The digital pressure gauge has a wide application range and a large number of uses. Whether it is used as a measurement standard for volume measurement or for working measurement instruments, it is convenient and efficient, but some problems in use should be noted. In this paper, the pressure gauge manufacturer Jinli instrument technicians carry out the stability of the digital pressure gauge, the maximum tolerance, the influence of the digital pressure gauge control technical indicators with control function on the measurement results, the requirements of the pressure transmission medium and the measurement environment. Discussed to ensure that the digital pressure gauge output is reliable and accurate.
The digital pressure gauge is a pressure sensor that acts on the pressure sensor, and outputs a corresponding electrical signal or digital signal, which is processed by the signal processing unit and directly displays the pressure value of the pressure gauge on the display in digital form, and can be used for measuring absolute pressure, Gauge pressure and differential pressure. There are many types of digital pressure gauges, a wide range of applications, a large number of uses, and simple and convenient operation. In order to use digital pressure gauges, some problems in their use must be emphasized.
1. Stability is an important technical index of digital pressure gauge as a measurement standard. In order to ensure the stability of the digital pressure gauge as the main standard, JJG875-2000 "Digital Pressure Gauge Calibration Regulations" specifically added a stability test. The procedure stipulates that the digital pressure gauge with an accuracy level of 0.05 or higher, the indication value change between two adjacent verification periods shall not exceed the absolute value of the maximum allowable error. If the stability check is unqualified, the digital pressure gauge verification period is generally not more than half a year, and the test certificate indicates that the instrument cannot be used as the main standard for the value transfer.
2. The maximum allowable error during mass transfer should meet the requirements of the mass transfer ratio. In the process of using the digital pressure gauge, you should not only look at the accuracy level of the digital pressure gauge, but also calculate whether the maximum allowable error meets the requirements of the mass transfer ratio. The accuracy level specified in JJG 875-2005 "Digital Pressure Gauge Verification Procedure" uses the reference error. The reference error is related to the range. For the same level of digital pressure gauge, the maximum tolerance will vary greatly due to the different ranges. Table 1 calculates the maximum allowable error for the 0.01 range of different range digital pressure gauges.
The same digital pressure gauge of 0.01, the maximum tolerance of the range of 7000 kPa is 70 times the maximum allowable error of the digital pressure gauge with the range of 100 kPa.
3, pay attention to the impact of digital pressure gauge control technical indicators with automatic control function Many digital pressure gauges now have automatic control functions, its control principle, control mode, control metering performance is very different, its control technology indicators The impact on the measurement results should be brought to the attention of everyone. When using digital pressure controller (digital pressure gauge with automatic pressure control function), the influence of automatic control performance and technical indicators on the measurement results should be analyzed. Table 2 is the technical indicators of different types of pressure control sensors matched with a series of digital pressure controllers produced by a company. Some of them must be considered when analyzing the uncertainty of evaluation, such as the default dynamic control retention limit: the current range ±0.005%. This retention limit can be changed, and the scope of change is limited by its own control ability and cannot be reduced indefinitely.
4. Pay attention to the influence of pressure transmitting medium. The digital pressure gauges of different types and different types of sensors have different requirements on the pressure transmitting medium. If the pressure transmitting medium is not used as required, it may affect the measurement accuracy, and may also damage the digital pressure gauge. . Therefore, the digital pressure gauge must pay attention to the pressure transmitting medium when it is used. The digital pressure gauge specification should have clear requirements for its pressure transmitting medium. In practice, the pressure transmitting medium often contains certain oil and dirt, and although it is periodically filtered or frequently replaced, it cannot be completely removed, which adversely affects the pressure measurement and calibration. Therefore, the removal of oil and dirt contamination has become another requirement for pressure transmitting media. In order to meet this requirement, in recent years, some companies have studied the removal of pressure medium pollution, and proposed a solution to filter oil and impurities in the pressure measurement and calibration system [3], and developed various types of pressure filtration. The problem of the influence of pressure medium fouling is better solved.
In pressure testing, pressure media are mainly divided into gas and liquid media. Oil pollution is the main pollutant of the gaseous medium, while dirt and impurities are the main pollutants of the liquid medium. Therefore, the pressure medium is different, the working pressure is different, and the filter selection is different, mainly having the following parameters and performance requirements.
(1) Filtration accuracy Filtration accuracy indicates the degree of filtration of particles of different sizes in the gas or liquid medium. Different media, different filter accuracy requirements, but also filter applications to choose Filters with different filtration accuracy.
(2) Descaling capacity The scale-removing ability mainly reflects the ability to discharge the filtrate. The fouling capacity is related to the order of the operating process, and the filter should have sufficient fouling capacity as long as the operation is satisfied.
(3) Nanoscale capacity requirement The nanoscale capacity mainly reflects the sufficient capacity of the filter chamber for the amount of filtrate therein, thereby ensuring that the filter does not need to be removed and washed for a sufficiently long period of time. The nanoscale capacity is related to the content and discharge of oil impurities. Under the premise of ensuring timely scale removal, the nanoscale capacity is generally greater than the amount of filtrate.
(4) Filtration Strength The filtration strength is the filtration capacity of the filter against the impact of the pressure medium. When developing and using the selection, the filtration strength is required to be greater than the working pressure.
(5) Corrosion resistance Corrosion resistance is the filter capacity of the filter to resist corrosion of dirt and debris during a sufficiently long period of time. Corrosion resistant materials are generally used to enhance corrosion resistance.
(6) The ability to disassemble and disassemble is a performance requirement that is considered in consideration of the convenience of the filter chamber for accommodating dirt and debris, and can be easily removed and washed.
5. The influence of the measurement environment The environmental factors that have a great influence on the measurement results of the digital pressure gauge are: ambient temperature, humidity, electromagnetic interference, air flow, and changes in atmospheric pressure. The influence of temperature is the largest and most common among various factors, and it affects almost all sensors [4]. The digital pressure gauge in use should meet the requirements of the instruction manual.
6, other problems in use For battery-powered portable, handheld digital pressure gauges, you must also pay attention to the impact of battery voltage. When the battery voltage is too low or too high, it may bring additional errors. Therefore, in order to maintain a good working condition of the digital pressure gauge, the battery should be kept charged. Some digital pressure gauges are also related to local gravitational acceleration, which is often overlooked. Most digital pressure gauges are measured independently of gravity acceleration, but because of the variety of pressure sensors, the principles vary, and some digital pressure gauges are related to local gravitational acceleration. The different placement of the digital pressure gauge (horizontal, tilt) also has an effect on its output pressure. In the use of digital pressure gauges, it is better to check the work on time. Unlike digital pressure gauges and liquid pressure gauges, digital pressure gauges are not easy to be discovered, so pay attention to the period check of digital pressure gauges. The results of the verification period are made with a piston pressure gauge or a liquid pressure gauge, and the results are more reliable.
7. Conclusions The use of digital pressure gauges should pay attention to the above problems. Measurement verification and calibration personnel should develop good work habits. The laboratories that carry out verification and calibration should strictly implement the regulations and establish digital pressure gauge technical data files, including The above-mentioned technical data files should be established for each digital pressure gauge, such as the resume used, the factory calibration (calibration) certificate, and the previous verification (calibration) certificate and the maintenance operation manual (instruction).
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