不适用于测量低雷诺数（ReD≤2×104）流体。 Vortex flowmeter is not suitable for measuring low Reynolds number (ReD≤2 × 104) fluid. When the Reynolds number is low, the Strouhal number changes with the Reynolds number, the linearity of the vortex flowmeter becomes poor, and the high viscosity of the fluid will significantly affect or even hinder the generation of vortices. Therefore, a limiting condition for the selection of vortex flowmeters It cannot be used below the bounded Reynolds number. Vortex flowmeters are suitable for a wide range of fluids, but pay attention to the dirty nature of the fluid. The scouring of the vortex generator of the vortex flowmeter by the fluid containing solid particles will generate noise and wear the vortex generator. If the short fibers contained are wound on the vortex generator, the meter coefficient will be changed. Vortex flowmeters have little application experience in mixed-phase fluids. Generally, they can be used to contain dispersed and uniform micro-bubbles, but the volumetric gas content should be less than 7% to 10% for gas-liquid two-phase flow. If it exceeds 2%, Correct the meter factor. Can be used for gas-solid, liquid-solid two-phase flow containing dispersed and uniform solid particles with a content of not more than 2%. It can be used for two-component liquid-liquid (such as oil and water) flows that do not dissolve each other. Pulsating and swirling flow can have serious effects on vortex flowmeters. If the pulsation frequency and the vortex frequency band are combined, it may cause resonance to damage the normal work and equipment, and cause the vortex signal to "lock". At this time, the signal is fixed at a certain frequency. "Locking" is related to the amplitude of the pulsation, the shape of the vortex generator, and the clogging ratio.
Maintenance knowledge of vortex flowmeter
Vortex flowmeter mainly includes three parts: vortex flow transmitter, flow indicator and connection cable. This article mainly introduces the maintenance of LUGB vortex flowmeter. In the following, the causes of various failures are analyzed one by one based on the failure phenomenon.
First, the indicator of the start-up display meter is off, and the meter head of the vortex flowmeter indicates the mechanical zero point. This phenomenon is because the AC power is not turned on, you should carefully check whether the 220V AC power supply line is connected properly, whether the fuse behind the display is fused and its contact with the socket.
2. The indicator of the start-up display meter is on, and the meter head of the vortex flowmeter indicates the mechanical zero point. At this time, you should first check whether the 250Ω resistor on the rear panel terminal of the display meter is connected, and then measure the 24V DC voltage of the terminal behind the meter. This voltage is the common power supply of the transmitter amplifier board and the digital-to-analog conversion board of the display meter. DC voltage, digital-to-analog conversion board does not work, vortex flowmeter meter head indicates the mechanical zero point, at this time you can focus on inspection 3JC1, 3BG1, 3BG2, 3BG4.
3. The instantaneous flow indication is normal, and the counter does not skip words. The vortex flowmeter's meter head indicates normal, indicating that the flow signal input is normal, and the vortex flow sensor is fine. The reason the counter doesn't skip words is because of the constant conversion part of the display table:
1. First check whether the counting switch is turned on and whether the counter itself has any problems. If the counter is stuck and does not jump, there will be a clicking sound.
2. Check the DC 24V power supply of the counting amplification part and the DC 10V power supply of the constant conversion part, and focus on the inspection of 3BG3, 3BG5, 3BG6.
3. No problem was found in the above inspection. You can use an oscilloscope to check the signal frequency of 2JC1-3 pins, monostable 2JC1-6 pins, widened 2JC-7, and 8 pins, and amplify and drive the waveforms of 2JC7-6 pins. Normally, they should be regular. Square wave. In addition, check whether 2BG1, 2BG2 and 2BG5 are normal.
表头指示电零点。 Fourth, the count is normal, the vortex flowmeter head indicates the electrical zero point. The accumulation is normal, which also indicates that the input signal of the vortex flowmeter sensor is normal, the fault point is in the digital-to-analog conversion circuit of the display meter, and after the output of the shaping circuit. Use an oscilloscope to view the transmission waveforms of pins 1JC2-6 of the monostable circuit, and the common E poles of the level conversion circuits 1BG1 and 1BG2, which should normally be square waves. Then use a multimeter to check the frequency and voltage conversion circuit 1JC3-6 step by step. Amplifier circuit 1JC4-6 pin with or without output voltage (the value varies with the frequency of the flow pulse), and the quality of 1BG3. Here, the role of the 1JC5 voltage follower must not be ignored. 1BG13 provides a 12V reference power supply. The reference power supply provides a reference voltage for 1JC1 to 1JC4 through the 1JC5 voltage follower. Without this voltage value, 1JC1 to 1JC4 cannot work normally. During maintenance, you should be good at using the oscilloscope to observe the waveform, especially in the inspection of shaping, monostable and level conversion circuits. Do not rely solely on the voltage value measured by the multimeter. For the pulse circuit, the static output is a stable value, and the dynamic output should be a frequency signal. This should be paid attention to during maintenance.
