Yokogawa 414 Batch Controller - Manual (Page 20)

18 Operation
3.2.5 Automatic Overrun Compensation
The Batch Controller can be programmed to automatically compensate for any
overrun at the end of a batch.
Typically, this could be 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
Calibration routine 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-energises 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.