Platinum thermal resistance signal conditioner internal circuit block diagram and typical application circuit

The figure shows the internal circuit block diagram and typical application circuit of the platinum thermal resistance signal conditioner . The chip mainly includes 5 parts:

1. 2.5V reference voltage source;

2. Two symmetrical output current sources;

3. Instrumentation amplifier A1;

4. Spare amplifier A2;

5. Turn off the circuit.

The picture uses dual power supply. To measure temperatures below 0°C, -Us must be at least -1V. The SGND, AGND and DGND terminals are all connected to ground. When SHUTDOWN is not connected to DGND, ADT70 is turned off; when this terminal is not used, it should be connected to +Us. The +5V power supply supplies power to the current source through the potentiometer. The 2.5V voltage reference provides bias for the current source. The two current sources provide excitation current to the nominal resistor (R1) and the platinum thermal resistor (R2) respectively. The voltage difference between R2 and R1 is used as the input voltage of the instrumentation amplifier. By appropriately adjusting the gain of the instrumentation amplifier, an output voltage Uo proportional to the measured temperature can be obtained, and finally sent to a digital voltmeter to display the measured temperature value. The resistance value of R1 is 1kΩ. R2 is a Pt1000 platinum thermal resistor , with a nominal resistance value of 1kΩ at 0oC. RP is the balance potentiometer. R3 is the gain resistor of the instrumentation amplifier.