Connection of resistance thermometers in 3-wire configuration

When resistance thermometers (Pt100, Pt1000, Ni1000, Cu50) are used, a constant current must flow through them to build the necessary voltage drop for the evaluation. For this, the module AI531 provides a constant current source which is multiplexed over the 4 analog channels.

The following figure shows the connection of resistance thermometers in 3-wire configuration.

Connection of resistance thermometers in 3-wire configuration. 1 analog sensor requires 1 channel.

The following measuring ranges can be configured AI531 Analog Input Module AI531 Analog Input Module (see also

Pt100	-50 °C … +70 °C / +400 °C; -200 °C … +850 °C	1 channel used
Pt1000	-50 °C … +400 °C	1 channel used
Ni1000	-50 °C … +150 °C	1 channel used
Cu50	-50 °C … +200 °C (1.426); -200 °C … +200 °C (1.428)	1 channel used

The function of the LEDs is described under Diagnosis and displays / displays AI531 Analog Input Module.

The module linearizes the resistance thermometer characteristics. In order to keep measuring errors as small as possible, it is necessary by all means, to have all the involved conductors in the same cable. All the conductors must have the same cross section.

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