Level measurement – The vibrating fork can do more, can’t it?

Hey guys, let’s talk about another important piece in level applications! Yup, the vibrating fork or level switch, you can pick your favorite name. I’ll use the vibrating fork along the article, ok? We already had a good chat here about level transmitters, talking about the works principle, applications, limitations and so on.

In fact, unscheduled problems can come up on any of your field devices, or even worst, the device can be measuring incorrectly and lead to an overfill in your tank. You need to have a plan B to avoid an overfill or any other possible problem, and here the vibrating fork shows up.

You can apply the vibrating fork in different sort of application. In fact, the majority of implementation is to protect the application.


Why should I use a vibrating fork?

While the level transmitter is working without problems, the vibrating fork will be there ready to get the control of the situation, avoiding an accident or loss of raw material. Furthermore, you have a new on/off control. The level switch can be a cheap and simple solution for your application. There are even particular applications where the vibrating fork comes as part of the solution.

For example, you can find out the density change in your product using a vibrating fork and other components. There is an interesting application of density measurement in mining, where they have this sort of solution to find out the slurry’s density. Moreover, they have a challenge with the abrasion on this application, but you can find vibrating forks with a good lifetime.

vibrating fork
Courtesy of Vega

Another interesting use is related to density measurement, but the purpose is entirely different. I mention the key application to vibrating forks, right? To avoid overfill or overspill in the tanks. Nonetheless, we are talking about the protection on the top. But what happens if you have a leakage problem at the bottom? This application is more common on storage tanks, where you have a protection around the tanks to avoid the contamination of the product in other areas in case of leakage.

All applications like that, you have a drain to rainwater. The solution is a floater with the vibrating fork and a conductive sensor, and if you have a different density there, the sensor will detect and understand you have a leakage happening. You can avoid loss of material and worst accidents, there are only two examples where you can implement this sort of device.

Let’s go to the basics, and exemplify the secrets behind the technology.

Courtesy of Giphy

Principle – What should I know?

Let’s go to the basics, how does a vibrating fork work? Don’t worry; I was trying to figure out the best way to explain that. Usually, the vibrating forks are recognized as a simple point level detection. However, you have other applications using it as one of the components.

The principle of the tuning fork was the base to create the vibrating forks devices. They were invented by Endress+Hauser in 1967. I used to try to use a tuning fork to check the tuning of musical instruments. I could have invented something, right?

Maybe not! Back to the topic, the device has two prong forks, and its forks are oscillating at its natural frequency. How is it possible? The responsible for creating the oscillation is a piezo-cristal assembly built-in, you have two sorts of piezo-crystal. Both work equally, the difference is how they are built inside.

vibrating fork
Courtesy of Emerson Automation Solutions

You can install the vibrating forks on the top or side of the tanks, or even on the pipes as well. When there is contact only with air, the two prong fork will oscillate at its natural frequency, and the transmitter will continuously be monitoring this oscillation.

As soon as the product cover the forks, the frequency of oscillation will change, dropping the oscillation. The transmitter will detect the change and translate this information into a switch output. You can turn on/off the equipment to avoid problems.


Let’s chat about common applications with vibrating forks. If you don’t know where to apply this sort of field instrument, don’t worry we are here to help!


  • Level detection:

The primary application is point level detection. And unlike many people may think, you can install your device in different places. Not just on top or on the side of the tank. In fact, the position of your device depends on your application. You can implement the forks to protect the overfill or to indicate low level.

If you want to detect high level, you have to install the vibrating forks on the top or side of your tank. However, if you want to detect low level, you need to have forks at the bottom or side of the reservoir as well. You can make both applications, and you can have different level detection, such as High level, or high-high level. The extension of the vibrating forks will be different, and in that case, you should install them on the top.

  • Filled pipe detection:

You can also detect whether you have filled pipe or not. Why should you install for filled pipe detection? Maybe you need to protect a pump to run without product into the pipe. In that case the vibrating forks can detect this statement, and protect the pump.

  • Density measurement:

If you have density measurement application, there are options on the market combining the vibrating forks, temperature, and pressure to density measurement. This is a particular application, but there are exciting possibilities with vibrating forks. The dudes from Micro Motion have the Micro Motion Fork density meter. You can also find a solution with the guys from Endress+Hauser with their vibronic measurement density computer FML621 and so on.

vibrating fork
Courtesy of Endress+Hauser


The working principle is not complicated at all, but the vibrating forks are a relevant part of the level measurement. If you need to protect your tank, pipe, or even a density measurement, maybe the forks will be a good solution.

Below you have a video explaining the working principle:


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