There are different kinds of food in different areas

Water can use electromagnetic flowmeter, in the field of industrial production there is a kind of flowmeter usage is particularly large, suitable for measuring the type of medium is also particularly many, but the requirements of the medium has conductivity, there is a certain dielectric constant, this is our common electromagnetic flowmeter.Municipal water supply there is a new type of water meter called electromagnetic water meter, actually electromagnetic water meter is also a kind of electromagnetic flowmeter, because of the particularity of the water supply industry, in view of the requirements of the working condition of the water supply industry, specially designed for a special water supply flow measurement electromagnetic flowmeter, this is electromagnetic water meter.

Therefore, the electromagnetic water meter is different from the general electromagnetic flowmeter, where is their area, for the production and manufacturing enterprises, familiar with the similarities and differences between electromagnetic flowmeter and electromagnetic water meter, for the design and research and development of two kinds of products have the meaning of getting.This paper not only introduces the principle of electromagnetic flowmeter, USES and advantages and disadvantages, from the use of field range, precision, diameter range (measuring velocity range) and range migration, repeatability, power (power consumption), sampling rate, straight section of pipe structure and measurement, instrument communication, and using the environment ten aspects, such as analyzing the difference between the electromagnetic flow meter and electromagnetic water meter.

1 application field

(1) electromagnetic flowmeter is widely used, which is suitable for continuous measurement of flow rate of various conductive media in industrial production, production process control and measurement and control field of scientific research.

(2) electromagnetic water meter is mainly used to measure clean water and raw water.It is widely used in the municipal area, mainly for the measurement, statistics, analysis and settlement of water sources and urban and rural water supply.

2 the precision

(1) the accuracy of electromagnetic flowmeter is usually ±0.5%, and the precision can be up to ±0.2% and ±0.3%.

(2) the precision of the electromagnetic water meter is commonly Ⅱ level (Q2 to Q4 plus or minus 2%, Q1 and Q2 + / - 5%), high precision can be up to grade I (Q2 to Q4 plus or minus 1%, Q1 and Q2 + / - 3%).

3 caliber

(1) most manufacturers of electromagnetic flowmeters can provide DN20 ~ DN500 products, larger professional manufacturers can provide DN10 ~ DN3000 electromagnetic flowmeters, DN25 ~ DN600 specifications of the number of applications.(2) there are many electromagnetic water meters with diameters from DN50 to DN300 in the market. A few advanced multinational professional manufacturers can produce the whole series of electromagnetic water meters with diameters from DN25 to DN800.

4 range (metering velocity range) and range migration

5 repetitive

(1) for electromagnetic flowmeters, repeatability is one of the important technical indicators, and its repeatability index is usually 1/3 of the accuracy. For example, the repeatability of electromagnetic flowmeters with 0.5 grade accuracy should be better than ±0.16%.The repeatability of 0.2 grade table should be better than ±0.06%.

(2) electromagnetic water meter does not take repeatability as a quality index of assessment, it is only a design and experimental index.The important technical indexes of electromagnetic water meter are precision, low initial flow rate, Q1 flow point and range ratio (Q3/Q1).Of course, for the flowmeter, it is very important that both of them can guarantee the long-term continuous and stable operation.

6 power supply mode (power consumption)

(1) generally, the processing rate of electromagnetic flowmeter is fast and the processing accuracy is high, and the control requirements are rapid, stable and accurate.Due to the complex communication mode of electromagnetic flowmeter and external information (output 4 ~ 20mA current signal, 0 ~ 10KC frequency signal, rs-485 communication, switch quantity control, etc.), the isolation degree is high, so the electronic circuit USES A lot of high-speed electronic components, the power consumption can reach 15 ~ 25V·A, which must be supplied by the municipal power (AC220V) and special external power (DC24V).Therefore, anti-interference, photoelectric isolation, electromagnetic isolation and other technical measures to prevent the strong electromagnetic impact of power supply are very necessary.

(2) the sampling rate of the electromagnetic water meter is relatively slow, and the electronic circuit is dominated by the advanced integrated circuit with low power consumption and ultra-low power consumption. The calculation method is a special high-efficiency power-saving method, so the power consumption is extremely low, and the internal battery can supply power continuously for a long time.This requires that the battery life of the electromagnetic water meter should be at least 5 ~ 6 years, and there are products of 8 ~ 10 years now.For electromagnetic water meters, reducing power consumption and improving battery life is a very difficult challenge.

