About accumulator variables

The accumulator variable supports multiple input values into a single accumulator stream. The delta is calculated from the last time that the variable caused the calculation to occur.

Note: When a negative transition greater than the defined AccumulatorThreshold occurs, the accumulator variable value is reset to zero. The AccumulatorResetPoint property does not change this behavior.

Reset Point

The AccumulatorResetPoint property can be specified as NegativeTransition or DefinedResetValue. The accumulator is reset to zero on a negative transition greater than the defined AccumulatorThreshold value.

• NegativeTransition - If the AccumulatorResetPoint is set to NegativeTransition, then on a negative transition the CalculatedSample value is calculated as the difference between the sample from the last polling interval and the value prior to the negative transition plus the sample at the current polling interval.

  For example, if the value from the last polling interval was 700 and the highest value between polling intervals was 800 and the current value is 600 the CalculatedSample value would be (800 - 700) + 600 = 700.

• DefinedResetValue - If the AccumulatorResetPoint is set to DefinedResetValue, then on a negative transition the CalculatedSample value is calculated as the difference between the value from the last polling interval and the AccumulatorResetPoint value plus the sample for the current polling interval.

  For example, if the sample from the last polling interval was 700 and the AccumulatorResetPoint was 1000 and the current value is 600, the calculated sample value would be (1000 - 700) + 600 = 900.

Threshold

AVEVA™ Production Management uses the AccumulatorThreshold property to filter out negative transitions that are less than the defined threshold in accumulated values. If the difference between the sample at the current polling interval and the sample at the previous polling interval is less than the value in the AccumulatorThreshold property, AVEVA™ Production Management treats the difference as zero.

Polling intervals for accumulator fields

In cases with a single reporting point, you could use a Production reporting point and Production field with the CalculationType property set to Accumulator to calculate the accumulated quantity. However, with the accumulator variable, you can use multiple reporting points and combine the collected data.

The accumulator variable is positioned between the reporting points and the SCADA tag and acts as an intermediary; the variable makes calculations that it passes back to the reporting points. This takes into consideration the data from the other reporting points. Because of the calculation performed by the accumulator variable, each reporting point reports the accurate totals.

Scenarios

You might use an accumulator variable in the following scenarios:

• Multiple products pass down the same production line with a different reporting point for each product that uses the same SCADA tag for quantity; however, you want to combine the production totals of products to create total overall production quantity.

• A product that passes through a production line and is shipped by means of several different shipping channels. For example, coal on a conveyor, which can be stacked on to one of six different stockpiles.

  Note: Accumulator variables exist specifically to support the Inventory module; however, you can use them in any AVEVA™ Production Management module.

Related topics

• Add and configure an accumulator variable

• Add and configure a Production reporting point

• Add a Production custom field

• Add and configure an accumulator condition

• Accumulating data with fields