Thermometers are tools that can accurately judge and measure temperature, including pointer thermometers andDigital thermometer。According to the different purposes of use, a variety of thermometers have been designed and manufactured.
On October 16, 2020, the State Food and Drug Administration released the Notice of the Comprehensive Department of the State Food and Drug Administration on Relevant Matters concerning the Implementation of the Minamata Convention on Mercury on its website.The Notice clearly requires that from January 1, 2026, China will completely ban the production of mercury containing thermometers and mercury containing sphygmomanometers.[1]
The earliest thermometer was made by Italian scientists in 1593Galileo(1564-1642).His first thermometer was open at one endglass tubeThe other end is covered with a walnut big glass bubble.When using, heat the glass bulb first, and then insert the glass tube into the water.With the change of temperature, the water surface in the glass tube will move up and down. According to the amount of movement, the temperature change and the temperature can be determined.The thermometer has the function of thermal expansion and cold contraction, so this kind of thermometer is greatly affected by environmental factors such as external atmospheric pressure, so the measurement error is large.
Later, Galileo's students and other scientists made repeated improvements on this basis, such asglass tubeInstead, put the liquid in the tube, seal the glass tube, etc.The outstanding one is the thermometer made by the Frenchman Briault in 1659. He reduced the size of the glass bubble and changed the temperature measuring material to mercury, which has the prototype of the thermometer.Later DutchWarren HaidtUtilized in 1709alcoholIn 1714MercuryAs a measuring material, more accurate thermometers are manufactured.He observed the boiling temperature of water, the temperature of mixing water and ice, and the temperature of mixing brine and ice;After repeated experiments and approval, the temperature of brine with a certain concentration during solidification is finally set as 0 ℉, the temperature of pure water during solidification is set as 32 ℉, the temperature of water boiling at standard atmospheric pressure is set as 212 ℉, and the Fahrenheit temperature is represented by ℉, which is called Fahrenheit thermometer.
thermometer
staythe fahrenheit thermometerAt the same time, the Frenchman Samuel (1683-1757) also designed and manufactured a thermometer.He believes that the expansion coefficient of mercury is too small to be used as a temperature measuring material.He concentrated on the advantages of using alcohol as a temperature measuring material.He repeatedly found that the volume of alcohol containing 1/5 of water expanded from 1000 volume units to 1080 volume units between the freezing temperature and boiling temperature of water.So he divided the temperature between the freezing point and the boiling point into 80 parts, which is the temperature division of his thermometer[2]Leeb thermometer。
the fahrenheit thermometerAfter more than 30 years, SwedesAnders Celsius Improved in 1742Warren Haidt[3]Later, his colleague Schlemmer reversed the values of the two temperature points (that is, the boiling point is 100 degrees, the freezing point is 0 degrees), which became the current percentage temperature, that isCelsius temperature, expressed in ℃.The relationship between Fahrenheit temperature and Celsius temperature is ℉=9/5 ℃+32, or ℃=5/9 (℉ - 32).
Fahrenheit temperature is commonly used in Britain and America, and in GermanyLeeb temperatureThe world's scientific and technological circles, industrial and agricultural production, as well as China, France and most other countries use the temperature of Celsius.
working principle
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According to the different purposes of use, a variety of thermometers have been designed and manufactured.The design basis is: the solid, liquid and gas are affected by temperatureThermal expansion and cold contractionPhenomenon of;Under the condition of constant volume, the pressure of gas (or vapor) changes due to different temperatures;Thermoelectric effect;The resistance changes with temperature;Influence of thermal radiation, etc.
1. Gas thermometer: hydrogen orheliumAs a temperature measuring material, becausehydrogenandheliumIts liquefaction temperature is very low, close to absolute zero, so its temperature measurement range is very wide.This kind of thermometer has high accuracy and is mostly used for precise measurement.
2. Resistance thermometer: divided into metal resistance thermometer and semiconductor resistance thermometer, which are made according to the characteristic that the resistance value changes with temperature.Metal thermometers are mainly used for pure metals such as platinum, gold, copper, nickel, and rhodium iron, phosphor bronze alloys;Semiconductor thermometerCarbon and germanium are mainly used.resistanceThe thermometer is convenient and reliable, and has been widely used.Its measuring range is about - 260 ℃ to 600 ℃.
High precision thermometer
3. Thermocouple thermometer: It is a temperature measuring instrument widely used in industry.It is made of thermoelectric phenomenon.Two different types of wireweldingThe working end is formed together, and the other two ends are connected with the measuring instrument to form a circuit.Put the working end at the measured temperature. When the temperature of the working end is different from that of the free end, the electromotive force will appear, so there is current passing throughloop。Through the measurement of electrical quantity, the temperature of a known place can be used to measure the temperature of another place.It is suitable for the measurement of high temperature and low turbidity between two substances with large temperature difference.Some thermocouples can measure high temperatures up to 3000 ℃, and some can measure low temperatures close to absolute zero.
