Flow meter for effluent water uses the principle of electromagnetic induction to measure the wastewater flow in the pipeline, it is
electromagnetic flow meter. All conductive liquids can be measured by electromagnetic flowmeter, which has a wide range of applications and can be used to measure the flow of effluent, wastewater , drainage , sanitary sewer ,various corrosive acids, alkalis, salt solutions, and conductive liquids containing solid particles and suspending solids (such as mud) or fibers. Since the electromagnetic flowmeter itself is easy to sterilize, it can also be used for flow measurement in the pharmaceutical industry and food industry with special hygiene requirements, such as plasma, cattle, Detect some milk, fruit juice, wine, etc. In addition, it can also be used as flow measurement for large pipes of tap water and sewage, can be made into large pipeline flow meter.
Effluent water flow meter is composed of two parts: flow sensor and conversion. The flow sensor is installed in the effluent pipeline, and the effluent flow is transformed into the induced potential; flow converter is to convert the induced potential into a unified DC signal of 4~10mA as the output for indication, recording or adjustment.
Flow sensor for effluent water
According to the principle of electromagnetic induction, when the conductive liquid moves in the magnetic field and cuts the magnetic field lines, an induced potential will be generated in the conductor. According to this principle, when the conductive fluid flows in the vertical direction in the magnetic field and cuts the magnetic field lines, an induced potential will also be generated on the two electrodes. The direction of the induced potential can be judged. The value is related as follows:
Ex=BDv•10-8
Where:
Ex--induced potential (V);
B—magnetic induction intensity (G);
D--pipe diameter, that is, the length of the conductor perpendicularly cutting the magnetic line of force (cm);
V—liquid velocity (cm/s) perpendicular to the direction of the magnetic field lines.
The relationship between the volume flow Q (cm3/s) and the flow velocity V is:
Q=1/4πD
2v
Substituting the above formula into “Ex=BDv•10-8” we get:
In the formula, K is called the flow meter constant. After the magnetic induction intensity B and the pipe diameter D are determined and kept constant, K is a constant. At this time, the induced potential has a linear relationship with the volume flow. In this way, by inserting an electrode on both sides of the pipe, the induced potential can be drawn out, and the waste water flow rate can be indicted out by the flow meter and flow transmitter. There are many structures of the flow sensor of the electromagnetic flowmeter, no matter what kind of structure; they are all composed of excitation coil, magnetic yoke, conduit, electrode and shell. But no matter what kind of structure, they are composed of excitation coil, yoke, conduit, electrode and shell and other parts. In order to avoid the short circuit of the magnetic field lines by the wall of the measuring conduit and to reduce the eddy current loss as much as possible in the strong alternating magnetic field, the measuring conduit is made of a non-magnetically conductive high-resistance material. Generally, it is stainless steel, glass fiber reinforced plastic or some aluminum alloys with high resistivity.
The lining of the flow measuring tube is made of acid-resistant rubber, epoxy resin, polytetrafluoroethylene and other materials, such as Teflon, PTFE,PFA,rubber.,etc. Its function is to prevent the two electrodes from being short-circuited by the metal conduit, and to adapt to the corrosiveness of the effluent water.
Electrodes are generally made of stainless steel, and are also made of platinum, tantalum, titanium, hastelloy, tungsten carbide.,etc . The electrodes are flush with the lining so that fluid flow is unimpeded; electrodes are generally installed horizontally in the pipe to prevent deposits from building up on the electrodes.
In order to reduce the quadrature interference, two wires are drawn from one of the electrodes, and respectively bypass the magnetic poles to form two loops, which are connected to a zero potentiometer. By adjusting the zero potentiometer, the interference entering the flow measuring instrument can be eliminated. The potentials cancel each other out and play the role of suppressing the quadrature interference signal.
Flow converter
The task of the electromagnetic flowmeter conversion part is to convert the output signal E of the detection part into a 4~10mA DC standard electrical signal.
The induced potential Bx is a weak alternating signal, generally only a few millivolts, and is accompanied by various interference components, so the converter is required to have high input impedance and be able to suppress various interference components.
Features of magnetic wastewater flow measurement
1. There are no moving parts in the measuring conduit or parts protruding from the inside of the tube, so the pressure loss of waste water flow meter is very small, almost equal to zero.