7 sampling rate

(1) the real-time measurement of electromagnetic flowmeter should meet the technological requirements of industrial control, which is characterized by high speed. Therefore, the sampling and processing rate is generally required to be higher than 100ms/ time.

(2) if the sampling rate of electromagnetic water meter is in the range of 1 ~ 30s/ time, the measured flow data can be obtained. Moreover, the lower the sampling rate is, the lower the power consumption will be.In general, when the sampling rate is 15s/ time, the internal battery can guarantee continuous metering for 6 years.

Pipe structure and measurement straight section

(1) the electromagnetic flowmeter can be powered by mains electricity, so the selection of electronic components and circuits is less affected by power consumption and has a wide range of choices;The excitation current of hundreds of milliamps also causes the signal output amplitude of the sensor to be larger, so there is no need to accelerate the fluid to enhance the signal amplitude.The measuring chamber of electromagnetic flowmeter is a straight tube with simple process and low processing cost.The structure of the straight pipe will hardly cause the disturbance of the measured flow field. The measured flow rate is basically the economic flow rate (the flow rate is lower than 8m/s or so), and the high-speed sampling rate can timely correct the errors caused by various changes in the flow field. Therefore, the straight pipe segment of the electromagnetic flowmeter can meet the measurement accuracy requirements with the first 5D and the second 3D.

(2) the electromagnetic water meter is powered by built-in lithium battery, and reducing power consumption and extending working life is the key to its design task. Therefore, only a low excitation current (usually its excitation current is only 1/10 or even lower than the electromagnetic flowmeter) can be used, so the effective output signal amplitude of the sensor is very weak.Electromagnetic water meter developers usually use two methods to enhance the signal: one is to increase the signal amplification;The second is to reduce the diameter of the measurement section to artificially increase the velocity of the medium, which will greatly improve the flow rate signal.Therefore, the measurement cavity of electromagnetic water meter almost all USES the reducing diameter process, the general reducing diameter is 70% ~ 80% of the original nominal diameter, reducing diameter ratio to not significantly affect the pressure loss of the meter and not significantly change the stability of the flow field as the principle.

9 instrument communication

(1) electromagnetic flowmeter is widely used, and its metering mode and flow control mode are multifarious, so the communication mode is relatively rich. General manufacturers have the following configuration: (1) quantitative pulse output, such as output a pulse on behalf of 1m3/h flow (optional 0.1m3/h, or even 0.01m3/h).(2) frequency output, indicating that the output range of 0 ~ 10kHz frequency represents 0 ~ Qmax flow.(3) output 4 ~ 20mA current, usually represents the instantaneous amount of Qmin ~ Qmax.The 4 ~ 20mA current analog signals designed in recent years can simultaneously carry out digital communication, that is, HART(protocol) communication.(4) rs-485 communication, usually the implementation of ModbusRTU communication standard.Switch output, there are generally 1 ~ 2 road output control, in order to execute the overflow upper limit switch, overflow lower limit switch and other process control.

Almost all of these communications are connected by cable to instruments and computers and control equipment to ensure accurate, real-time and reliable metering and process control.

(2) electromagnetic water meter is mainly used in the raw water and tap water residents on the measurement, statistics, analysis and settlement of almost no process control requirements, the internal battery supply and limited it cannot too much electricity, so communication mode is simple, general manufacturers choose several ways to communicate in the following configuration: (1) and the traditional cold water meter, can be artificial meter reading, and therefore have to traffic data display LCD screen.(2) switch output.(3) interface with wireless communication device, can be through wireless communication equipment networking communication.(4) rs-485 communication and electromagnetic flowmeter, usually the implementation of the ModbusRTU communication protocol, and the need for external power supply (DC24V), which often requires four cables.The electromagnetic water meter produced by donghai group can adopt micro-power consumption technology to carry out rs-485 communication, which can use internal lithium battery for power supply, eliminating 2 cables for external power supply and requiring only 2 cables for communication.(5) infrared communication, which is a kind of wireless two-way communication with low power consumption, can easily meet the harsh protection requirements of electromagnetic water meters installed in underground and water.

10 operating environment

Temperature requirements

(1) electromagnetic flowmeter is widely used, usually in -20 ~ 55℃ temperature environment can be continuous, stable, reliable work.Some specific areas, even in 70℃ conditions normal operation.

(2) generally, electromagnetic water meter can only work continuously in a temperature environment of 0.1 ~ 55℃. During design and performance test, the influence of direct baking under high temperature in summer should be considered.