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The role of electromagnetic flowmeter in aseptic filling system
The role of electromagnetic flowmeters in aseptic filling systems is increasing with the rapid improvement of people's living standards. People put forward higher requirements on the quality of products and production efficiency, requiring the filling device system to be fast, safe and accurate. Complete filling. Aseptic filling systems are increasingly used in food, beverage, pharmaceutical and other industries with their inherent advantages. The requirements for aseptic filling systems have changed in the way of quantitative control of filling. Some professional filling flowmeters enter the filling application field. This dynamic online measurement and control method brings new challenges. In addition, it is necessary to consider not only the installation and use of the flowmeter itself, but also the integration of the flowmeter. The interaction between the system and other parts.
Electromagnetic Flowmeter
1 electromagnetic flowmeter aseptic filling system introduction
1.1 Aseptic filling system requirements
(1) easy to clean and disinfection; (2) high yield, short cycle; (3) high precision and high repeatability; (4) low consumption and loss; (5) rapid processing of different product filling and different batch filling (6) High transparency to product and product quality factors; (7) No maintenance or easy maintenance.
1.2 Aseptic filling design features
(1) Simplification of the machine; (2) Smooth surface, no unevenness, no dead angle, good airtight sealing; (3) smooth drainage, no water accumulation; (4) good tightness to prevent external microbes; 5) Select appropriate materials, high temperature resistance, chemical resistance; (6) automated CIP (in-situ cleaning) / SIP (in-situ sterilization); (7) regular maintenance of key equipment; (8) division of production area, sterilized And non-sterile, isolation and control of materials, people, etc. in the production area.
1.3 Filling quantitative control
In each sub-system, the quantitative control system for filling is one of the core systems of Zui. The filling speed and accuracy of the whole filling machine are often determined by the performance of the system. The key components of the filling quantitative control system include flow meters. Controller, valve (Figure 1). The filling volume is measured by the flow meter, which can quickly and accurately measure the fluid flow in the connecting pipe of the filling head, and upload the signal to the controller, which is based on the controller. Set the quantitative, control the start / stop of the filling valve to achieve accurate filling.
1.4 Aseptic filling requirements for flow meters
1.4.1 Rapid response capability and accurate measurement capability. Each filling usually lasts for 2~5 seconds. This requires the flowmeter to measure very fast and the measurement interval is short. Only in this way can the flow rate curve be kept up.
1.4.2 Hygienic design and connection. Special materials and connection methods.
1.4.3 CIP and SIP requirements. In-situ cleaning and sterilization involve corrosive media such as acid and alkali. If high temperature steam sterilization is used, a temperature of about 140 °C will occur in the process.
1.4.4 Good stability and repeatability.
2 electromagnetic flowmeter introduction
Dosimag series flowmeter is a professional filling electromagnetic flowmeter developed by a well-known instrument company, which can ensure high accuracy and repeatability. The compact shape structure ensures that the various units in the filling production line can be installed very close. Fast and accurate measurement capability, short measurement cycle and high measurement frequency.
Dosimag flowmeter measurement principle: According to Faraday's law of electromagnetic induction, the induced electromotive force is generated due to the change of magnetic flux. A part of the conductor of the closed circuit is used to cut the magnetic induction line in the magnetic field, and an induced current is generated in the conductor. In the principle of electromagnetic measurement, the flow The medium is equivalent to the moving conductor, the induced voltage is proportional to the flow rate of the medium, and is directly sent to the amplifier through the two electrodes. The volume of the fluid can be calculated by the cross-sectional area of ​​the pipe.
Where: Ue - induced voltage
B——Magnetic field strength
L——pole spacing
v - fluid velocity
Q - fluid flow
A——pipe cross-sectional area
I——current intensity
It can be seen from the above formula that when the magnetic field strength and the magnetic pole spacing are constant, the fluid flow rate is proportional to the induced voltage.
3 electromagnetic flowmeter Dosimag flowmeter characteristics
3.1 Features
(1) Rapid measurement capability, accurate measurement of more than 80 times per second; (2) Flow rate up to 1.66 L/s; (3) Fluid temperature up to 130 ° C, withstand 150 ° C in half an hour; (4) Work Pressure up to 16 bar; (5) On-line in-situ cleaning (CIP) and in-situ sterilization (SIP); (6) Special application liner: PFA (soluble polytetrafluoroethylene); (7) Stainless steel casing.
