The thermometer is ordinary. Types of thermometers for measuring body temperature

A liquid thermometer is a device for measuring the temperature of technological processes using a liquid that reacts to changes in temperature. Liquid thermometers are well known to everyone in everyday life: for measuring room temperature or human body temperature.

Liquid thermometers are made up of five fundamental parts: the thermometer ball, liquid, capillary tube, bypass chamber, and scale.

The bulb of the thermometer is the part where the liquid is placed. The liquid reacts to changes in temperature by rising or falling through a capillary tube. The capillary tube is a narrow cylinder through which the liquid moves. Often, the capillary tube is equipped with a bypass chamber, which is a cavity where excess liquid flows. If there is no bypass chamber, after the capillary tube is full, sufficient pressure will build up to rupture the tube if the temperature continues to rise. The scale is the part of the liquid thermometer with which the reading is taken. The scale is calibrated in degrees. The scale can be fixed to the capillary tube, or it can be movable. A movable scale makes it possible to adjust it.

How a liquid thermometer works

The principle of operation of liquid thermometers is based on the property of liquids to contract and expand. When a liquid is heated, it usually expands; the liquid in the bulb of the thermometer expands and moves up the capillary tube, thereby indicating an increase in temperature. Conversely, when a liquid cools, it usually contracts; the liquid in the capillary tube of the liquid thermometer decreases and thus indicates a decrease in temperature. In the case when there is a change in the measured temperature of a substance, then heat is transferred: first from the substance, whose temperature is measured, to the thermometer ball, and then from the ball to the liquid. The fluid reacts to changes in temperature by moving up or down the capillary tube.

The type of liquid used in a liquid thermometer depends on the range of temperatures measured by the thermometer.

Mercury, -39-600 ° C (-38-1100 ° F);
Mercury alloys-60-120 ° C (-76-250 ° F);
Alcohol, -80-100 ° C (-112-212 ° F).

Partial Immersion Liquid Thermometers

The design of many liquid thermometers assumes that they will hang on the wall, and the entire surface of the thermometer comes into contact with the substance whose temperature is being measured. However, some types of industrial and laboratory liquid thermometers are designed and calibrated to be immersed in liquid.

Of the thermometers used in this manner, partial immersion thermometers are the most widely used. To obtain an accurate reading with a partial immersion thermometer, immerse the ball and capillary tube only up to this line.

Partial immersion thermometers are immersed up to the mark in order to compensate for changes in ambient temperature that can be caused by the liquid inside the capillary tube. If changes in ambient temperature (changes in air temperature around the thermometer) are likely, they can cause the liquid to expand or contract inside the capillary tube. As a result, the readings will be influenced not only by the temperature of the substance being measured, but also by the temperature of the surrounding air. Submerging the capillary tube to the marked line removes the effect of ambient temperature on the accuracy of the reading.

In industrial environments, it is often necessary to measure the temperatures of substances passing through pipes or in containers. Measuring temperature under these conditions creates two problems for instrument operators: how to measure the temperature of a substance if there is no direct access to this substance or liquid, and how to remove a liquid thermometer for inspection, check or replacement without stopping technological process... Both of these problems are eliminated by using measuring channels for thermometer input.

The measuring channel for a thermometer is a pipe-shaped channel that is closed at one end and open at the other. The measuring channel is designed to accommodate a liquid thermometer ball and thus protect it from substances that can cause corrosion, poisonous substances, or under high pressure... When measuring channels are used to enter thermometers, the heat exchange occurs in the form of an indirect contact (through the measuring channel) of the substance whose temperature is being measured and the thermometer ball. The measuring channels provide a seal for high blood pressure and prevent the liquid, the temperature of which is measured, from escaping to the outside.

Measuring channels are made standard sizes so they can be used with different types thermometers. When the thermometer is installed in the measuring channel, its ball is inserted into the channel, and a nut is screwed over the thermometer to secure the thermometer.

Translated from Greek means "measure heat". The history of the invention of the thermometer dates back to 1597, when Galileo created a thermoscope - a ball with a soldered tube - to determine the degree of heating of water. This device did not have a scale, and its readings depended on atmospheric pressure. With the development of science, the thermometer has changed. A liquid thermometer was first mentioned in 1667, and in 1742 the Swedish physicist Celsius created a thermometer with a scale in which point 0 corresponded to the freezing point of water and 100 to its boiling point.

