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Reasons for the Abnormal Working of Ultrasonic Liquid Level Gauge
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Reasons for the Abnormal Working of Ultrasonic Liquid Level Gauge

Because the ultrasonic waves emitted by the ultrasonic liquid level gauge are invisible to the human eye, there are the following situations in addition to the failure of the level gauge itself in case of abnormal operation on site:


1. The stirring in the on-site container and the liquid fluctuation will affect the measurement of the ultrasonic liquid level gauge

(1) Failure phenomenon: 

No signal or severe data fluctuation.


(2) Reason: 

The measuring distance of several meters of the ultrasonic liquid level gauge generally means that the maximum distance that can be measured from the calm water surface is 20 meters. In the case of 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.


(3) Solution:

  • Choose an ultrasonic liquid level gauge with a larger measuring range. If the actual measuring range is 5 meters, then use an ultrasonic liquid level gauge that exceeds the specifications of 5 meters.   

  • If the ultrasonic liquid level gauge is not changed, and the liquid in the tank is not viscous, you can also install a wave guide, and place the probe of the ultrasonic liquid level gauge in the wave guide to measure the height of the liquid level gauge, because the surface of the liquid in the wave guide is basically stable.


2. There is foam on the liquid surface of the ultrasonic liquid level gauge

(1) Failure phenomenon: 

The ultrasonic liquid level gauge is always searching, or it will display the "wave lost".


(2) Reason: 

The foam will obviously absorb the ultrasonic wave, which causes the echo signal to be very weak. Therefore, when more than 40 to 50% of the surface of the liquid is covered with foam, most of the signal emitted by the ultrasonic liquid 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, it is mainly related to the area covered by the foam.


(3) Solution:

  • Install the wave guide and place the probe of the ultrasonic liquid level gauge in the wave guide to measure the height of the level gauge, because the foam in the wave guide will decrease a lot.  

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


3. The high temperature in the on-site pool or tank affects the measurement of the ultrasonic liquid level gauge 

(1) Failure phenomenon: 

It can be measured when the water surface is close to the probe, but cannot be measured when the water surface is far away from the probe. When the water temperature is low, the ultrasonic liquid level gauge measures normally, but the ultrasonic liquid level gauge cannot measure when the water temperature is high.


(2) Reason: 

The liquid medium generally does not produce steam and mist below 30 to 40℃. When the temperature exceeds this temperature, steam or mist is easy to be generated. The ultrasonic wave emitted by the ultrasonic liquid level gauge will attenuate once through the steam during the transmission process. When it is reflected from the liquid surface, it will attenuate again, causing the ultrasonic signal to return to the probe to be very weak, so it cannot be measured. Moreover, in this environment, the probe of the ultrasonic liquid level gauge is prone to water droplets, which will hinder the transmission and reception of ultrasound.


(3) Solution:

  • To increase the measuring range. The tank height is actually 3 meters, so you should choose an ultrasonic liquid level gauge between 6 meters and 9 meters. It can reduce or weaken the influence of steam or mist on the measurement.

  • The probe should be made of PTFE or PVDF and made into a physically sealed type, so that water droplets are not easy to condense on the emitting surface of such a probe. As for the emitting surface of other materials, water droplets are easy to condense.


4. Electromagnetic interference at the working site of the ultrasonic liquid level gauge

(1) Failure phenomenon: 

The data of the ultrasonic liquid level gauge fluctuates irregularly, or it simply shows no signal.


(2) Reason: 

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


(3) Solution:

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

  • Its power supply cannot be the same with the power supply of the frequency converter and the motor, nor can the power be directly drawn from the power supply of the power system.

  • The installation site needs to be far away from frequency converters, frequency conversion motors, and high-power electric equipment. If it cannot be far away, a metal instrument box must be installed on the outside of the level gauge to isolate and shield it. This metal instrument box also needs to be grounded.

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