A thermocouple produces a low voltage. There are also thermal voltages produced where you connect it to the amplifier. Unless you compensate for those other voltages, your temperature measurements will drift. The simplest way to elliminate drift is to use two thermocouples back to back which eliminates the connector thermal differential voltages. You then accurately measure the temperature difference between the two thermocouples. Only when one is in melting ice will you get an accurate reading.
The other way is to use only one thermocouple, but with a thermal compensation voltage, so you don't need the bucket of ice. That is done in the circuit and kit I referenced.
The ICL7107 is a differential converter designed to run on a single 9V battery. The common voltage is set internally by the chip, so you must reference your input to the common, (pin 32). The amplifier will need to amplify relative to that common reference provided by the chip.
If I remember from 40 years ago, connecting the reference inputs to the signal inputs of the ICL7107 chip should give a reading of 1.000; Check that on your simulator. The display goes from 0.000 to 1.999 which will become 000.0°C to 199.9°C.
What type of thermocouple will you use ?
A common type K thermocouple, = chromel–alumel, produces 41 µV/°C, which for a 200°C range produces a total of only 8.2 mV. Without amplification, the differential reference voltage would need to be half that = 4.1 mV.
You could wind the converter reference voltage down to only 4.1mV and see how it goes. Conversion noise can be reduced by using a higher reference voltage, say about 250 mV. That suggests you need a gain of about (250mV/4.1mV) = 61 times. Your example circuit shows a gain of only 3.
I will not do all your work for you. You need to read and understand the way the 7107 generates it's common voltage and how the quad-slope converters work by switching between inputs. Get a copy of the full data sheet and read up on reference voltage range etc. Maybe it is time I had another look at that datasheet.
