Resistance Sensors (RTDs)
Recommended Use Limits and Tolerances:
In the USA, ASTM Specification E1137/E1137M “Standards Specification for Industrial Platinum Resistance Thermometers” gives many details and specifications for them over the range from -200 °C to 650 °C.
It defines two RTD grades, A and B with a resistance-temperature relationship that has the following tolerances:
- Grade A Tolerance = ±[0.13 +0.0017 *|t|] °C
- Grade B tolerance =±[0.25 +0.0042 *|t|] °C
Where:
|t| is the absolute value of the RTD’s temperature in °C.
Below are examples of these tolerances for a nominal 100 ohm (at 0 °C) Platinum RTD. The actual ASTM document includes more examples.
| Temperature Degrees C | Grade A Limits |
Grade B
Limits |
||
| °C | Ohms | °C | Ohms | |
|
-200
|
0.47 | 0.20 | 1.1 | 0.47 |
|
0
|
0.13 | 0.05 | 0.25 | 0.10 |
|
100
|
0.30 | 0.11 | 0.67 | 0.25 |
|
400
|
0.81 | 0.28 | 1.9 | 0.66 |
|
650
|
1.24 | 0.40 | 3.0 | 0.94 |
The DIN Standard (Industrial platinum resistance thermometers and platinum temperature sensors (IEC 60751:2008); German version EN 60751:2008) recognizes three different tolerance classes, they are:
DIN Class A tolerance: ±[0.15 + 0.002*|t|] °C
DIN Class B tolerance: ±[0.30 + 0.005*|t|] °C
DIN Class C tolerance: ±[1.20 + 0.005*|t|] °C
Some other RTD related information:
- Standard Our pages on RTD standards.
- Annotated links to online RTD resources
- Calibration & Traceability This link takes you to other pages on this website for details.
- Training Courses and Other Resources Training courses and other resources pages may be reached by clicking on the link above.
- Sensor Scientific’s web site has comparison of four popular contact temperature sensor types, Thermocouples, Resistance, Thermistors and Semiconductor, shown on a one page chart and in a very readable article.
- Some RTD Vendors Our RTD vendor lists
- RTD Vendor lists on our Self-service directory for temperature & moisture sensor vendors & resources
Some additional, free, downloadable reference documents available online.
From ISOTECH (www.isotech.co.uk):
- Industrial (Use) Platinum Resistance Thermometers and Common Errors in Industrial Temperature Measurement
- Industrial Resistance Thermometry upto 700°C without drift or contamination
- Industrial Platinum Resistance Thermometer Tables
- Standard Platinum Resistance Thermometers – Frequently Asked Questions
- The Standard Platinum Resistance Thermometer
- Measuring the Resistance of Standard Platinum Resistance Thermometers
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