1. Principle: It is the working principle diagram of the most commonly used single-coil spring tube. One end of the spring tube is closed and the other end is open. The closed end can move freely, and its displacement is used as the output signal. It is called The output end. The open end is fixed on the outer shell of the pressure gauge, and the measured fluid passes through the spring tube, so it is called the input end.
When the measured pressure P is input from the fixed end, the elliptical cross-section of the spring tube tends to be circular under the action of the internal pressure, forcing the free end of the spring tube to move from point B to point B' .The displacement along the center line is the radial displacement x.
The sensitivity of the spring tube is the displacement generated by unit pressure. When designing and manufacturing the spring tube, it is always hoped that the sensitivity will be constant within a large range of the measuring vessel, and the displacement and pressure will maintain a linear relationship. Theoretically, the above formula can be used to calculate. In fact, the performance of the ballistics has a lot to do with the materials and techniques. Therefore, it is necessary to determine the relevant parameters through preliminary design. After manufacturing, calibrate the instrument using the direct comparison method. The material of the spring tube is usually made of tin, copper, stainless steel, etc.
2. Structure: The structure of the spring tube pressure gauge is shown in Figure 4-15. It mainly consists of a spring tube. It is composed of remote transmission water meter connecting rod mechanism, indicating mechanism, etc.
The measured pressure passes through the spring tube, causing its free end to move upward. The connecting rod drives the sector wheel to rotate. The sector wheel drives the center gear coaxial with the pointer to deflect clockwise. The pointer is then at The corresponding measured pressure value is indicated on the dial.
The hairspring 5 is used to eliminate the gap in the transmission mechanism. Since there is a linear relationship between the displacement of the free end and the measured pressure, the scale scale of the dial is uniform.
The spring tube pressure varies with the size of the spring tube and the materials used. It can be made into various specifications to adapt to the different measurement ranges required in various engineering fields. 1 Its measuring range is 50- IO6KPa. For 104K Pa The low-pressure spring tube with F is usually made of tin-phosphor bronze. The radius of curvature, central angle, inner diameter of the tube and the ratio of the long and short axes of the tube are large. The tube wall is thin to improve sensitivity. That is, the closed end of the spring tube has a Larger displacement output (generally 3-5mm). For high-pressure spring tubes above 104K Pa, alloy steel is usually used. The curvature radius and central angle of the tube, the inner diameter of the tube and the ratio of the long and short axes are small, and the tube wall is thicker. Therefore, the displacement of the small end is also small (generally about 1. 5 ni, m ni).
The vertical error of the spring tube will only occur when the temperature used by the instrument is inconsistent with the degree a during indexing. Therefore, the project only stipulates the use of the im degree range, without correction and compensation. It is only considered when the im, degree changes greatly or when the tip density is measured.
Single-coil spring tube pressure gauges are divided into general industrial gauges and standard gauges. The accuracy level of general industrial gauges is 1.5. 2.5. 4. The allowable basic differences are the upper limit of measurement (full *1%. 11.5%. 12.5% ??and 1.4% of the measuring range). The squeeze level of the standard table is 0.25. 0.4. 0.6 level. The allowable basic errors are respectively ±0.25%. 10.4% and 1.0.6 of the upper limit of the measuring range. %. No matter what kind of product it is, it should be verified on time according to the relevant verification regulations before it can be used.
3. Calibration of single-turn spring tube pressure gauge: The following mainly introduces several issues related to the calibration.
(1) Calculation of the allowable basic error: For claw force gauges and vacuum gauges, the allowable basic error is calculated as a percentage of the upper limit of measurement; while for pressure and vacuum gauges, the absolute allowable error of the upper and lower limits of measurement is used. Calculated as a percentage of the sum of values.
(2) Selection of calibration points: The calibration points should be selected evenly within the measuring range of the instrument. Generally, industrial pressure gauges have no less than 4 points except for zero point; standard pressure gauges and vacuum gauges generally have at least ten There are no less than three pressure parts of the pressure and vacuum gauge; there are no less than 3 vacuum parts. The calibration point is generally selected at the large scale point with numbers.
(3) Calibration medium: Under normal circumstances, the upper limit of the calibration measuring vessel is less than or equal to 250K P. The following standard pressure gauges and industrial instruments must use air or inert gas as the working medium. This is because using gas medium makes it easier to check whether the spring tube is open and welded. In addition, it can also be used without oil at the output end of the tube when using oil medium. The residue causes the zero point drift of the instrument.
(4) During the calibration, the pressure reduction in the rising hall must be uniform. The pressure resistance test must be carried out at the upper limit of the measurement portion. Generally, industrial meters and vacuum gauges have a pressure resistance verification time of 3 minutes. ·The pressure resistance test time of standard clothing is 5 minutes. This is because the spring tube has elastic hysteresis, elastic aftereffect and other characteristics, and these characteristics can only be fully exposed after the maximum working pressure king has been working for a period of time. At the same time, it can also Check the leakage condition of the pipe.
(5) Correction of the liquid column height difference: When calibrating the standard pressure bomb below 1 MPa, the liquid column height difference must be corrected.
The calibration work is carried out on the piston pressure gauge. When installing, the piston lower aid of the piston pressure gauge must be on the same horizontal plane as the pointer axis of the test meter, so that the pressure of the medical force gauge and the test meter can be aligned. The Mei Er calibration point is under the same pressure. This is because the spring tube of the 3L pressure gauge has a higher sensitivity. If it is not on the same horizontal plane, additional errors will occur on the measured MOA produced by the liquid column. If they are not on the same horizontal plane, the liquid column height difference should be corrected.
Two methods can be used for correction. One method is to first calculate the pressure correction torque AP generated by the height difference of the liquid column, and then substitute this value into the arithmetic mean of each calibration point.