3.2 Application areas
It can be used for liquid measurement with conductivity of 5μs/cm or more, such as food industry, cosmetics industry, pharmaceutical industry, chemical industry 3.3 food/health industry related certification 3A certification / EHEDG test / FDA compliance.
4 electromagnetic flowmeter installation method, use conditions and precautions
4.1 electromagnetic flowmeter installation conditions
(1) The length of the inlet pipe is greater than 5 times DN, as shown in Figure 3; (2) the length of the outlet pipe is greater than 2 times DN, as shown in Figure 3; (3) the sensor and transmitter must be grounded; (4) the sensor is centered in the pipe .
4.2 Installation method and location
The filling flowmeter is easy to install and debug; it is not very sensitive to the vibration of the pipeline. The filling flowmeter can only be correctly measured under the condition that the pipeline is completely full. For this reason, it is recommended to do the filling test before mass production.
4.2.1 Installation method Generally speaking, there are rotary filling mode and linear filling mode, as shown in Figure 4 and Figure 5:
4.2.2 Installation position. Installed near the valve, the filling flowmeter cannot be installed downstream of the control valve (Fig. 6). If it is installed downstream of the control valve, the measuring pipe of the sensor is completely emptied after the end of one filling cycle. This will seriously affect the measurement of the next cycle.
Figure 6 Schematic diagram of the installation position of the flowmeter and valve (1 represents the filling flowmeter) 4.2.3 Installation direction. Reasonable installation direction (Figure 7), can avoid the accumulation and storage of air in the measuring pipeline.
4.2.4 Installation Precautions.
(1) When used in overheated conditions (such as online cleaning and online disinfection), the transmitter is strongly required to be installed below, which can reduce the risk of partial overheating of the transmitter, as shown in Figure 8.
(2) Under the condition of very strong vibration, ensure the safety of pipes and sensors.
4.3 General factors affecting filling
4.3.1 Metering accuracy of the flowmeter: This indicator is affected by flow rate, duration of filling, measurement of fluid conditions, etc.
Table 1 relationship between filling time and repeatability
4.3.2 Movement speed and mechanical repeatability of movable parts in the filling system: mainly the speed and consistency of the opening and closing operation of the shut-off valve.
4.3.3 The state stability of the fluid in the filling machine, including temperature change (influence density), whether the back pressure is stable (affecting the flow rate), and the liquid level.
4.3.4 Whether the control system works and the control program design is optimized.
Analysis of practical application problems of 5Dosimag filling flowmeter
The following is an example of the problem of poor reproducibility in the process of using a filling flowmeter in a domestic enterprise.
5.1 Basic situation of on-site filling of electromagnetic flowmeter
In the linear filling mode, 20 Dosimag5BH12/15 are installed on the filling machine, corresponding to 20 filling heads, respectively, as shown in Figure 5; the filling liquid comes from the tank above the equipment, through the downflow pipeline Enter the two-way split branch pipe (DN40), with 10 DN15 filling pipes under each branch pipe; after the flow meter, a pneumatic shut-off valve is installed at 100mm above the filling port (the structure is special, the two-stage stroke, the shut-off valve The rod is located in the fluid in the pipeline; about 220mL per filling, but the error is unstable, from the deviation of 1~2mL to 5~6mL.
5.2 Reasons for affecting accuracy in this application
The electromagnetic flowmeter is a speed flow meter. It calculates the volume flow by measuring the flow rate of the pipeline. The sudden change of the flow rate will increase the measurement error to a certain extent. In this application, the reason for the accuracy is the flow velocity of the liquid in the pipeline, and the liquid is analyzed by the test. The flow rate is affected by the following three aspects.
5.2.1 Process influence. The selection and arrangement of the pipeline will have an effect on the flow rate of the liquid. For example, if the downstream pipeline enters the two-way splitter branch and is much smaller than DN40, the flow rate of the liquid flowing through each filling pipe will be There is a large deviation, the appropriate total branch pipe and the correct arrangement can improve the imbalance of liquid flow rate in the filling pipe.
