/div> & nbsp;& nbsp;& nbsp;& nbsp; With the continuous improvement of automation in beer brewing process, the application of electromagnetic flowmeter is more and more widely. Electromagnetic flowmeter is used in the process of crushing water measurement, grain washing water measurement, filtered wort measurement, cold wort measurement, sake measurement and delivery packaging wine measurement. In order to ensure the measurement accuracy in the application process, we should understand and pay attention to the following problems.
 & nbsp;& nbsp;& nbsp;& nbsp; Structure and working principle of electromagnetic flowmeter
 & nbsp;& nbsp;& nbsp;& nbsp; 1.1 composition
 & nbsp;& nbsp;& nbsp;& nbsp; Electromagnetic flowmeter is an inductive instrument for measuring the volume flow of conductive medium, which consists of sensor and converter.
 & nbsp;& nbsp;& nbsp;& nbsp; 1.2 working principle
 & nbsp;& nbsp;& nbsp;& nbsp; According to Faraday's electromagnetic induction principle, a pair of detection electrodes are installed on the wall of the tube perpendicular to the axis of the measuring tube and the magnetic line of force. When the conductive liquid moves along the axis of the measuring tube, the conductive liquid cuts the magnetic line of force and generates the induced potential, which is detected by two detection electrodes, and the value is proportional to the flow rate. The sensor takes the induced potential as the flow signal and transmits it to the converter. After amplification, transformation, filtering and a series of digital processing, the instantaneous flow and cumulative flow are displayed on the dot matrix LCD with backlight. The converter outputs 4 ~ 20mA signal and pulse signal.
 & nbsp;& nbsp;& nbsp;& nbsp; 2. Installation of electromagnetic flowmeter
 & nbsp;& nbsp;& nbsp;& nbsp; 2.1 installation location and position of electromagnetic flowmeter sensor
 & nbsp;& nbsp;& nbsp;& nbsp; Horizontal, inclined or vertical installation can be selected as required, but the axis of the two electrodes should be in the horizontal position. No matter what type of installation is adopted, the measuring tube shall be full of the measured medium, and there shall be no phenomenon of non full tube or bubble gathering in the measuring tube. It is also not allowed to install the flowmeter at the suction end of the pump to prevent the negative pressure in the pipeline from damaging the village inside the sensor.
 & nbsp;& nbsp;& nbsp;& nbsp; 2.2 upstream and downstream pipelines
 & nbsp;& nbsp;& nbsp;& nbsp; The flowmeter is more or less affected by the inlet flow condition, so it is necessary to ensure a good flow condition. The most common one is the distortion of velocity distribution profile and vortex. The distortion of velocity profile is usually caused by local obstruction of pipe fittings (such as valves) or elbows, and vortex is generally caused by two or more spatial elbows. If the above effects are eliminated, the length of the straight pipe section on the upstream side of the sensor shall not be less than 5dn, and the length of the straight pipe section on the downstream side shall not be less than 2DN. DN is the diameter of the sensor. If this requirement can not be met on site, a flow regulator should be installed on the upstream side.
 & nbsp;& nbsp;& nbsp;& nbsp; In addition to the fittings immediately before the flow meter, the combination of pipe fittings further upstream should also be considered, as they may be the source of disturbance closest to the fittings. As far as possible, the distance between the disturbance generating parts should be widened to reduce the influence.
 & nbsp;& nbsp;& nbsp;& nbsp; 2.3 pipe diameter
 & nbsp;& nbsp;& nbsp;& nbsp; When measuring large pipe diameter, low flow rate, small pipe diameter and high flow rate, the flowmeter diameter different from the pipe diameter can be selected and connected with reducing pipe, so that the flow rate of the flowmeter can be within the specified range.
 & nbsp;& nbsp;& nbsp;& nbsp; 2.4 pipeline vibration
 & nbsp;& nbsp;& nbsp;& nbsp; If there is strong vibration in the pipeline system, support should be added to the pipeline before and after the flowmeter. If pulsation buffer has been installed on the pipeline (to eliminate the influence of the pump), but in the installation of flow timing, it is better to consider as far away from the vibration or pulsation source as possible.
 & nbsp;& nbsp;& nbsp;& nbsp; 2.5 valve position
 & nbsp;& nbsp;& nbsp;& nbsp; In order to check the zero point, the sensor should be filled with medium and the flow rate should be zero. This can be achieved by closing the stop valve upstream of the sensor and the control valve downstream. The control valve should be installed downstream of the flowmeter to avoid the distortion of velocity distribution caused by upstream valve.
