The thermometer is normal. 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 temperature changes. Liquid thermometers are well known to everyone in everyday life: for measuring room temperature or human body temperature.

Liquid thermometers consist of five principal parts, these are: the bulb of the thermometer, the liquid, the capillary tube, the bypass chamber, and the scale.

The bulb of the thermometer is the part where the liquid is placed. The liquid reacts to temperature changes by rising or falling down the capillary tube. A capillary tube is a narrow cylinder through which liquid moves. Often the capillary tube is equipped with a bypass chamber, which is a cavity where excess fluid enters. If there is no bypass chamber, then after the capillary tube is filled enough pressure will be created to destroy the tube if the temperature continues to rise. The scale is the part of a liquid thermometer that is used to take readings. The scale is calibrated in degrees. The scale can be fixed on the capillary tube or it can be movable. The movable scale makes it possible to adjust it.

The principle of operation of a liquid thermometer

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 a 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 liquid reacts to temperature changes 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

Many liquid thermometers are designed to be hung on a wall with the entire surface of the thermometer in contact with the substance being measured. However, some industrial and laboratory liquid thermometers are designed and calibrated to be immersed in liquid.

Of the thermometers used in this way, the most widely used are the partial immersion thermometers. To obtain accurate readings with a partial immersion thermometer, immerse its bulb and capillary tube only up to this line.

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

In industrial production, 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 makers: how to measure the temperature of a substance when there is no direct access to that substance or liquid, and how to take out a liquid thermometer for inspection, check, or replacement without stopping technological process. Both of these problems are eliminated if measuring channels are used to input thermometers.

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

Measuring channels are made standard sizes so that they can be used with various 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 "to 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. The liquid thermometer was first mentioned in 1667, and in 1742 the Swedish physicist Celsius created a thermometer with a scale where 0 was the freezing point of water and 100 was the boiling point.

We often use a thermometer to determine the temperature of the air outside or body temperature, but the use of a thermometer is by no means limited to this. Today, there are many ways to measure the temperature substances, and modern thermometers are still being improved. Let us 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 that use mercury as a liquid are often used in medicine to measure body temperature. Despite the toxicity of mercury, its use allows you to determine the temperature with greater accuracy than other liquids, since the expansion of mercury occurs according to a linear law. In meteorology, alcohol thermometers are used. This is primarily due to the fact that mercury thickens at a value of 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 they use an inert gas as a working medium. This type of thermometer is analogous to a manometer (a device for measuring pressure), the scale of which is graduated in units of temperature. 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 °С. Obtaining a high accuracy 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. The temperature of the substance is determined depending on the expansion of the 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.

Electric thermometer (resistance thermometer)

The operation of an electric thermometer is based on the dependence of the conductor resistance on temperature. The resistance of metals increases linearly with increasing temperature, which is why metals 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 grading the scale. The range of resistance thermometers directly depends on the working metal: for example, for copper it ranges 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 bundled 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, through the contact with a change in temperature, begins to pass electricity. The advantage of thermocouple thermometers is the ease of execution, a wide range of measurements, the possibility of grounding the junction. However, there are disadvantages: the thermocouple is subject to corrosion and other chemical processes with time. Thermocouples with electrodes made of noble metals and their alloys - platinum, platinum-rhodium, palladium, gold - have maximum accuracy. The upper limit of temperature measurement using a thermocouple is 2500 °C, the lower limit is about -100 °C. The measurement accuracy of the thermocouple sensor can reach 0.01 °C. A thermocouple-based thermometer is indispensable in industrial control and monitoring systems, as well as in measuring the temperature of liquid, solid, granular 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 of the fiber leads to changes in the propagation of light in it. Fiber optic temperature sensors are often used to ensure industrial safety, for fire warning, monitoring the tightness of containers with flammable and toxic substances, leak detection, etc. The range of such sensors does not exceed +400 °C, and the maximum accuracy is 0.1 °C.

Infrared thermometer (pyrometer)

Unlike all previous types of thermometers, it is a non-contact device. You can read more about pyrometers and their characteristics in a separate one on our website. A technical pyrometer is capable of measuring temperature in the range from 100 °C to 3000 °C, with an accuracy of several degrees. Infrared thermometers are convenient not only in production conditions. Increasingly, they are used to measure body temperature. This is due to the many advantages of pyrometers compared to mercury analogues: 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 complex sensors are installed in incubators, greenhouses, drying chambers, and in production.

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

The 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 needs and financial abilities.

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

Deviation of body temperature from the norm is often the result of various pathologies, ranging from inflammation to severe diseases of internal organs (cancer, brain disease).

