Monitoring a DiscreteDevice object via inputs
- Last UpdatedJul 19, 2024
- 2 minute read
If you configure the DiscreteDevice object to have inputs (feedback) from the field, the input values will be used to update the overall state of the device. A DiscreteDevice object can have up to four inputs. After defining the inputs, you will need to map the different input combinations to the possible states for the device.
For example, you might have a valve on your discrete device that can be either opened or closed. You have defined the passive state of the device as Closed, the first active state as Opened, and the fault state as Bad. You would then create references for two field inputs: one for the open position (Valve_Open), and one for the closed position (Valve_Close). You then would map the inputs to the defined states. For example:
|
Valve_Open |
Valve_Close |
Mapped State |
|---|---|---|
|
0 |
0 |
Bad |
|
0 |
1 |
Closed |
|
1 |
0 |
Opened |
|
1 |
1 |
Bad |
where:
1=TRUE
0=FALSE
By default, when the monitored discrete inputs change, the DiscreteDevice object determines the new actual state of the equipment and updates the value of the process value (PV) appropriately.
You can configure the DiscreteDevice object to allow or disallow overriding of the PV value. If you enable the PV override, then the object can be placed in Auto, Manual, or Simulate modes using the PVMode attribute.
-
When the object is in Auto mode, the PV updates from the field and matches the value and quality of PVAuto.
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When the object is in Manual mode, PVAuto continues to update from the field but the PV does not. Instead, the PV can be set by a user or script and the quality is always marked as UNCERTAIN.
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When the object is in Simulate mode, the PV value is set equal to the Cmd value, rather than read from the field.