Connection of Active-type Analog Sensors (Voltage) to Differential \ Analog Inputs

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

The evaluation using 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).

Attention

:strong:Risk of faulty measurements!

The negative pole/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).

Make sure that the potential difference never exceeds ± 1 V.

The following figure shows the connection of active-type analog sensors (voltage) to differential analog inputs AI0 and AI1. Proceed with AI2 and AI3 in the same way.

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

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

The measuring ranges are described in the section Measuring Ranges CI592-CS31 - Digital and Analog Inputs and Outputs CI592-CS31 - Digital and Analog Inputs and Outputs:

To avoid error messages from unused analog input channels, configure them as “unused”.