Documentation sections

Thermocouple Voltage & Temperature

POSThttps://rftools.io/api/py/v1/calculate

Slug thermocouple-voltage. Calculate thermocouple EMF voltage from temperature with cold junction compensation. Determine Seebeck output for Type K, J, T, and E sensors.

Inputs

Send every one of these in inputs, in the units shown. Most are required: a call without one is refused (400) and costs nothing; one the calculator can do without takes the default shown. An input outside its range is still computed and flagged in the provenance.

Inputs of thermocouple-voltage
Name	Unit	Range	Default	Description
typenumber	none	0 … 3	0	Each type is modelled by a constant Seebeck coefficientOne of: 0 Type K (41 μV/°C) · 1 Type J (51 μV/°C) · 2 Type T (43 μV/°C) · 3 Type E (68 μV/°C)
temperaturenumber	°C	−270 … 1372	200	Hot Junction Temperature
coldJunctionTempnumber	°C	−50 … 70	25	Cold Junction Temperature
frontGainnumber	V/V	0.01 … 100000	60	The gain between the thermocouple and the ADC. A gain of 60 brings a type K's 50 mV at 1250 °C to about 3 V.
adcRefnumber	V	0.1 … 50	3.3	The ADC full scale. The ADC is unipolar: a hot junction colder than the cold junction reads 0.
adcBitsnumber	bit	1 … 24	12	ADC resolution in bits

Outputs

Returned in values, by key. A value that is unbounded or undefined is null.

Outputs of thermocouple-voltage
Field	Unit	Description
voltageheadline	μV	Output Voltage
coldJunctionCorrection	μV	Cold Junction Correction
seebeck	μV/°C	Seebeck Coefficient
deltaT	°C	Temperature Difference
amplifiedVoltage	V	The thermocouple voltage times the amplifier gain
adcCode	none	The code an ideal ADC reads: floor(V_amp / V_ref × 2^N), 0 below zero
resolution	°C/LSB	The temperature one ADC step spans

Calling it

Calculate: one call, the request and response in full, and its errors.
Batch: this calculator with others, or a sweep, in one request.
Solve for a target: the value of one input that brings an output to a target.

curl -X POST https://rftools.io/api/py/v1/calculate \
  -H "X-API-Key: $RFTOOLS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "slug": "thermocouple-voltage",
    "inputs": {
      "type": 0,
      "temperature": 200,
      "coldJunctionTemp": 25,
      "frontGain": 60,
      "adcRef": 3.3,
      "adcBits": 12
    }
  }'

import rftools

client = rftools.Client()  # reads RFTOOLS_API_KEY, or the key `rftools login` saved

result = client.calculate("thermocouple-voltage", {
    "type": 0,
    "temperature": 200,
    "coldJunctionTemp": 25,
    "frontGain": 60,
    "adcRef": 3.3,
    "adcBits": 12,
})
print(result.values)
print(result.warnings, result.provenance.formula_ref)

const response = await fetch("https://rftools.io/api/py/v1/calculate", {
  method: "POST",
  headers: {
    "X-API-Key": process.env.RFTOOLS_API_KEY,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "slug": "thermocouple-voltage",
    "inputs": {
      "type": 0,
      "temperature": 200,
      "coldJunctionTemp": 25,
      "frontGain": 60,
      "adcRef": 3.3,
      "adcBits": 12
    }
  }),
});
console.log(response.status, await response.json());

package main

import (
	"bytes"
	"fmt"
	"io"
	"net/http"
	"os"
)

func main() {
	body := []byte(`{
	  "slug": "thermocouple-voltage",
	  "inputs": {
	    "type": 0,
	    "temperature": 200,
	    "coldJunctionTemp": 25,
	    "frontGain": 60,
	    "adcRef": 3.3,
	    "adcBits": 12
	  }
	}`)
	req, err := http.NewRequest("POST", "https://rftools.io/api/py/v1/calculate", bytes.NewReader(body))
	if err != nil {
		panic(err)
	}
	req.Header.Set("X-API-Key", os.Getenv("RFTOOLS_API_KEY"))
	req.Header.Set("Content-Type", "application/json")
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()
	out, _ := io.ReadAll(res.Body)
	fmt.Println(res.Status, string(out))
}

application/json

{
  "slug": "thermocouple-voltage",
  "values": {
    "voltage": 7175,
    "coldJunctionCorrection": 1025,
    "seebeck": 41,
    "deltaT": 175,
    "amplifiedVoltage": 0.4305,
    "adcCode": 534,
    "resolution": 0.32750571646341464
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:thermocouple-voltage",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "NIST Monograph 175",
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "type": {
          "min": 0,
          "max": 3,
          "unit": ""
        },
        "temperature": {
          "min": -270,
          "max": 1372,
          "unit": "°C"
        },
        "coldJunctionTemp": {
          "min": -50,
          "max": 70,
          "unit": "°C"
        },
        "frontGain": {
          "min": 0.01,
          "max": 100000,
          "unit": "V/V"
        },
        "adcRef": {
          "min": 0.1,
          "max": 50,
          "unit": "V"
        },
        "adcBits": {
          "min": 1,
          "max": 24,
          "unit": "bit"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "type": 0,
      "temperature": 200,
      "coldJunctionTemp": 25,
      "frontGain": 60,
      "adcRef": 3.3,
      "adcBits": 12
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "type"
      ],
      "msg": "Input should be a valid number, unable to parse string as a number",
      "input": "abc"
    }
  ]
}

An input sent as text. Nothing was counted.

{
  "detail": "More than 120 requests in 60 seconds from this address.",
  "errorKind": "rate_limited",
  "limit": 120,
  "windowSeconds": 60,
  "upgradeUrl": "https://rftools.io/pricing/"
}

Too many requests in a minute, with Retry-After.

Same inputs on the calculator pageThermocouple Voltage & Temperature, at these values