temperature-sense-rtd.yaml

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    1 # SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
    2 %YAML 1.2
    3 ---
    4 $id: http://devicetree.org/schemas/iio/afe/temperature-sense-rtd.yaml#
    5 $schema: http://devicetree.org/meta-schemas/core.yaml#
    6 
    7 title: Temperature Sense RTD
    8 
    9 maintainers:
   10   - Liam Beguin <liambeguin@gmail.com>
   11 
   12 description: |
   13   RTDs (Resistance Temperature Detectors) are a kind of temperature sensors
   14   used to get a linear voltage to temperature reading within a give range
   15   (usually 0 to 100 degrees Celsius).
   16 
   17   When an io-channel measures the output voltage across an RTD such as a
   18   PT1000, the interesting measurement is almost always the corresponding
   19   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) * iexc
   24     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            5V0
   30           -----
   31             |
   32         +---+----+
   33         |  R 5k  |
   34         +---+----+
   35             |
   36             V 1mA
   37             |
   38             +---- Vout
   39             |
   40         +---+----+
   41         | PT1000 |
   42         +---+----+
   43             |
   44           -----
   45            GND
   46 
   47 properties:
   48   compatible:
   49     const: temperature-sense-rtd
   50 
   51   io-channels:
   52     maxItems: 1
   53     description: |
   54       Channel node of a voltage io-channel.
   55 
   56   '#io-channel-cells':
   57     const: 0
   58 
   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 linear
   65       approximation of the resistance versus temperature relationship
   66       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, and
   71       R_0 (or r-naught-ohms) is the resistance of the sensor at 0 degrees
   72       Celsius.
   73 
   74       Pure platinum has an alpha of 3925. Industry standards such as IEC60751
   75       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 PT1000
   81 
   82 additionalProperties: false
   83 required:
   84   - compatible
   85   - io-channels
   86   - excitation-current-microamp
   87   - alpha-ppm-per-celsius
   88   - r-naught-ohms
   89 
   90 examples:
   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 ...

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FreeBSD/Linux Kernel Cross Reference sys/contrib/device-tree/Bindings/iio/afe/temperature-sense-rtd.yaml

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sys/contrib/device-tree/Bindings/iio/afe/temperature-sense-rtd.yaml