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Barometer used in laboratory

1. What is barometer?
    1.1 Working principle of barometer
2. Aneroid barometer
    2.1 Working principle of aneroid barometer
    2.2 Use of aneroid barometer
    2.3 Notes on aneroid barometer
3. Mercury barometer
    3.1 Working principle of mercury barometer
    3.2 Structure composition of mercury barometer
4. Barometric altimeter
5. Use of barometer
6. How to buy barometer?

What is barometer?

Barometer is an instrument used to measure air pressure.

Working principle of barometer

The principle of the barometer is that there is a calibration lever inside the tube body for taking pressure readings.

The calibration rod is located at the top of the piston and is not connected to the piston, but to the plug. When the piston moves to the right, it will push the calibration rod. When the pressure is released, the piston will move back to the left and the calibration rod will stay at its maximum displacement, at which point the pressure reading can be taken.

The method to view the air pressure of the barometer is as follows.

a. Press the snap and align the wheel valve.

b. Push forward to the end, the valve nozzle fixed, and then release the clasp.

c. The digital barometer generally has an activation button on top of the instrument display. After pressing it, the display will light up, which can play the role of a bright screen when the light is not very sufficient.

d. Then you can see if the data values are within the normal range.

Aneroid barometer

Aneroid barometer is an instrument that uses an empty metal box as a sensing element to measure atmospheric pressure by balancing the elasticity of the empty box with atmospheric pressure.

Aneroid barometer is a kind of atmospheric pressure measuring instrument with a deformation element for induction. It has the advantages of being easy to carry, accurate measurement, a wide range of pressure measurements, easy to use and maintain, and no mercury pollution. It is widely used in the fields of meteorology, military, aviation, navigation, agriculture, measurement, geology, industrial and mining enterprises, and scientific research, and has become a conventional instrument for measuring atmospheric pressure. Its disadvantage is that the accuracy is lower than the mercury barometer, and with the use of time to increase the balance point has drift changes.

Working principle of aneroid barometer

A thin film cassette made of elastic metal is used as the sensing element to convert the atmospheric pressure into the elastic displacement of the cassette and drive the pointer through the lever and transmission mechanism. When the clockwise deflection, the pointer indicates the change of air pressure increase and vice versa, which indicates the change of air pressure decrease. When the elastic stress of the empty box is balanced with the atmospheric pressure, the pointer will stop moving and the air pressure value indicated by the pointer is the atmospheric pressure value at that time.

Use of aneroid barometer

a. Place the empty box barometer horizontally when using it.

b. Before reading, gently tap the instrument shell or surface glass with your finger to eliminate the frictional stress in the transmission mechanism.

c. Observe the pointer and the mirror pointer overlap, then the pointer refers to the value of the barometric pressure, and the reading is accurate to one decimal. The read air pressure value is revised before the air pressure value.

d. Temperature revision. The change in ambient temperature will have an impact on the elasticity of the instrument metal, so the temperature must be revised.

e. Index correction. Because of the nonlinearity of the air box and its transmission, when the air pressure changes, it will produce an indication error, so it is necessary to carry out the indication revision.

f. Supplementary revision. To eliminate the impact of the remaining deformation of the air box with the time difference on the indicated value, the supplementary revised value △pd is obtained from the calibration certificate. the supplementary revised value shall not exceed six months of use and must be re-calibrated when it exceeds.

Notes on aneroid barometer

According to the requirements of the World Meteorological Organization, the aneroid barometer must meet the following requirements.

a. There must be temperature compensation measures to reduce the effect of temperature. On this basis, when the temperature changes 30 degrees Celsius, the change in the reading of the aneroid barometer should not exceed 0.5 hectopascals.

b. The scale revision value of any point on the aneroid barometer scale should not exceed ±0.5hPa, and at least maintain a year does not exceed.

c. When the air pressure changes 50hPa and then returns to the original state, the hysteresis of the reading of the aneroid barometer should not exceed 0.5hPa.

d. After normal movement, the aneroid barometer still meets all the above requirements.

Mercury barometer

Mercury barometer was invented by Moreland in 1670 and improved by German A. Sprung. It is an instrumental device for measuring atmospheric pressure.

