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The first one is that there will be stirring inside the container and the liquid will fluctuate more, which will affect the measurement of the ultrasonic level gauge.
Symptoms: No signal or data fluctuations.
The reason: The ultrasonic level gauge said to measure a distance of several meters refers to the calm water. For example, an ultrasonic level gauge like the 5 meter range generally means that the maximum distance for measuring calm water is 5 meters, and the actual delivery will be 6 meters. When there is stirring in the container, the water surface is not calm and the reflected signal will be reduced to less than half of the normal signal.
Solution:
1. Choose a more large-scale ultrasonic level gauge. If the actual range is 5 meters, then use a 10 meters or 15 meters ultrasonic level gauge to measure.
2. If the ultrasonic level gauge is not changed and the liquid in the tank is not viscous, you can also install the waveguide, and set the ultrasonic liquid level probe probe in the waveguide to measure the height of the level gauge, because the liquid in the waveguide The surface is basically stable.
3. It is recommended to change the two-wire ultrasonic level gauge to four-wire.
Second: There is foam on the liquid surface.
Symptoms: Ultrasonic level gauges are always searching, or they will show "wave drop" status.
Cause: The foam will absorb ultrasound significantly, causing the echo signal to be very weak. Therefore, when the surface of the liquid is more than 40-50% of the area covered with foam, the signal emitted by the ultrasonic level gauge will be absorbed most of the time, causing the liquid level gauge to receive no reflected signal. This is not much related to the thickness of the foam, mainly related to the area covered by the foam.
Solution:
1. Install the waveguide, and place the probe of the ultrasonic level gauge in the waveguide to measure the height of the level gauge, because the foam inside the waveguide will be reduced much.
2. Replace it with a radar level gauge. The radar level gauge can penetrate the foam within 5 centimeters.
The third type; high temperature in the water tank or tank on site, which affects the ultrasonic level gauge measurement.
Symptom: When the water surface is near the probe, it can be measured. The water surface cannot be measured far from the probe. When the water temperature is low, ultrasonic level gauge measurement is normal, and if the water temperature is high, the ultrasonic level gauge cannot measure it.
Cause: The liquid medium does not generally generate steam and mist below 30-40°C. Above this temperature, it is prone to produce steam or mist. Ultrasonic waves emitted by the ultrasonic level gauge will attenuate once through the steam during the emission process, from the liquid level. When it is reflected back, it will be attenuated one more time, causing the ultrasonic signal finally returning to the probe to be weak, so it cannot be measured. And in this environment, the probe of the ultrasonic level gauge is easy to get water droplets, and water droplets will hinder the transmission and reception of ultrasonic waves.
Solution:
1. To increase the 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. The effect of steam or fog on the measurement can be reduced or reduced.
2. The probe is to be made of PTFE or PVDF, made into a physical seal type, so that the probe is not easy to condense on the emission surface. As for the emission surface of other materials, water droplets are relatively easy to condense.
Fourth: There is electromagnetic interference in the scene.
Symptoms: Ultrasonic liquid level meter data is not regularly beat, or simply show no signal.
Cause: Many electric motors, frequency converters, and electric welding on the industrial site will affect the measurement of ultrasonic level gauges. Electromagnetic interference will exceed the echo signal received by the probe.
Solution:
1. The ultrasonic level gauge must be grounded reliably. After the grounding, some interference on the circuit board will run off through the ground. And this grounding is to be grounded alone and cannot share a ground with other equipment.
2. The power supply can not be the same power supply as the inverter or motor, nor can it be directly powered from the power system power supply.
3. The installation site needs to be far away from the inverter, variable frequency motor, and high-power electrical equipment. If it can not be far away, it is necessary to install a metal instrument box on the outside of the level gauge to isolate the shield. This instrument box also needs to be grounded.
The fifth type: entering the blind spot fault phenomenon: full scale or any data will appear.
Reason: Ultrasonic level gauges will have blind areas, usually within 5 meters of the range, the blind area is 0.3-0.4 meters. Within a range of 10 meters is 0.4-0.5 meters. After entering the blind spot, the ultrasound will appear to have an arbitrary value and will not work properly.
Solution: 1. When installing, you need to consider the height of the blind spot. After installation, the distance between the probe and the highest water level must be greater than the blind spot.
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Because ultrasonic waves emitted by ultrasonic level gauges are invisible to the human eye, the abnormal working conditions at the site may be affected by the following conditions in addition to the failure of the level gauge itself: