This information model provides information about process values, for example provided by actuators or sensors. In 6.2, the integration of such devices as components of a machine is described. This includes information about the identification of a device as well as health information and specific errors. In 9.1, the VariableType representing process value setpoints is introduced. In 6.4, an ObjectType using the VariableType and providing the process value as well as adding additional mechanisms for alarming and zero-point adjustment is described. Examples of the overall usage of process values are described in 6.5.
In order to integrate process values in the Machinery Information Model including device information, the device should be represented as component of a machine. An example ObjectType X:MySensorType is shown in Figure 1. It provides identification information using the 4:MachineryComponentIdentificationType. The process values – a device can potentially provide more than one process value – are grouped by the 3:SignalSet defined in the 3:ISignalSetType of OPC 30081. To provide the overall health status of the device as well as specific errors, the 2:IDeviceHealthType is implemented, defined in OPC 10000-100.
Note that it is not required to provide any device information to use the process values defined in this specification. However, this mechanism provides information about the identification and health status of the device.
Figure 1 – Integration as Device in Machinery Specification
In Figure 2, illustrates the 3:AnalogSignalVariableType and the ProcessValueSetpointVariableType and their supertypes with key InstanceDeclarations. The 3:AnalogSignalVariableType provides the optional Properties 0:ValuePrecision and 0:InstrumentRange and the mandatory Properties 0:EURange and 0:EngineeringUnits and are used as defined in OPC 10000-8. They provide information about the precision, ranges and unit of the process value. The optional Variables 3:ActualValue, 3:SimulationValue, and 3:SimulationState are used as defined in OPC 30081 and provide a simulation value and a flag to define, which value is used.
The ProcessValueSetpointVariableType defined in 9.1 adds additional, optional meta data.
Figure 2 – ProcessValueSetpointVariableType
In Figure 3, the ProcessValueType and its supertypes with key InstanceDeclarations is shown. The mandatory 3:SignalTag contains a unique name as defined by OPC 30081. The optional 3:ZeroPointAdjustment Method allows to set a zero point as defined in OPC 30081. The ProcessValueType adds a reference to the ZeroPointAdjustmentEventType. Events of this EventType are generated, when the zero-point adjustment is executed (see 8.1). The 3:AnalogSignal defined in OPC 30081 is extended with additional meta data. The ProcessValueType is defined in 7.1, having additional optional components like process value setpoint and alarm information.
This ObjectType was introduced to bind functionality to the process value that cannot be added to the 3:AnalogSignal directly, like Objects and Methods.
In Figure 4, an example of applying the device values in a machine is given, providing all information defined in this specification. The X:MyMachine Object contains a X:Sensor1 in its 4:Components folder. The X:Sensor1 provides identification information and health status. In addition, it contains two process values, X:Temperature and X:Pressure. Those Objects can be referenced from other paths as well, like the X:Monitoring Object of X:MyMachine. The X:Pressure Object contains various capabilities like the 3:ZeroPointAdjustment Method, DeviationAlarm, and the 3:AnalogSignal containing the process value. This Variable contains various sub-variables with meta data for ranges and unit, deviation etc.
Figure 4 – Example applying Device Values with all information
In Figure 5, an example is given using the base infrastructure defined in this specification to provide process values. In this case, no device information or the optional information is given, the X:MyMachine just provided some process values under the X:Monitoring Object.
Figure 5 – Example applying Device Values with base information
The ProcessValueType is designed to represent a process value having optionally a process value setpoint. It is not designed to represent a setpoint without a process value. If a setpoint without an associated process values should be represented, using the ProcessValueType is inappropriate. Information models may use the ProcessValueSetpointVariableType as representation of a setpoint. But also this VariableType has optional subvariables that imply a process value (everything associated to deviation) that should not be used without an associated process value.