Delta Setpoint; Delta Setpoint Description - Baelz Automatic 6490B Device Manual

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Device manual 6490B / 6490B-y / 6590B

3.14 Delta setpoint

dSP
Setting range: 0 to ± scope of measuring range [phys. units]
dSP = 0 No delta setpoint.
dSP ≠ 0 As soon as the STOP command is deactivated by an assigned digital input the setpoint will be
changed by the value [phys. unit] set in dSP.
Assigning the control function STOP to a digital input, see 3.24.

3.15 Delta setpoint description

3.15.1 Remarks concerning the start up behaviour of tenters
Improving the start up behaviour by using the delta setpoint dSP and/or a setpoint ramp SP.r.
3.15.2 Start up behaviour without delta setpoint or setpoint ramp
Fig. 1)
After the plant has been switched off, the temperature in the tenter has to drop below the hysteresis of the alarm
relay until the control of the burner is released again (1).
Then the burner can be moved to its ignition position and be started. As soon as the STOP command is inactive
the controller switches to the automatic mode (2).
Problem: As a result of the given ignition position of the mixer, during the ignition phase of the burner the
thermal energy put into the plant is considerable. However, this does not immediately result in a measurable rise
of temperature due to the time delay of the plant.
As soon as the STOP command is inactive the controller immediately generates a longer OPEN pulse because
of the under-temperature Xw.
The addition of these processes (quantity of heat of the ignition + quantity of heat of the first OPEN pulse)
results in a temperature overshoot which, in turn, can trigger the alarm relay (3).
This causes switching off the plant and a restart of the procedure.
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