I'm trying to connect a Turner C-Sense pCO2 sensor to an RPi2B using an MCP3008 ADC. The probe is powered via dedicated 9V inverter. The probe's analog output wires include a signal out (+) and AGND (-). I can use a multimeter to read the voltage (0-5VDC) across the two wires, but I'm interested in having the RPi read/log the voltages.
I've completed several tutorials using the RPi/MCP3008 to connect several 10K thermistor resistors using voltage dividers, and thought I could connect this sensor in a similar way. I tried several different connection options that seemed logical to me, but only ended up with either 0 or 1023 outputs readings.
I'm using the rpi.gpio python package to communicate with the ADC and verified with a 10K thermistor that CH0 can send accurate data. So I am interested in the correct wiring configuration for the CO2 sensor's two output wires.
Edit: I think I had it working there for a minute when I connected the ADC VREF pin to 5V and grounded the sensor's AGND and ADC's AGND to a common GND pin on the RPi. I was getting variable voltage readings from the sensor. BUT the ADC got extremely HOT and the values were offset from true.