When choosing a thermometer, there are several things to consider
It is crucial to select the correct thermometer for the reference probe and the tested equipment during temperature calibration. The following factors need to be considered: accuracy. Many thermometers of resistance thermometers provide ppm, ohm, and/or temperature technical indicators. The conversion from ohms or ppm to temperature depends on the thermometer used. For a probe with 100 Ω at 0 ° C, 0.001 Ω (1m Ω) is equal to 0.0025 ° C or 2.5mK. 1ppm is equivalent to 0.1m Ω or 0.25mK. It is also necessary to pay attention to whether the technical indicators are "reading" or "range".
measurement error
When conducting high-precision resistance measurements, it is important to ensure that the thermometer can eliminate thermoelectric potential errors generated at different metal connections in the measurement system. A common technique for eliminating thermoelectric errors is to use switch mode DC or low-frequency AC current sources.
resolution
Be careful with this indicator. Some thermometer manufacturers confuse resolution and accuracy. A resolution of 0.001 ° C does not necessarily mean an accuracy of 0.001 ° C. Generally speaking, a thermometer with an accuracy of 0.001 ° C should have a resolution of at least 0.001 ° C. When detecting small temperature changes, display resolution is very important - for example, when monitoring the solidification curve of a fixed point container or checking the stability of a calibration slot.
Linearity
Most thermometer manufacturers provide accuracy technical indicators at a temperature (usually 0 ° C). This is very useful, but you usually need to measure a wide temperature range, so it is very important to understand the accuracy of the thermometer within its working range. If the linearity of the thermometer is very good, then its accuracy index will be the same throughout its entire temperature range. However, all thermometers have a certain degree of nonlinearity and are not completely linear. Please ensure that the manufacturer provides accuracy technical indicators within the scope of work, or provides linearity technical indicators that you use when calculating uncertainty.
