Instruments that measure fluid flow are collectively referred to as flow meters or flow meters. The flowmeter is one of the important instruments in industrial measurement. With the development of industrial production, the accuracy and range of flow measurement requirements are getting higher and higher, and the flow measurement technology is changing with each passing day. Various types of flow meters have been introduced to suit various applications. More than 100 flow meters have been put into use. From different perspectives, flow meters have different classification methods. There are two commonly used classification methods. One is to classify according to the measurement principle adopted by the flowmeter: the second is to classify according to the structural principle of the flowmeter.
Sort by measurement principle
a. Mechanical principle:
Instruments belonging to such principles have differential pressure type, rotor type using Bernoulli's theorem;
Impulse type using the momentum theorem, movable tube type;
Direct mass equation using Newton's second law;
a target using the principle of fluid momentum;
Turbine using the angular momentum theorem;
Vortex type using vortex principle of fluid oscillation;
Use the total static pressure difference of the pitot tube type as well as volumetric and sputum, trough and so on.
b. Electrical principle:
Differential capacitor type,
Strain resistance type, etc.
c. Acoustic principle:
d. Thermal principles:
Indirect calorimetry and so on.
Maintenance of the turbine flowmeter sensor section:
1. Before the sensor is installed, use the mouth to blow or hand the impeller to make it rotate quickly to see if there is any display. Install the sensor when there is display. If there is no display, check the relevant parts and troubleshoot.
2. When using, keep the measured medium clean and free of impurities such as fibers and particles.
3. When the turbine flow sensor starts to use, the sensor should be slowly filled with the medium, and then the outlet valve should be opened (the valve should be installed at the back end of the flowmeter). It is forbidden to be impacted by the high-speed fluid when the sensor is in the mediumless state.
4. The maintenance period of the turbine flow sensor is generally half a year. When cleaning and cleaning, please be careful not to damage the parts in the measuring chamber, especially the impeller. Please be optimistic about the positional relationship between the guide and the impeller during assembly.
5. When the turbine flow sensor is not in use, the internal medium should be cleaned, and after drying, a protective cover is added at both ends of the sensor to prevent dust from entering, and then stored in a dry place.
6. The filter used in the turbine flowmeter should be cleaned regularly. When not in use, the internal medium should be cleaned. As with the sensor, add a dust jacket and store it in a dry place.
Test equipment: one 500MΩ insulation resistance tester, one multimeter.
(1) When the pipeline is filled with medium, measure the resistance between terminals A, B and C with a multimeter. The resistance between A-C and B-C should be equal. If the difference is more than 1 time, there may be leakage of the electrode, condensation on the outer wall of the measuring tube or the junction box.
(2) In the case of lining drying, measure the insulation resistance between A-C and B-C with MΩ meter (should be greater than 200MΩ). Then use a multimeter to measure the resistance of the two electrodes in terminals A and B and the measuring tube (should be in short-circuit communication). If the insulation resistance is small, indicating that the electrode is leaking, the entire flowmeter should be returned to the factory for repair. If the insulation is reduced but there is still more than 50 MΩ and the inspection result of step (1) is normal, the outer wall of the measuring tube may be damp, and the inside of the outer casing may be dried by a hot air blower.
(3) Use a multimeter to measure the resistance between X and Y. If it exceeds 200 Ω, the excitation coil and its lead wire may be open or poorly connected. Remove the terminal block check.
(4) Check the insulation resistance between X, Y and C, which should be above 200 MΩ. If it is lowered, dry the inside of the casing with hot air. In actual operation, the decrease in coil insulation will result in increased measurement error and unstable instrument output signal.
(5) If it is determined that the sensor is faulty, please contact the manufacturer of the electromagnetic flowmeter. The general site cannot be solved and needs to be repaired by the manufacturer.