We often use a thermometer to measure the outside air temperature or body temperature, but the thermometer is not limited to this. Today, there are many ways to measure the temperature substances, and modern thermometers are still being improved. Let's describe the most common types of temperature meters.

The principle of operation of this type of thermometer is based on the effect of liquid expansion when heated. Thermometers, which use mercury as a liquid, are often used in medicine to measure body temperature. Despite the toxicity of mercury, its use makes it possible to determine the temperature with greater accuracy compared to other liquids, since the expansion of mercury follows a linear law. In meteorology, alcohol thermometers are used. This is primarily due to the fact that mercury thickens at 38 ° C and is not suitable for measuring more than low temperatures... The range of liquid thermometers is on average from 30 ° C to +600 ° C, and the accuracy does not exceed one tenth of a degree.

Gas thermometer

Gas thermometers work on the same principle as liquid thermometers, only an inert gas is used as a working substance. This type of thermometer is analogous to a manometer (pressure measuring device), the scale of which is graduated in temperature units. The main advantage of a gas thermometer is the ability to measure temperatures near absolute zero (its range is from 271 ° C to +1000 ° C). The maximum achievable measurement accuracy is 2 * 10 -3 ° C. Obtaining a high precision gas thermometer is challenging task, therefore, such thermometers are not used in laboratory measurements, but are used for the primary determination of the temperature of a substance.

This type of thermometer works by analogy with gas and liquid thermometers. The temperature of a substance is determined depending on the expansion of a metal spiral or bimetal strip. The mechanical thermometer is highly reliable and easy to use. As independent devices such thermometers widespread have not received and are currently used mainly as devices for signaling and temperature control in automation systems.

Electrical thermometer (resistance thermometer)

The basis of the operation of an electric thermometer is the dependence of the resistance of a conductor on temperature. The resistance of metals increases linearly with increasing temperature, which is why it is metals that are used to create this type of thermometer. Semiconductors, in comparison with metals, provide greater measurement accuracy, however, thermometers based on them are practically not produced due to the difficulties associated with the graduation of the scale. The range of resistance thermometers directly depends on the working metal: for example, for copper it is from -50 ° C to +180 ° C, and for platinum - from -200 ° C to +750 ° C. Electric thermometers are installed as temperature sensors in production, in laboratories, on experimental stands. They are often completed in conjunction with other measuring devices.

Also called thermocouple. A thermocouple is a contact between two different conductors that measure temperature based on the Seebeck effect, discovered in 1822. This effect consists in the appearance of a potential difference at the contact between two conductors in the presence of a temperature gradient between them. Thus, when the temperature changes, it begins to pass through the contact. electricity... The advantage of thermocouple thermometers is their simplicity, wide measurement range, and the possibility of grounding the junction. However, there are also disadvantages: the thermocouple is prone to corrosion and other chemical processes with time. Thermocouples with electrodes made of noble metals and their alloys - platinum, platinum-rhodium, palladium, gold - have the maximum accuracy. The upper limit of temperature measurement with a thermocouple is 2500 ° С, the lower one is about -100 ° С. The measurement accuracy of a thermocouple sensor can reach 0.01 ° C. A thermocouple thermometer is indispensable in industrial control and monitoring systems, as well as when measuring the temperature of liquid, solid, bulk and porous substances.

Fiber Optic Thermometer

With the development of optical fiber manufacturing technologies, new opportunities for its use have arisen. Fiber optic sensors are highly sensitive to various changes in external environment... The slightest fluctuation in temperature, pressure, or tension in a fiber will alter the propagation of light in it. Fiber-optic temperature sensors are often used for industrial safety, fire alarms, leak monitoring of containers with flammable and toxic substances, leak detection, etc. The range of such sensors does not exceed +400 ° С, and the maximum accuracy is 0.1 ° С.

Infrared thermometer (pyrometer)

Unlike all previous types of thermometers, it is a non-contact device. You can read more about the pyrometers and their characteristics in a separate page on our website. A technical pyrometer is capable of measuring temperatures in the range from 100 ° C to 3000 ° C, with an accuracy of several degrees. Infrared thermometers are convenient not only in production environments. They are increasingly used to measure body temperature. This is due to the many advantages of pyrometers over mercury analogs: safety of use, high accuracy, minimum time for temperature measurement.

