How does a thermometer work? What is the principle of a thermometer?

Electronic thermometers use the physical parameters of certain substances, such as resistance, voltage, current, etc., to display the body temperature in the form of numbers.

The body temperature varies over time, from a lower body temperature in the early morning to a slightly higher temperature in the evening. So it's normal to have a slight discrepancy in the results of your body temperature measurements in a single day.

All electronic thermometers have at least; f(, so can be used as a base thermometer.

The working principle of a thermometer is the same as that of a general thermometer, which is to expand by heat. The biggest difference between a thermometer and a regular thermometer is that the bottom connection is very thin and meniscus-shaped. As long as you take it out of your clothes, the mercury column at the bottom will be disconnected immediately, and the mercury on it will not be left, so that it is easy for you to read, otherwise it will shrink as soon as it is cold, and it will not be able to read.

As long as you take it out of your clothes, the volume of mercury will not change, and we will use centrifugal force to shake the mercury down, not to work on it, to press it back, so it will not burst the bottom of the mercury meter.

Because the temperature will drop after leaving the human body, so that the mercury is bounded by the curved tube (because the curved tube is very thin, thinner than other places, the tube cools the fastest, shrinks the fastest, and then it is disconnected), separated, the temperature drops, and the mercury on both sides shrinks to both sides and the mercury column is broken, so that the mercury in the glass tube will not return to the glass bubble, so even if it leaves the human body, the thermometer shows the temperature of the human body, so that the thermometer can leave the human body and read!

Throwing the thermometer does not need to be explained by physics, no matter how thin the neck is, it is still connected after all, and the mercury is thrown back into the glass bubble by throwing (the centrifugal force of physics).

Laboratory thermometer:

The principle of mercury thermometer is very simple - it is because of the heat rise and contraction of mercury, as for why not use water, because when the water is at 4 degrees, the heat expands and the cold also expands, and the expansion coefficient of mercury is relatively large, and the change is more obvious There is also alcohol inside, that is, the red kind The alcohol thermometer is suitable for measuring low temperature (about -78 +110 degrees), and the mercury thermometer is suitable for higher temperatures (about 15 300 degrees).There is also a kerosene thermometer.

There are also some industrial thermometers:

The principle of pressure thermometer is based on --- law of liquid expansion, that is, the pressure and temperature of a certain mass of liquid are linear under the condition that the volume is constant. The pressure and temperature of gases and vapors are also a certain function of the relationship, so the scale of the pressure thermometer should be evenly divided. A pressure thermometer consists of a temperature pack filled with a temperature-sensing medium, a pressure transfer element (capillary) and a pressure-sensitive element (spring tube).

The principle of infrared thermometer--- infrared thermometer consists of an optical system, a photodetector, a signal amplifier and signal processing. Display output and other parts. The optical system concentrates the infrared radiation energy of the target in its field of view, which is focused on the photodetector and converted into the corresponding electrical signal, which is then converted into the temperature value of the measured target.

The principle of thermocouple thermometer --- principle of thermocouple thermometer is to connect the galvanometer copper wire iron wire copper wire into a loop, at this time the two ends of the iron wire and the copper wire connection, will form two junctions (junction), if the temperature of the two junctions is different, voltage will be generated between them, and the micro amperometer can measure the weak current flowing through the iron wire and copper wire. To use a thermocouple as a thermometer, the following calibration must be performed first. Put one joint in ice water and the other joint in boiling water, and note the current intensity at this time, which is the current value at a temperature difference of 100.

For two known metal wires, the current value is proportional to the temperature difference between the two joints, and the measurement range is very large, i.e. from -200 to 1700, and the sensitivity is very high.

Explanation of the principles and advantages and disadvantages of 3 kinds of electronic thermometers.

Physical thermometers, whether alcohol or mercury, are used to stabilize the reading, so when they are produced, they have to press a very fine capillary part, commonly known as a neck, and the bottom of the place where the alcohol or watermark is stored is slightly higher. In this way, when the alcohol or mercury rises into the upper tube after being heated, it is difficult to automatically fall back, and the corresponding value of the carenoon can be easily recognized. Moreover, after leaving the body temperature, although the alcohol or watermark shrinks, it will be disconnected in the weakest part of the capillary, and the state is cautious and cannot automatically retract, and the cooling of the environment at this time cannot affect the degree of fall.

If you want to get these liquid objects back, you have to shake them. If it is not a thermometer but a thermometer, then all physical thermometers will not press out this finer necking part after stretching out the capillary, and they can be automatically lowered by the heat level when it is cold.

The principle of the thermometer is mainly thermal expansion and contraction.

