I have designed a PCB to read oxygen galvanic sensors, the output for this sensors is in mV (0-100mV).
I'm using the attached schematic connection. (Non inverted amplifier)
-Sensor positive to the non-inverted input of the LM358P and parallel with a 10k pulldown resistor.
-Sensor Negative connected to ground
-Inverted input connected to 1K to ground and to the output through a 10k resistor. (gain of 11).
-The output is connected to the uC analog input.
As the chip has 2 amplifier i'm connecting 1 sensor to each.
The kind of resistors Im using for this are an array of resistor for the 10k pulldown and RF resistors (this ones: 10k array resistor) and another array resistor for the 1k resistor (this one 1k array resitor). As I needed to read 10 sensors.
The problem is that when I connect one sensor the measurement is ok, but when I connect more than one the measurement is not accurate. The gain varies down and different on each Opamp. Why would be this happening?
Im also attaching the PCB layout.
Thanks beforehand for any help