General principles for electromagnetic flowmeter selection
(1) Whether the medium to be tested is a conductive liquid or slurry, thereby determining whether an electromagnetic flow meter is selected;
(2) The conductivity of the measured medium determines the type of electromagnetic flowmeter—whether it is high conductivity or low conductivity;
(3) The nominal diameter of the large, small and common flow process pipelines required by the process, determine whether the flow rate of the medium is at a more economical flow point, whether the pipeline needs to be reduced, and then determine the diameter of the flowmeter;
(4) Determine whether to use an integrated or split flowmeter, and the degree of protection of the flowmeter, etc., based on the layout of the process piping.
(5) Selecting the electrode type according to whether the measured medium is easy to crystallize or crusting;
(6) selecting an electrode material according to the corrosiveness of the measured medium;
(7) The corrosiveness, wear and temperature of the measured medium determine the lining material to be used;
(8) The high working pressure of the measured medium determines the nominal pressure of the flow meter;
(9) The insulation of the process piping determines the type of grounding ring.
The flowmeter weighing impulse flowmeter that measures the flow using the impulse theorem is used to measure the flow rate of the granular solid medium, and is also used to measure the flow rate of the mud, the crystalline liquid, and the abrasive. Flow measurement ranges from a few kilograms per hour to nearly 10,000 tons. The typical instrument is a horizontal force-separated impulse flowmeter. The measurement principle is that when the measured medium falls freely from a certain height h to a detection plate with a tilt angle, an impulse is generated, and the horizontal force component of the impulse is proportional to the mass flow rate. Measuring this horizontal component can reflect the mass flow.
The electromagnetic flowmeter is made by applying the electric conductor to generate an induced electromotive force in a magnetic field, and the induced electromotive force is proportional to the flow rate, and is measured by measuring the electromotive force to reflect the flow of the pipeline. Its measurement accuracy and sensitivity are high. Industrially used to measure the flow of water, slurry and other media. The maximum diameter can be measured up to 2m, and the pressure loss is extremely small. However, media with low conductivity, such as gas and steam, cannot be used.
The electromagnetic flowmeter has a high cost, and the signal is susceptible to external magnetic field interference, which affects the wide application in industrial tube flow measurement. To this end, the product is constantly improving and updating, to the development of computer.
How the turbine flow meter works
The working principle of the turbine flowmeter: the fluid flows through the sensor housing. Since the blade of the impeller has a certain angle with the flow direction, the momentum of the fluid causes the blade to have a rotational moment. After the friction torque and the fluid resistance are overcome, the blade rotates, and the rotational speed is stabilized after the torque balance. Under certain conditions, the rotational speed is proportional to the flow rate. Due to the magnetic permeability of the blade, it is in the magnetic field of the signal detector (composed of permanent magnet and coil). The rotating blade cuts the magnetic field lines and periodically changes the coil. Magnetic flux, so that the two ends of the coil induce electricity
Pulse signal, which is amplified and shaped by the amplifier to form a continuous rectangular pulse wave with a certain amplitude, which can be transmitted to the display instrument to display the instantaneous flow rate and cumulative amount of the fluid. Within a certain flow range, the pulse frequency f is proportional to the instantaneous flow rate Q of the fluid flowing through the sensor. The flow equation is: Q = 3600 × f / k
In the formula:
F——pulse frequency [Hz];
K——the meter factor of the sensor [1/m], given by the checklist. If [1/L] is used, Q=3.6×f/k
Q——the instantaneous flow rate of the fluid (under working condition) [m3/h];
3600 - conversion factor.
The meter factor of each sensor is filled in the verification certificate by the manufacturer, and the k value is set in the matching display meter to display the instantaneous flow rate and the cumulative total amount.