4. Pointer thermometer: a thermometer shaped like an instrument panel, also calledthermometer, used to measure room temperature, is made of the principle of metal expansion and contraction.It is based onBimetallic sheetAs a temperature sensing element, it is used to control the pointer.The bimetallic sheet is usually riveted together with copper sheet and iron sheet, and the copper sheet is on the left and the iron sheet is on the right.As the effect of thermal expansion and cold contraction of copper is more obvious than that of iron, when the temperature rises, the copper sheet pulls the iron sheet to bend to the right, and the pointer deflects to the right (pointing to high temperature) under the drive of the bimetallic sheet;On the contrary, when the temperature becomes lower, the pointer will deflect to the left (pointing to the low temperature) under the drive of the bimetallic sheet.
5．Glass thermometer: The glass thermometer is used to measure the temperature based on the principle of thermal expansion and cold contraction.Since the expansion coefficient of the temperature measuring medium is different from the boiling point and freezing point, our common glass tube thermometers mainly include:Kerosene thermometer, mercury thermometer, redPenWater thermometer.Its advantages are simple structure, convenient use, relatively high measurement accuracy and low price.The disadvantage is that the upper and lower limits and accuracy of measurement are limited by the quality of glass and the nature of temperature measuring medium.It cannot be transmitted far away and is fragile.
6. Pressure thermometer: The pressure thermometer uses the volume expansion or pressure change of the liquid, gas or saturated steam in the closed container as the measuring signal after being heated.Its basic structure is composed ofcapillaryAnd indicator table.The advantages of pressure thermometer are: simple structure, high mechanical strength, and fear of vibration.Low price, no need for external energy.Disadvantages: temperature measurement range is limited, generally - 80~400 ℃;Large heat loss and slow response time.
7．Mercury thermometerIt is a kind of expansion thermometer. The freezing point of mercury is -38.87 ℃, and the boiling point is 356.7 ℃. It is used to measure the temperature within 0 - 150 ℃ or 500 ℃. It can only be used as an instrument for local supervision.Using it to measure temperature is not only simple and intuitive, but also can avoid the error of external remote thermometer.
Instrument type
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Rotary thermometer
Rotary thermometer[4]Is made up of a curlyBimetallic sheetmake.One end of the bimetallic sheet is fixed, and the other end is connected with a pointer.Due to the different expansion degree of the two metal sheets, at different temperatures, the bimetallic sheets have different curl degrees. The pointer then points to different positions on the dial, and its temperature can be known from the readings on the dial.
Semiconductor thermometer
The resistance change of semiconductor is different from that of metal. When the temperature rises, the resistance decreases, and the range of change is large.Therefore, a small amount of temperature change can also make the resistance change significantly. The thermometer made has high precision and is often called a temperature sensor.
Thermocouple thermometer
Thermocouple thermometerIt is composed of two different metals connected with a sensitive voltmeter.At different temperatures, metal contacts will produce different potential differences at both ends of the metal.The potential difference is very small, so a sensitive voltmeter is required to measure it.From the reading of the voltmeter, we can know what the temperature is.
Optical pyrometer
If the temperature of an object is high enough to emit a lot of visible light, its temperature can be determined by measuring the amount of its thermal radiation. This thermometer is called a light thermometer.This thermometer is mainly composed of a telescope equipped with a red filter and a set of small bulbs, galvanometers and variableresistanceCircuit.Before use, establish the relationship between the temperature corresponding to different filament brightness and the reading on the galvanometer.When using, align the telescope with the object to be measured and adjust the resistance so that the brightness of the bulb is the same as that of the object to be measured. At this time, the temperature of the object to be measured can be read from the galvanometer.[4]
Liquid crystal thermometer
Made with different formulasliquid crystalThe optical properties of the liquid crystal will also change when its phase transition temperature is different, making the liquid crystal look colored.If liquid crystals with different phase transition temperatures are coated on a piece of paper, the temperature can be known from the change of liquid crystal color.The advantage of this thermometer is that it is easy to read, while the disadvantage is that it is not accurate enough. It is often used in ornamental fish tanks to indicate water temperature.[4]
Digital thermometer
The digital thermometer usesTemperature sensorConvert (temperature) into a digital signal,
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Then through the display (such as LCD, nixie tubeLEDMatrix, etc.) displays the temperature in digital form, which can quickly and accurately measure the highest value of human body temperature. Compared with traditional mercury thermometers, it has the advantages of convenient reading of numbers, short measurement time, high measurement accuracy, memory and prompt sound. In particular, digital thermometers do not contain mercury, which is harmless to human body and the surrounding environment, especially suitable for hospitals and families.The use method is divided into the following steps:
1. Before using the thermometer, the head of the thermometer should be sterilized with alcohol.
2. Press the switch, the buzzer will beep immediately, and the display is shown in Figure A for about 2 seconds.
3. Then the display shows the temperature of the last side measurement as shown in Figure B (if the last measurement was 36.5 ℃), and the well lasts for about 2 seconds.Then the display may display as shown in Figure C. The "℃" symbol flashes, indicating that the thermometer is in standby state.(When the room temperature is higher than 32 ℃, the thermometer will display the room temperature instead of the figure D, and the "℃" symbol will flash continuously).