The principle of measurement is derived from the Torricelli experiment. The principle of measuring atmospheric pressure is derived from Torricelli's experiment. The weight of mercury in a column of glass tube inverted in a mercury bath is balanced with the surrounding atmospheric pressure, and the height of the column of mercury is used to express the atmospheric pressure. One standard atmospheric pressure is equal to a 76 cm column of mercury.

Working principle of mercury barometer

The lower end of the barometer mercury tube is inserted into the mercury tank mercury but is not fixed. The upper end of the mercury tube is closed to vacuum. There is a hanging ring on it, hanging on the hook of one end of the balance so that it hangs down naturally and remains vertical.

The mercury in the mercury tank supports the height of the mercury column in the mercury tube, on the other hand, the top of the mercury tube plane also from the outside to accept the role of air pressure, but not from the tube and the role of pressure, so the top of the mercury tube by the force of air pressure to balance the weight of his end. Balance with the size of the atmospheric pressure and move, you can measure the change in air pressure.

Structure composition of mercury barometer

The mercury barometer is a device that uses the Torricelli tube to determine atmospheric pressure. The mercury tank at the bottom of the glass tube is replaced by a leather capsule with an ivory needle that can be adjusted to indicate the mercury surface, called the "Fortin type mercury barometer". Outside the glass tube with a metal sheath, the sleeve is engraved with a scale to measure the height of the mercury column. At the top of the mercury trough another ivory needle, the tip of the needle is located just outside the zero point of the scale, and another leather bag is the bottom of the mercury trough.

When using, lightly turn the spiral under the leather bag, so that the surface of the mercury in the slot is exactly with the ivory needle tip contact (that is, with the zero point of the scale on a horizontal line), and then read out the height of the mercury column by the scale on the tube. This height is the size of the local atmospheric pressure at that time. In addition, there is no need to adjust the ivory needle with the observatory barometer, which can measure low-pressure mountains with the barometer, as well as the ship's rocking insensitive to the barometer for navigation.

Barometric altimeter

Barometric altimeter is an instrument placed in the aircraft to measure the altitude of the aircraft flight by observing the air pressure in the relationship between air pressure and altitude during the aerial survey.

The pressure in water is determined only by the water depth, P=ρgh. Divers can simply estimate their dive depth from the current pressure. Atmospheric pressure is similar and is generated by the gravity of the air at the surface. As the altitude rises, the thickness of the air at the surface decreases and the air pressure falls. So you can measure the atmospheric pressure at the location and compare it with the standard value to get the altitude value, which is the basic working principle of barometric altimeter.

Use of barometer

a. Slowly rotate the spiral to adjust the height of the mercury surface in the mercury tank so that the mercury surface in the tank rises. Use the reflection of the magnetic plate behind the mercury trough, watching the mercury surface and the gap between the ivory tip, until the mercury surface and the ivory tip are just in contact, and then gently buckle the top of the copper tube with your hand, so that the upper part of the glass tube mercury surface convex surface normal. Wait a few seconds, wait for the ivory needle tip and the mercury surface to contact without change.

b. Adjusting the vernier. Turn the spiral next to the barometer, so that the vernier scales up, and make the lower edge slightly higher than the mercury surface. Then slowly adjust the vernier until the bottom edge of the vernier scale and its back side of the bottom edge of the metal sheet while tangent to the top of the convex surface of the mercury. At this point, the position of the observer's eye should be on the same level as the edge of the bottom edge of the vernier scale before and after the two.

c. Reading the height of the mercury column. When the zero line of the vernier ruler and the brass ruler in a scale coincides, the brass ruler on the scale of the value is the atmospheric pressure value, do not need to use the vernier ruler. When the zero line of the vernier scale does not coincide with the brass scale on any scale, then the vernier scale zero line on the scale is the integer part of the atmospheric pressure value (mm). And then from the vernier scale to find a scale that happens to coincide with the scale on the scale, then the value of the vernier scale on the scale is the decimal part of the air pressure value.

d. Finishing work. After noting down the reading, move the bottom spiral of the barometer down so that the mercury surface leaves the ivory needle tip. Note down the temperature of the barometer and the attached card on the barometer instrument error value, and then correct.

How to buy barometer?

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