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Pressure instrument selection, installation and use precautions
First, the pressure (differential) proper selection of instrumentation
Pressure instrumentation to determine the correct selection of instruments including the type, scale, scope, accuracy and sensitivity, dimensions and the need for remote and have other functions, such as instructions, records, regulation, alarm and so on.
The main basis for selection:
1. Process of measuring the production process requirements, including range and accuracy. In the static test (or change slowly) in the case, provided the maximum test pressure gauge used for two-thirds of full scale; the pulse (wave) under pressure, the maximum use pressure gauge measured the pressure full-scale value of one half.
Common pressure instrumentation grade accuracy with 0.4, 1.0, 1.5 and 2.5 four-level, etc., from the accuracy requirements of the production process and the most economic point of use. Maximum permissible error of the instrument is the instrument's range and accuracy rating percentages of the product, if the error exceeds the accuracy of process requirements, you need to replace the high accuracy level of the pressure gauge.
2. The nature of the measured medium, such as state (gas, liquid), temperature, viscosity, corrosion, pollution law degree, the degree of flammable and explosive. Table such as oxygen, acetylene table, with "no oil" signs, designed for special media corrosion gauge, temperature gauge, diaphragm pressure gauges, etc.
3. On-site environmental conditions, such as ambient temperature, corrosion, vibration, humidity and so on. Environmental conditions, such as for vibration shock pressure gauge.
4. For staff observation. According to the location of instrumentation and lighting to choose the table diameter (size) range of the instrument.
Second, the pressure (pressure) test instrumentation and calibration
Instruments in use, you must test and calibration. Long-term use of the instrument should also regularly test its use should be considered cycle frequency and extent of focus. When the instrument with a long-distance transmission systems and the second instrument, the instrument should be together with the second test, calibration.
Third, the pressure (DP) instrumentation and related matters properly installed
For pressure testing, in fact, a measurement system needs to achieve. To achieve accurate measurement, in addition to the proper instrument selection and verification (calibration), but also must pay attention to the whole system is properly installed. If only the instrument itself is accurate, the indication does not fully represent the actual parameters measured media, because the measurement system error does not mean that the instrument error.
Correct installation, including pressure port opening position, the rational connection pipe laying and installation location of the correct instruments and so on.
1. Position of pressure taps
(1) in the pipeline to avoid bending, bifurcation, and bundle formation of vortex flow region.
(2) When a prominent object in the pipeline (such as temperature components), the pressure port should be taken in front of it.
(3) When you must take the pressure regulating valve in the vicinity, if the pressure port at its front, the distance and the valve should not be less than 2 times the diameter; if the pressure port is in the following, the distance and the valve should be not less than three times the diameter. (4) for a wide container, pressure port is in fluid flow should be smooth and non-vortex area. In short, the process does
Given pressure port location should be able to ensure that the measured process parameters to be selected.
2. Connection pipe laying
Horizontal section connecting tube should be a slope, in order to facilitate condensate liquid or gas. When the measured medium is gas, the tube should be inclined to take the low pressure port direction; When measured medium is liquid, the tube should be tilted to the direction of pressure measurement instruments; When measured parameters to a smaller differential value tilt degree may be slightly larger. In addition, the upper and lower corner in the catheter, the catheter should be based on the media situation, placed at the lowest point of the liquid condensate drainage device or devices at the highest placement of the exhaust, to ensure a long period of time not due to accumulation of condensation in the conduit liquid or gas which affects the measurement accuracy. Condensed liquid or gas emissions on a regular basis.
3. Installation and use of pressure measurement instrumentation Notes
(1) The instrument should be installed perpendicular to the horizontal plane;
(2) instrument measuring points and instruments installed at the same horizontal position, consider additional height error correction;
(3) instrument installed at the measurement point and the distance between as short as possible so as not to indicate slow;
(4) to ensure sealing, leakage should not occur, especially flammable and explosive gases and toxic media.
Instrument used in the following situations should be added additional devices, but should not produce additional errors, or should be considered correct.
(1) In order to ensure the instrument from the measured viscosity is too large or medium erosion, Crystallization, isolation devices should be installed;
(2) In order to ensure the instrument is not measured dramatic changes in media or pulse pressure, and the installation of buffers. In particular, steep drop in the pressure surge and pressure, pressure damage to the instrument most likely to scrap, and even spring tube to crack, leak phenomenon;
(3) In order to ensure the instrument from vibration, pressure gauge should be the installation of damping devices and fixtures;
(4) In order to ensure the instrument is not measured the impact of media heat, fluid-filled pipe should be the installation of equipment;
(5) dedicated a special instrument, he is strictly prohibited, and prohibited in the absence of specific and reliable device to measure, but is prohibited to use special media for general gauge pressure measurement;
(6) for the newly acquired pressure instrumentation, in the installation, be sure to test for measurement, to prevent pressure shock transit instrument, damage, or other factors that undermine accuracy.
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