DTXr

Had to move this to ver 3.1.7

Some reading about polarity due to BACnet spec:

Only applicable in Binary Input and Binary Output objects.

Facts
In some applications, electronic circuits may reverse the relationship between the application-level logical states, ACTIVE and INACTIVE, and the physical state of the underlying hardware. For example, a normally open relay contact may result in an ACTIVE state (device energized) when the relay is energized, while a normally closed relay contact may result in an ACTIVE state (device energized) when the relay is not energized.

Present_Value (Commandable)
This property, of type BACnetBinaryPV, reflects the logical state of the Binary Output. The logical state of the output shall be either INACTIVE or ACTIVE. The relationship between the Present_Value and the physical state of the output is determined by the Polarity property. The possible states are summarized in Table 12-9. Table 12-9. BACnet Polarity Relationships Present_Value Polarity Physical State of Output Physical State of Device INACTIVE NORMAL OFF or INACTIVE not running ACTIVE NORMAL ON or ACTIVE running INACTIVE REVERSE ON or ACTIVE not running ACTIVE REVERSE OFF or INACTIVE running

Polarity
This property, of type BACnetPolarity, indicates the relationship between the physical state of the output and the logical state represented by the Present_Value property. If the Polarity property is NORMAL, then the ACTIVE state of the Present_Value property is also the ACTIVE or ON state of the physical output as long as Out_Of_Service is FALSE. If the Polarity property is REVERSE, then the ACTIVE state of the Present_Value property is the INACTIVE or OFF state of the physical output as long as Out_Of_Service is FALSE. See Table 12-9. If Out_Of_Service is TRUE, then the Polarity property shall have no effect on the physical output state.