I'm trying to measure several high impedance signals with an ADC-20 and it's doing things that I don't expect.
One signal is a 10K thermistor in an existing divider, 3V - 10K - 10K NTC - GND. The ADC-20 is connected to the center of the divider with 10K series resistance into the ADC-20, but it is changing the signal when connected, seemingly reflecting changes that occur on other ADC channels. What's up?
On an adjacent channel, I am measuring a voltage with a high impedance divider, 0-8V signal - 301K - 100K - GND, with the ADC-20 in the middle of the divider and configured for +-2.5V range. The documenation indicates that Radc is 1 MOhm, but what I see seems to be below 800K Ohms. Is this typical?
Are the channels measured in parallel or serially? Is this a Sigma-Delta converter that is directly connected to the pins and capacitively loading them with switching currents or is it buffered?
I'm getting excellet results with low impedance setups, but this isn't working at all well for these