1 # SPDX-License-Identifier: (GPL-2.0 OR BSD-2-C
2 %YAML 1.2
3 ---
4 $id: http://devicetree.org/schemas/iio/afe/tem
5 $schema: http://devicetree.org/meta-schemas/co
6
7 title: Temperature Sense RTD
8
9 maintainers:
10 - Liam Beguin <liambeguin@gmail.com>
11
12 description: |
13 RTDs (Resistance Temperature Detectors) are
14 used to get a linear voltage to temperature
15 (usually 0 to 100 degrees Celsius).
16
17 When an io-channel measures the output volta
18 PT1000, the interesting measurement is almos
19 temperature, not the voltage output. This bi
20
21 The general transfer function here is (using
22
23 V = R(T) * iexc
24 R(T) = r0 * (1 + alpha * T)
25 T = 1 / (alpha * r0 * iexc) * (V - r0 * ie
26
27 The following circuit matches what's in the
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 R
61
62 alpha-ppm-per-celsius:
63 description: |
64 alpha can also be expressed in micro-ohm
65 approximation of the resistance versus t
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 se
71 R_0 (or r-naught-ohms) is the resistance
72 Celsius.
73
74 Pure platinum has an alpha of 3925. Indu
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 Ce
80 Common values are 100 for PT100, 500 for
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>;
98 alpha-ppm-per-celsius = <3908>;
99 r-naught-ohms = <1000>;
100 };
101 ...
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