Liquid level measurement technology includes a variety of sensors to solve a mixed bag of application challenges. It’s a good thing, too, because there isn’t one sensor technology that doesn’t have a few weaknesses. None of them can take all level measurements, yet they’re all perfect in the right situation.
Ultrasonic sensors are a standout because they don’t come in contact with the liquid media that they’re measuring. This adds a level of versatility that contact sensors simply don’t have.
However, they’re tied directly to the interaction of sound waves with their target, and anything else that might get in the way. One of these obstacles is condensation.
It may seem counter-intuitive that condensation would be considered an obstacle to sound. After all, doesn’t sound travel through liquids? Yes it does. In fact, that’s the operating principle of sonar, ultrasonic cleaners, and flipper. However, the liquid surface is a barrier, even in the small amount that accumulates from condensation.
The surface tension of the liquid creates a lot of impedance – becoming reflective to sound waves. So when condensation builds on the face of an ultrasonic level sensor, much of the signal is immediately bounced back to the transducer.
In fact, condensation is also a problem on the walls of small tanks and especially inside stilling wells. When these vertical surfaces are inside the conical beam pattern of the sound wave, the condensation droplets will reflect sound back to the sensor, giving a false level.
Ultrasonic sensors detect liquid surfaces really well, which is why they typically make great liquid level sensors. It’s also why the small droplets that form from condensation are problematic.
Some variables, like temperature, tend to affect any and all sensors. However, and luckily, condensation is not one of these variables. It has no affect on most other sensors.
With a lot of options, it’s not difficult to find a suitable alternative to ultrasonic sensors. We recommend a pressure transducer installed at the bottom of the tank – either a submersible that you can drop in, or a standard threaded type that you can put on a drain valve.
A submersible sensor will automatically convert a PSI measurement into feet of liquid – calibrated to the density of your liquid. Standard pressure transducers would simply give you a PSI measurement that you could easily convert using your control system. Either type would get the job done nicely.
Continuous float level transmitters are another good alternative, though typically more expensive than pressure sensors and ultrasonics. These are very accurate and work well in liquids that are not overly sticky or viscous.
The key is to work with a supplier who understands and can offer alternatives based on application variables. Let us know if we can help you navigate your next liquid level measurement application.
