From patchwork Sat Jan 8 20:53:18 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Liam Beguin X-Patchwork-Id: 12707626 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E06D9C433EF for ; Sat, 8 Jan 2022 20:54:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233013AbiAHUyN (ORCPT ); Sat, 8 Jan 2022 15:54:13 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50966 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233169AbiAHUx5 (ORCPT ); Sat, 8 Jan 2022 15:53:57 -0500 Received: from mail-qv1-xf36.google.com (mail-qv1-xf36.google.com [IPv6:2607:f8b0:4864:20::f36]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 81F1FC06175D; Sat, 8 Jan 2022 12:53:51 -0800 (PST) Received: by mail-qv1-xf36.google.com with SMTP id o10so9475378qvc.5; Sat, 08 Jan 2022 12:53:51 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=EoVz/z4Kv5flD6bBPkUi3ywu6/Ph5Pi55G9NAdUbUhI=; b=JB/GGwTvKXgIXawkydGQfQNe8QeBW4/7mg95LnrEOmNGY1FLmz2zvuWdELEyvGnmtO CWFv0w+dJi8RPeQbJ58aOxGuXx21EywvqD1i31qikp182z3Hj7LeKAWttii+y7VsVjjY UwVDIg0NWkDBj4M/hxNZBMgfp50V5/oUZmj+f9f7tRspkkdqcgeP4AwjBAAzYupcIKOw RYfX9FqZiWjaqcPxKYsCXXci4uQtqtjBCgZoPB31NIJLhm4KHtzTt/+fpMsypKv3pFJ0 MnLapqlSUJ4cnyYdG+zu66pgDggKqqvmTThrh4DTTTdlrlnw/znbtPxzz5ssvO63tyj0 rudQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=EoVz/z4Kv5flD6bBPkUi3ywu6/Ph5Pi55G9NAdUbUhI=; b=CuVJuZD2GpbBXJETNEuu2qupKqAga3RXMLIAP75TDK2gyfKMWFVni0sq5eQlJ2DLF9 knrnkmt+s2QPr+z6yD0Ich/fyzs0MbvL8/VhAUvuhwZrZQSKmMRVBO9x42nmqrQ3dgy3 SofCKQZTGbEtCD61hjosV9AHfa3jW22fd5VFTMhLPflKRsp7iu3b1be8RjtaquVhwb9r bY9X9pD5cLFaLlPgrL2CqYWoMutSN0Rm+fzTe13SvyoQ9mWOHg7IVDwEBWPlxlT/qces 1crRYOnOJlT/dJJfwwj6nv6V06bUmx30u9FfbXVL0xc5bT7WqNr6rBIpv3W1CxIQqQPW DX2g== X-Gm-Message-State: AOAM530cX5jCiTQuVDkpvreOxKJMpmSHCZmFD+UjiLYmnFqhexy5DBk/ XQK71b5T57XHz4YfdpnsWm8= X-Google-Smtp-Source: ABdhPJzLPlQ8CBQvgk9O6QmzPTsggxfUU7F1JEjXhTmn6djftHEiMjlGAPFdZTb5AaOl0W/4bM2+aQ== X-Received: by 2002:a05:6214:27cc:: with SMTP id ge12mr62552008qvb.122.1641675230675; Sat, 08 Jan 2022 12:53:50 -0800 (PST) Received: from shaak.. (69-165-204-82.cable.teksavvy.com. [69.165.204.82]) by smtp.gmail.com with ESMTPSA id p16sm1650377qtx.19.2022.01.08.12.53.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 08 Jan 2022 12:53:50 -0800 (PST) From: Liam Beguin To: liambeguin@gmail.com, peda@axentia.se, jic23@kernel.org, andy.shevchenko@gmail.com, lars@metafoo.de Cc: linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org, devicetree@vger.kernel.org, robh+dt@kernel.org Subject: [PATCH v12 15/16] dt-bindings: iio: afe: add bindings for temperature-sense-rtd Date: Sat, 8 Jan 2022 15:53:18 -0500 Message-Id: <20220108205319.2046348-16-liambeguin@gmail.com> X-Mailer: git-send-email 2.34.0 In-Reply-To: <20220108205319.2046348-1-liambeguin@gmail.com> References: <20220108205319.2046348-1-liambeguin@gmail.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-iio@vger.kernel.org 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 Reviewed-by: Rob Herring Reviewed-by: Peter Rosin --- .../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..336ce96371db --- /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 + +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>; + }; +...