Thermocouple voltage calculator
A thermocouple measures the difference between the measuring junction and the reference. Cold junction compensation adds the reference back.
V
Compensated output
20.5000mV
- Raw junction output
- 19.4750 mV
- Cold junction compensation
- 1025.0 microvolts
- After the amplifier
- 3.895 00 V
- ADC least significant bit
- 76.294 microvolts
- Temperature resolution
- 0.0093 degrees C
- Junction temperature difference
- 475.0 K
Show the working
- Measuring junction temperature = 500
- Cold junction temperature = 25
- Thermocouple type = 41
- Amplifier gain = 200
- ADC resolution = 16
- ADC input range = 5
- Junction temperature difference = 500 - 25 = 475
- raw_uv = 475 * 41 = 19 475
- Cold junction compensation = 25 * 41 = 1025
- total_uv = 19 475 + 1025 = 20 500
- Raw junction output = 19 475 / 1000 = 19.475
- Compensated output = 20 500 / 1000 = 20.5
- After the amplifier = 19 475 / 1e6 * 200 = 3.895
- ADC least significant bit = 5 / 2^16 * 1e6 = 76.2939
- resolution_c = 41 * 200 > 0 ? 76.2939 / (41 * 200) * 1e6 / 1e6 : 0 = 0.009 304 14
- Temperature resolution = 41 > 0 ? 76.2939 / 200 / 41 : 0 = 0.009 304 14
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- output = Seebeck coefficient x (hot - cold junction temperature)
- compensation adds the voltage the cold junction would produce against 0 degrees
Seebeck coefficients are not constant with temperature. A real instrument uses polynomial tables, not a single sensitivity.
A thermocouple with no cold junction compensation reads the difference, not the temperature. That mistake is invisible until the room temperature changes.