Tank Level Monitoring
To measure the level of the content in a tank sound like an easy enough task but there are a couple of things to consider. Here we address things to keep in mind when designing your product. We also recommend to use our A121 sensor for any tank level application.
The first and most important recommendation: Validate your use case in steps. If you bring in everything at once it will always be much harder to determine and understand why you do not get the results you expect. If you start validating your target material or the physical tank integration does not really matter, But it is our firm recommendation that you validate them separately.
Target material
Understanding the material properties, such as reflectivity, at 60 GHz is very important. Water is a near perfect reflector, but many other liquids and solid materials are not equally good and will create unwanted effects on your measurements. Oils, for example, are much more transparent to radar compared to water and this will cause the measured distance to be slightly longer than the actual distance. You will have an offset which will be different per liquid type, but always constant with the same type of liquid.
You will need to deduct the offset from your measured results to get the true distance. You must also keep in mind that if the offset is, for example, 30mm then at some point you will start getting reflections from the bottom of the tank. When the liquid level is less than the offset there is a high risk that the reflection from the bottom is the strongest reflection.
Tank shape, size and material
Try first to verify the performance without any content in the tank. The optimal result when verifying sensor performance in the tank is that you only see the bottom and no other reflections.
For tanks with a depth above 5m meters we recommend that you add a lens into your setup.
Try to secure a sensor integration that is at least 5cm from maximum height of the content in the tank. This is to avoid the effects of sensor direct leakage. Also, never overextend the range you measure. If the maximum height of the liquid in the tank is 100mm from sensor, then start you range as close as possible to that distance and end your range as close to the tank bottom as possible. Do not overextend. There is no point in collecting data from ranges you are not interested in as it will only complicate interpretation of your results.
Independent if the tank material is metal or plastic it is always a good idea to use a lens or a hyperbolic reflector to limit your field of view and shield off unwanted reflections from the tank walls. Only when the tank width is greater than the depth will it be easy to detect the level without lens and not get unwanted reflections from the side of the tank that potentially could be interpreted as TRUE reflections.
Temperature
Temperature creates two potential issues. The temperature itself, which will affect the performance of the sensor independent of use case, and also condensation. A121 has a built-in temperature sensor which is used to flag if the temperature deviates more than 15 degrees from the temperature at latest calibration. This flag gives you the opportunity to trigger a calibration from your application and that will solve most of the temperature related issues.
Condensation is different problem. A little bit of condensation will not disturb radar performance as long as there are gaps between the water droplets. But if radar sensor is placed in a high humidity environment the condensation might never really dry out naturally. Instead, it can accumulate over time you might end up with a thin water surface covering the sensor or the casing. There are no solutions if the sensor is covered with water. The same phenomena can also happen with smaller amount of condensation when the ambient temperature goes back and forth from subzero to positive temperatures. When condensation freezes the radar signal will easily penetrate the ice. But when it melts it will not be in the droplet shape and a thin water surface could form. The only way to completely remove these issues is to ensure condensation does not go into your product in the first place.
For more information and details about our reference application and it’s algorithms please go to: Tank level — Acconeer docs
REFERENCE VIDEO TANK LEVEL
This video will give you an overview of our reference application capabilities.