Accuracy class and function According to the measurement requirements and the use occasions, the instrument accuracy level is selected to achieve economical efficiency. For example, in the case of trade settlement, product handover and energy measurement, the accuracy level should be higher, such as 1.0, 0.5, or higher; for process control, select different accuracy levels according to control requirements; It is to detect the process flow, no need to do precise control and measurement, you can choose a lower accuracy level, such as 1.5, 2.5, or even 4.0, then you can use a low-cost plug-in electromagnetic flowmeter.
Measuring medium flow rate, meter range and diameter When measuring general medium, the full flow of electromagnetic flowmeter can be selected within the range of 0.5-12m/s of measuring medium flow, and the range is wider. The meter specification (caliber) is not necessarily the same as the process pipeline. It should be determined whether the measured flow range is within the flow rate range. That is, when the pipeline flow rate is too low to meet the flow meter requirements or the measurement accuracy cannot be guaranteed at this flow rate, It is necessary to reduce the gauge diameter, thereby increasing the flow rate inside the tube and obtaining satisfactory measurement results.
Try to avoid ferromagnetic objects and equipment with strong electromagnetic fields to prevent the magnetic field from affecting the working magnetic field and flow signal of the sensor.
Should be installed in the dry and ventilated place, to avoid sun and rain, the ambient temperature should be -20 ~ +60 ° C, relative humidity is less than 85%.
There should be ample space around the flowmeter for easy testing and maintenance.
Executive Standard: JB/T 9248-1999
Nominal diameter: 15, 20, 25, 32, 40, 50, 65, 80, 100, 125, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1200, 1400, 1600, 1800, 2000, 2200, 2400, 2600, 2800, 3000
Maximum flow rate: 15m/s
Accuracy: DNl5~DN600, indication: ±0.3% (flow rate ≥1m/s); ±3mm/s (flow rate <1m/s)
DN700-DN3000, ±0.5% of the indicated value (flow rate ≥0.8m/S); ±4mm/s (flow rate <0.8m/S)
Fluid conductivity ≥5uS/cm
Nominal pressure:
DNl5～DN: 1504.0MPa, DNl5～DN600: 1.6MPa, DN200～DN1000: 1.0MPa, DN700～DN3000: 0.6MPa, Special order: 6.3, 10MPa
Ambient temperature
Sensor: -25 °C - ten 60 °C
Converter and integrated type: -10 ° C - ten 60 °C
Lining material: PTFE, neoprene, polyurethane, polytetrafluoroethylene (F46), screened PFA
Maximum fluid temperature
- Body type 70 °C
Separate type: Polychloroprene lining 80 ° C; 120 °C (specify when ordering)
Polyurethane lining 80 °C
PTFE lining
Polytetrafluoroethylene propylene (F46) 100 °C; 150 °C (specify when ordering)
Screening PFA
Signal electrode and grounding electrode material: stainless steel 0Crl8Nil2M02Ti, Hastelloy C, Hastelloy B, titanium, tantalum, platinum/rhodium alloy, stainless steel coated tungsten carbide
Electrode scraper mechanism: DN300-DN3000
Connecting flange material: carbon steel
Grounding flange material: stainless steel 1Crl8Ni9Ti
Import protection:
DN65—DNl50: Stainless steel 1Crl8Ni9Ti
Flange material
DN200～DNl600: Carbon steel ten stainless steel 1Crl8Ni9Ti
Shell protection
DNl5～DN3000 separate rubber or polyurethane lining sensor: IP65 or IP68
Other sensors, body flow meters and split converters: IP65
Spacing (separate type): The converter distance sensor generally does not exceed 100m
Second, choose from the type of flow meter
Various flow meters, such as volumetric flowmeters, speedmeters, and differential pressuremeters, have different characteristics. Different flowmeter types have different turndown ratios. The turbine flowmeter has a turndown ratio of 1:20 to 1:30, the Roots flowmeter has a turndown ratio of 1:20 to 1:160, and the film gauge has a turndown ratio of 1: 160 (The error characteristic curves of these three kinds of flow meters are shown in Figure 1), and the appropriate flow meter should be selected according to the actual situation.
By comparing the error characteristics of the above flowmeters, it can be seen that the starting flow of the membrane meter and the Roots flowmeter is small, the initial flow of the turbine meter is relatively large, and the membrane surface exhibits a positive deviation in the small flow state. The Roots flowmeter exhibits a negative deviation. At low flow rates, the gas supply company is more willing to select a membrane meter for metering.