Sanitary type electromagnetic flowmeter precision grade and function

1, the performance of the general type on the market has a big difference, some high precision, more functions, some low precision, simple functions.The basic error of hygienic electromagnetic flowmeter with high precision is (±0.5% ~ ±1%) R, and that of instrument with low precision is (±1.5% ~ ±2.5%) FS, the price difference between them is 1 ~ 2 times.Therefore, it is not economically cost-effective to select high-precision instruments in places where measurement accuracy is not required (for example, places where non-trade accounting only requires high reliability and excellent repeatability for control purposes).

2, some models and health type electromagnetic flowmeter says it has a higher accuracy, only basic error (plus or minus 0.2% to plus or minus 0.3%) R, but there are strict installation requirements and terms of reference, such as environmental temperature 20 ~ 22 ℃ and straight pipe length requirements respectively before and after more than 10 d and 3 d (usually 5 d and 2 d), and even flow sensor is put forward to and straight pipe before and after integration in the flow standard device for solid flow calibration, to reduce the loading effect.Therefore, in the selection of a variety of models do not simply look at high indicators, to read the manufacturer's samples or specifications for comprehensive analysis.

3. The function of the market is also very different. The simple one is to measure one-way flow and only output analog signals to drive the back-level instrument;The multifunctional health electromagnetic flowmeter includes two-way flow measurement, range switching, upper and lower limit flow alarm, air tube and power cut-off alarm, small signal excising, flow display and total calculation, automatic check and fault self-diagnosis, communication with upper computer and motion configuration, etc.A variety of communication interfaces and special chip (ASIC) can be selected to connect HART protocol system, PROFTBUS, Modbus, CONFIG, FF field bus and so on.

Flow rate, full flow rate, range and caliber

1. The diameter of the selected sanitary electromagnetic flowmeter may not be the same as the pipe diameter, but should be determined according to the flow rate.Flow industry to transport water and other liquids with different viscosity, the pipe flow rate is generally economic flow rate of 1.5 ~ 3m/s.EMF is used in such a pipeline, the sensor diameter and the same.

2. Liquid velocity at full flow can be selected within the range of 1 ~ 10m/s, and the range is relatively wide.The upper flow rate is not limited in principle, however it is generally recommended not to exceed 5m/s. Unless the lining material is able to withstand fluid erosion, it is rarely more than 7m/s in practical use, and more rarely more than 10m/s.The lower limit of the full flow velocity is generally 1m/s, while some models are 0.5m/s.For piping system with low flow rate or low flow rate in the initial stage of some new construction projects, from the perspective of measurement accuracy, the gauge diameter should be changed to be smaller than the pipe diameter and connected with the reducing pipe.

3. For fluids with substances easy to adhere, deposit and scale formation, the flow rate should be no less than 2m/s and be raised to 3 ~ 4m/s or above, playing a role of self-cleaning and preventing adhesion and deposition.For ore slurry and other highly abrasive fluids, the common flow rate should be lower than 2 ~ 3m/s, in order to reduce the lining and electrode wear.

4. When measuring the low conductivity liquid close to the threshold value (i.e. the lower limit value), select the lower flow velocity as far as possible (less than 0.5 ~ 1m/s). As the flow noise increases with the increase of flow velocity, output sloshing will occur.

5, the range is relatively large, usually not less than 20, with the range of automatic switching function of the instrument, can exceed 50 ~ 100.The diameters of the type products available in China range from 10mm to 3000mm. However, in practical applications, the majority of them are small and medium diameters. However, compared with most other principle flow meters (such as positive displacement, turbine, vortex street or Coriolis mass type), large diameter meters account for a larger proportion.Among nearly ten thousand meters in an enterprise, small diameter below 50mm, medium diameter between 65-250mm, large diameter between 300-900mm and large diameter above 1000mm account for 37%, 45%, 15% and 3% respectively.

Sanitary electromagnetic flowmeter for liquid conductivity requirements

1. The premise of use is that the liquid under test must be conductive and not lower than the threshold value (i.e., the lower limit value).If the conductivity is lower than the threshold, it will produce measurement error or even cannot be used. If the conductivity is higher than the threshold, it can be measured even if it changes. The error of the value shows little change.It also depends on the length of the flow signal line between the sensor and the converter and its distributed capacitance. The manufacturer's operating instructions usually specify the length of the signal line corresponding to the conductivity.Instruments with non-contact capacitance-coupled large-area electrodes can measure liquids with conductivity as low as 5× 10-8s /cm.

2. The conductivity of industrial water and its aqueous solution is greater than 10-4s /cm, the conductivity of acid, alkali and salt solution is between 10-4 ~ 10-1s /cm, so there is no problem with the use, and there is no problem with the low-grade distilled water being 10-5s /cm.Petroleum products and organic solvents are too low conductivity to be used.Table 1 shows the conductivity of several liquids.From the data found that some pure liquid or aqueous solution conductivity is low, that can not be used, but the actual work will encounter impurities and can be used, this kind of impurities increased the conductivity.For aqueous solution, the conductivity in the data is measured in the laboratory by the ratio of pure water, and the actual aqueous solution may use the ratio of industrial water, and the conductivity will be higher than that obtained, which is also conducive to flow measurement.

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