Electromagnetic Flow Meter
What is Precision Flow Measurement Technology?
The electromagnetic flow meter is a device used for measuring the flow of the liquid when it passes through the pipeline. Or we can say that the electromagnetic flowmeter uses for measuring the flow rate of the electrically conducting fluid. The electrically conductive liquid means the liquid allows the current to pass through it. The electromagnetic flowmeters work on the principle that the obstruction is created in the path of the liquid and the pressure of the liquid induces the voltage across the coil.
Working Principle of Electromagnetic Flowmeter
The electromagnetic flowmeter works on the principle of Faraday’s Law of electromagnetic induction. This law states that when the conductive liquid passes through the magnetic field, the voltage induces across the conductor. The magnitude of the voltage is directly proportional to the velocity, length of the conductor and the strength of the magnetic field. The magnetic field is generated by the coil which is mounted on the external metallic body of the pipe. The liquid acts as a conductor and when passes through the magnetic field induce the voltage across the coil. The magnitude of the voltage depends on the velocity of the liquid.
Construction of Electromagnetic Flowmeter
The electromagnetic flow meter consists of the electrically insulated pipe made of fibre. Electrodes placed opposite to each other; magnetic coil placed on the pipe for generating the magnetic field etc. The insulated pipe carries the liquid whose flow needs to be measured. The electromagnet is placed around the insulated pipe. This electromagnet induces the magnetic field around the pipe. The arrangement is similar to the conductor moving in the magnetic field. The voltage is induced across the coil because of the flow of the liquid. The induces voltage is expressed as, If the magnetic field around the pipe remains constant than the generating voltage is proportional to the velocity of the fluid.
Where, v – velocity of conductor (flow); m/s
l – length of conductor = diameter of pipe; m
B = flux X density; wb/m2
- E = Induced voltage
- K = Constant
- B = Magnetic field strength,
- D = Distance between electrodes,
- V = Liquid flow velocity
Types of Electromagnetic Flowmeter
Insertion
Is a type of magmeter with a shape resembling a headed stick whose installation is perpendicular to the flow of liquid. Unlike standard magnetic flow meters, the magnetic field in this magmeter is formed from a magnet in the stick. This type is very suitable for pipes with a wide cross-sectional area.
In-line
Is a type of standard magmeter that has an inline pipe location (in line) with the direction of flow. The location of the components is as described above. This type is more suitable for pipes with a small-medium cross-sectional area and requires higher accuracy.
With magnetically actuated float sensors, switching occurs when a permanent magnet sealed inside a float rises or falls to the actuation level. With a mechanically actuated float, switching occurs as a result of the movement of a float against a miniature (micro) switch. For both magnetic and mechanical float level sensors, chemical compatibility, temperature, specific gravity (density), buoyancy, and viscosity affect the selection of the stem and the float. For example, larger floats may be used with liquids with specific gravities as low as 0.5 while still maintaining buoyancy. The choice of float material is also influenced by temperature-induced changes in specific gravity and viscosity – changes that directly affect buoyancy.
Conductive level sensors are ideal for the point level detection of a wide range of conductive liquids such as water, and is especially well suited for highly corrosive liquids such as caustic soda, hydrochloric acid, nitric acid, ferric chloride, and similar liquids. For those conductive liquids that are corrosive, the sensor’s electrodes need to be constructed from titanium, Hastelloy B or C, or 316 stainless steel and insulated with spacers, separators or holders of ceramic, polyethylene and Teflon-based materials. Depending on their design, multiple electrodes of differing lengths can be used with one holder. Since corrosive liquids become more aggressive as temperature and pressure increase, these extreme conditions need to be considered when specifying these sensors.
Conductive level sensors use a low-voltage, current-limited power source applied across separate electrodes. The power supply is matched to the conductivity of the liquid, with higher voltage versions designed to operate in less conductive (higher resistance) mediums. The power source frequently incorporates some aspect of control, such as high-low or alternating pump control. A conductive liquid contacting both the longest probe (common) and a shorter probe (return) completes a conductive circuit. Conductive sensors are extremely safe because they use low voltages and currents. Since the current and voltage used is inherently small, for personal safety reasons, the technique is also capable of being made “Intrinsically Safe” to meet international standards for hazardous locations. Conductive probes have the additional benefit of being solid-state devices and are very simple to install and use. In some liquids and applications, maintenance can be an issue. The probe must continue to be conductive. If buildup insulates the probe from the medium, it will stop working properly. A simple inspection of the probe will require an ohmmeter connected across the suspect probe and the ground reference.
Flow measurement methods other than positive-displacement flowmeters rely on forces produced by the flowing stream as it overcomes a known constriction, to indirectly calculate flow. Flow may be measured by measuring the velocity of fluid over a known area. For very large flows, tracer methods may be used to deduce the flow rate from the change in concentration of a dye or radioisotope.
is a type of flow meter that measures the velocity of a fluid with ultrasound to calculate volume flow. Using ultrasonic transducers, the flow meter can measure the average velocity along the path of an emitted beam of ultrasound, by averaging the difference in measured transit time between the pulses of ultrasound propagating into and against the direction of the flow or by measuring the frequency shift from the Doppler effect. Ultrasonic flow meters are affected by the acoustic properties of the fluid and can be impacted by temperature, density, viscosity and suspended particulates depending on the exact flow meter. They vary greatly in purchase price but are often inexpensive to use and maintain because they do not use moving parts, unlike mechanical flow meters.