Several possible faults of ultrasonic liquid level gauge

Because the ultrasonic waves emitted by the ultrasonic liquid level gauge are invisible to the human eye, there are several situations in which abnormal work occurs on site, in addition to the failure of the liquid level gauge itself, there will be the following situations:

The first type: There will be stirring in the container on site, and the liquid will fluctuate greatly, which will affect the measurement of the ultrasonic level gauge.

Symptom: No signal or severe data fluctuation.

Reason: The measurement distance of a few meters mentioned by the ultrasonic level gauge refers to the calm water surface. For example, an ultrasonic liquid level gauge with a range of 5 meters generally means that the distance to measure the calm water surface is 5 meters, and the actual factory will reach 6 meters. When there is stirring in the container, the water surface is not calm, and the reflected signal will be weakened to less than half of the normal signal.

Solution:

1. Select an ultrasonic level gauge with a larger range. If the actual range is 5 meters, then use a 10-meter or 15-meter ultrasonic level gauge for measurement.

2. If the ultrasonic liquid level gauge is not replaced, and the liquid in the tank is non-viscous, a waveguide can also be installed, and the probe of the ultrasonic liquid level gauge is placed in the waveguide to measure the height of the liquid level gauge, because the liquid in the waveguide The surface is basically stable.

3. It is recommended to change the two-wire ultrasonic liquid level gauge to a four-wire system.

The second type: there is foam on the surface of the liquid.

Fault phenomenon: The ultrasonic level gauge is always searching, or it will display the state of "lost wave".

Reason: Foam can obviously absorb ultrasonic waves, resulting in very weak echo signals. Therefore, when more than 40-50% of the surface of the liquid is covered with foam, most of the signal emitted by the ultrasonic level gauge will be absorbed, causing the level gauge to fail to receive the reflected signal. This has nothing to do with the thickness of the foam, but mainly with the coverage area of the foam.

Solution:

1. Install the waveguide, put the probe of the ultrasonic liquid level gauge in the waveguide to measure the height of the liquid level gauge, because the foam in the waveguide will be reduced a lot.

2. Replace it with a radar level gauge for measurement. The radar level gauge can penetrate foam within 5 cm.

The third type: the temperature in the on-site pool or tank is high, which affects the measurement of the ultrasonic level gauge.

Fault phenomenon: When the water surface is close to the probe, it can be measured, but when the water surface is far away from the probe, it cannot be measured. When the water temperature is low, the measurement of the ultrasonic liquid level gauge is normal, but when the water temperature is high, the ultrasonic liquid level gauge cannot measure it.

Reason: The liquid medium generally does not produce steam and mist below 30-40°C, and it is easy to produce steam or mist when the temperature exceeds this temperature. When it is reflected back, it will be attenuated again, causing the ultrasonic signal back to the probe to be very weak, so it cannot be measured. Moreover, in this environment, the probe of the ultrasonic level gauge is prone to water droplets, and the water droplets will hinder the transmission and reception of ultrasonic waves.

Solution:

1. To increase the measuring range, in fact, the height of the tank is 3 meters, and an ultrasonic level gauge between 6 meters and 9 meters should be selected. Can reduce or weaken the influence of steam or mist on the measurement.

2. The probe should be made of polytetrafluoroethylene or PVDF to make it physically sealed, so that it is not easy to condense water droplets on the emitting surface of such a probe. As for the emitting surface of other materials, water droplets are relatively easy to condense.

The fourth type: There is electromagnetic interference on site.

Fault phenomenon: The data of the ultrasonic level gauge is beating irregularly, or it simply shows no signal.

Reason: There will be many motors, frequency converters and electric welding in the industrial site, which will affect the measurement of the ultrasonic level gauge. Electromagnetic interference will exceed the echo signal received by the probe.

Solution:

1. The ultrasonic liquid level gauge must be reliably grounded. After grounding, some interference on the circuit board will run away through the ground wire. And this grounding must be grounded separately, and cannot share a ground with other equipment.

2. The power supply cannot be the same as the frequency converter and motor, nor can it be directly drawn from the power system power supply.

3. The installation site needs to be far away from frequency converters, variable frequency motors, and high-power electric equipment. If it cannot be kept away, a metal instrument box should be installed outside the liquid level gauge to isolate the shield, and the instrument box also needs to be grounded.

Type 5: Entering the blind zone

Symptom: Full scale or arbitrary data will appear.

Reason: Ultrasonic liquid level gauges will have a blind area, generally within a range of 5 meters, the blind area is 0.3-0.4 meters. The range within 10 meters is 0.4-0.5 meters. After entering the blind zone, the ultrasonic wave will have arbitrary values and cannot work normally.

Solution: 1. The height of the blind area needs to be considered during installation. After installation, the distance between the probe and the water level must be greater than the blind area.