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Appendix B Using Setpoints

9. Appendix B Using Setpoints

The PM172EH has an embedded logical controller that can run different

actions in response to user-defined internal and external events. Unlike a

PLC, the PM172EH uses a simplified setpoint programming technique

that allows the user to define a logical expression based on measured

analog and digital values that will produce a required action.

The PM172EH provides 16 setpoints with programmable operate and

release delays. Each setpoint can evaluate a logical expression with up to

four arguments using OR/AND logic. Whenever an expression is

evaluated as “true”, the setpoint performs up to four consequent actions

that can send a command to the output relays, increment or decrement a

counter, or trigger a recorder.

The scan time for all setpoints is 50 ms.

Using Logical Expressions

Logical operators OR/AND are treated in a simplified manner. They have

no specific priority or precedence rules.

Any trigger condition bound to the logical expression by the OR operator

and evaluated as “true” will override any preceding condition evaluated as

“false”. Similarly, any trigger condition evaluated as “false” and bound by

the AND operator will override any condition evaluated before it as “true”.

To avoid confusion, it is recommended not to alternate different logical

operators in one expression. Instead, bring all conditions that use the

same logical operator together to one side of the expression, and the

others - to the opposite side.

To explicitly override all other conditions with the critical trigger, put it at

the end of the expression using the OR operator if you want the setpoint

to be operated anyway when the trigger condition is asserted, and with

the AND operator, if the setpoint should not be operated while the critical

trigger is not asserted.

Using Numeric Triggers

For numeric (analog) triggers, a setpoint allows you to specify two

thresholds for each trigger to provide hysteresis (dead band) for setpoint

operations. The operate limit defines the operating threshold, and the

second release limit defines the release threshold for the trigger. The

trigger thresholds are specified in primary units.

If you do not want to use hysteresis for the trigger, set the release limit to

the same as the operate limit.

Satec PM172EH series User Manual

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