From: Liam Beguin <liambeguin@gmail.com>
To: liambeguin@gmail.com, peda@axentia.se, jic23@kernel.org,
lars@metafoo.de, pmeerw@pmeerw.net
Cc: linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org,
devicetree@vger.kernel.org, robh+dt@kernel.org
Subject: [PATCH v4 09/10] dt-bindings: iio: afe: add bindings for temperature-sense-rtd
Date: Tue, 6 Jul 2021 12:09:41 -0400 [thread overview]
Message-ID: <20210706160942.3181474-10-liambeguin@gmail.com> (raw)
In-Reply-To: <20210706160942.3181474-1-liambeguin@gmail.com>
From: Liam Beguin <lvb@xiphos.com>
An ADC is often used to measure other quantities indirectly. This
binding describe one case, the measurement of a temperature through the
voltage across an RTD resistor such as a PT1000.
Signed-off-by: Liam Beguin <lvb@xiphos.com>
---
.../iio/afe/temperature-sense-rtd.yaml | 101 ++++++++++++++++++
1 file changed, 101 insertions(+)
create mode 100644 Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml
diff --git a/Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml b/Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml
new file mode 100644
index 000000000000..11a3d4bd3065
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml
@@ -0,0 +1,101 @@
+# 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 <lvb@xiphos.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>;
+ };
+...
--
2.30.1.489.g328c10930387
next prev parent reply other threads:[~2021-07-06 16:10 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-06 16:09 [PATCH v4 00/10] iio: afe: add temperature rescaling support Liam Beguin
2021-07-06 16:09 ` [PATCH v4 01/10] iio: inkern: apply consumer scale on IIO_VAL_INT cases Liam Beguin
2021-07-06 16:09 ` [PATCH v4 02/10] iio: inkern: apply consumer scale when no channel scale is available Liam Beguin
2021-07-06 16:09 ` [PATCH v4 03/10] iio: inkern: make a best effort on offset calculation Liam Beguin
2021-07-06 16:09 ` [PATCH v4 04/10] iio: afe: rescale: reduce risk of integer overflow Liam Beguin
2021-07-09 16:24 ` Peter Rosin
2021-07-09 19:22 ` Liam Beguin
2021-07-06 16:09 ` [PATCH v4 05/10] iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support Liam Beguin
2021-07-09 16:29 ` Peter Rosin
2021-07-09 19:30 ` Liam Beguin
2021-07-10 8:14 ` Peter Rosin
2021-07-10 17:45 ` Liam Beguin
2021-07-06 16:09 ` [PATCH v4 06/10] iio: afe: rescale: add offset support Liam Beguin
2021-07-06 16:09 ` [PATCH v4 07/10] iio: afe: rescale: add RTD temperature sensor support Liam Beguin
2021-07-06 16:09 ` [PATCH v4 08/10] iio: afe: rescale: add temperature transducers Liam Beguin
2021-07-06 16:09 ` Liam Beguin [this message]
2021-07-12 16:08 ` [PATCH v4 09/10] dt-bindings: iio: afe: add bindings for temperature-sense-rtd Rob Herring
2021-07-06 16:09 ` [PATCH v4 10/10] dt-bindings: iio: afe: add bindings for temperature transducers Liam Beguin
2021-07-12 16:11 ` Rob Herring
2021-07-13 4:20 ` Liam Beguin
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