Publish Time: 2022-06-06 Origin: Site
It can be considered from five aspects: flowmeter performance, fluid characteristics, installation conditions, environmental conditions and economic factors. The detailed factors of the five aspects are as follows:
Instrument performance: accuracy, repeatability, linearity, range, flow range, signal output characteristics, response time, pressure loss, etc;
Fluid characteristics: temperature, pressure, density, viscosity, chemical corrosion, abrasiveness, scaling, miscibility, phase change, conductivity, sound velocity, thermal conductivity, specific heat capacity, isentropic index;
Installation conditions: pipeline layout direction, flow direction, length of straight pipe section on the upstream and downstream sides of the test piece, pipeline diameter, maintenance space, power supply, grounding, auxiliary equipment (filter, degasser), installation, etc;
Environmental conditions: environmental temperature, humidity, electromagnetic interference, safety, explosion-proof, pipeline vibration, etc;
Economic factors: instrument purchase cost, installation cost, operation cost, calibration cost, maintenance cost, instrument service life, spare parts, etc.
The steps of flowmeter instrument selection are as follows:
1. Primary selection of available instrument types according to fluid types and five considerations (there should be several types for selection);
2. Collect data and price information for the primary types to prepare conditions for in-depth analysis and comparison;
3. Adopt the elimination method to gradually concentrate on 1 ~ 2 types, repeatedly compare and analyze the five factors, and finally determine the pre selection goal.
Fluid characteristics mainly refer to the pressure, temperature, density, viscosity and compressibility of gas. Since the volume of gas changes with temperature and pressure, whether compensation and correction should be considered.
Instrument performance refers to the accuracy, repeatability, linearity, range ratio, pressure loss, initial flow, output signal and response time of the instrument. The selected flow meter shall carefully analyze and compare the above indicators, and select the instrument that can meet the flow requirements of measuring medium.
Installation conditions refer to gas flow direction, pipeline direction, length of upstream and downstream straight pipes, pipe diameter, spatial location and pipe fittings, which will affect the accurate operation, maintenance and service life of gas flowmeter.
Economic factors refer to purchase cost, installation cost, maintenance cost, calibration cost and spare parts, which are also affected by the performance, reliability and service life of gas flowmeter.
Accuracy grade and function: select the accuracy grade of the instrument according to the measurement requirements and application occasions, so as to achieve economic efficiency. For example, it is used for trade settlement, product handover and energy measurement,
In the selection of accuracy grade, such as grade 1.0, grade 0.5 or higher, for process control, different Accuracy grades shall be selected according to the control requirements. In some cases where only the process flow is detected and there is no need for accurate control and measurement, you can choose those with a slightly lower accuracy level, such as level 1.5, level 2.5, or even level 4.0. At this time, the low-cost plug-in electromagnetic flowmeter can be selected to measure the medium flow rate. When the instrument range and caliber measure the medium in general, the full-scale flow of the electromagnetic flowmeter can be selected in the range of 0.5-12m / s. The specification (caliber) of the selected instrument is not necessarily the same as that of the process pipeline. It should be determined according to whether the measured flow range is within the flow rate range. That is, when the flow rate of the pipeline is too low to meet the requirements of the flow instrument or the measurement accuracy under this flow rate cannot be guaranteed, it is necessary to reduce the instrument caliber, so as to improve the flow rate in the pipe and obtain satisfactory measurement results.