Daily maintenance (1)
Only need to periodically check the instrument, check the environment around the instrument, remove the dirt, ensure that no water and other substances are inspected, check whether the wiring is good, check whether there is a new strong electromagnetic field device near the instrument or a new installed wire across the instrument. If the measuring medium is easy to contaminate the electrode or precipitate or scale in the measuring tube wall, it should be regularly cleaned and cleaned.
Folding fault finding
After the flowmeter starts to be put into operation or is put into operation for a period of time, it is found that the instrument is not working properly. First, check the external condition of the flowmeter, such as whether the power supply is good, whether the pipeline is leaking or is in a state of non-full pipe, whether there is air bubble in the pipe, whether the signal cable is Damage, converter output signal (ie rear position meter input loop) is open circuit. Remember to blindly disassemble the flowmeter.
Sensor check
Test equipment: one 500MΩ insulation resistance tester, one multimeter.
Test steps:
(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.
Vortex flowmeter analysis and solution
3. Reasons for parameter setting direction. The instrument is incorrectly indicated due to a parameter error. The parameter error makes the secondary meter full frequency calculation error, and the reason for this is mainly related to questions 1 and 3. The full-scale frequency is similar, indicating that the long-term inaccuracy is indicated. The full-scale frequency of the actual full-scale frequency and large-dry calculation indicates that the range is fluctuating and cannot be read. The inconsistency of the parameters on the data affects the final determination of the parameters, and finally passes. Recalibration combined with mutual comparison to determine the parameters solves this problem.
4. The secondary instrument is faulty. There are many faults in this part, including: when the instrument board is disconnected, the range setting has individual bit display bad, and the K coefficient setting has individual bit display bad, which makes it impossible to determine the range setting and K factor setting. Part of the reason is mainly related to questions 1, 2. The problem is solved by fixing the corresponding fault.
5, Four-way line connection problem. On the surface of some circuits, the line connection is very good. Check carefully. Some connectors are actually loose and the circuit is interrupted. Some connectors are tightly connected, but the fastening screws are fastened to the wire due to the secondary line problem. Interruption, this part of the reason is mainly related to question.
Ultrasonic flowmeter measurement principle
When the ultrasonic beam propagates in the liquid, the flow of the liquid will cause a small change in the propagation time, and the change in the propagation time is proportional to the flow velocity of the liquid, and its relationship conforms to the following expression.
among them
θ is the angle between the sound beam and the direction of flow of the liquid
M is the number of linear travels of the sound beam in the liquid
D is the inner diameter of the pipe
Tup is the propagation time of the sound beam in the positive direction
Tdown is the propagation time of the sound beam in the reverse direction
ΔT=Tup –Tdown
Let the speed of sound in the stationary fluid be c, the velocity of the fluid flow be u, and the propagation distance be L. When the sound wave is in the same direction as the fluid flow direction (ie, the downstream direction), the propagation velocity is c+u; otherwise, the propagation velocity is cu. Two sets of ultrasonic generators and receivers (T1, R1) and (T2, R2) are placed at two places separated by L. When T1 is in the forward direction and T2 transmits ultrasonic waves in the reverse direction, the time required for the ultrasonic waves to reach the receivers R1 and R2 respectively is t1 and t2, then
T1=L/(c+u); t2=L/(c-u)
Since the flow velocity of the fluid in the industrial pipeline is much smaller than the sound velocity, that is, c>>u, the time difference between the two is ▽t=t2-t1=2Lu/cc. Thus, the propagation velocity of the acoustic wave in the fluid is known. When it is known, the flow rate u can be obtained by measuring the time difference ▽t, and the flow rate Q can be obtained. The method of measuring the flow using this principle is called the time difference method. In addition, a phase difference method, a frequency difference method, or the like can be used.