Flowmeter is a meter that indicates the measured flow rate and/or the total amount of fluid over a selected time interval. Simply put, it is a meter used to measure the flow of fluid in a pipe or open channel.
According to the measurement principle, it can be divided into the following major categories:
1. Mechanics: Instruments belonging to such principles have differential pressure and rotor type using Bernoulli's theorem; impulse type and movable tube type using momentum theorem; direct mass type using Newton's second law; using fluid momentum The target type of the principle; the turbine type using the angular momentum theorem; the vortex type using the principle of fluid oscillation, the vortex type; the pitot tube type using the total static pressure difference, and the volumetric type, the enthalpy, the trough type and the like.
2. Electrical principles: instruments used in such principles are electromagnetic, differential capacitive, inductive, strain resistance and so on.
3. Acoustic principle: The ultrasonic method is used to measure the flow using the acoustic principle. Acoustic (shock wave) and the like.
4. The principle of thermal: the use of thermal principles to measure the flow of the heat, direct calorimetry, indirect calorimetry and so on.
5. Optical principle: laser, photoelectric, etc. are instruments of this type.
6. The principle of atomic physics: nuclear magnetic resonance, nuclear radiation, etc. are instruments of this type.
7. Other principles: the principle of marking (trace principle, NMR principle), related principles.
Failure analysis
(1) When the flow control instrument system indicates that the value reaches the minimum, first check the on-site detection instrument. If it is normal, the fault is on the display instrument. When the on-site instrumentation indicator is also the smallest, check the valve opening degree. If the valve opening degree is zero, it is often a fault between the regulator valve and the regulator. When the on-site detection instrument indicates the minimum and the adjustment valve opening is normal, the cause of the failure may be caused by insufficient system pressure, system piping blockage, pump failure, media crystallization, improper operation, and the like. If it is a fault in the instrument, the reasons are: the orifice differential pressure flowmeter may be a positive pressure pilot conduit plug; the differential pressure transmitter positive pressure chamber leak; the mechanical flowmeter is a gear stuck or a filter plug.
(2) When the flow control instrument system indicates that the value reaches the maximum, the test instrument will often indicate the maximum. At this point, the manual remote control valve can be opened or closed. If the flow rate can be lowered, it is generally caused by the process operation. If the flow value does not fall, it is caused by the instrument system. Check whether the regulating valve of the flow control instrument system is operating; check whether the measuring system is normal; check whether the signal transmission system of the instrument is normal.
(3) The flow control instrument system indicates that the value fluctuates frequently, and the control can be changed to manual. If the fluctuation is reduced, the instrument is the cause or the instrument control parameter PID is not suitable. If the fluctuation is still frequent, it is the process operation.
