One of the prevalent piston position measurement technologies used for mobile hydraulic cylinders is based on the Magnetostrictive properties of ferromagnetic metals. The physics of these sensors is quite complicated, taking advantage of something called the Villari and Wiedemann effects to produce an ultrasonic wave that travels down a hollow tubular waveguide at the speed of sound. A diagram of this physics is shown below.
How Do Magnetostrictive Position Sensors Work?
To measure the position of a piston within a hydraulic cylinder, the cylinder has to be carefully designed to accommodate both the movable position magnet, and the length of the waveguide rod for which a hole must be carefully bored through the center of the cylinder. The location of the position magnet is determined by first applying a current pulse to the waveguide while simultaneously starting a timer. This current pulse causes a sonic wave to be generated at the location of the position magnet (Wiedemann effect). The sonic wave travels along the waveguide until it is detected by the pickup. This stops the timer. The elapsed time indicated by the timer can then be calibrated to represent the position of the piston.
Magnetostrictive Sensor Challenges for Mobile Hydraulics.
Magnetostrictive sensors are highly accurate and are a technology that field mechanics understand how to service. They are designed into many hydraulic cylinder applications including non-automotive vehicular industries like Construction, Drilling, Mining equipment, and long stroke hydraulics.
The problem is, they are one of the most intrinsically vulnerable position sensing technologies for these robust applications. Their high resolution is complete overkill for most long-stroke applications, and their vulnerability increases both costs and complexity of field servicing.
A Drop-In Magnetostrictive Position Sensor Replacement.
We get it: You’ve used magnetostrictive sensors for years; you know them, you like them. When they break or stop operating you know how to replace them.
But what if there was another technology that could be a cost neutral move to providing more robust position measurement in the field? What if this technology was a field proven, drop-in replacement for most existing sensors and electronic interfaces?
In our next blog, we’ll talk about how CPI was able to engineer a superior solution to linear position measurement in large scale mobile hydraulics, and why its time to get out of your comfort zone and try something new.