An ultrasonic level gauge is a device used to measure the level of various liquids or solids. Below are some common ultrasonic level gauge faults and solutions.
There is electromagnetic interference on site
Fault
Ultrasonic level sensor data fluctuates irregularly or no signal is received. Industrial site is always occupied with motors, frequency converters and electric welding equipment. Most of the time electromagnetic interference affects the echo signal that the probe receives.
How to fix this problem?
Grounding is essential for an ultrasonic liquid level indicator. Once the ground wire is grounded, some interference disappears through the circuit board. This ground wire needs to be grounded separately and cannot be shared with any other device. The power supply must be independent of the power system and cannot be directly pulled from it. The installation site must be far from variable frequency motors, frequency converters, and high power electrical equipment. If it is not possible to keep the instrument box away from the sensor, the metal instrument box must be installed outside of the sensor to provide isolation and shielding.
Stirring in the container fluctuates the liquid level
Fault
No signal or big data fluctuations
Cause
Ultrasonic level sensors measure distance to calm water surface. For example: Ultrasonic sensor with measuring range 5m indicates maximum distance to measure calm water surface. When agitation occurs in container reflected signal weakens to less than 50% of normal
Solution.
What are the solutions?
- Use a larger range ultrasound liquid level sensor. If the actual range of the sensor is 5m then use a larger range sensor (10m, 15m).
- If the liquid is non viscous then you can install a waveguide and place the probe in the waveguidance to measure height of liquid level because the liquid level inside the waveguideline is essentially stable.
- Change the ultrasonic sensor to a 4-wire system.
There is foam on the surface of the container
Fault
Ultrasonic level gauge is constantly searching, or shows the status of wave loss. The reason for this is that the foam absorbs most of the ultrasonic waves resulting in a very low echo signal.
For example, if more than 40 – 50 % of the liquid surface of the level gauge is covered by foam then most of the signals transmitted by the gauge will be absorbed resulting in signal receiving failure. This does not depend on the thickness of foam but mostly on the area covered by foam.
Steps to solve this problem:
- Install the waveguide, place the probe in the waveguide to measure the level, as the foam’ volume will be reduced in the waveguide
- Use radar level sensor instead of foam. Radar level gauge penetrates foam up to 5 cm.
Ultrasonic wave enters the blind
Full scale data or arbitrary data will appear
What is the cause?
Ultrasonic liquid level sensors have a blind zone. This blind zone is usually for a measuring range of 5m. For a measuring range of 10m, the blind zone will be 0.3 m – 0.4 m, or 0.4 m – 0.5 m. When an ultrasonic wave passes through this blind zone, arbitrary values will appear and the sensor will not function correctly.
How to fix this?
When installing the sensor, the height of this blind zone should be taken into account. The probe’s distance between the top water level and the bottom water level should be greater than 0.4 m.
