Connection of active-type analog sensors (voltage) to differential \ inputs

Differential inputs are very useful if analog sensors are which are remotely non-isolated (e.g. the minus terminal is remotely earthed) are used.

The use of differential inputs helps to considerably increase the measuring accuracy and to avoid earthing loops.

With differential input configurations, two adjacent analog channels belong together (e.g. the channels 0 and 1). In this case, both channels are configured according to the desired operating mode. The lower address must be the even address (channel 0), the next higher address must be the odd address (channel 1). The converted analog value is available at the higher address (channel 1).

The analog value is calculated by subtraction of the input value with the higher address from the input value of the lower address.

The converted analog value is available at the odd channel (higher address).

Caution

The earthing potential at the sensors must not have too large a potential difference with respect to ZP (max. ± 1 V within the full signal range). Otherwise, problems may occur concerning the common-mode input voltages of the involved analog inputs.

Connection example

Note

The negative pole of the sensor must be earthed next to the sensor.

Voltage	0…10 V	with differential inputs, 2 channels used
Voltage	-10 V…+10 V	with differential inputs, 2 channels used

In order to avoid error messages or long processing times, it is useful to configure unused analog input channels as “unused”.