With the function "Differential counting” two adjacent channels of the binary input are used and configured together.
The prerequisite for this function is that the "Pairwise” option is selected in the device settings for the adjacent channel concerned.
“Function of channels A + B” parameter
With difference counting, for example, the telegrams from two sensors are recorded, counted and the difference is calculated. The difference is calculated using the formula “counter reading B minus counter reading A."
The telegrams of both sensors are recorded separately and used in a further step in the difference calculation. This makes it possible to configure channels of both sensors separately and optionally to query the counter readings of both counters separately after corresponding configuration.
For both input channels it can be set separately via parameters whether the counter reading is incremented with a rising and/or falling signal edge. It is also possible to set separately for both channels when the counter is incremented and with which increment the counter is incremented.
The counter readings are stored in the communication objects "A Count” (42), "B Count” (45) and the difference value in the communication object "A + B Count” (53). Depending on the configuration, the values can be sent on request or automatically after a change by a certain value or cyclically.
Via the communication objects "A Count” (41) and "B Count” (44) the counter readings can be reset to the value "0” or another value by telegram if required.
Optionally, a limit value for the difference of the two channels and a monitoring of the limit value can be set.
Application example
Access control:
Red light when there are too many people in the room: One sensor (e.g. a light barrier or a contact in a turnstile) sends a telegram as soon as a person enters the room, and a second sensor sends a telegram as soon as a person leaves the room. The binary input counts the telegrams, calculates the difference and sends another telegram as soon as the difference exceeds a certain number. This further telegram can be used, for example, to switch a traffic light.
The difference is calculated using the formula “counter reading B minus counter reading A." Therefore, the sensor for counting people entering the room must be connected to channel B and the sensor for counting people leaving the room must be connected to channel A.