A thermometer it is an instrument with sensitive components that can be damaged by misuse. Cases should not be dropped or placed on hot surfaces. Probes should be used with respect – not used for opening cans nor drum-sticks; and if designed as “hand-held” the handles should not be subjected to high temperatures. Regular servicing and calibration will provide confidence that your instrument is functioning correctly.
Comparison can be undertaken by placing the two (or more) probes close together in different temperatures. A glass with a mixture of crushed ice and a little water will provide a temperature of near to 0°C to within ±0.5°C. This therefore enables comparison against a known temperature, and is a good indication of a thermometer’s performance.
Boiling water can provide a temperature of approximately 100°C but great care must be taken to avoid scalding and it must be realised that the temperature will drop very quickly when taken from the heat source. A container of warm/hot water can provide a comparison of instruments at a temperature between zero and 100°C but the actual temperature cannot be specifically proved.
The two or more probes should be placed together (an elastic band can hold the probes together securely) and they should then be placed in the water, allowed to stand for at least 30 seconds, and then steadily stirred in the water for at least another 30 seconds. The stirring should ensure that the water is the same, uniform temperature throughout, and will improve the speed of response of the readings.
The two instruments should read the same ±1.5°C. This tolerance allows for the fact that both instruments may be slightly out of adjustment and if one instrument is reading 0.7°C high, and the other 0.7°C low, there will be an apparent difference of 1.4°C.
Because of the frequency of damage inflicted on the probe, ETI recommend that a spare probe for each type of instrument be kept, to cover for instances of malfunction.
Whichever method is used, confidence that a reference thermometer is reading correctly and is traceable to National Standards requires a UKAS certificate, and whilst an individual’s organisation will determine how often calibration is made, the manufacturer will recommend that an annual UKAS certificate is obtained.
Electronic Temperature Instruments Ltd - 2016