In conclusion, we note that now it is difficult to imagine life without this universal and irreplaceable device. Simple thermometers can be found in everyday life: they are used to maintain the temperature in the iron, washing machine, refrigerator, ambient temperature measurement. More sophisticated sensors are installed in incubators, greenhouses, drying chambers, in production.

The choice of a thermometer or temperature sensor depends on the scope of its use, the measuring range, the accuracy of the readings, overall dimensions... And the rest - it all depends on your imagination.

A thermometer is important in identifying certain ailments. A medical thermometer should be in every home first-aid kit. Which type to choose is decided individually, based on the needs and financial capabilities.

The main types of thermometers for measuring body temperature according to the principle of operation, their features and comparisons.

The deviation of body temperature from the norm is often the result of various pathologies, ranging from inflammatory phenomena to severe diseases of internal organs (cancer, brain diseases).

According to existing medical standards, the ideal body temperature should be equal to the mark 36.6 C. However, these data are not necessary for everyone: body temperature can change, depending on the time of day, biological processes (ovulation, menstruation) - this does not apply to violations.

Medical thermometers, due to the specifics of the structure, are divided into three types:

• Digital Thermometer

The fundamental part of this device is a thermistor, which, against the background of temperature fluctuations, is able to change the resistance level. To protect the electrical circuit of the device from moisture, its body is made of moisture-proof materials.

By means of a sound signal, a notification is made that the measurement of body temperature has been completed - you can familiarize yourself with the information that is on the thermometer display.

Replaceable caps, which are sold together with the device, are hygienic.

Such thermometers have a lot of advantages:

• Work safety. If the thermometer breaks down, there will be no negative health effects.
• Versatility. The temperature of the thermometer in question can be measured by various methods: groin, axillary zone, rectum, area under the tongue.
• Adequate price.
• High speed of temperature measurement. The maximum time it takes to get information is 3 minutes.

The disadvantages of electronic thermometers are due to the area of ​​the body where the device is applied:

• If you change the temperature in the armpit with the indicated devices, the information will be inaccurate.
• The holding time of the thermometer under the arm is 5-10 minutes (even if the signal about the completion of measurements sounded earlier).

• Mercury thermometer

Nowadays, the mercury thermometer is the leader in the market for the sale of medical thermometers. They are also called maximum, in view of the presence of a mercury capillary, which is able to "memorize" the previous information.

This type of thermometer works on the basis of mercury, which is a toxic substance for the human body. By their structure, these thermometers are quite fragile - this can provoke the release of mercury to the outside.

Some manufacturers of medical supplies, in order to minimize damage in such cases, complete mercury thermometers in a capsule shell. This guarantees the retention of mercury inside the capsule in the event of a breakdown of the thermometer.

Advantages of mercury thermometer some:

• Versatility. With its help, it is possible to measure the temperature in several parts of the body. Oral temperature measurement in infants is not recommended.
• Ease of use.
• The reliability of the information received. The error can be minimal (no more than 0.1C).
• Low cost.

Negative sides of mercury thermometers:

• The combination of the fragility of glass (may break, injure the skin) + health hazard from mercury.
• The need for a long wait (in comparison with other types of thermometers) to obtain information. When measuring body temperature in the armpit, wait 10 minutes. It is very impractical to inquire about the baby's body temperature.

• Infrared thermometer

The specified type of thermometers is useful for families with newborns. They are also ideal when it is necessary to measure the body temperature of a person who is dormant / unconscious. Their use does not always require contact with the body.

These thermometers are equipped with a supersensitive component that reacts to infrared rays emanating from the human body. The temperature information can be seen on the LCD screen. The end of the device operation is signaled by a sound signal.

Some thermometers may have a backlit screen to help you see the readings at night.

The positive aspects of infrared thermometers are:

• A scanty period between the beginning of the measurement of body temperature, the receipt of the results. This process often takes about 2 seconds.
• Ease of use. To measure the temperature of a sleeping person, you should not wake him up. With the help of the considered type of device, it is permissible to measure the temperature of water / air.
• Additional functions , with which these thermometers can be completed, can be useful: shockproof case, removable sterile tips, temperature rise signal. The presence / absence of such functions will determine the price of the specified device.

