Level transmitters are an essential part of many applications from food production to wastewater treatment. Accuracy is key. If tank levels are too low, pump damage can occur. If tank levels are too high, vessels can overflow, causing product loss, safety issues, and environmental problems.
Some liquids are very easy to measure. Clean water, for example, is easy for almost any level transmitter. But some fluids, like those that produce foam, have characteristics that need special attention to get accurate measurement.
Measuring Through Foam
When processed, some fluids produce a layer of foam. Liquids such as soap, beer, or other caustic blends are good examples. Some level transmitting technologies have difficult time determining the exact fluid level.
Ultrasonic technology measures level by emitting short bursts of energy, then measuring the duration and intensity of the echoes. This works great for almost any fluid or solid. But foam absorbs these signals, preventing the sensor from accurately measuring the liquid level.
Other technologies like lasers, pressure transmitters, and floats all have their own challenges when faced with foam. But you're not here to read about which level transmitting technologies don't work. So to find out what works best, I talked with one of Crane Engineering's most experienced valve and instrumentation engineers, Ralph Lechner.
According to Ralph, to get the best results, he looks to pulse or guided wave radar level transmitters first for foam.
Microwave (aka guided radar) uses the same technology used to find breaks in underground cables and cable installations in buildings. These transmitters can come in a couple of different forms, one comes in direct contact with the fluid, one does not.
This transmitter is unaffected by many potentially disturbing process conditions (foam, vapor, condensation, temperature, etc.).
The radar sensor emits a pulse from its antenna. The pulse reflects against the fluid and returns. The sensor measures the time it took for the pulse to return and translates it to liquid level.
This technology is best for bulk tank applications.
This method, too, is unaffected by process conditions like foam, vapor, condensation, temperature, etc. Unlike pulse radar, guided radar comes in contact with the fluid.
The sensor emits a RF pulse through a probe inserted in the tank. The pulse travels down the probe and reflects against the liquid, and returns to the sensor. Again, the sensor measures the time it took for then pulse to return and translates it to liquid level.
This method is great for small tank applications.
Depending upon the application, other methods can be used too. Transmitters such as lasers, tuning forks, and floats have also been applied in foam, but this is dependent upon unique situations. Check with an engineer well versed in instrumentation to help if you're not sure.
Is foam in the tank causing pump problems in your process? Ask us about it! We gladly provide technical help to businesses in Wisconsin and upper Michigan.