We talked a bit about level detection in our earlier reviews this month. So now let’s discuss level detection as part of a bigger solution, like density measurement. The working principle of the vibration fork can help here, as can the Vibronic Liquiphant FTL51 from Endress+Hauser. Stick with me and let’s dive into this device!

Disclaimer: This product review examines only features, not performance. If you’ve used this device, feel free to share your experience in the comments. This content serves the purpose of providing information if you want a new device.

Whatcha got there?

The Liquiphant FTL51 has more than one design – compact, robust, or even hygienic. Beyond that, it follows the same style of other Endress+Hauser devices, with different housing materials and an extension tube.

If you need to learn more about the vibration fork working principle, you can find articles at Visaya explaining it. The developers designed this device to measure liquids in general use for various industries. Also, the FTL51 can operate in safety applications; it has SIL2 and SIL3 approvals and overfill prevention according to the WHG (German Water Resources Act).

Like our earlier products, you can skip the display and configuration here, but you still get the red, yellow, and green LEDs for alerts.

What can it do?

This switch measures liquids in tanks or pipes for most industrial applications. Its working principle makes it flexible and quick yet robust.

The FTL51 comes in different flavors to offer different outputs and power supplies. For example, the FEL50A has PROFIBUS PA, and the FEL55 has an 8-16 milliamp output and 11-35 direct-current power supply. You can see the entire list on our device page here.

Back to the FTL51! It can work in temps from -50 to 150 °C (-58 to 302 °F) and pressures from -1 to 100 bar (-14.5 to 1,450 psi). For process connections, it sports a huge list – threads such as NPT ¾, flanges from DN25 to DN100, and more. E+H will even cater to certain requests if you don’t see what you need on the list.

Why should I care?

If you need to connect your level detection to your control system digitally, the Liquiphant FTL51 can get you there with PROFIBUS PA. Plus you can get a handful of sensor lengths.

And let’s not forget the density application and foam detection! You can get that if you go with the FML621, although some processes need extra pressure and temperature measurements.

Last but not least, the FTL51  has several wetted materials, certifications, and approvals for just about anything. This device offers good cost benefits for any liquid application with a minimum density of 0.5 grams per cubic centimeter.


If you need to monitor level in liquids or detect foam or density, the Vibronic Liquiphant FTL51 from Endress+Hauser presents a solid choice. You can easily compare it to others in our device directory and decide the best one for your application.

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