Below we provide the full text of an article published in the magazine SPROS 11/2009.
At the height of the flu epidemic, “DEMAND” checked how accurate and convenient electronic thermometers are. Judging by surveys conducted by the Russian Institute of Consumer Testing, 25% of respondents prefer these devices to traditional mercury thermometers.
In two stages
The test was attended by 8 models worth up to 250 rubles of famous brands: Amros, AND, Bremed, Citizen, Little Doctor, Microlife, Omron, Thermoval. The tests were carried out in two stages. First, the thermometers were taken to the laboratory, where they checked the accuracy of their testimony, and then distributed to approbants (All measurements were performed on healthy adults with normal body temperature.). Those measured the temperature in the traditional “axillary” way and evaluated whether it is convenient to use thermometers and how much the attached instruction helps in this.
The accuracy of the readings was determined using the so-called calibration. The laboratory specialists found out what the temperature reads correspond to the thermometers at two points: 37.10C and 38.5 ° C. Why in them? Yes, because 37.1 ° C is a transitional body temperature from normal to elevated, and 38.5 ° C is from elevated to high.
According to the results of laboratory tests, each thermometer received a calibration passport, on the basis of which the models were assessed. All samples coped with the task adequately: none exceeded the permissible measurement error – 0.1 ° C. The models whose readings completely coincided with the reference ones received a score of 5. If the deviations were recorded at one point, the thermometer was set to 4.5, and if two were fixed at 4 (see Table 2). With the accuracy of electronic thermometers, everything turned out to be in order, but with the convenience of use, the picture was completely different.
During the test, a number of myths about these devices were debunked. In particular, the fact that they measure the temperature quickly, that they need to be removed on a signal that they are more reliable and durable than glass thermometers. All this, to put it mildly, is not quite so.
Table 1 Technical characteristics of electronic thermometers
Soon the fairy tale affects …
Let’s start with the first “myth” that electronic thermometers measure body temperature very quickly – in just a minute. This is stated in their instructions by the manufacturers of most of the models tested. So, the authors of the thermometer manual AND declare that their device is capable of producing the final result in 10–15 seconds, Bremed – in 30–60 seconds. Slightly more time for measurements, judging by the instructions, required models Omron (about 1.5 minutes) and Thermoval (60–90 seconds).
However, tests have shown that lightning performance of electronic thermometers is nothing more than a legend. Even the most operational of them – AND and Bremed for measurements it took from 1.5 to 2 minutes. Have Citizen, Little Doctor, Microlife and Amros It took from 2.5 to 3.5 minutes, and Omron and Thermoval and even more – from 4 to 5 minutes. And this is the minimum time required to measure the temperature with a tightly pressed thermometer.
The second misconception associated with electronic thermometers: they need to be removed by an audible signal. So most users think, and so, by the way, is written in the instructions for models AND, Thermoval, Little Doctor and Amros. However, if you follow this rule, you can miss from 0.3 to 0.7 degrees Celsius! Because after the “final whistle” the measurement continues, only more slowly.
Why does a beep sound? For us, it remains a mystery. The explanations given in most of the instructions did not help to solve it, but even more confused. Let’s say with models AND, Little Doctor, Microlife and Omron everything is more or less clear – these thermometers give a vote only once, and their squeak can be taken for the beginning of the end. But what about thermometers Citizen, Thermoval and Amros, if they, at some point, with a squeak, raise the temperature for every tenth of a degree? How, in this case, to know what squeak will be the last?
The thermometer sounds many times Bremed, issuing trills in response to a change of every hundredth of a degree. However, the test showed that there is no sense in listening to these melodies – the thermometer can be removed after the first signal, since the temperature rise after it is insignificant.
In general, we made sure that the sound signal does not carry any meaning and is only annoying. Small children, for example, are almost impossible to force to keep a thermometer after it has squeaked. At the same time, to obtain an accurate result, an electronic thermometer should be held for at least 5–7 minutes.
Convenient or not?
Electronic thermometers do not contain mercury and, unlike their glass precursors, are made of plastic. It is safer, but still you should not drop them, so as not to disrupt the work of the electronics inside. In addition, such thermometers should be protected from vibration, direct sunlight and electrical appliances. So it is necessary to handle the thermometers of the new generation no less carefully than with mercury ones. So that the thermometer does not slip out of the hands of models Microlife and Omron side surface is embossed.
Three test samples (AND, Little Doctor and Microlife) tip flexible. Such models are recommended for use in oral or rectal temperature measurement in young children. However, during the test, the temperature was measured by adults, inserting a thermometer in the armpit, so that no one noted the advantages of a flexible tip. Moreover, it seemed inconvenient to some, because the thermometer was constantly trying to bend and slide out.
All models except Thermoval, Sold in a protective case that protects the device from dust and mechanical damage. And opaque thermometer cases Bremed and Amros also protect from sunlight, unsafe for the electronic circuit of the device.
