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.