About using an AnalogDevice object as a basic analog input/output object
- Last UpdatedJul 18, 2024
- 2 minute read
When configured as a basic analog device, this object provides a means for reading and optionally writing analog signals from the field or from another object. The basic I/O characteristics are:
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The process value (PV) is read from the field (except when the AnalogDevice object is configured to be in Manual mode).
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You can configure the AnalogDevice object to enable or disable analog output. If you enable output, you can configure the output destination address to be the same (default) or different from the input source address. Commands to change the PV will result in an output to field. For data integrity, the value of PV represents the value read from the external controller (except when the AnalogDevice object is in Manual mode), not the requested PV that is output to the external controller.
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The input and outputs can be optionally scaled between raw counts and engineering unit values using either linear or square-root conversions.
The AnalogDevice object supports alarming for PV conditions, such as when the PV:
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Exceeds level limits, such as Lo, Hi, LoLo, and HiHi.
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Exceeds rate-of-change limits, for both positive and negative directions.
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Exceeds major and minor deviations from a target value.
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Has a quality value of BAD.
In addition, you can configure the AnalogDevice object to allow or disallow the overriding of the PV value. If you enable the PV override, then you can use the PV.Mode attribute to place the AnalogDevice object into either Auto or Manual mode. When the AnalogDevice object is in Auto mode, the PV is updated from the field and matches the value and quality of the PVAuto attribute. When the AnalogDevice object is in Manual mode, the PVAuto attribute continues to be updated from the field, but the PV value does not. Instead, the PV can be set by a user write or a script, and the quality is always set to UNCERTAIN.
Finally, you can configure the AnalogDevice object to historize key variables, including PV and PV.Mode.