Hi Mahdi,
It appears that your board is designed for measuring either RTDs or TCs. With this type of configuration you have to be careful. For example, you have what appears to be 130 ohm compensation resistors in the input path. This adds error, especially if there is current running through your system. An example is the BCS. This will create an offset and will drift over temperature variations. It is best to only turn on the BCS when checking for a sensor short/open. You should never leave it on for the actual measurement. I would also suggest removing the 130 ohm resistors.
How are you calibrating your system? You should at the very least issue a SELFOCAL command to remove any offset of the converter.
Best regards,
Bob B