The ProcessItemType is used to measure and monitor over time a measurement point. The ProcessItemType also provides aggregates (Avg, Max, Min, Std, Total) that are computed by the underlying system. The aggregates are computed over a time period or for a product quantity and can be configured by a client altogether with the sampling time.
The ProcessItemType is formally defined in the following table.
Table 129 – ProcessItemType Definition
|
Attribute |
Value |
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|
BrowseName |
ProcessItemType |
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|
IsAbstract |
False |
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|
References |
Node Class |
BrowseName |
DataType |
TypeDefinition |
Other |
|
Subtype of the BaseObjectType defined in OPC 10000-5 - Part 5: Information Model, i.e. inheriting the Instance Declarations of that Node. |
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|
0:HasProperty |
Variable |
AggregationWindow |
0:UInt32 |
0:PropertyType |
M, RW |
|
0:HasComponent |
Object |
LimitAlarms |
|
0:NonExclusiveLevelAlarmType |
M |
|
0:HasComponent |
Variable |
Value |
0:Double |
DisplayAnalogUnitType |
M, RO, HR |
|
0:HasComponent |
Variable |
Avg |
0:Double |
0:BaseDataVariableType |
M, RO, HR |
|
0:HasProperty |
Variable |
LastResetTime |
0:UtcTime |
0:PropertyType |
M, RO |
|
0:HasComponent |
Variable |
Max |
0:Double |
0:BaseDataVariableType |
M, RO |
|
0:HasComponent |
Variable |
Min |
0:Double |
0:BaseDataVariableType |
M, RO |
|
0:HasComponent |
Method |
ResetAggregates |
See below. |
M |
|
|
0:HasComponent |
Variable |
SamplingRate |
0:Double |
0:AnalogUnitRangeType |
M, RW |
|
0:HasComponent |
Variable |
Std |
0:Double |
0:BaseDataVariableType |
M, RO, HR |
|
0:HasComponent |
Variable |
Total |
0:Double |
0:BaseDataVariableType |
M, RO |
|
0:HasComponent |
Object |
UIInfo |
|
UIInformationType |
O |
|
0:GeneratesEvent |
ObjectType |
0:NonExclusiveLevelAlarmType |
|
|
|
|
0:GeneratesEvent |
ObjectType |
ProcessItemResetLogType |
|
|
|
|
Conformance Units |
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|
TMC Process Variables Ingestion and Control |
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Each valid ProcessItem can have one or more Precedes References pointing to other downstream ProcessItems.
The components of the ProcessItemType are further described below.
|
BrowseName |
Description |
|
AggregationWindow |
Tthe number of samples over which the aggregates are computed. When the number of aggregated samples since the last reset exceeds the AggregationWindow, the aggregates are rolled over, i.e. computed over the last AggregationWindow number of samples. The value of the AggregationWindow can be set by a client to obtain the desired aggregation. If the written value is below (above) the minimum (maximum) value that can be managed by the underlying system, the underlying system will overwrite it with the minimum (maximum). |
|
LimitAlarms |
The deviation alarm with 4 thresholds: HighHigh, High, Low, LowLow. All 4 thresholds shall be supported. |
|
Value |
Value represents the current value measured by the sensor. |
|
Avg |
The average of valid values over the last AggregationWindow samples and after the last reset. It is only reset by the successful execution of the ResetAggregates method. |
|
LastResetTime |
The time (in UTC) when ResetAggregates was last successfully executed. |
|
Max |
The maximum valid value for the last AggregationWindow samples and after the last reset. It is only reset by the successful execution of the ResetAggregates method. |
|
Min |
The minimum valid value for the last AggregationWindow samples and after the last reset. It is only reset by the successful execution of the ResetAggregates method. |
|
SamplingRate |
The rate samples are collected for aggregation. The rate is referred to the either product or time, as indicated by the EURange property. For example, SamplingRate equal to 100 ms means that the value is measured and collected for aggregation every 100 ms. SamplingRate equal to 10 kg means that the value is measured and collected for aggregation every 10 kg of product. SamplingRate equal to 100 rods means that the value is measured and collected for aggregation every 100 rods of product. The EURange property of the SamplingRate is read only and defines both the unit of measure and the supported range. The value of the SamplingRate can be set by a client to obtain the desired sampling rate for aggregation. If the written value is below (above) the minimum (maximum) value that can be managed by the underlying system, the underlying system will overwrite it with the minimum (maximum). The underlying system will support equivalent sampling rates of 100ms or better. |
|
Std |
The standard deviation of the valid value for the last AggregationWindow samples and after the last reset. After reset, when only one value is available, the standard deviation is not defined and zero will be returned. It is only reset by the successful execution of the ResetAggregates method. |
|
Total |
The accumulated total of the valid value for the last AggregationWindow samples and after the last reset. It is only reset by the successful execution of the ResetAggregates method. |
|
UIInfo |
The visualization resources to display the ProcessItemType on the UserInterface. |
The ResetAggregates Method restarts from new the computation of aggregates performed by the underlying system.
The signature of this Method is specified below. Table 130 specifies the Arguments representation.
Signature
ResetAggregates (
[out] MethodExecutionFeedbackType ExecutionFeedback);
Table 130 – ResetAggregates Method Arguments
|
Argument |
Description |
|
ExecutionFeedback |
The extended feedback returning a detailed message in case of execution failure. |
When the ResetAggregates method is invoked, an event of type ProcessItemResetLogType is generated with the last value of the aggregate variables, then the aggregates are reset as specified and the LastResetTime is set at the time when the method completes successfully.