Whether the verification of the duplex pressure gauge is in place will greatly affect the safety production and daily operation of the enterprise. The pressure gauge should be selected scientifically, and its appearance, zero position and indication error should be checked. In the process of calibrating the pressure gauge, data errors such as pointer, check point out of tolerance and indicated value will be processed and corrected. After properly solving the problems found in the pressure gauge verification, the pressure gauge must be re-verified according to the requirements of relevant regulations.

Because the pressure gauge can measure the pressure value, it is widely used in industrial technology measurement and process control. It is not only a very important safety accessory for industrial special equipment (boilers, pressure vessels, etc.), but its verification will greatly affect the safety production and daily operations of the enterprise. Because the instrument requires many verification items and the process is cumbersome, especially when the pressure gauge is checked centrally, the workload of the verification personnel will be greatly increased. Therefore, it is very necessary to simplify the operation process to shorten the verification time.

1. The scientific choice of Duplex Pressure Gauge

The internal structure of the pressure gauge is not very complicated, the manufacturing cost is not high, and the measured value can be displayed accurately and intuitively during the work. Select a suitable pressure gauge model, and install and maintain it correctly, which will make it measure The value is more accurate, which can greatly extend the service life of the pressure gauge. For the currently commonly used pressure gauges, the full-scale indication scale is between up to times the Z high working pressure that the vessel can withstand, and twice Z is suitable. At the same time, the diameter of the pressure dial must exceed 10 cm, and a red line scale is marked on the dial, so as to objectively display the Z-high working pressure of the container system.

2. How to calibrate the pressure gauge correctly

Before using the pressure gauge, the verification work must be carried out by the country's regular metrology department. If the result obtained is qualified, a written certification must be given. The environment where the verification is located must meet the following requirements: the relative humidity is less than 85%, the temperature is (20?5), and the pressure is normal atmospheric pressure. The pressure gauge to be checked should be allowed to stand for 2 hours in an environment that meets the above requirements before it can be checked. The following 3 items need to be checked.

1. Check the appearance

The appearance of the pressure gauge must conform to the JJG52-2013 standard, especially the appearance and structure of the pressure gauge. The various parts of the pressure gauge should be installed in the designated position, and ensured to be firm and not loose. The connection of the pressure gauge is not allowed to have significant damage and Burr, its exposed surface is also not allowed to have significant scratches and defects. The pressure gauge must be marked with the following content: product name, production date, factory number, and measurement range, accuracy level, measurement number and unit, etc.; indicating device Aspect: The outer layer of the pressure gauge cannot be equipped with colored glass, and there should be no problems that affect the reading. The surface of the index plate must be smooth and not dented. The numbers and related signs must be clearly displayed. In addition, the pointer indicates The end should not be too wide, and its width should not exceed the width of the graduation line. Some pressure gauges can be zero-adjusted, and the stability and flexibility of the zero-adjustment device need to be ensured.

2. Check the zero position

When the pressure gauge is equipped with a stop pin, the pointer must be closely connected to the stop pin when the atmosphere is open. The value of the "indentation" should meet the requirements of the relevant specifications. When the pressure gauge is not equipped with a stop pin, it is in the atmosphere. In the case of communication, the pointer must be in the zero mark, and the width of the zero mark must be less than twice the absolute value of the maximum allowable error required by the specification.

3. Verification and indication error

By adopting the method of direct comparison, to compare the indication value of the pressure gauge to be checked and the indication value of the pressure gauge, the indication value should be determined according to the numbered graduation line to determine the indication error verification point; when verifying each verification point, correct Tap the front and back of the case, and the maximum change indication of the pressure gauge should not exceed half of the absolute value of the maximum allowable error. At this time, after tapping the case, carefully record the displayed value; check the indication error The verification done with the return error shall be implemented together, and at the same time, the return error shall not exceed the specified maximum allowable error.

3. Data processing and correction in Duplex Pressure Gauge verification

In the process of verifying the pressure gauge, the following problems are prone to occur, which is not conducive to the smooth completion of the verification work. Data processing and error correction must be carried out, mainly including the following aspects.

1. The pointer cannot be returned to zero

If the pointer is bent or unstable, use tweezers to correct the bent part. For the unstable part, tap it first before verifying. If the balance spring torque is insufficient, leave the mesh of the central gear and the sector gear. , Rotate the center gear shaft in a counterclockwise direction, so that the torque of the balance spring can be increased.

2. Skipped stitches or delayed stitches

If there is a collision between the pointer and the watch glass or the dial from time to time, the following methods can be used to correct it, appropriately increasing the shaft hole on the pointer or thickening the washer part under the glass. When the central gear shaft is bent, which causes the shaft diameter to be inconsistent and concentric, the gear can be removed and then straightened with a wooden hammer or flat-nose pliers. If there are impurities in the gear meshing part, remove the two gears and clean them.

3. A certain verification point is out of tolerance

In accordance with the relevant regulations of the verification, the process of verifying the pressure gauge must be implemented according to the graduation line of the marked value above. Therefore, if there is an out-of-tolerance phenomenon in a certain scale, you must stay in the scale. This will help to check the joint working conditions of different parts in the scale point. The following aspects should be observed: Whether the meshing point appears Damage, whether the drive shaft hole is blocked, whether all foreign objects are eliminated, whether the connecting rod is in a flexible state, etc., the main reason for the positive error of a certain point is that there are impurities and burrs at the tooth meshing point. Errors occur mainly due to defects inside the teeth or damage to the shape. At this time, they need to be replaced or repaired.

4. The indicated value cannot be stable, and the pressure drops significantly

At this time, first check whether there is oil leakage at the contact part of the

pressure gauge and the pressure gauge calibrator. If there is no oil leakage and there is no problem with the calibration instrument, then it can be concluded that there is leakage inside the spring tube, and the scale plate must be removed for a deeper inspection. If it is due to the continuous action of pulse pressure that the spring tube is prone to fatigue, or the seal at both ends is not tight, you can re-tighten or repair the sealing position at both ends. If there is a crack, then Change another pressure gauge.

5. The error of the pressure value is not uniform

If the spring tube is deformed and loses its due role, so that the pressure no longer increases with the increase in displacement, a new spring tube needs to be replaced. If the distance between the free end of the spring tube and the sector gear is not adjusted well, or the wheel-to-bar transmission ratio is not adjusted well, it needs to be adjusted again. If the contact position between the gear base plate and the splint is wrong, loosen the screw first and drive the splint in a counterclockwise direction.

6. The pressure gauge pointer stops rotating

When the pressure value is at the maximum allowable value measured by the pressure gauge, if the pointer in the pressure gauge is still at rest, it indicates that the spring tube has not received pressure. At this time, it is necessary to check whether the passage of the gasket joint part connected with the pressure gauge calibrator is in a smooth state. If no problem is found after inspection, then it can be concluded that the inside of the pressure gauge is blocked, and it needs to be

disassembled and then dredged. After dredging, the verification can be done.

4. Verification

After properly solving the problems found in the pressure gauge verification, the pressure gauge must be re-verified in accordance with the requirements of the relevant specifications, so that the measured value will be more accurate. If after continuous adjustment, the indication error has not been eliminated, or other errors have occurred, then a downgrade verification of the pressure gauge is required. If the pressure gauge still does not meet the specified requirements after the downgrade verification, then It can give the conclusion that the verification is unqualified, and at the same time, give the written document of the unqualified verification.