The growing need for temperature calibration
June 2009
Temperature Measurement
No thermometer will remain entirely consistent in its indication. Thermometers and sensors such as Mercury-in-glass (MIG), thermocouples (T/C), thermistors, resistance thermometers (RTDs) change their characteristics with time and temperature cycling – and they can become contaminated. This means that all thermometers need to be characterised or calibrated. There is a need to calibrate to meet quality standards, and in medical and safety applications this may be vital to safeguard life. Often real savings can be achieved simply by accurately determining a thermometer’s characteristics.
There are three levels of temperature calibration:
* Primary laboratories – these are often National Laboratories, now known as National Metrology Institutes, NMIs.
* Secondary laboratories – so called because they do not maintain 'Primary Standards'. These labs generally calibrate thermometers against standards in comparison baths.
* Industrial calibration – here temperature indicators are often calibrated with electrical simulators which are connected to the instruments sensor input. The device can then be rapidly checked by programming the equivalent 'temperature' input into the indicator.
Heat sources
Note that the temperature sensors themselves have the potential for significant drift, so it is important to test and calibrate these sensors using a heat source.
There is a wide variety of heat sources for industrial calibration, the most popular being dry block calibrators. These are able to provide temperatures ranging from 65°C below ambient up to 1200°C. More recently multipurpose sources and liquid baths have become increasingly popular.
The Isocal-6 range of products from Isotech is believed to be unique, as it can be used in six different ways. As standard the units can be used as dry block calibrators with a removable metal block drilled to accept temperature sensors. The block can be removed and replaced with a tank of liquid which is stirred as it is heated or cooled. Other accessories allow it to be used to calibrate surface sensors and infrared thermometers.
For more information contact Lenton Laboratory & Scientific Equipment, +27 (0)11 476 4662, info@lenton.co.za, www.lenton.co.za
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