The disadvantages of the considered thermometers include:

• Basal temperature cannot be determined.
• The cost of the devices is high.

Types of medical thermometers for measuring body temperature by method of application, their characteristics: ear, rectal, forehead.

Based on the shape of the tip that the device in question has, the method for measuring body temperature will be different:

• Rectal thermometer

Must necessarily have a thin short tip. For this, a mercury / electronic thermometer can be used, in which the tip should be inserted into the rectum. Waiting for the result - 5 minutes. Do not forget that the normal temperature is rectal temperature, which is in the armpit. This method is often used by women to determine the days of ovulation. If the rectal temperature needs to be measured in newborns, doctors advise using an electronic thermometer.

• Ear thermometer

One of the subspecies of infrared thermometer. The component that senses the temperature near the eardrum is built into the body of the device. To take measurements, you need to pull the earlobe, where the device nozzle will be inserted.

The design of the thermometer is such that it is almost impossible to injure the eardrum due to deep penetration. The ears should not contain a lot of sulfur - the information will be inaccurate.

In the presence of inflammation in the middle ear, the device will not show the true temperature.

Positive, negative sides This type of thermometer is similar to that of infrared thermometers.

• Forehead thermometer

Another type of infrared thermometers, which combines all its advantages / disadvantages.

There are several subspecies of the thermometers under consideration: those that require contact with the skin (applied to the forehead, the area at the temple) are non-contact. The measurement speed is high, but may fluctuate depending on the thermometer model (1-6 sec.). Such devices can only be used for the forehead.

For measuring the temperature of a newborn, an infrared forehead thermometer is a good choice. If it is necessary to measure the basal temperature, it is worth referring to other types of these devices.

He arranged something like a thermobaroscope (thermoscope). Galileo studied at this time Heron of Alexandria, who already described a similar device, but not for measuring the degrees of heat, but for raising water by heating. The thermoscope was a small glass ball with a glass tube soldered to it. The ball was slightly heated and the end of the tube was dipped into a vessel with water. After some time, the air in the ball cooled down, its pressure decreased, and the water, under the influence of atmospheric pressure, rose in the tube up to a certain height. Subsequently, with warming, the air pressure in the ball increased and the water level in the tube decreased while cooling, while the water in it rose. With the help of a thermoscope, it was possible to judge only about the change in the degree of heating of the body: it did not show numerical values ​​of temperature, since it did not have a scale. In addition, the water level in the tube depended not only on temperature, but also on atmospheric pressure. In 1657, Galileo's thermoscope was improved by Florentine scientists. They equipped the device with a bead scale and evacuated air from the reservoir (ball) and tube. This made it possible not only qualitatively, but also quantitatively to compare the temperatures of bodies. Subsequently, the thermoscope was changed: it was turned upside down with a ball, and alcohol was poured into the tube instead of water and the vessel was removed. The operation of this device was based on the expansion of measures; the temperatures of the hottest summer day and the coldest winter day were taken as "constant" points. The invention of the thermometer is also credited to Lord Bacon, Robert Fludd, Sanctorius, Scarpi, Cornelius Drebbel ( Cornelius drebbel), Porte and Salomon de Kaus, who wrote later and partly had a personal relationship with Galileo. All these thermometers were air and consisted of a vessel with a tube containing air separated from the atmosphere by a column of water; they changed their readings both from temperature changes and from changes in atmospheric pressure.

Mercury medical thermometer

Liquid thermometers are described for the first time in the Saggi di naturale esperienze fatte nell'Accademia del Cimento, where they are spoken of as objects long made by skillful artisans called Confia, who heat glass on a blown fire and make amazing and very delicate products made of it. First, these thermometers were filled with water, and they burst when it froze; they began to use wine alcohol for this in 1654, according to the idea of ​​the Grand Duke of Tuscan Ferdinand II. Florentine thermometers are not only depicted in the Saggi, but have been preserved in several copies to this day in the Galilean Museum in Florence; their preparation is described in detail.