According to existing medical standards, the ideal body temperature should be equal to the mark 36.6 C. However, these data are not mandatory 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 case is made of moisture-proof materials.

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

Replaceable caps, which are sold in conjunction with the device, have a hygienic purpose.

The advantages of such thermometers are many:

• Safety at work. If the thermometer breaks, there will be no negative health effects.
• Versatility. It is permissible to measure the temperature with the thermometer in question by various methods: groin, axillary zone, rectum, area under the tongue.
• Adequate price.
• High speed temperature measurement. The maximum time it takes to get the information is 3 minutes.

The disadvantages of electronic thermometers are due to the area of ​​\u200b\u200bthe body where the device is applied:

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

• mercury thermometer

Today, the mercury thermometer is the market leader in medical thermometer sales. They are also called maximum, in view of the presence of a mercury capillary, which is able to "remember" previous information.

The specified type of thermometers 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 products, 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 breakage of the thermometer.

Pros mercury thermometer several:

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

Negative aspects of mercury thermometers:

• The combination of the fragility of glass (may break, injure the skin) + the danger of mercury to health.
• The need for a long wait (compared to other types of thermometers) to receive information. When measuring body temperature in the armpit, you should expect 10 minutes. It is very impractical if you need to inquire about the temperature of the child's body.

• Infrared thermometer

This type of thermometer is useful for families with newborns. They are also ideal when you need to take the body temperature of a person who is asleep/unconscious. Their use does not always require contact with the body.

Such thermometers are equipped with an ultra-sensitive component that reacts to infrared rays that come 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 that will help to see the received data at night.

The positive aspects of infrared thermometers are:

• The meager period between the start of measuring body temperature, obtaining results. Often this process takes about 2 seconds.
• Ease of use. To measure the temperature of a sleeping person, you should not wake him up. Using this type of device, it is permissible to measure the temperature of water / air.
• Additional functions , which can be equipped with these thermometers, can be useful: shockproof housing, removable sterile tips, temperature increase alarm. The presence / absence of such functions will determine the price of the specified device.

The disadvantages of the considered thermometers include:

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

Types of medical thermometers for measuring body temperature according to the 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 normal temperature is rectal temperature, which is in the armpit. This method is often used by women to determine the days of ovulation. If rectal temperature needs to be measured in newborns, doctors advise using an electronic thermometer.

• Ear thermometer

One of the subspecies of the infrared thermometer. The component that detects the temperature near the eardrum is built into the body of the device. To carry out measurements, you need to pull the earlobe, where the nozzle of the device 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 thermometer that 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, area at the temple), non-contact. The measurement speed is high, but may vary depending on the thermometer model (1-6 sec.). Such devices can only be used for the forehead.

To measure the temperature of a newborn, an infrared forehead thermometer is a good choice. If you need to measure the basal temperature, you should turn to other varieties 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 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 lowered into a vessel with water. After some time, the air in the ball cooled, its pressure decreased, and the water, under the action of atmospheric pressure, rose up in the tube to a certain height. Subsequently, with warming, the air pressure in the ball increased and the water level in the tube decreased; when cooled, 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 the numerical values ​​of the 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 fitted the instrument with a scale of beads and bled the air out of the tank (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, 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, Santorius, Scarpi, Cornelius Drebbel ( Cornelius Drebbel), Porte and Salomon de Caus, who wrote later and partly had personal relations 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 ago made by skillful craftsmen called "Confia", who heated the glass on the fanned fire of the lamp and made from it amazing and very delicate products. At first these thermometers were filled with water, and they burst when it froze; they began to use wine spirit for this in 1654 at the thought of the Grand Duke of Tuscany Ferdinand II. Florentine thermometers are not only depicted in Saggi, but several copies have survived to our time in the Galilean Museum, in Florence; their preparation is described in detail.

First, the master had to make divisions on the tube, considering its relative dimensions and the size of the ball: divisions were applied with melted enamel on a tube heated on a lamp, every tenth was indicated by a white dot, and others by black. Usually they made 50 divisions in such a way that when the snow melted, the alcohol did not fall below 10, and in the sun it did not rise above 40. good craftsmen made such thermometers so successfully 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 bulb and lowering the end of the tube into alcohol; filling was completed using a glass funnel with a thinly drawn end that freely entered a fairly wide tube. After adjusting the amount of liquid, the opening of the tube was sealed with sealing wax, called "hermetic". From this it is clear that these thermometers were large and could serve to determine the temperature of the air, but 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, melting ice and boiling water, in 1742, but initially he set 0 ° at the boiling point, and 100 ° at the freezing point, and adopted the reverse designation only on the advice of M. Störmer. The surviving copies of Fahrenheit thermometers are distinguished by their meticulous workmanship. However, the “inverted” scale turned out to be more convenient, on which the melting temperatures of ice were designated 0 C, and the boiling point was 100 C. Swedish scientists, botanist K. Linnaeus and astronomer M. Strömer, were the first to use such a thermometer. 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.

