If a 3-wire Pt100 measurement is required (reducing the influence of the sensors supply cable resistance), external 7K5 resistors can also be used and the sensors should then be connected in accordance with the following diagram.
Fig. 1 An example of a three-wire connection of the Pt100 sensors to the IT-1604 module
All sensors are powered via serial resistors (a 7k5 resistor, ideally with 0.1 % accuracy) from the Vref terminal of reference voltage. A9 The accuracy of the 7K5 resistor has a key impact on the accuracy of measurement of resistive sensors.
To maintain the accuracy in accordance with the module specification, it is necessary to use resistors with the basic accuracy of 0.1 % and the minimum temperature coefficient of 25 ppm.
The resistors must be fitted outside the module into the control panel.