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Operation 15
HP289
3.2.5 Automatic Overrun Compensation
The Batch Controller can be configured to automatically compensate
for any overrun at the end of a batch.
Typically, this is due to the slowness of a valve to close or a pump to
stop pumping on receiving a signal from the Batch Controller. The
result is that the batch quantity will always read higher than the batch
quantity set.
The Automatic Overrun Compensation can be enabled or disabled
during the configuration process and this feature should only be used if
the overrun is repeatable. The user is cautioned against using
Automatic Overrun Compensation if the overrun is erratic such as may
occur with changing back pressures or sticking valves.
In calculating the amount of overrun to be compensated for, the Batch
Controller uses the average overrun on the last three batches.
The overrun is defined as the difference between the batch quantity set
by the user and the batch total once the flow has stopped.
With Automatic Overrun Compensation, the Signal Timeout must be
set to a value greater than zero.
Once the Batch Controller de-energizes both relays, the instrument
looks for a Signal Timeout, indicating that the maximum interval
between pulses has occurred and that the flow must, therefore, have
stopped. It then uses the overrun quantity measured during this period
and averages this together with the overrun on the last two batches.
The resulting value is then subtracted from the next batch.