 & nbsp;& nbsp;& nbsp;& nbsp; 2.6 maintenance space
 & nbsp;& nbsp;& nbsp;& nbsp; Generally speaking, the maintenance personnel should be able to enter the flow meter, easy to maintain and have the position to change the whole machine. Moreover, enough space is required at the flange of the pipeline connected with the sensor, because the distance between the flange of the sensor and the shell is limited, and the connecting bolt needs to be penetrated from the side of the pipeline.
 & nbsp;& nbsp;& nbsp;& nbsp; 2.7 electrical connection and electromagnetic interference
 & nbsp;& nbsp;& nbsp;& nbsp; The installation position of flowmeter should be far away from strong electromagnetic field (such as motor, transformer or other power supply). Signal cables should be as far away from power cables and power sources as possible to minimize electromagnetic interference and radio frequency interference. The connecting wire between sensor and transmitter shall not exceed 50m.
 & nbsp;& nbsp;& nbsp;& nbsp; two8 grounding
 & nbsp;& nbsp;& nbsp;& nbsp; The working grounding of the flowmeter should be grounded separately instead of using the common grounding wire; The distance between the grounding device and the sensor should be as short as possible; Moreover, the grounding resistance should strictly meet the requirements of the instrument manual. If the sensor is installed on the metal pipe and there is no insulating layer on the inner wall of the metal pipe, the grounding wire can be connected to two pipe flanges to maintain reliable grounding with the fluid through the metal pipe. If the interference is too strong and the grounding is not enough to resist the interference, the grounding conductor shall be connected from the two pipe flanges along the metal pipe to the place where the interference can be eliminated. In addition, the loop grounding and shielding grounding between sensors, transmitters and secondary instruments should not be ignored.
 & nbsp;& nbsp;& nbsp;& nbsp; 3 selection of diameter, flow rate and sensor lining of electromagnetic flowmeter
 & nbsp;& nbsp;& nbsp;& nbsp; 3.1 selection of caliber
 & nbsp;& nbsp;& nbsp;& nbsp; Generally, the flow rate of medium in flowmeter should be 2 ~ 6 m / s, the minimum should not be less than 0.3 M / s, and the maximum should not be more than 12 m / s. If the flow rate is too low, the electromagnetic signal will decrease, resulting in the decline of measurement accuracy. If the fluid contains solid particles, the flow rate should be less than 3 M / s. For viscous liquid, the corresponding flow rate is higher, which helps to automatically eliminate the dirt on the electrode and improve the measurement accuracy.
 & nbsp;& nbsp;& nbsp;& nbsp; The calculation formula of the relationship among flow rate, velocity and diameter is as follows:
 & nbsp;& nbsp;& nbsp;& nbsp; Q＝900JID2V
 & nbsp;& nbsp;& nbsp;& nbsp; Q: flow rate (m3 / h), V: velocity (M / s), D: diameter (m).
  & nbsp;& nbsp;& nbsp; According to the formula, the outlet diameter can be calculated.
 & nbsp;& nbsp;& nbsp;& nbsp; 3.2 selection of flow
 & nbsp;& nbsp;& nbsp;& nbsp; After the diameter of the flowmeter is determined, the full scale value should be increased by 15% ~ 30% according to the preset maximum flow rate of the process. In practical application, the flow should not exceed the full scale value. If it exceeds the full scale value, the flow error of this part is large, and the normal accuracy range of full scale and minimum flow should not exceed 20 times.
