How to Calibrate Thermocouples

Calibration of a thermocouple in progress.

When you have a fever, you use a thermometer to decide how high your fever actually is. To keep temperatures constant in machinery, you have to use a different instrument to measure temperature. When industries use machinery, they have to measure temperatures that are very hot or very cold. That's where thermocouples come in.

What Is a Thermocouple?

Thermocouples are temperature sensors that use electric cables to measure temperatures in all different kinds of machinery. The cables, or wire legs, have two kinds of metals to generate the electricity needed to measure extreme temperatures precisely.

Thermocouples are used in countless industries - power, oil, gas, biotech, and laboratories. Nearly every industry uses thermocouples. They are also found in appliances you use every day, such as toasters, furnaces, and stoves.

Methods of Calibrating Thermocouples

Laboratory Method

In order for thermocouples to work properly, they need to be calibrated. The most accurate way of calibrating a thermocouple is done over time in a laboratory. Scientists use fixed points within thermodynamics to calibrate these thermocouples. The laboratory method is usually done when an absolutely accurate measurement needs to take place.

Comparison Calculation Method

In this method, thermocouples are still calibrated in a lab. The thermocouple is placed in a bath or a furnace and paired with a thermocouple that has already been calibrated. After the temperature is stabilized, the thermocouple readings are then compared to determine accuracy.

Dry-Block Calculation Method

Thermocouples are inserted into a piece of machinery called a calibrator, which is a metal block with holes. The block is either heated or cooled to the temperature needed, and the thermocouples are then compared to the temperature of the metal block for accuracy.

How Often Does a Thermocouple Need to be Calibrated?

Most industrial workers calibrate their thermocouples at least once a year. However, there are times that these important pieces of machinery have to be calibrated more often. You need to calibrate a thermocouple periodically so that it maintains its accuracy. You also need to recalibrate the thermocouple if it has been subjected to conditions that are unusual or unexpected. If you doubt a thermocouple's performance, you may need to calibrate it again.

When to Change a Thermocouple

If you calibrate your thermocouple and the reading is off, it may be time to change it. There are several situations that would require a thermocouple to be replaced.

  1. You've attempted to calibrate the thermocouple a couple of times, but it is still not measuring temperature accurately.
  2. The thermocouple is showing an open circuit.
  3. The thermocouple shows low isolation from the housing or sheath.
  4. The thermocouple sheath has been damaged by corrosion or oxidation.

Request Calibration Certificates from RAM Sensors

Accuracy is critical for calibration, as it can reduce error-related costs incurred and ensure safety during industrial processes. RAM Sensors can provide certificates of calibration with the highest level of accuracy. Our experienced staff can offer suggestions and ideas to help meet your organization's calibration needs on wires, probes, and thermocouples. Request a calibration certification today!