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How to Convert RTD Resistance to Temperature

Many manufacturing plants require accurate monitoring and control of process temperature. Resistance temperature detectors are sensors with resistance values that are proportional to temperature. They can withstand temperatures from minus 200 degrees Celsius (minus 328 F) to those approaching 1,000 C (1,800 F). Typically manufactured from platinum, RTDs are highly stable and tolerate aggressive conditions, making them suitable for most industrial environments. Adopted worldwide, the European standard for RTDs specifies a nominal 100-ohm resistance and a uniform temperature coefficient of resistance between zero and 100 C.

Things You'll Need

RTD resistance data
RTD temperature-versus-resistance tables

Instructions

- 1
  Check the type of RTD for which you have resistance data. Common types are European Standard and American Standard RTDs with 100-ohm nominal resistance at zero C (32 F). Select the appropriate resistance-versus-temperature table for your RTD type.
- 2
  Note the first resistance data value, which should be given in ohms. Temperatures below zero C will have values less than 100 ohms. Values for temperatures above zero C will be greater than 100 ohms.
- 3
  Scan the table and locate the column that contains values for the temperature range that you are measuring. For example, if you are measuring temperatures in the range 150 C to 200 C, select the column containing values around 175 C.
- 4
  Compare the resistance value in the table with your data value. Scan up or down the table until you find the resistance value that is closest to your data value. Note the position of this value.
- 5
  Check the temperature value immediately to the left of the position you have noted. Record this value, which is the RTD resistance converted to a temperature value in Celsius.

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