During the day, the temperature of the human body is constantly changing. The maximum values are observed between 17 and 21 hours, and the minimum, as a rule, between 3 and 6 am. The normal difference between morning and evening body temperature does not exceed 0.1 ° C in adults and can reach up to 1.4 ° C in children. Daily fluctuations are more significant in girls than in boys. 36.6 ° C – the temperature taken as the norm. However, this is an average figure. Every person has his own average normal body temperature. It can be recognized by conducting a series of measurements over several days at different times. A double measurement is carried out at 7–8 in the morning and at 18–20 in the evening. More accurate data are obtained at three times (8, 15, 20 hours) or four times (8, 13, 18, 22 hours) body thermometry.
Physicians distinguish three degrees of body temperature rise: a slight (37.2–38 ° С), significant (38–40 ° С) and very high (over 40 ° С). 420 is considered a critical value for both children and adults. At this temperature, a metabolic disorder occurs in the brain tissues.
Attention to the screen!
The readings of electronic thermometers are highlighted on the liquid crystal display. This is more convenient than looking for the top of a mercury column on an ordinary thermometer. In addition, for all test samples, the last measurement is stored in the device’s memory and displayed when it is turned on again. However Little Doctor, Omron, Bremed, Citizen, Thermoval and Amros it holds on the screen for only 1-2 seconds. Then the thermometer goes into readiness mode for a new dimension – and here, as they say, who did not have time, he was late.
Thermometers are more convenient in this sense. AND and Microlife. Here, access to the last measured value is possible all the time while the power button is pressed. It eliminates unnecessary fuss and haste.
Ease of use of the device depends largely on the size and clarity of characters on the display. The largest and sharp figures were at the thermometer AND. They read well Little Doctor and Bremed. The rest of the thermometers show the numbers worse due to the smaller font, while Amros – due to the convex screen creating glare.
By the way, the power button also differs in degree of convenience. Have Bremed rubberized button protrudes above the surface of the thermometer and highlighted in color. The large button of the thermometer is easily pressed AND. Have Omron the button is inconspicuous in appearance, but is located in a special recess “under the finger”. But the models Little Doctor, Microlife, Citizen, Thermoval and Amros the buttons are very small, so you can’t push them with a big finger.
Changing of the Guard
Electronic thermometers are powered by batteries, which need to be changed from time to time. During the test, we found out if it was easy to do.
Only in thermometers Citizen and Thermoval You can replace the battery without risking breaking the device. They have a battery inserted into a special compartment, isolated from the board with a microcircuit. In the remaining samples, the place for the battery and the microcircuit are located nearby. So, trying to get to the battery, you can pull out the board with a microcircuit and tear off the sensor – the device will fail. Difficulties in replacing the battery have samples AND and Amros, but Little doctor women’s hands could not open at all. Have Omron battery replacement is an additional challenge. This requires a “clock” Phillips screwdriver, which is not in every home.
table 2 The test results of electronic thermometers
- excellent – from 4.5 to 5
- good – from 3.5 to 4.5 (inclusive)
- satisfactory – from 2.5 to 3.5 (inclusive)
- with disabilities – from 1.5 to 2.5 (inclusive)
- not recommended – from 0 to 1.5 (inclusive)
- Laboratory measurements confirmed the accuracy of all tested thermometers: the error did not exceed 0.1 ° C.
- Tests have refuted the widespread belief that electronic thermometers quickly measure temperature. In the instructions for models AND DT-6239, Omron Eco temp (MC-203-E), Bremed BD-1170, Thermoval Basic indicated a higher measurement speed than in reality.
- None of the tested samples sound signal corresponds to the end of the temperature measurement. Only the model Bremed BD-1170 He is as close as possible to this moment.
- The stated measurement speed and value of the sound signal correspond to reality only in Microlife MT1931. Instructions of other models in this sense can not be trusted.
- Construction of thermometers Citizen CT-513W and Thermoval Basic provides safe access to batteries. In other models, careless battery replacement may damage the instrument.
Characteristics of models
Virtues: Accuracy of readings within the error. After the signal, the temperature rise is insignificant, within the limits of error. The numbers on the display are clear. The power button is quite large, convex, made of rubberized material, which makes it possible to find it by touch. On readiness for work is indicated by a sign L on the display, as well as a sound signal. The battery compartment is closed tight, easy to open. The thermometer cover is comfortable, stylish. The thermometer is fixed in it.
disadvantages: Replacing the battery may cause the thermometer to break * (Note: * – trying to get to the battery, you can pull out the board with a microcircuit and tear off the sensor). Battery polarity is not clear. The instruction is incomplete. In particular, it does not contain information about different methods of measuring temperature, but one common time is given.
Virtues: Accurate readings. On readiness for work is indicated by a sign L on the display and a sound signal. The successful design of the battery compartment. Convenient battery replacement.
disadvantages: The small screen of this thermometer is inconvenient for people with low vision. The power button is small, not highlighted. The first beep cannot complete the temperature measurement, as the process is still ongoing. The manual does not have unambiguous information about the duration of measurements.
Virtues: Accuracy of readings within the error. The measurement time stated in the instructions was confirmed (5–10 min). The display of the previous measurement on the screen does not disappear while the key is pressed. The polarity of the batteries is clearly marked – this is convenient when replacing them.
disadvantages: The characters on the screen are not large enough. The power button is small, not highlighted. The first beep cannot complete the temperature measurement, as the process is still ongoing. Changing the battery may cause the thermometer to break *.
