How do mercury thermometers work

Different clinical thermometers explained

From the classic expansion thermometer to the infrared thermometer

The patient sweats and complains of general malaise? Does the head feel warm? Various thermometers are available to make sure that the person concerned has a fever. In principle, a distinction is made between expansion thermometers, digital clinical thermometers and infrared clinical thermometers.

In principle, you can choose between a Contact thermometer and one Infrared thermometerthat measures the radiated heat.

Contact thermometer

The contact thermometers include the classic Expansion thermometer (Glass thermometer) and that digital clinical thermometer.

When taking measurements in the mouth, you should not drink cold or hot drinks beforehand, as this can falsify the result. In addition, warming up the clinical thermometer or its tip to body temperature is a good way of obtaining a value that is as real as possible. When measuring the temperature you have to count 0.3% orally under the arms and 0.5% of the temperature in the groin. A rectal measurement promises the most believable result.

Expansion thermometer (glass thermometer)

Expansion thermometers contain a liquid that expands when exposed to heat.

The fever can be measured either in the anus (accurate but uncomfortable), under the tongue (make sure it is used correctly) or in the armpit (rather not recommended due to the large deviations).

In view of the risk of breakage and the long measuring times of several minutes, glass thermometers are rarely bought today.

Until some time ago, a body temperature measurement was used Mercury thermometer used. Since April 2009, the sale of thermometers containing mercury within the EU has been banned because this substance is poisonous and could escape if damaged.

Tip 1: Dispose of mercury thermometers properly

Anyone who still keeps a mercury thermometer in their household should definitely dispose of it properly. Mercury thermometers can be handed in in a hazardous substance mobile and do not belong in the household waste.

Alternatively, mercury is used today alcohol, gallium or Galinstan, a mixture of gallium, indium and tin. This is also a peak thermometer. The gallium or Galinstan climbs up in a glass tube according to the temperature. The temperature can be read off the adjacent scale. Before taking another measurement, shake the thermometer and the liquid returns to its place of origin.

Tip 2: Glass thermometers for people with nickel contact allergy

Glass thermometers are suitable for patients with a nickel contact allergywhere the use of electronic probes is problematic.

Expansion thermometers are now being replaced by the digital clinical thermometer or the infrared clinical thermometer. That likes about the Disadvantages lie. On the one hand there is a risk of breakage with the glass thermometers, on the other hand the measuring process takes several minutes. But they also have many advantages: They do not require a battery, are 100 percent waterproof and can be easily cleaned and disinfected.

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Digital thermometer

Digital thermometer have electronic temperature measurement technology. That is why they are also called electronic clinical thermometers. The value is shown on an LCD display. These thermometers have a few compared to the analog thermometers advantages such as higher breaking strength, faster measurement, acoustic signal at the end of the measurement process and easy readability. In addition, they are easy to use and very reliable in terms of measurement results. The disadvantage is the need for batteries. The measurement can be uncomfortable for children.

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The measurement is made in the anus, under the tongue or in the armpit. The former promises high measurement accuracy and the latter can only be recommended to a limited extent. Most digital thermometers emit a signal tone when the measurement is finished and the temperature can be read.

Infrared thermometer

Infrared thermometers measure the heat radiated from the forehead or eardrum. This is recorded via a lens and, after being converted into a temperature value, displayed as body temperature. A distinction is made between ear thermometers, forehead thermometers and combined ear / forehead thermometers.

Infrared thermometers are very popular with doctors and, because of their high measuring speed, they are primarily used to record temperatures with children popular.

Ear thermometer

A Ear thermometer measures the infrared rays emitted by the eardrum and surrounding tissue. From this, the thermometer determines the core body temperature and shows it on the display. The high measurement accuracy is one of the Benefits of the ear thermometer. In addition, the result can be read in a few seconds and is an extremely pleasant process, especially for children. The temperature measurement within a few seconds. This device also knows some disadvantage. It must not be used in babies under 6 months, as the ear canal is still too narrow for this. It is also not suitable for an ear infection or ear wax.

However, incorrect positioning in the ear canal can result in errors in the measurement. Depending on the features of the ear thermometer, this can detect incorrect positioning or is equipped with a heated tip in order to obtain better measurement results.

Forehead thermometer (temple thermometer)

Forehead thermometers measure the temperature of the forehead using an infrared sensor. They are guided, for example, by gently rolling them over the surface of the skin of the forehead or held against the temple. These thermometers are extremely hygienic as they do not have to be inserted into body orifices. They are particularly suitable for infants and children and not only offer comfortable measurements, but also measurement accuracy. But because they are held over the forehead or temples and thus remain on the surface of the skin, they are not as accurate as an ear thermometer.

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Combined ear / forehead thermometer

Combination thermometer can often be converted from an ear thermometer to a forehead thermometer with an attachment.


Excursus: When does one have a fever?

It is often mistakenly assumed that a fever begins at a body temperature of over 37 ° C. For many, however, temperatures around 37 ° C are completely normal. A fever is only spoken of at temperatures above 38.1 ° C. From 37.5 to 30 ° C one only assumes an increase in body temperature.

More on the subject:fever


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As of: 09/29/2020

For reasons of better legibility, the male form is used in the text for personal designations. It goes without saying, however, that the information relates to members of both sexes.