Electrical thermometers

Medical electrical thermometer

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

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

home weather station

The most accurate and stable over time are resistance thermometers based on platinum wire or platinum sputtering on ceramics. The most common are PT100 (resistance at 0 °C - 100Ω) PT1000 (resistance at 0 °C - 1000Ω) (IEC751). The dependence on temperature is almost linear and obeys a quadratic law at positive temperatures and a 4th degree equation at negative ones (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 by changing the level of luminosity, spectrum and other parameters (see Fiber-optic temperature measurement) with temperature. For example, infrared body temperature meters.

Infrared thermometers

An infrared thermometer allows you to measure temperature without direct contact with a person. In some countries, there has long been a tendency to abandon mercury thermometers in favor of infrared, 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 procedure time (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 and public utilities, transport, construction, medicine, in a word, in all spheres of life.

There are such types of technical thermometers:

• technical liquid thermometers ТТЖ-М;
• bimetallic thermometers TB, TBT, TBI;
• agricultural thermometers TS-7-M1;
• thermometers maximum SP-83 M;
• thermometers for special chambers low-degree SP-100;
• special vibration-resistant thermometers SP-V;
• mercury electrocontact thermometers TPK;
• laboratory thermometers TLS;
• thermometers for petroleum products TN;
• thermometers for testing oil 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 that was! And yet another thing surprises: how did humanity manage without such important devices before? Medicine, science, industry and without them... It's scary to even imagine now! How much these devices simplify our life and yet, in modern world temperature measurements are acute new problem: how to choose the most suitable one from a huge variety of thermometers?

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

Medical thermometers: choose wisely!

The most famous thermometer is perhaps the medical one. Everyone has known him since childhood, but choosing the best one in the endless sea of ​​\u200b\u200bthe modern assortment can be difficult.
On the one hand, traditional mercury will not leave our everyday life for a long time, although in Europe it is no longer used due to the high probability of glass damage and mercury pollution of the environment. 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 include measurement accuracy (error not more than 0.1 degrees), ease of disinfection, because it is made of glass, and glass is resistant to the most aggressive chemicals.

An electronic or digital thermometer has recently entered our lives and for this a short time became almost indispensable. The principle of its operation is the measurement of body temperature by means of a special sensitive sensor built into it. The measurement result is displayed digitally on the display. A number of models have additional functions: memory of the last measurements, sound signals of the end of the measurement, interchangeable tips. The undoubted advantages of this type of thermometer, of course, include safety and ease of reading the results (if the device is backlit, you can find out the result even in the dark). In addition, the measurement scale is interchangeable: "Celsius-Fahrenheit". Also attractive is the short measurement time. There are models for children. They have bright colors different shape(especially convenient in the form of nipples). Most importantly, children's thermometers are equipped with flexible, low-impact tips.

The infrared medical thermometer has a measuring element that measures the infrared radiation of the human body. The advantage of this device in comparison with electronic 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 interchangeable, which allows you to solve such important questions disinfection and hygiene.

Technical thermometers

These devices are used at 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 areas of life.

A technical thermometer is a cylindrical glass tube in which a scale plate or glass plate 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 TTP (technical straight thermometer. Angular thermometers, respectively, have an angular lower part and are called TTU (technical angular 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 mounted 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 familiarize yourself with technical specifications and choose among the variety of models best suited to your needs.

There are several types of technical thermometers:
1. technical liquid thermometer ТТЖ-М;
2. bimetallic thermometer TB, TBT, TBI;
3. agricultural thermometer TS-7-M1;
4. maximum thermometer SP-83 M;
5. thermometer for special chambers (low degree) SP-100;
6. special vibration-resistant thermometer SP-V;
7. mercury electrocontact thermometers of the TPK type;
8. laboratory thermometers TLS;
9. thermometer for petroleum products TN;
10. thermometer for testing oil products 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 liquids, such as petroleum ether for low-degree instruments.

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, resistance thermometers, bimetallic, thermoelectric, transistor, radiation, and many others are widely used in meteorology.

You understand that in this article there is no opportunity to tell about all the subtleties 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 appliances High Quality and at a low price!