 & nbsp;& nbsp;& nbsp;& nbsp; 3.3 selection of sensor villages (see Table 1)
Lining material
main performance
Scope of application
Polyethylene < br > (PE)
< br > it has good resistance to corrosion and contamination of chemicals. It is resistant to aqueous solutions of inorganic salts, dilute or concentrated solutions of inorganic acids and bases, and has almost no solvent to dissolve it at room temperature< BR style="mso-special-character: line-break">

A：-40℃~85℃  & nbsp;< Br > b: water, sewage, mud, pulp, inorganic acid, inorganic salt, alkali solution < br > C: it can be used for sanitary medium
Polypropylene < br > (PS)
< br > it is resistant to organic acids, bases, salts, lower alcohols and their aqueous solutions, but not to hydrocarbons, ketones, fats, oils, aromatics, antioxidants and ultrasonic radiation (high frequency)< BR style="mso-special-character: line-break">
< br > A: - 20 ℃ ~ 60 ℃ < br > b: measure general water, sewage, mud, coal slurry, inorganic acid and alkali, salt and other aqueous solutions
Poly (perfluoro) < br > ethylene propylene < br > (FEP, F46)
< br > it is one of the most stable materials in chemical properties, which can be used in any organic solvent or reagent medium and is not affected at high temperature< BR style="mso-special-character: line-break">
< br > A: - 60 ℃ ~ 200 ℃ < br > b: suitable for any strong corrosive medium < br > C: suitable for sanitary medium
Soluble < br > polytetrafluoroethylene < br > (PFA)
< br > it has excellent chemical resistance, high temperature resistance, low temperature resistance, strong acid aqua regia, strong alkali resistance and strong corrosive agent uranium pentafluoride used in atomic industry< BR style="mso-special-character: line-break">
< br > A: - 80 ℃ ~ 250 ℃ < br > b: suitable for any strong corrosive medium < br > C: suitable for sanitary medium
Chloroprene rubber
< br > it has excellent elasticity, toughness, wear resistance, corrosion resistance in general low concentration acid, alkali and salt medium, and corrosion resistance in oxidizing medium< BR style="mso-special-character: line-break">

A：< 65 ℃ < br > b: measure general water, sewage, mud and pulp
PVC < br > (PVC)
< br > it is suitable for all kinds of alkali, salt, sulfuric acid, nitric acid, phosphoric acid and their aqueous solutions, but not resistant to concentrated sulfuric acid, fuming sulfuric acid, acetic anhydride, ether, halogenated aromatic amine< BR style="mso-special-character: line-break">
< br > A: - 25 ℃ ~ 70 ℃ < br > b: general water, sewage, slurry, coal slurry and mineral slurry < br > C: general acid, alkali and salt solution
 & nbsp;& nbsp;& nbsp;& nbsp;& nbsp; 4 characteristics of electromagnetic flowmeter
 & nbsp;& nbsp;& nbsp;& nbsp; four1 advantages
 & nbsp;& nbsp;& nbsp;& nbsp; （ 1) There is no choke in the measuring pipe, the pressure loss is zero, and it is not easy to block< BR> & nbsp;& nbsp;& nbsp;& nbsp; （ 2) As long as the electrode and village material are selected reasonably, the requirements of corrosion resistance and wear resistance can be achieved< BR> & nbsp;& nbsp;& nbsp;& nbsp; （ 3) The measurement results are consistent with the pressure, temperature, density, viscosity and conductivity of the liquid (not less than 5% of the minimum conductivity) μ S / cm) and other physical parameters are basically independent and not affected by the environment, so the measurement accuracy is high, the work is stable and reliable< BR> & nbsp;& nbsp;& nbsp;& nbsp; （ 4) Using the latest analog signal technology and high performance VLSI chip, the signal is isolated, filtered, amplified and digital processed. Accurate display of measurement results< BR> & nbsp;& nbsp;& nbsp;& nbsp; （ 5) It can be used for large diameter pipeline measurement< BR> & nbsp;& nbsp;& nbsp;& nbsp; （ 6) The parameters that affect the measurement results are automatically monitored and corrected, and the sectional flow coefficient is set and corrected for the full range, so the measurement range is expanded, the intelligent degree and measurement accuracy are improved, and the stability performance is greatly improved< BR> & nbsp;& nbsp;& nbsp;& nbsp; （ 7) It has the functions of air pipe protection, power-off protection of measured value and over range alarm. The sensor installation is not limited by the liquid flow direction, and can realize two-way flow measurement< BR> & nbsp;& nbsp;& nbsp;& nbsp; （ 8) It adopts dot matrix dual row flow display with backlight, which can display instantaneous flow, cumulative flow, working status, parameters, measurement unit, etc< BR> & nbsp;& nbsp;& nbsp;& nbsp; （ 9) Wide range, normal application range 20:1, generally 30:1 or more.
 & nbsp;& nbsp;& nbsp;& nbsp; four2. Disadvantages
 & nbsp;& nbsp;& nbsp;& nbsp; （ 1) The conductivity must be higher than the minimum conductivity required by the manufacturer in order to work normally< BR> & nbsp;& nbsp;& nbsp;& nbsp; （ 2) The flowmeter must measure when the medium is full of the pipe< BR> & nbsp;& nbsp;& nbsp;& nbsp; （ 3) The measurement error will be caused when liquid entrains bubbles< BR> & nbsp;& nbsp;& nbsp;& nbsp; （ 4) In some media, the electrode will produce dirt, causing the voltage signal error< BR> & nbsp;& nbsp;& nbsp;& nbsp; （ 5) It is required to be installed on the pipeline< BR> & nbsp;& nbsp;& nbsp;& nbsp; （ 6) The price is high< BR> & nbsp;& nbsp;& nbsp;& nbsp; （ 7) When the flowmeter is installed in the electrical dangerous area, the explosion-proof type must be selected.
