How the bellows pressure gauge works
Bellows pressure gauges (bilose pressure gauges) are thin-walled metal cylinders with deep torsions, one end of which is sealed and the other end open. The closed end can move freely while the open end is fixed.
Features of Blues
When pressure is applied to the end of the package, as in the animation below, the bellows are compressed. The closed end will move upwards and the link, ie the rod between the closed end of the rings and the transfer mechanism, will go up and rotate the hand. Compared to diaphragm and capsule pressure gauges, the following gauges have the advantage of length. They have a longer impact and produce larger forces. The number of rings can vary from 5 to 20. Most loops mean longer impact length and larger measuring range.
The diameter of the rings determines the force that can be transmitted to the transmission mechanism. Therefore, a larger diameter is chosen to measure very low pressures so that it can have a sufficient surface to operate the measured pressure. A larger diameter also means higher sensitivity and improved accuracy. Blues may be made of different materials. . Each of these materials has its own hardness, which is proportional to the Young’s modulus of the material used, and inversely proportional to the outer diameter and number of loops. The relationship between pressure and deflection is linear and only if Reaching the elastic limit is impaired.
The amount of deviation can be expressed as follows:
δ = Deviation from rings
n = number of complexities
Ae = effective level of bellows
Pressure = P
R = average radius of the rings
E = Young’s modulus
t = wall thickness
Beloses are sensitive to changes in temperature, hardening, deflection, friction, hysteresis, and vibration. To compensate for these problems, a blues ring is usually used in combination with a calibrated spring. As a feature, the measuring range Can be determined by selecting a spring. The choice of a strong spring leads to the measurement of a large range, which can make it possible to measure large pressures with a pressure gauge .
For this reason, most circular gauges have springs. The spring also protects against excessive contraction or stretching, thus extending its life.
Range of gauge pressure gauge
Belose pressure gauge The pressure range is mainly determined by the effective area of the rings and the spring slope and to some extent by the material from which the rings are made. To measure higher ranges, higher measuring ranges with smaller diameters are used. This type of pressure gauge can be used to measure different types of pressure, but is generally used to measure low pressures, from vacuum to About 3.5 barg (pressure barg) Pressure difference gauges consisting of 2 opposing bellows with springs of heavy internal range that can be used at much higher static pressures (up to 750 bar) with a range of 69 bar pressure difference.
Blouses are usually made of thin-walled seamless tubes under hydraulic pressure, or are mechanically rolled. Wall thicknesses from 0.008 to 0.3 mm are used for instrumentation purposes. Can be produced from beryllium copper, phosphorus bronze, monel, inconel and stainless steel. When using phosphorus bronze, the bubbles have good hysteresis properties, while beryllium copper has better mechanical properties. Stainless steel is used when the blouses come in contact with corrosive materials, but it has the advantage that it has less elastic properties.
Relative pressure sensors
Belose pressure gauges may be used in compression and contraction modes. When relatively low pressures are measured, ebels are usually used in expansion mode. The process pressure then enters the inside of the loops and causes the loops to increase. If larger pressures are measured, it is best for the process pressure to operate on the outside of the loops.
In this case, the rings are compressed. When measuring larger pressures, the rings are always equipped with a heavy spring. has it. So both pressure sounds work in compression mode. The only difference between the two is the position of the springs, which can be located on the inside of the blouse or on the outside.
Such sensors are also used to measure pressure differences. It is only necessary to replace the atmospheric pressure in the blues with the pressure of the second process. Positively be different. If the hand turns to the left, it is under low pressure, on the right means too much pressure.
To measure absolute pressure, we need two bellows. The first blues is a reference with a complete vacuum. The second bellows is for measuring the pressure of the process. Because these absolute pressure sensors are commonly used to measure low pressure, the bellows are not equipped with calibrated springs and are used in the expansion state.
As the process pressure increases, the bellows are pulled. The deflection of the rings is transmitted to the hand through the transfer mechanism. Absolutes exist in two different states. On the one hand, there is the principle of beam balance and on the other hand, there is the principle of reciprocity, as in the pictures below.
Absolute pressure sensors
Just as the pressure difference can be measured with a single bellows, as described above, we can also use a dual bellows. The low pressure of the process is connected to the first bellows while the high pressure of the process to The second bellows is attached. Both of these process pressures exert a force on the effective area of the bellows applied to them. The resulting force rotates the hand.
Belose pressure gauge: pressure difference
These measuring devices can be designed to measure pressure differences up to 70 bar or more, with a static pressure limit of more than 750 barg applied on both sides of the device. At such high pressures, bellows with a diameter Small ones are preferred, which are optionally provided with an internal or external spring. The accuracy will be lower due to the use of smaller diameters. At high pressure differences, the accuracy is about 1.5% of the measuring range . At lower pressure differences of up to 1 bar, with an accuracy of 0.5% of the measuring range is possible.
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