"Offset" Ambiguity

[connorjcantrell]

Our industry uses the term "Offset" in various contexts. This issue aims to discuss and define these variations, determining the most appropriate terminology for each. Let's consider the following concepts:

(The following list of terms and definitions is a work in progress and I will update it as discussion continues)

• TBD: The difference between a process value and target value [1][2]
• TBD: The difference between a Setpoint and Threshold (e.g., Zone Air Temperature Setpoint and Cooling Threshold)

Please comment to add other relevant concepts or provide insights, improvements on these definitions. The placeholder names will be updated once consensus is reached.

References:
[1] Computrols. Automation Glossary. https://www.computrols.com/support/automation-glossary/#o
[2] Automation Forum. What is Offset in Process Control? https://automationforum.co/what-is-offset-in-process-control/

[wroantree]

@connorjcantrell

I think the term offset should be reserved for sensor correction. As an example, when a flow sensor is calibrated, it's measured value will differ from the known value (i.e. a calibrated instrument measured 600 gpm, the instrument being calibrated measured 550 gpm), and then an offset and a scale are applied to get the instrument being calibrated to read correctly.

The difference between a process value and target value

In control systems, this value is referred to as the Error, and I think that should be used here as well

The difference between a Setpoint and Threshold (e.g., Zone Air Temperature Setpoint and Cooling Threshold)

I think that should be called Deadband, and the difference between the target setpoint and the center of the deadband should be called the Deadband Bias. However, that doesn't address single-sided deadbands, like you might have with a cooling only device, and it also doesn't address the difference between an enable threshold and a disable threshold (i.e. enable heating at 68 deg F zone temp, disable heating at 71 deg F zone temp).

Thoughts?