Channels 1 and 2 of the PD 640 module can be configured to work as either an analogue input or an analogue output.

When configured as an analogue output, the analogue input is still active and can be used as a read back feature to monitor the output current.
All analogue input channel features, such as notification, alarms etc., continue to work in the same way as if the channel were configured for analogue input.

An analogue output can be configured as 0-20mA or 4-20mA.

The control signal for the analogue output can be written to the channel in two ways:
– Percentage value
– Scaled SI unit value

Writing in percentage (0-100) will set the output current to the required percentage of the selected output range: 0-20mA or 4-20mA.

Writing in Scaled SI unit, will calculate the output signal based on ZeroPoint and Span, using the same calculation principle as described for Analogue Input channels.

Writing to one of the two output control registers will always result in the value being automatically re-calculated and written to the other register. Both registers will thus always show the actual value.

(See also: OutputSetpointPercentage, OutputSetpointScaled.)