decreased and vice versa. The purpose is to minimize the batch error. There are limits
and rules on the Preact update, See
Preact Limit
,
Pre Max Chang
and
Preact Apply
,
below.
Preact Limit
Preact will never go beyond this limit, negative or positive. If you are using Fine Feed,
start with 1% of Design Weight. With no Fine Feed, the limit typically has to be set higher.
As you start batching, observe the Preact fluctuations (
Prea:
Screen, see page 13). Set the limit to twice the actual Preact you observe, after the value
has stabilized. A value of Zero in
Curr Preact
and
Preact Limit
will disable the Preact
mechanism.
Pre Max Chang
This is a limit of the change of the Preact from batch to batch. The purpose is to avoid a
situation where an arbitrary event, such as someone touching the weigh hopper during
batching, causes an upset that affects batch accuracy for a number of batches. Set to a
value higher than the observed batch to batch fluctuation of the Preact. A value of Zero
will freeze the Preact at its current value.
Preact Apply
The Preact is updated, based on the batch error (setpoint minus final batch total). The
Preact Apply parameter determines the aggressiveness of this update. With a setting of
100%, the entire batch error is added to the Preact after every batch. If you are
optimizing for good average batch accuracy, this is the optimal setting. If you want to
minimize the standard deviation of the batch weight, use a setting of 50%, which will
apply half of the batch error to the Preact.
Max Batch Tm
If the time used for a batch exceeds
Max Batch Tm
, the logical output
Batch Timeout
goes on. No other action is taken, meaning that the batch will complete in a normal
fashion. The
Batch Timeout
output typically qualifies a Warning. See Logical Outputs on
Batch Dev Hi, Lo
These are the batch tolerances, in percent of the batch setpoint. If the batch error, after
finishing the Stable Check is above
Batch Dev Hi
, the logical output
High Batch Wt
goes
on. If the batch error is below
Batch Dev Lo
, the logical output Low Batch Wt goes on. No
other action is taken. The
High Batch Wt
and
Low Batch Wt
outputs typically qualify
Warnings. See Logical Outputs on page 39.
Auto Batch Tm
By turning on the logical input
Auto-Batch
, the controller will issue a start batch command
at
Auto Batch Tm
intervals. If the time required for a batch is greater than
Auto Batch Tm
,
a new batch is started immediately. See Logical Inputs, on page 35.
B Settle Time
At the beginning and end of every batch, the weight value has to be stable, as the
controller goes through Stable Chk Before and Stable Chk After states. A non-zero value
in
B Settle Time
adds a mandatory wait time before checking stability and taking the
stable weight. This is useful when mechanical disturbances are present at the start or
end of the bathing.
If the stability parameters and
Fine Feed Spd
are set such that the stable indicator is on
during fine feed, it is also recommended to set a non-zero value, to avoid a situation
where the controller takes the weight value at the end of the fine feed rather than the
weight value when all material is settled in the weigh hopper.
35.00.EX O&M Manual
25
Summary of Contents for MC3 35.00.EX
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