The type of instrument must meet the requirements of the production process, such as whether it requires the remote transmission or transmission of the indicating value, automatic recording or alarm; Whether the nature and state of the measured medium (such as corrosion strength, temperature, viscosity, dirt, inflammable and explosive, etc.) put forward special requirements for the instrument; The installation environment of the instrument is regulated, such as the ambient temperature, electromagnetic field, and vibration. After overall analysis of these conditions, the correct selection of the instrument type is an important prerequisite for the normal operation of the instrument and to ensure the safety of production. (2) Measuring range of the instrument: the measuring range of the instrument is considered according to the size of the measured pressure and to ensure the life of the instrument, etc., usually the upper limit value of the instrument should be slightly greater than the maximum value of the measured pressure of the process. In order to avoid the failure of the pressure gauge over load, the upper limit value of the instrument should be higher than the maximum pressure value that may occur in the production process. For elastic manometer, when the measured pressure is relatively stable, the measured maximum pressure should be 3/4 of the upper limit value of the manometer; In the case of large pressure fluctuation measurement, the maximum pressure to be measured should be 2/3 of the upper limit value of the pressure gauge. In general, in order to ensure the accuracy of the measurement, the minimum value of the measured pressure should not be less than 1/3 of the full range. (3) The accuracy level of the instrument should be determined according to the maximum error allowed by the production process for the pressure measurement. The selection of the position of the pressure measurement point shall comply with the following provisions: a The measurement point for measuring the pressure of the pipeline shall be set on the straight pipe section with stable flow rate, and shall not be set on the part with eddy current. b The distance between the pressure source component and the adjustment on the pipeline: the upstream side should be greater than 2D; The downstream side should be greater than 5D (D is the inner diameter of the process pipe). c When measuring pressure below 0.1MPa, additional errors caused by liquid columns should be minimized. d The position of the furnace pressure source component should comply with the provisions of the boiler factory, and should be set in the upper part of the combustion chamber flame center. e The pipe resistance between the pressure measuring point of each primary or secondary air duct of the boiler and the burner should be equal. The former shall be installed in the inlet diameter part of the mill, and the latter shall be installed on the air powder mixture pipeline near the coarse powder separator. g The turbine lubricating oil pressure measurement point should be selected at the lower pressure of the end section of the oil pipe. The installation orientation of the pressure measuring point on the horizontal or inclined pipeline shall comply with the following provisions: a. When measuring the gas pressure, the measuring point is on the upper part of the pipeline; B. When measuring liquid pressure, the measuring point is within the range of 45° Angle between the lower half of the pipeline and the horizontal center line of the pipeline; C. When measuring steam pressure, the measuring point is within the range of 45° Angle between the upper and lower half of the pipeline and the horizontal center line of the pipeline. When measuring gas pressure, the source component should be in the upper half of the process pipe
When measuring liquid pressure, the source component should be in the lower half of the process pipe and the horizontal center line of the process pipe at an Angle of 0 to 45 degrees. When measuring steam pressure, the source component should be in the upper and lower half of the process pipe and the horizontal center line of the process pipe at an Angle of 0 ~ 45 degrees. The pressure source component installation precautions: 1. When the pressure source component and the temperature source component are in the same pipe segment, they should be installed on the upstream side of the temperature source component. 2. When measuring the pressure with a medium such as dust or air powder mixture, a pressure taking device with an anti-blocking and/or purge structure should be adopted. The installation direction of the pressure tube should meet the following requirements: a, in the vertical pipeline, furnace wall or flue, the pressure tube should be inclined upward installation, and the Angle formed by the horizontal line should be greater than 30°; B. On the horizontal pipeline, the pressure tube should be above the pipeline and should be installed at an acute Angle along the flow beam. 3. The setting of the pressure point must be representative, and the pressure point should be selected in a place that can correctly and timely reflect the actual value of the measured pressure. For example, set in the part of the measured medium flow smoothly, should not be too close to local resistance or other disturbed places. The inner wall of the end face of the pressure tube and the connection of the equipment should be kept flush, and there should be no protruding objects or burrs, so as not to affect the balanced flow of the liquid. 4. The end of the pressure source component should not exceed the inner wall of the process equipment or pipeline. 5. When measuring steam pressure, a condensing tube should be installed to avoid direct contact between high temperature steam and the pressure measuring element. For corrosive or large viscosity, crystallization, precipitation and other media, can be installed isolation tank, tank filled with neutral isolation liquid, in order to prevent corrosion or plug the pressure tube and pressure gauge. 