I've been working with signal conditioning, thermocouple out specifically. I'm working with a span of 450 °C, that is, from -50 °C to 400 °C. For those values of temperatures I get, according to the table, -2.431 mV and 21.848 mV. The problem is that I need to convert that into 0-5V signal. I am thinking of using the AD620, which is an Instrumentation Amplifier. It's been impossible for me to convert -2.431mV into 0V. Do you have any suggestions about this?
Unless you have the "cold-junction" offset handled by some other method which you did not mention in your question, it is not recommended to use a simple op-amp to "condition" a thermocouple signal.
Analog Devices makes a range of specialty "Thermocouple Interface Amplifiers". Highly recommended to use one of those. There are some "break-out boards" which feature the complete thermocouple conditioning ready to use.
The building block pieces you'll typically need are:
- Cold junction (a.k.a., reference junction) compensation
- Voltage amplification circuit (typically an instrumentation amplifier)
- Voltage linearization circuit (optional)
- Band limiting filter (low pass filter) to mitigate the the corrupting effects of high frequency signal aliases in the digitized data (recommended)
- Analog-to-digital (ADC) conversion
I agree with @user2943160 that a commercial off-the-shelf (COTS) thermocouple amplifier IC is the simplest way to go, rather than trying to build the cold junction compensation, amplifier circuitry, etc. from scratch.
(n.b. COTS thermocouple amplifier ICs typically do not provide the band limiting filter function/circuitry. The filters are external to the IC and are designed/provided by the circuit designer.)
For what it's worth, Analog Devices published a series of eight short videos on YouTube titled Thermocouple 101 that are worth watching in my opinion. (HINT: This video series describes how to set the 2.5 VDC common mode input voltage at the instrumentation amplifier's inverting and non-inverting inputs, to manage the -2.431 mV voltage.)