At first, the master had to make divisions on the tube, considering its relative dimensions and the dimensions of the ball: the divisions were applied with molten enamel on a tube heated on a lamp, every tenth was indicated by a white dot, and others by black. Usually, 50 divisions were made in such a way that when the snow melted, the alcohol did not fall below 10, and in the sun did not rise above 40. Good masters made such thermometers so well that they all showed the same temperature value under the same conditions, but this could not be achieved if the tube was divided into 100 or 300 parts in order to obtain greater accuracy. The thermometers were filled by heating the ball and lowering the end of the tube into alcohol, and finishing the filling using a glass funnel with a thinly drawn end that freely fit into a rather wide tube. After adjusting the amount of liquid, the tube opening was sealed with sealing wax, called "hermetic". From this it is clear that these thermometers were large and could serve to determine the air temperature, but they were still inconvenient for other, more diverse experiments, and the degrees of different thermometers were not comparable with each other.

The Swedish physicist Celsius finally established both constant points of melting ice and boiling water in 1742, but initially he set 0 ° at the boiling point, and 100 ° at the freezing point, and took the opposite designation only on the advice of M. Störmer. The surviving examples of Fahrenheit thermometers are distinguished by their meticulous workmanship. However, the “inverted” scale turned out to be more convenient, on which the ice melting temperatures were designated 0 C, and the boiling point 100 C. This thermometer was first used by the Swedish scientists botanist K. Linnaeus and astronomer M. Stremer. This thermometer is widely used.

Mechanical thermometers

Mechanical thermometer

Window Mechanical Thermometer

Thermometers of this type operate on the same principle as liquid thermometers, but a metal spiral or bimetal tape is usually used as a sensor.

Electric thermometers

Medical Electric Thermometer

The principle of operation of electric thermometers is based on a change in the resistance of a conductor with a change in temperature the environment.

Electric thermometers of a wider range are based on thermocouples (contact between metals with different electronegativity creates a contact potential difference depending on temperature).

Home weather station

The most accurate and stable over time are resistance thermometers based on platinum wire or platinum sputtered on ceramics. The most widely used are PT100 (resistance at 0 ° C - 100Ω) PT1000 (resistance at 0 ° C - 1000Ω) (IEC751). The temperature dependence is almost linear and obeys a quadratic law at positive temperatures and a 4-degree equation at negative temperatures (the corresponding constants are very small, and in the first approximation this dependence can be considered linear). Temperature range -200 - +850 ° C.

Hence, the resistance at T° C, resistance at 0 ° C, and constants (for platinum resistance) -

Optical thermometers

Optical thermometers allow you to record temperature due to the change in the luminosity level, spectrum and other parameters (see Fiber-optic temperature measurement) when the temperature changes. For example, infrared body temperature meters.

Infrared thermometers

An infrared thermometer allows you to measure temperature without direct human contact. In some countries, there has long been a tendency to abandon mercury thermometers in favor of infrared thermometers, not only in medical institutions, but also at the household level.

The infrared thermometer has a number of undeniable advantages, namely:

• safety of use (even with serious mechanical damage, nothing threatens health)
• higher measurement accuracy
• minimum time for the procedure (measurement is carried out within 0.5 seconds)
• possibility of group data collection

Technical thermometers

Technical liquid thermometers are used at enterprises in agriculture, petrochemical, chemical, mining and metallurgical industries, in mechanical engineering, housing utilities, transport, construction, medicine, in a word, in all spheres of life.

There are the following types of technical thermometers:

• technical liquid thermometers TTZh-M;
• bimetallic thermometers TB, TBT, TBI;
• agricultural thermometers TS-7-M1;
• maximum thermometers SP-83 M;
• low-degree thermometers for special cameras SP-100;
• special vibration-resistant thermometers SP-V;
• thermometers mercury electrocontact TPK;
• laboratory thermometers TLS;
• thermometers for petroleum products TN;
• thermometers for testing petroleum products TIN1, TIN2, TIN3, TIN4.

The idea of ​​creating a thermometer originated in the rebellious brain of Galileo Galilei. In 1597, as his students testified, he created a thermoscope - the prototype of the modern thermometer. Just think how long ago it was! And yet another thing surprises: how did mankind manage without such important devices before? Medicine, science, industry and without them ... Even to imagine such a thing now is scary! How much these devices simplify our life and yet, in modern world temperature measurements new problem: how to choose the most suitable from a huge variety of thermometers?