6, the pressure aperture of the wind pressure should be consistent with the outside diameter of the pressure device to prevent blockage. The pressure taking device shall have a plug for purging and a removable pipe joint. A cut-off valve should be installed between the pressure inlet and the pressure gauge for use when inspecting the pressure gauge. The cut-off valve shall be installed near the pressure opening. Where on-site calibration or frequent flushing of the pressure guide is required, the cut-off valve can be used as a three-way valve. 7, the pressure hole and the source parts should be free of burrs. The inner wall of the end face of the pressure tube and the connection of the equipment should be kept flush, and there should be no protruding objects or burrs, so as not to affect the balanced flow of the liquid. 8, when the measured pressure is small, and the pressure gauge and the pressure port are not at the same height, the measurement error caused by the height difference of the liquid column should be corrected. 9. When the measured pressure fluctuates violently and frequently (such as the outlet pressure of the pump and compressor), a buffer or damper should be installed. Flow meter: flow throttling parts installation: 1, the upstream of the adjacent throttling parts (if there is a clamping ring, it is close to the clamping ring) at least within the 2D length range, the internal section of the pipeline should be cylindrical. When the diameter is measured on any plane, the difference between any diameter and the mean diameter measured (the arithmetic mean of the four diameters with roughly equal angles to each other) does not exceed ±0.3% of the mean diameter. Within the remaining required minimum pipe length, the cross-section can be considered round as long as the visual inspection indicates that it is round. The inner surface of the pipe shall be clean and conform to the roughness grade parameters within a length range of at least 10D upstream and at least 4D downstream of the throttle. 2. Each pressure taking device of the throttling device shall have at least one upstream pressure taking port and one downstream pressure taking port, and have the same diameter. The positions and diameters of the upper and lower pressure outlets of different pressure taking methods shall comply with the relevant provisions of GB/T2642. The axis of the pressure opening should intersect with the pipe axis and be at a right Angle to it (if the pressure opening is drilled separately, the axis of the pressure opening should intersect with the pipe axis at a 90° Angle as far as possible). The inner edge of the pressure opening should be flush with the inner wall of the pipeline. 3. When the differential pressure of the throttling device is used to take pressure with the equalizing ring, the number of pressure holes on the upper and downstream sides must be equal, and the pressure holes on the same side should be evenly set on the same section. 4. The installation direction of the throttle part in the pipeline must make the fluid flow from the upstream end face of the throttle part to the downstream end face of the throttle part. For the orifice plate, the upstream end face is perpendicular to the cylindrical cylinder of the orifice; For the nozzle, the upstream end face is perpendicular to the inlet plane portion of the axis. 5, the installation of throttling parts in the pipeline should be perpendicular to the pipeline axis, and its deviation is allowed between ±1°. The throttling part should be coaxial with the pipe or the clamping ring (when used), and the distance between the axis of the throttling part and the axis of the pipe on the upper and downstream side is: ex≤0.0025D/0.1+2.3β4β=d/D type: D - the inner diameter of the upstream pipe under working conditions; β-diameter ratio; d - the diameter of the throttling hole or throat of the throttling part under working conditions. 6, when using the clamping ring, attention should be paid to the center, any part of the clamping ring shall not burst into the pipeline, such as the throttling part and the clamping ring used between the washer, the washer should not burst into the clamping ring. 7. If the gasket is used in the installation of the throttling part, the gasket should not burst into the pipeline. When the pressure taking device is used, the gasket should not block the pressure taking port or slot. 8, the measurement of steam flow on the throttling parts, the downstream pressure port installed condenser should meet the design requirements, the volume of the condenser should be greater than the full range of the differential pressure gauge or differential pressure transmitter working space of the maximum volume change of 3 times, the horizontal cross-sectional area should not be less than the differential pressure gauge or differential pressure transmitter working area. During installation, the liquid level of the two condensers should be at the same height and not lower than the pressure opening. When the differential pressure meter is higher than the throttling device, the condenser should be higher than the differential pressure meter. The pipe from condenser to throttling device should be insulated. For throttling devices installed on horizontal or inclined steam pipelines, the bearing of the pressure opening shall be within the range of an Angle of 45° between the upper half of the pipeline and the horizontal center line of the pipeline. 