5.2.2 Influence of other components. In the aseptic filling system, four kinds of valves are generally used, namely the quantitative valve (feeding valve), the pilot valve, the pressure control valve, and the control valve.
In the filling system, a quick shut-off valve (quantitative valve) is used to control the start and stop of the filling. The control principle of the fast shut-off valve: when the solenoid valve receives the output signal of the PLC (after the pulse signal of the filling flowmeter is collected by the PLC) When the processed output signal is started, the actuator moves the valve stem and the valve core upward, the valve core and the valve seat are separated, and the fluid enters the filling pipe through the valve seat to start filling, and when the solenoid valve receives the PLC output signal, the signal is closed. When the valve is moved, the valve stem moves downwards, which drives the valve core to move downwards, so that the valve core and the valve seat contact, thereby cutting off the fluid to complete the filling. In this application, the valve stem of the control valve is in the pipeline, and the fluid flows from the top to the bottom. The entire valve body, the action stroke of the valve stem is divided into two levels, corresponding to small flow and large flow.
When it is opened, the valve stem is lifted upwards and flows upwards, which causes a backlash to the fluid in the pipeline, and instantaneously reduces the flow velocity of the pipeline; the greater the relative speed, the greater the influence; when closed, the valve stem is pressed downward, for the pipeline The fluid is accelerated and the pipe flow rate is increased instantaneously (Figure 9).
The filling control valve in this application has two stages of stroke. When changing from small flow to large flow, the secondary action of the valve stem significantly reduces the flow velocity in the pipe, increasing the measurement error (Fig. 9). Filling control The structure and working mode of the valve affect the flow rate of the liquid in the pipeline, which is the main source of the error. However, the test proves that it can be improved by adjusting the stroke of the valve stem.
5.2.3 Liquid level control and back pressure control. The liquid level and back pressure affect the flow rate during the filling process. The fluctuation of the flow rate will cause fluctuations in the filling volume. The effect of this fluctuation is mainly reflected in the system issuing the valve cutting command to the valve completely. Closed delay period.
The upper tank in the filling system is small in size, about 60L. If the liquid level is controlled at 80%, the upper gas space is 12L, and the lower liquid space is 48L; if 250mL is filled every time, within 2s, then 20 bottles need 5000mL, ie 5L, the effect on the liquid level is 8%, the effect on the air pressure is 5L/12L=40%; due to the intermittent pause of filling, for the automatic control of liquid level and back pressure, The process is non-continuous steady state, the control is more difficult than the general process (the pressure transmitter sees a change in pressure value, in fact there may be damping within 1~2 seconds, the actual process may be more rapid fluctuations Big).
The filling head has a total of about 400 mm in the filling control valve and the lower filling head due to the need to install the filling control valve.
Part of the DN25 pipeline, the inner diameter of the pipe above the filling flowmeter and the flowmeter is 15mm/16mm. The cross-sectional area of ​​the two pipes is nearly 2 times different. Under the steady flow, the flow rates of the two parts are nearly 2 times different. For the flowmeter to be fast, the lower pipe is slow. Considering the influence of the valve stem, the flow rate differs by about 1 time.
The final exit part of the filling head is 10~14mm replaceable shrinkage. Through the shrinkage, back pressure can be generated, and the honeycomb siphon is built in the general shrinkage to ensure the pipe is full before and after filling. From the flow waveform of the test Look, the 10mm filling head produces proper damping and the flow curve is stable.
5.3 solution
Option 1: The first control of the filling valve, that is, a single opening and closing with a small flow stroke.
Test results: the flow smoothness increases, and the filling error is significantly reduced.
Option 2: Control the second stroke change of the filling valve, reduce the speed of the second time of the valve stem by slowing down the pneumatic exhaust of the valve, as shown in Figure 10:
Increase the exhaust filter valve to slow down the flow curve after the valve stem uplifting speed when the flow rate is reduced to a large flow rate. Scheme 3: Reduce the liquid level appropriately, such as 50% or lower to reduce the batch filling pressure. The effect, while helping to improve back pressure stability.