About using an AnalogDevice object as an analog regulator object

When configured as an analog regulator device, the AnalogDevice object provides a means for reading and optionally writing two separate analog signals from the field or from another object: one PV value and one setpoint (SP) value. The basic I/O characteristics are:

• The process value (PV) is read from the field (except when the AnalogDevice object is configured to be in Manual mode), but is never written.

• The SP value is both read from the field and written to the field. You can configure the SP output destination address to be the same (default) or different from the input source address. Commands to change SP result in an output to field. For data integrity, the value of SP always represents the value read from the external controller, not the requested SP that is output to the external controller.

• The PV and SP 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, including when the PV:

• Exceeds level limits, such as Lo, Hi, LoLo, and HiHi.

• Exceeds rate-of-change limits, for both positive and negative directions.

• Exceeds major and minor deviations from the SP value.

• 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.

Other controller-oriented features that can be configured for an AnalogDevice object of type analog regulator include:

• Controller mode (CtrlMode attribute). You can use the controller mode to govern what types of writes are allowed to the SP value within the system. Controller mode options are Manual, Cascade, and None. When the object is in Manual mode, only end users are allowed to command a change in the value of SP. In Cascade mode, only scripts or other supervisory objects are allowed to command a change to SP. Finally, if None is specified for the controller mode, any type of write is allowed for the SP.

• Control tracking. A Boolean control track flag can be read from an external device or object. When tracking is on, the external controller "owns" the value of the SP; the SP is purely read-only and cannot be commanded to be changed and output to the field.