For many years we have been selling technical, special, industrial, meteorological, laboratory thermometers. Thermometers for Agriculture and incubators or for testing petroleum products ... The most varied and mostly the best - listen to our opinion, we can help you.

Medical thermometers: choose smartly!

The most famous thermometer is perhaps a medical one. Everyone has known him since childhood, but choosing the best one in the endless sea of ​​modern assortment can be difficult.
On the one hand, traditional mercury will not go away from our use for a long time, although in Europe it is no longer used due to the high probability of glass damage and environmental pollution with mercury. Why is it still popular with us? Firstly, low price... Secondly, it does not need a power source and it fails only in case of mechanical damage, that is, it can be trusted. Additional advantages can be considered the accuracy of measurements (the error is not more than 0.1 degrees), ease of disinfection, because it is glass, and the glass is resistant to the most aggressive chemicals.

An electronic thermometer or digital has relatively recently entered our life and for this a short time has become almost irreplaceable. Its principle of operation is to measure body temperature by means of a special sensitive sensor built into it. The measurement result is displayed in digital form on the display. A number of models have additional functions: memory of the last measurements, sound signals of the end of measurement, replaceable tips. The undoubted advantages of this type of thermometer, of course, include safety and ease of reading the results (if the device is backlit, then you can find out the result even in the dark). In addition, the measurement scale is interchangeable: "Celsius-Farentate". The short measurement time is also attractive. Models for children are available. They have bright colors, different shape(especially convenient in the form of a nipple). Most importantly, baby thermometers are equipped with flexible, low-traumatic tips.

An infrared medical thermometer has a measuring element that measures the infrared radiation of the human body. The advantage of this device in comparison with an electronic one is even shorter measurement time (from 5 seconds). There is a non-contact version of the device that allows you to measure the temperature even in crying children or sleeping patients. The tips are replaceable, which makes it possible to solve such important questions disinfection and hygiene.

Technical thermometers

These devices are used in enterprises, both in agriculture and in the chemical, petrochemical, mining and metallurgical industries, as well as in mechanical engineering and in housing and communal services, transport and construction, in a word, in almost all spheres of life.

A technical thermometer is a cylindrical glass tube in which a scale plate or a glass one is inserted, milky or cardboard. The lower part of such thermometers can be straight or angular (at an angle of 90 degrees).

A device with a straight lower part is designated in the nomenclature as ТТП (technical straight thermometer. Angle thermometers, respectively, have an angled lower part and are called TTU (technical angle thermometer).

The direct purpose of technical thermometers is to measure the temperature of liquids or gases. They are widely used for measurements in vessels and pipelines. The temperature range can range from -35 to +600 degrees Celsius. Thermometers are installed in pipelines and on tanks, as well as installations and machines of chemical or food industries and in other industries.

When planning to buy a technical thermometer, you must first of all familiarize yourself with technical characteristics and choose from a variety of models that best suits your needs.

There are several types of technical thermometers:
1.Termometer technical liquid TTZH-M;
2. bimetallic thermometer TB, TBT, TBI;
3. Agricultural thermometer TS-7-M1;
4. maximum thermometer SP-83 M;
5. thermometer for special cameras (low-degree) SP-100;
6. special vibration-resistant thermometer SP-V;
7. thermometers mercury electrocontact TPK type;
8. laboratory thermometers TLS;
9. Thermometer for TN petroleum products;
10. Thermometer for testing petroleum products of types TIN1, TIN2, TIN3, TIN4.

The principle of operation of all liquid thermometers is based on a dynamic change in the volume of liquid poured into it. Usually it is either alcohol (alcohol) or mercury (mercury). However, there are other thermometric fluids such as petroleum ether for low-degree devices.

Liquid thermometers are widely used when the ambient temperature changes - meteorological thermometers. Unlike household thermometers, instruments used at weather stations must be much more accurate, which means that much more stringent requirements are imposed on their manufacture. In addition to liquid thermometers, resistance thermometers, bimetallic, thermoelectric, transistor, radiation, and many others are widely used in meteorology.

You understand that in this article there is no way to tell about all the intricacies optimal choice... But, if you contact us, our consultants will be able to explain to you the features of the work, the pros and cons of each model that you need right now. Yes, we forgot to say the most important thing, we only offer devices High Quality and at a low price!