Continuous Float Level Transmitters

How They Work

Our float level transmitters measure levels continuously. There are two key technologies for float transmitter construction that can affect both price and performance, depending on the application. Our application engineers can help you understand which type of sensor is best for your needs.

Magnetostrictive Level Measurement Sensors

Magnetostrictive liquid level sensors consist of a float that moves up and down a stem, or rod. The float contains a permanent magnet, and the stem houses a wire waveguide.

The float position can be measured because the waveguide is made of metal with ferromagnetic characteristics. This means the molecules in the metal waveguide align themselves with magnetic fields. A magnetostrictive level transmitter uses two magnetic fields to align the molecules in different directions to create a detectable point on the wire waveguide.

An electrical pulse travels down the waveguide and magnetizes it, aligning the molecules in one direction. When the pulse meets the competing magnetic field from the float, with molecules aligned in a different direction, a vibration travels back to the sensor housing at a known speed. This vibration is known as a strain pulse.

By measuring the time delay between the initial electrical pulse and resulting strain pulse, the distance to the float can be determined with a high degree of accuracy.

This provides continuous level measurement as the sensor sends a pulse down the waveguide several times a second. Dual level measurement is also an option, where the location of two floats is determined. The electrical pulse will continue down the waveguide after hitting the first float, creating another strain pulse when it hits the second float. This is especially useful when measuring the interface between two liquids such as oil and water.

Magnetostrictive level sensors provide a high degree of repeatability, and are our most accurate liquid level measurement solution, with a resolution of about 1 mm. They are good for vaporous liquids or in heavy foam where non-contact sensors may have difficulty. Additionally, the float weight and specific gravity can be customized if the application calls for it.

Resistive Level Measurement Technology

Resistive level sensors comprise a float and stem, or sensing rod. The float holds a magnet, and the stem houses closely spaced reed switches and resistors. The float closes the reed switches as it travels up and down the sensing rod.

As the float closes the reed switches, the total resistance value of the circuit is changed. The entire sensor acts as a voltage divider to the voltage supplied to the sensor, where the voltage fluctuation across the circuit is directly proportional to the position of the float on the sensing rod.

Resistive is a simple, reliable, and highly repeatable way to measure liquid level. This is another form of continuous level measurement for real-time level data. Heavier floats, like on the RPM, work very well in applications where heavy build-up is present. The RPM also has the thickest stem, or sensing rod, for applications with high turbulence or flow. Float weight and specific gravity can be customized if the application calls for it.

Features Tour

Our continuous float level transmitters are approved for class 1 division 1 hazardous locations. The RPM is approved by ATEX as intrinsically safe for use in Europe. Their biggest strength is their durability and simplicity.

Because of their size, shipping and installation is the trickiest part. Our float level transmitters can be up to 25 ft. long, and quite heavy. They may require a lift to install (scissor lifts, forklift, etc). However, installation is not complicated. Simply put the probe into the tank. Larger floats may require you to install the floats on the rod after it has been inserted into its mount.

The best part is, once installed, there is no programming. The transmitters simply work in just about any liquid.

Finally, there are few variables that upset the operating principle of a continuous float level transmitter. Chemical compatibility is always a concern with any contact measurement solution. There are a few different float materials to choose from, but you’ll want to talk to us about the liquid you need to measure.

Temperature is another concern for just about any sensor. Our float level transmitters operating temperature is -40º - 185ºF (-40º - 85ºC).

If you’re okay on compatibility and temperature, then the only other variable is buoyancy, or specific gravity. Our float transmitters can work in liquids with a specific gravity as low as 0.5.

Applications

Continuous float level transmitters can be used in a very wide variety of liquids. As stated, there are only a few variables to be concerned with. Applications that require a heavy duty sensor with a simple setup and long lifespan are an ideal fit for our float transmitters.

The hazardous location certifications are crucial for many in the Oil and Gas industry, where most of these sensors are currently installed. However, they have also been installed in chemical tanks, wastewater lift stations, and various process tanks with great results.

Specifically, our float level transmitters are market leaders in mud tanks on drilling platforms throughout North America. This is a particularly demanding application. Powerful pumps move the drilling mud rapidly, causing violent turbulence inside the tanks. Despite this, we simply don’t hear about bent probes or stuck floats. Our customers are very happy with the performance and durability.

Another great application for our float transmitters is oil and water interface level inside production tanks. This has long been considered one of the most difficult applications. There are a few other sensors that are capable of detecting the interface between the liquids. However, they are more expensive and only give you one level.

Our magnetostrictive sensor, the MPX, will give you both the top level and the interface level with a single sensor. The MPX does dual/interface level measurement very effectively, without a complex setup.

FAQs