Three methods for calibrating temperature sensors: pros and cons

There are three common methods for calibrating temperature sensors:

• Calibrating just the electronics with a simulator

• Calibrating both the electronics and the sensor in a dry-well

• Calibrating both the electronics and the sensor in a dry-well with a reference thermometer

Here is a quick look at these methods and the pros and cons of each.

Calibrating just the electronics with a simulator

To calibrate the electronics of a temperature measurement/control system, a temperature simulator takes an input temperature and outputs (simulates) the corresponding voltage (thermocouple) or resistance (RTD or thermistor) based upon accepted national tables.

Pros of this method:

• It’s fast. The electrical settings are instant and require no stabilization times.

• The calibration equipment may be more portable than the equipment used in other methods.

• The meter can still be used with interchangeable probes.

Cons of this method:

• You’ll need a separate calibration procedure for the probe or…

• The probe remains uncalibrated.

• Therefore, the thermometer system remains uncalibrated and measurements made with it are untraceable.

Calibrating both the electronics and the sensor in a dry-well

In this method, the dry-well is set to the desired test temperature and the thermometer, meter and probe combined, is placed in the well. The thermometer reading is compared to the reading on the dry-well’s built-in thermometer.

Pros of this method:

• The probe and meter are calibrated as a system.

• The actual temperature is used.

• System setup is simple as only a single instrument (the dry-well) is used.

Cons of this method:

• Accuracy is limited by the calibrated accuracy of the dry-well.

• If the probe does not reach the bottom of the well, additional error can occur.

• Unit-under-test probes are not interchangeable after the calibration.

• The dry-well requires time to change temperatures.

Calibrating both the electronics and the sensor in a dry-well with a reference thermometer

In this method, a dry-well is used as a stable heat source and the thermometer is compared against a more accurate thermometer placed in an adjacent hole in the well.

Pros of this method:

• This method has the best accuracy results.

• Calibration is traceable to the separate reference.

• You have more versatility in matching unit-under-test sizes.

Cons of this method:

• It’s more expensive than the other two methods.

• Because two instruments are used, setup is slightly more complex.

• The probes under test are not interchangeable after calibration.

• The dry-well requires time to change temperatures. Want to know more?

Conclusion

There are three primary methods for calibrating temperature sensors, and each method has distinct pros and cons. In summary, these methods are:

• Calibrating just the electronics with a simulator – This method is quick, but you’ll need a separate calibration procedure for the probe.

• Calibrating both the electronics and the sensor in the dry-well – This method allows you to calibrate the probe and meter as a system, but the accuracy will be limited by the calibrated accuracy of the dry-well.

• Calibrating both the electronics and the sensor in a dry-well with a reference thermometer – This method provides the best accuracy, but it is more expensive and complex than the other two methods.