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Because the ultrasonic wave emitted by the ultrasonic level gauge is invisible to the human eye, there are cases in which the work is not working properly. In addition to the failure of the level gauge itself, there are the following situations:
The first type: There will be stirring in the on-site container, and the liquid fluctuation is relatively large, which will affect the measurement of the ultrasonic level gauge.
Symptom: No signal or strong fluctuations in data.
Reason: The distance meter measured by the ultrasonic level gauge refers to the calm water surface. For example, an ultrasonic level gauge such as a 5-meter range generally means that the maximum distance of the measured water surface is 5 meters, and the actual factory will be 6 meters. In the case of agitation 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. Use a larger range of ultrasonic level gauges. If the actual range is 5 meters, measure with a 10 meter or 15 meter ultrasonic level gauge.
2. If the ultrasonic level gauge is not changed, and the liquid in the tank is not sticky, the waveguide can be installed, and the ultrasonic level gauge probe is placed in the waveguide to measure the height of the liquid level gauge, because the liquid in the waveguide The surface is basically smooth.
3. It is recommended to change the two-wire ultrasonic level gauge to four-wire system.
Second: There is a foam on the surface of the liquid.
Symptom: The ultrasonic level gauge is always searching, or it will display the “lost wave†status.
Cause: The foam will absorb the ultrasound significantly, resulting in a very weak echo signal. Therefore, when the surface of the liquid is 40-50% or more, the foam is covered, and the signal emitted by the ultrasonic level gauge is absorbed most, causing the level gauge to receive no reflected signal. This has little to do with 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 much reduced.
2. Replace with a radar level gauge to measure, the radar level gauge can penetrate the foam within 5 cm.
The third type; the high temperature in the on-site pool or tank affects the measurement of the ultrasonic level gauge.
Symptom: When the water surface is close to the probe, it can be measured. The water surface is not measured far from the probe. When the water temperature is low, the ultrasonic level gauge is measured normally, and the water temperature is high and the ultrasonic level gauge is not measured.
Reason: The liquid medium generally does not generate steam and mist below 30-40 °C. When this temperature is exceeded, steam or mist is easily generated. The ultrasonic wave emitted by the ultrasonic level gauge will attenuate once through the steam during the launching process. When the reflection comes back, it will be attenuated again, causing the ultrasonic signal to return to the probe to be weak, so it cannot be measured. Moreover, under this environment, the probe of the ultrasonic level gauge is prone to water droplets, and the water droplets hinder the transmission and reception of ultrasonic waves.
Solution:
1. To increase the range, in fact, the height of the can is 3 meters, and the ultrasonic level gauge between 6 meters and 9 meters should be selected. The effect of steam or mist on the measurement can be reduced or weakened.
2. The probe is made of Teflon or PVDF and made into a physical seal type. Such a probe does not easily condense water droplets on the emitting surface. As for the emitting surface of other materials, the water droplets are relatively easy to condense.
The fourth type: electromagnetic interference at the scene.
Symptom: The ultrasonic level gauge data is irregularly beaten, or simply shows no signal.
Reason: There will be many motors, inverters and electric welding on the industrial site that will affect the measurement of the ultrasonic level gauge. Electromagnetic interference will exceed the echo signal received by the probe.
Solution:
1. The ultrasonic level gauge must be grounded reliably. After grounding, some interference on the circuit board will run off through the ground. Moreover, this grounding is to be grounded separately and cannot share a ground with other equipment.
2. The power supply cannot be connected to the same power source as the inverter or the motor, nor can it be directly powered from the power system power supply.
3. The installation site needs to be away from the inverter, variable frequency motor, and high-power electric equipment. If you can't stay away, install a metal instrument box outside the level gauge to isolate the shield. This instrument box also needs to be grounded.
The fifth type: entering the blind zone failure phenomenon: full scale or arbitrary data will appear.
Reason: The ultrasonic level gauge will have a blind zone, generally within a range of 5 meters, and the blind zone 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 any value and it will not work properly.
Solution: 1. When installing, you need to consider the height of the blind zone. After installation, the distance between the probe and the water level must be greater than the blind zone.
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