Hach-Lange WTOS P-RTC - Manual (Page 33)

33
Parameterization and operation
Example:
A derivative time of 1 minute means that closed-loop control
takes place according to the phosphate concentration that is
actually achieved in only 1 minute (if the current measured
value change remains the same).
The integration time takes effect by means of the temporal
integration of the control deviation (PO
4
-P setpoint to PO
4
-P
actual value), to the actuating variable with the weighting by the
INTEGRALTIME . The integral time states when the integral
proportion has the same effect as the P proportion. A short
timeframe can lead to an overshoot or strong oscillations of the
PO
4
-P concentration. An increase in the integral time reduces the
oscillation. In this case, the I proportion of the closed-loop control
can be specified through the entry of
INTEGRAL TIME = 0.
Setting tips: As a DERIVATIVE TIME >0 min has a highly
significant impact on the metered precipitant quantity, this should
be used only in exceptional cases, e.g. plants demonstrating
rapid escalations in PO
4
-P concentrations.
To ensure the metered precipitant quantity increases/decreases
more quickly, the
GAIN P CONTR. must be increased or the
INTEGRALTIME reduced. To ensure the metered quantity
changes more slowly, the GAIN P CONTR. must be reduced or the
INTEGRAL TIME increased.
4.5.6 Pump runtime
The on/off duration in pulse/pause mode can be influenced via
the control cycle time (
CONTROL CYCLE ). For example, with a
cycle time of 100 seconds and a dosing control value of 60 %, the
dosing pump is periodically switched on for 60 seconds and off
for 40 seconds. Short cycle times increase the switch frequency,
but enable more precise adaptation to individual requirements.
A minimum on-time is also configured to protect the dosing pump.
The pump is not activated for less than this time span. The time
must be a fraction of the control cycle time.