9. The installation direction of the throttling part is shown in the figure. The sharp edge of the cylinder of the hole plate should face the direction of the medium stream beam, and the nozzle surface should face the direction of the medium stream beam. The installation requirements of the rotameter are as follows: (1) The rotameter must be installed vertically, and the flow direction of the medium must be from the bottom up. (2) Install bypass valves and front and rear cut-off valves. Turbine flowmeter installation requirements are as follows: (1) Turbine flowmeter should be installed on the horizontal pipeline. (2) In the case of accurate measurement, the upstream straight pipe section (including the rectifier) should not be less than 20D, and the downstream side is 5D. In general, the upstream side of the straight pipe section can be 10D, and the downstream side is 5D.(3) In the continuous operation of the occasion, the bypass valve and the front and rear cut-off valve should be installed.(4) The upstream side should be installed with a filter, if the measured liquid contains gas, the upstream side should also be installed with a degasser. The filter and degasser should be located in front of the straight pipe section. The installation requirements of the electromagnetic flowmeter are as follows: (1) The electromagnetic flowmeter should be installed on the pipeline that is completely filled with the measured medium.(2) In general metering occasions, the length of the upstream straight pipe section should not be less than 3D, and the length of the downstream straight pipe section should not be less than 2D; When accurate measurement is required, the length of the upstream straight pipe section should not be less than 10D, and the length of the downstream straight pipe section should not be less than 3D. (3) When the plug-in electromagnetic flowmeter is installed on the horizontal or inclined pipeline, the probe should be installed in the range of 45° above and below the center line plane of the pipeline. (4) The center line of the probe of the plug-in electromagnetic flowmeter should be perpendicular to the center line of the pipeline. (5) When the measured body is not grounded, the electromagnetic flowmeter should be isolated from the process pipeline, and its power supply and output signal should be isolated by a transformer. (6) When the measured body is grounded, the electromagnetic flowmeter body and the process pipe should be well connected and grounded. The installation requirements of the vortex flowmeter are as follows: (1) When measuring liquid, the vortex flowmeter should be installed on the pipeline where the measured medium is completely filled. (2) When the vortex flowmeter is installed on the horizontal pipeline, the influence of the medium temperature on the transmitter should be fully considered. (3) When the vortex flowmeter is installed on the vertical pipeline, it should meet the following requirements: a When measuring gas. Fluid can flow in any direction; b When measuring liquids, the liquid should flow from the bottom up. (4) The downstream of the vortex flowmeter should have a straight pipe section length of not less than 5D(meter diameter), and the upstream straight pipe section length of the vortex flowmeter should meet the following requirements: a When the diameter of the process pipe is greater than the diameter of the instrument (D) to reduce the diameter, not less than 15D; b When the diameter of the process pipe is less than the diameter of the instrument (D), it needs to be expanded, not less than 18D; c flowmeter front with a 90° elbow or tee, not less than 20D; d flowmeter front with two consecutive 90 ° elbow in the same plane, not less than 40D; e flowmeter before the connection of two 90 ° elbows in different planes, not less than 40D; f flowmeter installed in the downstream of the regulating valve, not less than 50D; g The flowmeter is equipped with a rectifier of not less than 2D length before the rectifier, there should be 2D before the rectifier, and there should be a straight pipe section length of not less than 8D after the rectifier. (5) When gas may appear in the measured liquid, a degasser should be installed. (6) Vortex flowmeters should be installed in a position that will not cause liquid gasification. (7) The deviation between the inner diameter of the straight pipe section before and after the vortex flowmeter and the inner diameter of the flowmeter should not be greater than 3%. (8) The front and rear stop valves and side valves should be added to the disaster street flowmeter installed in the place where the detection element (vortex generator) is likely to be damaged, and the plug-in vortex flowmeter should be installed with a cut-off ball valve. (9) Vortex flowmeters should not be installed in places with vibration. The installation requirements of the mass flowmeter are as follows: (1) The mass flowmeter should be installed on the pipeline where the measured medium is completely filled. (2) The mass flowmeter should be installed on the horizontal pipeline; When installed on a vertical pipe, the fluid should flow from bottom to bottom, and the outlet has an appropriate straight pipe length. (3) When used to measure volatile liquids (such as light hydrocarbons, liquefied gas, etc.), the pressure at the outlet of the flow meter should be higher than the saturated steam pressure of the liquid: the flow meter should not be installed on the pump inlet pipeline; When installed on a vertical pipe, it should be installed at the lowest part of the pipe. (4) The installation of the ω-type mass flowmeter on the horizontal pipe should meet the following requirements: When measuring gas, the ω-type pipe should be placed above the pipe; B When measuring liquid, the Ω tube should be placed under the pipe. (5) When the straight pipe mass flowmeter is installed on the horizontal pipe, the influence of the medium temperature on the transmitter should be fully considered. The ambient temperature at the transmitter should not be higher than 60 ° C. (6) Mass flowmeters with diameters greater than or equal to 80mm should be supported. (7) When the measured liquid may contain gas, a degasser should be added. (8) The mass flowmeter should be added before and after the cut-off valve and bypass valve.