V. There is flow, neither the meter head nor the accumulated amount of the vortex flowmeter. This phenomenon indicates that there is no flow signal input to the display meter. Check the 24V DC voltage at the terminals behind the display meter. If not, check and display the table 3JC1, 3BG1, 3BG2, 3BG4; if the 24V DC voltage is normal, the vortex flow sensor is damaged. LUGB vortex flowmeters include sensors and preamplifiers. Inspection of it also requires two aspects:
1. First check the voltage of the output terminal of the vortex flowmeter amplifier to ground. Normally, it should be about 9V which is unstable. If the output is zero, there must be a problem with the amplifier. You can focus on checking the quality of BG1 to BG6 and the output waveforms of JC1 and JC2. If the amplifier output voltage is stable around 15V, you still need to check the voltage of the sensor input to ground. This value is usually about 5V. If it is zero, there must be a problem with the amplifier, and generally there is a problem with the constant current source and input circuit , You can focus on BG1, BG2, BG4, BG5; if the sensor input terminal voltage to ground is about 8V, you can conclude that the sensor itself has a problem.
2. To judge the quality of the vortex flowmeter sensor, generally measure its resistance. The sensors of the LUGB vortex flowmeter are two sets of diffused silicon force-sensitive sheets, one set is put in, and the other set is reserved. Under normal circumstances, the resistance of the silicon force-sensitive chip to ground (housing) should not be less than 100MΩ, and the resistance of the chip itself should be 2Ω to 3kΩ. Disassemble the silicon force sensor lead in the transmitter preamp and measure its resistance to ground. If it is less than 100MΩ, remove the test head and its lead plug, dry and put it into use; if the silicon force sensor is insulated from the case, Reliable, then test the resistance value of the film itself, too large or too small can not be used. Note that in the sensor silicon chip, as long as one of the resistance to ground and the resistance itself are normal at the same time, you can avoid replacing the vortex probe and directly exchange the leads of the diffusion silicon force sensitive sheet. In addition, if the measured liquid has strong adhesion or viscosity, or has other impurities, the detection head is easily covered by the attachment. When the attachment is thick to a certain extent, the T-shaped cantilever tail of the detection head is If it is stuck, the T-shaped tail will no longer be able to produce a slight deflection with the vortex, and it will not cause a small amount of deformation of the elastomer. The resistance value of the silicon force-sensitive sheet in the bullet will not change periodically. Therefore, there is no flow signal, and the display meter naturally has no flow indication. In this case, you should first rotate the insertion rod 180 degrees to backwash the vortex street; if it still does not work, you have to remove the transmitter and clean the vortex street with a small brush until it is clean.
6. The instantaneous flow is normal, and the cumulative amount is half less than the actual flow. This phenomenon is because there is no output in a certain stage of the signal frequency circuit, and 2JC1 and the differential circuit can be checked.
7. The instantaneous flow is normal, and the cumulative amount is significantly or doubled than the actual flow. There are two possible causes for this failure: one is that there is no output in one stage of the twelve-stage frequency divider circuits 2JC2 to 2JC4; the other is that the four-input AND gates 2JC5 and 2JC6 have one stage of input open, which also includes Dial in place.
8. When there is no flow, the display table has instructions, and the counter jumps. This phenomenon is mostly caused by interference, and the flowmeter should be installed away from interference sources such as large motors and strong power sources. To judge whether there is interference, just use the pointing rod to rotate the insertion rod 90 degrees. If the meter head still shows, interference is introduced. The channels of interference introduction are:
1. The detection piece of the vortex flowmeter is damp, and the insulation resistance with the casing is reduced. At this time, the vortex probe and the chip lead plug must be removed and dried before use. 2. The sensitivity of the vortex flowmeter amplifier is too high. The sensitivity potentiometer on the amplifier board can be adjusted until the meter head reaches zero when there is no flow. 放大器本身纹波太大，电解电容漏电或容量下降都有可能引入干扰。 3. The ripple of the vortex flowmeter amplifier itself is too large, and leakage or reduction in capacity of the electrolytic capacitor may introduce interference. Can check and display the table 3C5, 3C7, 3C9 and C1, C3, C7 and other electrolytic capacitors in the amplifier.