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1# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)2%YAML 1.23---4$id: http://devicetree.org/schemas/iio/afe/temperature-sense-rtd.yaml#5$schema: http://devicetree.org/meta-schemas/core.yaml#6 7title: Temperature Sense RTD8 9maintainers:10 - Liam Beguin <liambeguin@gmail.com>11 12description: |13 RTDs (Resistance Temperature Detectors) are a kind of temperature sensors14 used to get a linear voltage to temperature reading within a give range15 (usually 0 to 100 degrees Celsius).16 17 When an io-channel measures the output voltage across an RTD such as a18 PT1000, the interesting measurement is almost always the corresponding19 temperature, not the voltage output. This binding describes such a circuit.20 21 The general transfer function here is (using SI units)22 23 V = R(T) * iexc24 R(T) = r0 * (1 + alpha * T)25 T = 1 / (alpha * r0 * iexc) * (V - r0 * iexc)26 27 The following circuit matches what's in the examples section.28 29 5V030 -----31 |32 +---+----+33 | R 5k |34 +---+----+35 |36 V 1mA37 |38 +---- Vout39 |40 +---+----+41 | PT1000 |42 +---+----+43 |44 -----45 GND46 47properties:48 compatible:49 const: temperature-sense-rtd50 51 io-channels:52 maxItems: 153 description: |54 Channel node of a voltage io-channel.55 56 '#io-channel-cells':57 const: 058 59 excitation-current-microamp:60 description: The current fed through the RTD sensor.61 62 alpha-ppm-per-celsius:63 description: |64 alpha can also be expressed in micro-ohms per ohm Celsius. It's a linear65 approximation of the resistance versus temperature relationship66 between 0 and 100 degrees Celsius.67 68 alpha = (R_100 - R_0) / (100 * R_0)69 70 Where, R_100 is the resistance of the sensor at 100 degrees Celsius, and71 R_0 (or r-naught-ohms) is the resistance of the sensor at 0 degrees72 Celsius.73 74 Pure platinum has an alpha of 3925. Industry standards such as IEC6075175 and ASTM E-1137 specify an alpha of 3850.76 77 r-naught-ohms:78 description: |79 Resistance of the sensor at 0 degrees Celsius.80 Common values are 100 for PT100, 500 for PT500, and 1000 for PT100081 82additionalProperties: false83required:84 - compatible85 - io-channels86 - excitation-current-microamp87 - alpha-ppm-per-celsius88 - r-naught-ohms89 90examples:91 - |92 pt1000_1: temperature-sensor0 {93 compatible = "temperature-sense-rtd";94 #io-channel-cells = <0>;95 io-channels = <&temp_adc1 0>;96 97 excitation-current-microamp = <1000>; /* i = U/R = 5 / 5000 */98 alpha-ppm-per-celsius = <3908>;99 r-naught-ohms = <1000>;100 };101...102