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