The working substance of the thermometer is mercury. Its glass bubble volume is much larger than that of the thin tube above. Due to the influence of body temperature, the mercury in the bubble produces slight changes, and the expansion of the mercury volume causes a significant change in the length of the mercury column in the tube.

The temperature of the human body varies between 35 and 42, so the scale of the thermometer is 35 to 42, and the range of each degree is divided into 10 parts, so the thermometer can be accurate to 1 10 degrees. When reading, take it out of the armpit or mouth, at which point the temperature of the glass bubble beneath it will decrease. In order for his readings to still be representative of body temperature, a special design had to be made, which was a very thin tube between the glass bubble and the straight glass tube, the neck, as shown in Figure 1.

The lower part of the thermometer is close to the neck of the vacuole is a very narrow curved neck, when the body temperature is measured, the mercury in the glass bubble expands with the increase of temperature, squeezes through the thin tube to the straight tube, rises from the neck part to a certain position in the tube, and when the thermal equilibrium with the body temperature is reached, the mercury column is constant. When the outside temperature is low, the volume of mercury shrinks when it is cold, and it is disconnected in the narrow curved neck, so that the mercury in the thin tube cannot be returned to the glass bubble, and still maintains the height reached by the mercury column when it is in contact with the human body, so it still represents the temperature of the human body when it leaves the body. After use, the thermometer should be "returned to the table", that is, the upper part of the thermometer should be thrown down forcefully, so that the mercury that has risen into the tube can be returned to the glass bubble.

Other thermometers should never be shaken, which is a major difference between thermometers and other liquid thermometers.

There is a very thin curved tube in the thermometer that is a neck, function: the lower part of the thermometer near the vacue is a very narrow curved neck, when measuring the body temperature, the mercury in the glass bubble expands with the increase of temperature, squeezes to the straight tube through the thin tube, rises from the neck part to a certain position in the tube, and when the thermal equilibrium is reached with the body temperature, the mercury column is constant.

There is a hollow spherical bulge part at the bottom end of the thermometer, which is connected to a small hollow tubular part, and the hollow part is filled with mercury, and the temperature indication range is to (to.

When the temperature rises, the mercury expands and flows out of the bulging part and into the hollow tubular part. The temperature value is read out by means of an engraved mark on the thermometer. At the bottom of the spherical bulge, the connection with the hollow tubular part is a compact design (interception zone).

The thermometer is an instrument used to measure body temperature, in the past, people often used mercury thermometers to measure, but mercury thermometers are troublesome to use, and the harm to the human body is great, now many people are using electronic thermometers, electronic thermometers measure temperature quickly, easy to use, and cause little harm. So what principle is the thermometer based on?

Mercury thermometer is made according to the principle of thermal expansion and contraction of mercury, the structure of the thermometer is very special, in the place where the glass bubble and the thin tube meet, there is a very thin neck. When the thermometer leaves the human body, the mercury becomes cold and shrinks, and the mercury column is disconnected at the neck, and the mercury on it cannot be returned, so the thermometer can continue to display the body temperature after leaving the human body.

The electronic thermometer uses the temperature sensor to output electrical signals, directly output digital signals or convert current signals (analog signals) into digital signals that can be recognized by the internal integrated circuit, and then display the temperature in digital form through the display (such as liquid crystal, digital tube, LED matrix, etc.), which can record and read the highest value of the measured temperature.

A thermometer usually measures the temperature of the body by measuring the armpits, mouth, and rectum. Among them, the armpit measurement method is the most common one

1.If the mercury thermometer is not used alone, wipe it dry with an alcohol swab before measuring;

2.Throwing the mercury in a traditional mercury thermometer below 35 degrees;

3.The mercury thermometer is clamped under the armpit, and the mercury needs to be searched in the middle of the armpit;

4.Do not release your arms or move when clamped;

5.After measuring, take out the mercury thermometer to see the results, and then clean it.

Reading method: Hold the tail of the thermometer with one hand, that is, away from the end of the mercury column, so that the eye and the thermometer are at the same level, and then slowly turn the thermometer, and the corresponding temperature value can be read when you see the thick mercury column from the front. Be careful not to touch the mercury end of the thermometer with your hands, as this will affect the mercury column and cause inaccurate measurement.

In order to solve this problem, the upper part of the thermometer was made into a cylinder with a triangular cross-section and a cylindrical surface on the side. In this way, the side of the triangular prism is used to refract and amplify the light reflected from the mercury column at the junction between the glass and the air.

Measurement of oral temperature, rectal temperature and axillary temperature. Today we talk about the armpit temperature measurement method, first put the sterilized thermometer and mercury end in the armpit of the person being measured, clamp it, take it out after 10 minutes, and read out the count by looking at the thermometer scale with both eyes. The normal range is 36-37 degrees.