The voltage offset of ADS1115

I would like to use the ADS to translate voltage into raspberry pi.
The output of the voltage range is 0-60mv.
I connect one to the ground on the ADS board and the other to the A0 pin.
and then I test the voltage between these two pins and it becomes 2.1V. In theory, the voltage will still be 0-60mv as the input voltage into the ADS
How can I offset this kind of voltage? Where does this voltage come from?

Hi, @KAI48636
For us to best help figure out what’s happening, do you mind uploading a drawing of your schematic, including notes of expected voltages?

I do a draft in the attached picture, if you need any more detail, please contact me.

Everything else aside, trying to read a 0-60mV signal with a 3.3V referenced ADC is not going to make good use of it’s resolution and I doubt the pressure sensor is intended to be connected directly to an ADC input.
What is the pressure sensor? Do you have a datasheet for it?

I have done a test with the power supply. And the ADC can quite good for recognizing the mv voltage.
Because I can set the gain of the ADS to make the full-scale input be 0-256mv, the resolution will be good enough.
All the problem is the 2.1V voltage. Quite strange.
The datasheet of the pore pressure I need to check later.