Simple Thermocouple Amplifier
The OP07 is in a non inverting amplifier so as not load the mV of thermocouple, the zeners are to protect circuit if junction contacts heaters or the earth gets broken.
The RC is to filter out 50Hz pick up in thermocouple wires if near heater wiring and also reduces reading jumps when high current three phase contacter operates.
The Pull-up 10M is when a Thermocouple breaks the output of circuit will be max. This is open sensor protection, in case Thermocouple breaks, Required only in industrial temperature controllers for protection. This means it will be 3.5V which should make you turn off the heater in software.
J and K Thermocouple with 4-20 mA
The other opamp is for further amplification as OP07 is set to around 30 gain and offset has to be adjusted with R9. If OP07 is kept in > 100 gain it may be difficult to adjust offset of 75uV. If you need very high gain in the first stage use some instrumentation amplifier or chopper stabilized amplifier. I am not very sure. This is the very basic Thermocouple Amplifier used as a front end signal conditioning in Process Control.
