I have developed a 4-20mA sensor reading board using ADS1115 16-bit ADC and precision 100 ohm resistors so the current will flow through the resistors and be converted into voltages.
I hooked up a TP100 temperature probe to a 4-20mA converter and 12V source. I was using channel 0 of the ADC. Everything looked as they should be. I left it on the carpet and didn't look at it until today. Now channel 0 reads 1.967V when it should read 0V and about 2.367V when it should read 0.8V. I probed the channel with my multimeter. It's receiving the correct input voltage.
Notice the difference is about half the voltage it should be reading: 0.8/2~=2.367-1.967
I checked channel 1. It works as expected, reading 0.8V. I doubt it's firmware issue. I've used this firmware for a number of years to flash my boards and when I last did that on several boards, my tests were correct. This ADC has a single programmable gain pre-amplifier that is multiplexed with 4 single-ended channels or 2 differential channels. I think the preamplifier is good but maybe the multiplexer is broken?
So I wonder if someone has seen similar "damages" on an ADC or specifically an ADS1115. My temperature probe has a metal sheath and metal mesh around the cable. I could have shorted something without knowing so.