Temperature is one of the most frequently measured parameters in industrial processes. A wide variety of mechanical and electrical thermometers are used to sense and control process temperature. Regular calibration of these thermometers is critical to ensure consistent quality of the product manufactured, as well as providing regulatory compliance in some industries.

Simply stated, temperature calibration consists of placing the thermometer under test into a known, stable temperature environment. A comparison is then made between the actual temperature and the reading indicated by the thermometer under test and the difference is noted.

Adjustments can then be made either directly to the thermometer or to its readout. Electrical thermometers are adjusted by mathematically recreating the coefficients used by SMART transmitters or other readout devices to translate electrical output to a temperature value. Many mechanical thermometers, such as dial gauges, can be adjusted by turning a dial or other mechanical device. In some cases, such as liquid-in-glass thermometers, direct adjustments are not possible and offsets must be noted.

In industrial applications, the temperature environment is usually provided by a drywell, or dry-block calibrator, or a micro-bath. Both offer portability and a wide range of temperatures. Drywells use high-stability metal blocks with drilled wells to accept the reference and the component under test. Drywells typically cover ranges from −45°C to 1200°C and micro-baths cover ranges from −25°C to 200°C. Micro-baths are similar in size to drywells but use a small tank of stirred fluid instead of a metal block. Micro-baths offer significant advantages when calibrating short or oddly shaped probes.

The “actual” temperature of the bath or dry-well is determined by a reference thermometer, which may be either a thermometer internal to the heat source, or an external reference thermometer operating independently.