 & nbsp;& nbsp;& nbsp;& nbsp; 5 maintenance of electromagnetic flowmeter
 & nbsp;& nbsp;& nbsp;& nbsp; （ 1) Check the converter regularly for water, moisture and corrosion. Waterproof treatment shall be made for the inlet end of instrument< BR> & nbsp;& nbsp;& nbsp;& nbsp; （ 2) Clean the sensor electrode and measuring tube regularly. Do not damage the electrode and lining during cleaning< BR> & nbsp;& nbsp;& nbsp;& nbsp; （ 3) Regularly check whether the aging and contact degree of the connecting cable are intact (including the grounding wire)< BR> & nbsp;& nbsp;& nbsp;& nbsp; （ 4) Strict management system shall be formulated, and it is strictly forbidden for operators to change internal parameters at will.
 & nbsp;& nbsp;& nbsp;& nbsp; 6 factors affecting the accurate operation of electromagnetic flowmeter and measures taken
 & nbsp;& nbsp;& nbsp;& nbsp; （ 1) There is an adhesive layer on the inner wall of the sensor, which is mainly the scale layer and sludge layer formed after the flowmeter works for a long time. The main effect of the adhesion layer is to change the resistance between the two electrodes, except that it can slightly change the flow section in the pipe. If the conductivity of the adhesive layer is significantly higher than that of the fluid, there will be a short circuit in the electrode circuit, and there will be no flow signal output. If the adhesive layer is insulating layer, the electrode circuit will be open circuit, so that the insulation between the electrodes can not send the flow signal.
 & nbsp;& nbsp;& nbsp;& nbsp; Measures taken:
 & nbsp;& nbsp;& nbsp;& nbsp; ① In the brewing process, most of the flow meters are not equipped with cleaning pipes, so it is necessary to remove the sensor regularly to clean the electrode. If possible, the flushing pipe can be installed and the electrode can be flushed regularly< BR> & nbsp;& nbsp;& nbsp;& nbsp; ② Under the condition of meeting the process requirements, small diameter instruments should be selected as far as possible to increase the flow velocity, increase the scouring effect and reduce deposition.
 & nbsp;& nbsp;& nbsp;& nbsp; （ 2) During the normal operation of the flowmeter, it must be ensured that the fluid is full of the pipe, and bubbles are not allowed in the liquid. If the pipeline is not filled with liquid, the result is that the cross section of the fluid will not be consistent with the cross section of the pipeline, resulting in the deviation of the calculated volume flow value. If there are evenly distributed tiny bubbles in the measured liquid, the normal operation of the flowmeter will not be affected. However, with the increase of bubbles, the output signal of the instrument will fluctuate. If the bubbles are large enough to cover the whole electrode surface, the electrode circuit will break instantly as the bubbles flow through the electrode surface, resulting in greater fluctuation of the output signal.
 & nbsp;& nbsp;& nbsp;& nbsp; Measures taken: install the flowmeter in strict accordance with the above installation requirements.
 & nbsp;& nbsp;& nbsp;& nbsp; （ 3) During the normal operation of the flowmeter, the external parasitic potential and its own interference should be avoided. Electromagnetic flowmeter works according to the principle of electromagnetic induction. Its flow signal is very small, only a few millivolts at the full scale, and only tens of microvolts at the lower limit of flow. Therefore, it is very vulnerable to electromagnetic induction interference produced by surrounding such as motors, transformers and some other electrical equipment. There are the following interference sources
 & nbsp;& nbsp;& nbsp;& nbsp; ① The stray current (such as welding operation on the pipe) is generated by the electrical equipment in operation around the metal pipe, which affects the electromagnetic flowmeter through the pipe and the fluid in the pipe< BR> & nbsp;& nbsp;& nbsp;& nbsp; ② The electromagnetic flowmeter and the motor and electrical equipment are connected to the common ground or to the upper and lower pipes, so that the leakage current of the power equipment is introduced into the electromagnetic flowmeter through the common ground< BR> & nbsp;& nbsp;& nbsp;& nbsp; ③ Interference of electromagnetic field of surrounding electromagnetic equipment on signal transmission line and electronic circuit.
 & nbsp;& nbsp;& nbsp;& nbsp; Measures taken: install the flowmeter in strict accordance with the installation requirements.
 & nbsp;& nbsp;& nbsp;& nbsp; 7 conclusion
 & nbsp;& nbsp;& nbsp;& nbsp; Electromagnetic flowmeter plays an important role in the measurement process of beer brewing, with low failure rate and high measurement accuracy.