Connection of resistance thermometers in 2-wire configuration

When resistance thermometers (Pt100, Pt1000, Ni1000) are used, a constant current must flow through them to build the necessary voltage drop for the evaluation. For this, the module AX521 provides a constant current source which is multiplexed over the 8 analog channels.

The following figure shows the connection of resistance thermometers in 2-wire configuration.

1 analog input requires 1 channel

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

Pt100	-50 °C…+70 °C	2-wire configuration, one channel used
Pt100	-50 °C…+400 °C	2-wire configuration, one channel used
Pt1000	-50 °C…+400 °C	2-wire configuration, one channel used
Ni1000	-50 °C…+150 °C	2-wire configuration, one channel used

The function of the LEDs is described under Displays.

The module AX521 performs a linearization of the resistance characteristic.

In order to avoid error messages from unused analog input channels, it is useful to configure them as “unused”.