Yokogawa 414 Batch Controller User Manual

Page 19

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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 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.

Operation 17

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