The first type: There is stirring in the container on site, and the liquid fluctuates relatively large, which affects 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 maximum distance for measuring a 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.
1. Choose an ultrasonic level gauge with a larger range. If the actual range is 5 meters, use a 10-meter or 15-meter ultrasonic level gauge for measurement.
2. If you do not change the ultrasonic level gauge, and the liquid in the tank is non-viscous, you can also install a waveguide, put the probe of the ultrasonic level gauge in the waveguide to measure the height of the liquid level gauge, because the liquid level in the waveguide 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 liquid level gauge keeps searching, or displays the state of “lost wave”.
Reason: Foam absorbs ultrasonic waves significantly, resulting in a very weak echo signal. 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.
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. Above this temperature, steam or mist is easily produced. The ultrasonic wave emitted by the ultrasonic level gauge will attenuate once through the steam during the emission process and reflect back from the liquid surface. When it needs to attenuate again, the ultrasonic signal that ## returns to the probe is very weak, so it cannot be measured. Moreover, in this environment, the ultrasonic level gauge probe is prone to water droplets, which will hinder the transmission and reception of ultrasonic waves.
1. To increase the measuring range, the actual height of the tank is 3 meters, and an ultrasonic level gauge of 6 meters to 9 meters should be selected. The influence of steam or mist on the measurement can be reduced or weakened.
2. The probe should be made of polytetrafluoroethylene or PVDF, making it physically sealed, so that the emitting surface of such a probe is not easy to condense water droplets. Water droplets are more likely to condense on the emitting surface of other materials.
The fourth type: There is electromagnetic interference on site.
Fault phenomenon: The data of the ultrasonic level gauge jumps irregularly, or 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 can overwhelm the echo signal received by the probe.
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 should 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 and shield, and the instrument box should also be grounded.
Type Five: Entering the blind zone
Fault phenomenon: full scale or arbitrary data appears.
Reason: Ultrasonic liquid level gauges have blind areas, generally within a range of 5 meters, and 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.
1. The height of the blind area must be considered during installation. After installation, the distance between the probe and the highest water level must be greater than the blind area.
The above reasons may lead to abnormal operation of the ultrasonic level gauge, so when purchasing an ultrasonic level gauge, be sure to tell the working conditions on site to experienced customer service, so as to help you choose the model, and suggest how to install it. Ensure that the ultrasonic level gauge works normally.