LCT1051 low offset op-amp means the input offset of the amplifier is only 5μV, meaning we can skip all of the zero offset circuitry normally needed for these types of DC amplifiers. The two potentiometers are used to calibrate the thermocouples to the target 10mV/degree Celsius output from the amplifier.
The one concern with using thermocouples is that they create a voltage signal (which is very small, on the order of 60uV/degree) based on a temperature difference. This means that to find out the temperature at the end of the thermocouple, you need to also know the temperature at the base of the thermocouple, and then add these two temperature signals together to get the actual temperature at the bead of the thermocouple. Luckily, Linear also makes a very nice thermocouple compensator, which does exactly this. I did little more than build a pair of the reference applications from the LT1025 datasheet.
I am only using a positive power supply, so this amplifier cannot measure negative temperatures, and I wouldn't trust it much below room temperature. This was designed to measure temperature elevation from machining, so this limitation is fine, but make sure this is alright for your application.
- 2x 255k 1% resistor ($0.112 Digikey)
- 2x 1k 1% resistor ($0.112 Digikey)
- 2x 100Ω high turn pot ($0.92 Digikey)
- 5x 0.1μF capacitor ($0.16 Digikey)
- 1x 100 μF capacitor ($0.17 Digikey)
- 2x 8DIP3 socket ($0.13 Digikey)
- 1x LT1025 thermocouple compensator ($5.10 Digikey)
- 1x LTC1051 dual low offset op-amp ($8.10 Digikey)
- 9x screw terminals (Salvaged)