Temperature measurement. Measurement chain

This summary article is an introduction to the Thermometry section. As such, frequent reference will be made to the various articles in this section, where the specific methods for each sensor are detailed.

Choosing a measuring instrument is not always easy. First and foremost, you need to ask yourself the right questions, find out about the various measurement options available, and answer these questions reasonably. This choice also takes into account the influence of the particular conditions of the measurement in question on the accuracy of the measurement.

The aim of this article is to guide the thermometry experimenter through this process, since temperature measurement can vary greatly depending on the situation encountered.

In the first chapter, [R 2516v2] , we review a number of fundamental concepts and ask the essential questions before making a choice.

In this article, the sensors and methods of use will be briefly described, with reference to the specialist articles in this Measurement & Control treatise.

A thermometer chain consists of three parts that are sometimes difficult to separate:

• the sensor converts thermal energy drawn from the medium under study into electrical or mechanical energy;

• the transmission zone conditions and often amplifies the signal;

• the playback or recording device is almost always electronic, because of the ease of signal processing provided by this technology. Nowadays, the signal is digitized, making playback even more direct.

Here are a few examples:

• In a liquid expansion thermometer, the sensor is represented by the bulb containing the expanding liquid, the transmission zone is represented by the capillary tube containing the liquid, and the reading device is a simple scale;

• In a thermomanometer, the area where the gas expands represents the sensor, while the transmission area is the tube containing the gas, which is connected to the manometer forming the reading device;

• in the case of a thermoelectric couple, the distinction between the three parts is simple: the hot and cold welds make up the sensor, which is connected to the amplifier or voltmeter by the connecting leads.

In pyrometry, the atmosphere in the beam's path is part of the transmission chain and will generate corrections.

It is often possible to separate and replace individual...