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

Caution

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

The following figure shows the connection of active-type analog sensors (voltage) to differential inputs.

1 analog differential input requires 2 channels

Note

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

The following measuring ranges can be configured Analog Input/Output Module AX521 Analog Input/Output Module AX521:

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

The function of the LEDs is described under Displays.

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