2. There is a linear relationship between the output current and the flow rate, and is not affected by changes in the physical properties of the effluent (temperature, pressure, viscosity) and flow state. The flow rate range is also wide, can be made into 100:1.
3. The sensing element is not in contact with the effluent water and can be used for the aggressive and corrosive waste water which may contain HCL, H2SO4, and nitric acid;
4. Effluent flow meter has quick response, can be used for the measurement of effluent pulsating flow.
5. The range ratio is as high as 1:100, and the wastewater flow measurement range is large to adapt large change of waste water.
6. A wide range of flow sensor can be made, normal request 1/2”, 1 inch, DN50, 2 inch, 3 inch, 4 inch, DN100, DN200, 6 inch effluent water flow meter, 8 inch, 10 inch, 12”, 14”, 16”,18 inch.etc waste water flow meter.
Limitations and shortcomings for magnetic effluent flow meter
1. The measured effluent must be a conductive liquid, and its conductivity is generally required to be above 10-4s/cm, gravity sewer flow meter.
2. Due to the limitation of the conduit lining material, the temperature range generally used is 0~200°C. And because the electrode is embedded on the conduit, the working pressure of the electromagnetic flowmeter is also limited to a certain extent.
3. The waste water should not contain too much oil, fat or grease, it will stick on the electrodes to affect normal working of magnetic flow meter.
Installation of electromagnetic flowmeter for effluent water
1. The installation position should ensure that the measuring conduit can be filled with effluent at any time, preferably vertical installation and waste water flow from bottom to top install position in order to reduce the error caused by the bubbles on the electrode when the liquid flows. When installing horizontally, the two electrodes must be on the same level. The distance between the valve and the effluent flow sensor should be at least 5 times the diameter of the pipe.
2. Set the grounding separately and never connects the grounding wire to the common grounding wire such as motors and electrical appliances or to the upper and lower drains. The conversion part has been grounded through the cable, and must not be grounded again.
3. The installation site should be far away from all magnetic sources, and there should be no vibration.
4. The transmitter and the metal pipeline are connected by flanges or threads, if they are not reliable, they should be connected with metal wires.
Maintenance of electromagnetic flowmeter for waste water
The electromagnetic flowmeter installed according to the above requirements, even if the transmitter is well grounded, when the power equipment near the transmitter has a strong ground leakage current, or there is a large stray current on the pipeline where the transmitter is installed, Or electric welding will cause the increase of interference potential, which will affect the normal operation of the instrument, which should be paid special attention in use.
In addition, it should be noted that the measured effluent should not contain a large amount of magnetic substances during use; after the instrument is put into normal operation, the potentiometers should not be adjusted arbitrarily, and the pipeline should be free of leakage.
The effluent flow sensor tube that has been used for a long time should be regularly maintained and cleaned to prevent the deposition of scale layers on the inner wall of the conduit, which will affect the measurement accuracy. For transmitters that work for a long time under harsh environmental conditions, the signal socket is easily corroded and the insulation is easily damaged, which requires regular maintenance.
How to order and choose electromagnetic flowmeter for effluent water
You’d better provide below information to effluent flow meter manufacture to choose suitable flow meters:
Is waste water corrosive or not? What is effluent composition? Such as any acids or fat, grease contained? any solids or particles contained ?
If there is solids contained, you should inform flow meter factory solids content, within 5%, 10% or 20% ? Too much solids, we will consider slurry flow meter.
Is it Industrial sewage or civil sewage?
Pipeline size to install effluent flow meter?
Effluent flow range? Waste water min flow , normal operation flow and max flow
What is effluent working pressure, temperature, ambient temperature?
Do you need integral display for effluent or remote indication for waste water?
Any communication you need? Such as MODBUS RTU or HART ? OR Profibus-DP?
Wastewater flow meter price
Eletromagnetic flow meter for waste water measurement is cheap, price starts from $ 400. The effluent water flow meter price varies by flow meter dial size, liner material, electrodes material, communication types, shell material .,etc. Best flow meters for wastewater are magnetic flow meter for its low cost and reliable working and zero pressure loss.
