Hi,
I have problem with differential amplifier which not working how should be. The circuit is not designed by me and I can speak with design engineer in this moment. The problem is the output (UT+ and UT-) I measuring all the time same voltage. Not changing when is changing resistance on PT100 probe. When I measure input voltage on AJ4 connector then I can measure changes on PT100 probe. In this moment, I use 138.51ohm for 100°C and 175.86ohm for 200°C resistor to emulate PT100 probe. I checked PCB for obvious fault like short, component not soldered properly, component on right place, power supply voltages and noise.
Here is what can I measure on circuit.
when I am using 138.51ohm for 100°C
Between AJ4 connector pin 2 and 3 : 0.238V
Between UT+ and UT- output measured : 2.321V (should be around 1.95V)
when I am using 175.86ohm for 200°C
Between AJ4 connector pin 2 and 3: 0.308
Between UT+ and UT- output measured : 2.321V (should be around 2.45V)
Vcom is 2.5V
I'm just start to running out of idea what is problem whit circuit.
I just need idea what could be wrong whit this circuit. And I will be need to repair it....
Thank you,
Rudolf