processing. If the actual value drops below the lower control range, a
re-start can occur.
NOTICE
This function can replace the control thermostat, which is required on the plant.
It does not replace a safety thermostat.
Fig. 5-3 Control range
Summary of Contents for VMS Series
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