OMRON ECO TEMP (MC-203-E)
Virtues: Accuracy of readings within the error. Convenient on / off button with a fingerhole. If the included thermometer is not used for its intended purpose, it spontaneously turns off after 1 min. This allows you to extend the battery life.
disadvantages: The claimed temperature measurement time (1.5 min) does not correspond to the real (up to 5 min). The first beep cannot complete the temperature measurement, as the process is still ongoing. The characters on the screen are not large enough. Changing the battery may cause the thermometer to break *. In addition, insert a new battery is not possible without a cross-head screwdriver. Information on the packaging is not Russified.
Virtues: Accuracy of readings within the error. On readiness for work is indicated by a sign L on the display, as well as a sound signal.
disadvantages: The first beep cannot complete the temperature measurement, as the process is still ongoing. Convex display glare. Because of this, the numbers are not visible very well. The on / off button is pressed tight. Changing the battery may cause the thermometer to break *. When you open the battery compartment, the battery may get stuck in the removable cap. No polarity indication. Protective case in the form of a case opens with difficulty. Fastening the cover to the case is unreliable.
Virtues: Accurate readings. Large display with large clear numbers. Large power button, responsive to pressing. The display of the previous measurement on the screen does not disappear while the key is held down.
disadvantages: The first beep cannot complete the temperature measurement, as the process is still ongoing. Contradictory information in the instructions on the time of measurement is misleading consumers. The claimed temperature measurement time (10–15 s) does not correspond to the real (up to 2 min). Changing the battery may cause the thermometer to break *. The battery compartment is difficult to open. No indication of battery polarity.
Virtues: Accurate readings. On readiness for work is indicated by a sign L on the display, as well as a sound signal. The successful design of the battery compartment. Convenient battery replacement. Their polarity is clearly marked.
disadvantages: The claimed temperature measurement time (1–2 min) does not correspond to the real (up to 5 min). The first beep cannot complete the temperature measurement, as the process is still ongoing. The characters on the screen are not large enough. The power button is small, not highlighted. No protective cover. The instruction was rated only 1 point. Moreover, it contains a description of two models at once (Basic and Classic Color), and even with numerous translation errors. And the paragraph on battery replacement intriguingly ends with the word: “Then …”.
LITTLE DOCTOR LD-302
Virtues: Accuracy of readings within the error. The numbers on the display are clear.
disadvantages: The first beep cannot complete the temperature measurement, as the process is still ongoing. The power button is small. Difficult battery replacement – it needs to be pinched with something thin and sharp. The battery cover opens very tight. Battery polarity is not indicated. Changing the battery may cause the thermometer to break *.
- When buying an electronic thermometer, pay attention to the display, whether it is glaring, whether the numbers are large and clear enough.
- Do not rely on the instructions, and independently study the nature of the electronic thermometer.
- When measuring temperature, keep to the rule: “It is better to overdo it than under-exposure”.
- Be very careful when replacing the battery in the thermometer. Do not apply excessive effort, but rather contact the workshop.
- Do not use or store the thermometer near electrical appliances that emit a strong electromagnetic field (TV, radio, cell phone).
We thank the testing, calibration and testing laboratory of thermophysical measuring instruments of FSI “Rostest-Moscow” for conducting the test.
Expert commentary (thermometers)
Commented pediatrician MU DGP number 13 of Yekaterinburg, Ph.D. Ryk Pavel Vladimirovich, who acted as an expert on the identified problem with electronic thermometers:
The main “heat carrying medium” of the human body is blood, and the less tissue separates it from the sensor of the thermometer, the faster the “equalization” of their temperature will occur.
Companies supplying electronic thermometers are guided by the medical traditions of their countries, where body temperature measurement is performed in the rectum (in young children) and in the oral cavity (in all others). On the border of the blood-sensor in these cavities is a thin layer of tissue and mucous membrane. In our country, the traditions of the founder of medical thermometry, Fahrenheit, are “strong” —the temperature is measured in the armpit. In this case, the “blood-sensor” boundary is formed by not comparing tissue with greater thickness and worse thermal conductivity than in the mouth or in the rectum.
For the convenience of users, electronic thermometers give a signal if the readings do not change for a certain time (for example, 16 seconds), which occurs approximately 1-2 minutes after the start of measurement. This setting allows in most cases to state the onset of thermodynamic equilibrium between the tissues in the rectum or oral cavity and the thermometer sensor. And it also “confuses” users who measure the temperature in the armpit, where more time is needed to “warm up” the tissues. Clinical studies have convincingly shown that the duration of thermometry in such cases should be 7 minutes. However, not everyone knows that to obtain similar data using a mercury thermometer is necessary to spend about 10 minutes.
The problem with electronic thermometers is also complemented by the lack of adaptation of long-term thermometry in some of them. So some models are turned off almost immediately after the signal, which makes it impossible to obtain correct results. However, there are opposing examples, since the Omron thermometer (i-Temp) not only allows for a long-term temperature measurement (up to 10 minutes), but also has a flattened shape of the sensor adapted for the armpit.