Common fault repair processing of ultrasonic flowmeter

definition

Ultrasonic flow meters are meters that measure the flow by detecting the effect of fluid flow on the ultrasound beam (or ultrasound pulse).

principle

According to the principle of signal detection, ultrasonic flowmeter can be divided into propagation velocity difference method (direct time difference method, time difference method, phase difference method and frequency difference method), beam offset method, Doppler method, cross correlation method, spatial filtering method. And noise law, etc.

Ultrasonic flowmeter is the same as ultrasonic flowmeter. It is an unobstructed flowmeter because it does not have any obstruction in the flow passage of the instrument. It is a kind of flowmeter suitable for solving the problem of difficult flow measurement, especially in the measurement of large-diameter flow. The advantage is that it is one of the fastest growing types of flow meters.

Ultrasonic flowmeter adopts the principle of time difference measurement: one probe transmits the signal through the pipe wall, the medium and the other side of the pipe wall, and is received by the other probe. At the same time, the second probe also transmits the signal and is received by the first probe. Due to the influence of the flow velocity of the medium, there is a time difference Δt between the two. According to the calculation, the conversion relationship V=(C2/2L)×Δt between the flow velocity V and the time difference Δt can be obtained, and the flow rate value Q can be obtained.

Ultrasonic flowmeters will have some abnormal phenomena and faults during use. Some fault phenomena are analyzed as follows:

First, the failure phenomenon: the reading is unstable and the change is severe

Analysis of the cause: the pipe with ultrasonic flow sensor installed has large vibration or there is a device that changes the flow state (such as the flow meter installed in the regulating valve, pump, downflow hole)

Solution: Modify the flow sensor away from the vibration source or move to the upstream of the changing flow device

Second, the fault phenomenon: the reading is not accurate, the error is large

Cause Analysis:

1. Ultrasonic flowmeter sensor The sediment on the top and bottom of the horizontal pipe interferes with the ultrasonic signal. Solution: Install the sensor on both sides of the pipe.

2. The ultrasonic flowmeter sensor is mounted on a pipe with a downward flow of water, and the pipe is not filled with fluid. Solution: Mount the sensor on a fluid-filled pipe section.

3. There are devices that cause the flow regime to fluctuate strongly, such as venturi, orifice, vortex, turbine or partially closed valves, which are within the range of sensor transmission and reception, making the readings inaccurate. Solution: The sensor is mounted away from the device, and the sensor is upstream from the device 30D, downstream from the device 10D or moved upstream of the device.

4. The input pipe diameter of the ultrasonic flowmeter does not match the inner diameter of the pipe. Solution: Modify the pipe diameter to match.

Third, the fault phenomenon: the sensor is good, but the flow rate is low or no flow rate

Cause Analysis:

1. The paint and rust outside the pipeline have not been cleaned up. Workaround: Re-clean the pipe and install the sensor.

2. The surface of the pipe is uneven or the ultrasonic flowmeter is installed at the welded joint. Solution: Smooth the pipe or away from the weld.

3, the pipe roundness is not good, the inner surface is not smooth, there is pipe lining scaling. This may occur if the pipe is a cast iron pipe. Solution: Choose a material such as steel pipe with a smooth inner pipe or lining.

4. The measured medium is pure or the suspended solids are too low. Solution: Choose the other type of instrument that is suitable.

5. The sensor is mounted on the pipe of fiberglass. Solution: Remove the glass fibers.

6. The sensor is mounted on the bushing, which will weaken the ultrasonic signal. Solution: Move the sensor to the uncased section.

7. The sensor and the pipeline are not well coupled, and the coupling surface has gaps or air bubbles. Solution: Reinstall the couplant.

4. Fault phenomenon: when the control valve is partially closed or the flow is reduced, the reading will increase.

Analysis of the cause: The sensor is placed too close to the downstream of the control valve. When the valve is partially closed, the actual measurement of the flowmeter is to control the flow rate of the valve's reduced diameter flow rate, and the flow rate increases due to the reduced diameter.

Solution: Move the sensor away from the control valve, move the sensor upstream from the control valve 30D or move the sensor to the control valve upstream from the control valve 5D.

V. Fault phenomenon: The ultrasonic flowmeter works normally, and suddenly the ultrasonic flowmeter no longer measures the flow.

Cause Analysis:

1. The measured medium changes. Solution: Change the measurement method.

2. The measured medium is vaporized due to excessive temperature. Solution: Cool down

3. The temperature of the measured medium exceeds the limit temperature of the sensor. Solution: Cool down

4. The couplant under the sensor is aged or consumed. Solution: Recoat the coupling agent

5. The instrument exceeds its own filtering value due to high frequency interference. Solution: Keep away from interference sources

6. Data loss in the computer. Solution: Re-enter the correct parameters

7, the computer crashes. Workaround: Restart your computer