On the below circuit the feedback resister value must be 9K.But with 9K I get those errors.
Op amp output disconnected from PIC ADC
@ 30’C, PT100=111.6 Ohms, op amp output shows 0.515V.
Op amp output connected to the PIC
@ 30’C, PT100=111.6 Ohms, op amp output shows 0.44V.
There is a 4’C difference. So the temperature shows 26’C instead of 30’C.
I changed four CA3140 op amps from different manufactures & all shows different outputs.
The problem solves when I adjust the gain until I get the correct values. But then again when I disconnected the Op amp output from PIC ADC the op amp output value will be too higher.
Why is this happening? How to solve this?
Op amp output disconnected from PIC ADC
@ 30’C, PT100=111.6 Ohms, op amp output shows 0.515V.
Op amp output connected to the PIC
@ 30’C, PT100=111.6 Ohms, op amp output shows 0.44V.
There is a 4’C difference. So the temperature shows 26’C instead of 30’C.
I changed four CA3140 op amps from different manufactures & all shows different outputs.
The problem solves when I adjust the gain until I get the correct values. But then again when I disconnected the Op amp output from PIC ADC the op amp output value will be too higher.
Why is this happening? How to solve this?
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