102 lines
2.6 KiB
YAML
102 lines
2.6 KiB
YAML
# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
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%YAML 1.2
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---
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$id: http://devicetree.org/schemas/iio/afe/temperature-sense-rtd.yaml#
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$schema: http://devicetree.org/meta-schemas/core.yaml#
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title: Temperature Sense RTD
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maintainers:
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- Liam Beguin <liambeguin@gmail.com>
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description: |
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RTDs (Resistance Temperature Detectors) are a kind of temperature sensors
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used to get a linear voltage to temperature reading within a give range
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(usually 0 to 100 degrees Celsius).
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When an io-channel measures the output voltage across an RTD such as a
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PT1000, the interesting measurement is almost always the corresponding
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temperature, not the voltage output. This binding describes such a circuit.
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The general transfer function here is (using SI units)
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V = R(T) * iexc
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R(T) = r0 * (1 + alpha * T)
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T = 1 / (alpha * r0 * iexc) * (V - r0 * iexc)
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The following circuit matches what's in the examples section.
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5V0
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-----
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+---+----+
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| R 5k |
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+---+----+
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V 1mA
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+---- Vout
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+---+----+
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| PT1000 |
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+---+----+
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-----
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GND
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properties:
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compatible:
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const: temperature-sense-rtd
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io-channels:
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maxItems: 1
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description: |
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Channel node of a voltage io-channel.
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'#io-channel-cells':
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const: 0
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excitation-current-microamp:
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description: The current fed through the RTD sensor.
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alpha-ppm-per-celsius:
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description: |
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alpha can also be expressed in micro-ohms per ohm Celsius. It's a linear
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approximation of the resistance versus temperature relationship
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between 0 and 100 degrees Celsius.
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alpha = (R_100 - R_0) / (100 * R_0)
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Where, R_100 is the resistance of the sensor at 100 degrees Celsius, and
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R_0 (or r-naught-ohms) is the resistance of the sensor at 0 degrees
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Celsius.
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Pure platinum has an alpha of 3925. Industry standards such as IEC60751
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and ASTM E-1137 specify an alpha of 3850.
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r-naught-ohms:
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description: |
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Resistance of the sensor at 0 degrees Celsius.
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Common values are 100 for PT100, 500 for PT500, and 1000 for PT1000
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additionalProperties: false
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required:
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- compatible
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- io-channels
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- excitation-current-microamp
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- alpha-ppm-per-celsius
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- r-naught-ohms
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examples:
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- |
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pt1000_1: temperature-sensor0 {
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compatible = "temperature-sense-rtd";
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#io-channel-cells = <0>;
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io-channels = <&temp_adc1 0>;
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excitation-current-microamp = <1000>; /* i = U/R = 5 / 5000 */
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alpha-ppm-per-celsius = <3908>;
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r-naught-ohms = <1000>;
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};
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...
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