4. Use a thermometer to measure body temperature.The temperature displayed during body temperature measurement rises gradually, and the "℃" symbol flashes continuously.
5. When the temperature rise rate is less than 0.1 ℃ within 16 seconds, the "℃" symbol stopstwinkleAt the same time, the thermometer emits a beeping prompt sound for about 5 seconds. At this time, after the thermometer has finished measuring, the displayed temperature value can be read.[4]
Mercury thermometer
Digital thermometer display information description
The spilled mercury must be immediately collected with a dropper and a brush, and covered with water (preferably glycerin). Then sulfur powder should be sprinkled on the contaminated area. After there is no liquid (generally about a week), it can be cleaned.
1. Calibration shall be carried out before use (the standard liquid temperature multi branch comparison method can be used for calibration or the thermometer with higher accuracy can be used for calibration).
2. It is not allowed to use the measured value whose temperature exceeds the maximum scale value of the thermometer.
3. Thermometer hasThermal inertiaThe readings shall be taken after the thermometer reaches a stable state.The readings shall be taken in the highest tangent direction of the temperature convex meniscus, and the eyes shall be direct.
4. Do not use it as a stirring rod.
5. The mercury thermometer shall be perpendicular or inclined to the flow direction of the measured working medium.
6. The mercury thermometer often breaks the mercury column. The elimination methods are as follows:
① Cold repair method: insert the thermometer into the mixture of dry ice and alcohol (the temperature shall not exceed - 38 ℃) for cold shrinkagecapillaryAll mercury in the temperature measuring bag shrinks to the temperature measuring bag.
② Hot repair method: insert the thermometer slowly into the thermostatic bath whose temperature is slightly higher than the upper limit of measurement to connect the broken part of mercury with the whole mercury column, then slowly take out the thermometer and gradually cool it to room temperature in the air.[4]
1. First observe the range, division value and zero point, and the measured liquid temperature cannot exceed the range;
2. The glass bulb of the thermometer shall be completely immersed in the measured liquid, and shall not touch the bottom or wall of the container;
3. After the bulb of the thermometer is immersed in the measured liquid, wait for a while, and then read after the reading of the thermometer is stable;
4. The glass bubble of the thermometer shall remain in the liquid when reading, and the line of sight shall be level with the upper surface of the liquid column in the thermometer.
Note: Never throw it before measuring temperature.
Comparison of three thermometers: thermometer, thermometer, thermometer (mercury, alcohol, kerosene):
Temperature measuring skills
When measuring the surface temperature of light-emitting objects, such as aluminum and stainless steel, the reflection of the surface will affect the reading of the infrared thermometer.Before reading the temperature, place a rubber strip on the metal surface. After the temperature is balanced, measure the temperature of the rubber strip area.
To thinkInfrared temperature instrumentIt can still provide accurate temperature measurement when walking back and forth from the kitchen to the cold storage area. It is necessary to measure after a period of time in the new environment to achieve temperature balance.It is better to place the thermometer in a place where it is often used.
Use an infrared thermometer to read the internal temperature of liquid food, such as soup or sauce, which must be stirred, and then the surface temperature can be measured.Keep the thermometer away from steam to avoid polluting the lens and causing incorrect readings.
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The world's largest thermometer
The world's largest thermometer
The world's largest thermometer is located in the Flaming Mountain Scenic Area in Turpan, XinjiangFlaming Mountain Scenic SpotIn the center of the underground palace, there stands a huge thermometer. This three-dimensional thermometer, named "Golden Stirrup Stick", was completed on August 16, 2004 and won the Guinness World Record.
The giant thermometer is 0.65 meters in diameter and 12 meters in height. The temperature display is 5.4 meters high. It can measure the surface temperature and air temperature within 100 degrees Celsius, with an error of no more than plus or minus 0.5 degrees.
Shaanxi Province's largest thermometer
At the end of July 2014, a large "thermometer" with a height of 68 meters appeared outside Liuba County.The thermometer was transformed from an abandoned chimney, which cost 430000 yuan.It is understood that this is the largest thermometer in Shaanxi Province.[5]
