Magnetostrictive linear transducers are feedback sensors that give an analog or digital signal relative to the position of a magnet along the waveguide. One of the common questions we are asked is should I use a captive or floating magnet? The answer depends on the application and the environment.
Floating Magnets
Floating magnets are attached to the moving part with the transducer mounted parallel. The magnet is not directly coupled to the transducer and thus an air gap exists between the transducer and the magnet.
- Floating magnets overcome the typical issue of debris and sticky fluid buildup overtime on the transducer track or rod. This is the main cause of mechanical failure on a sliding track magnet.
- They can be mounted directly on the moving part, so machine wear is compensated, giving you a more realistic position over time. It allows you to monitor machine part wear.
- They are easier to mount to the moving part versus a rod and possibly 2 ball or eye swivels- where you have 1 on the magnet and one on moving part.
- Magnetostrictive technology has advanced to allow a greater gap between the sensor inside the track and the magnet itself. Distance is dependent on transducer and magnet type.
- The technology advances have also allowed slightly more variance in magnet to transducer distance (X) over the length of the device within reason. Also, non- parallel movement (Y) is now more forgiving. Still should not allow both! The transducer should be mounted parallel to the moving part.
- There are many options available for floating magnet types.
- One issue is they cannot be mounted directly to steel or iron. Insulated mounting blocks are available with the magnets, or you can make your own non-ferrous mount.
- EMF or high inductive local interference will also affect floating magnets. In these environments do not use a floating magnet.
Captive Magnets
Captive magnets ride in a track on the transducer and are linked with a mechanical linkage to the moving part.
- Captive magnets are used in relatively clean environments.
- They are used where you cannot put the transducer body close to the moving part.
- A common perception is that the bearing surfaces and swivel eyes will wear with time. This is true only where direction change is sudden and at high speeds. Also -dirt/oil. Usually not an issue.
- As position repeatability is the most typical and desired function of any transducer even if play develops it may not be an issue if measurement is only in one direction.
- 3 more parts to break.
- The main reason for captive magnet use? X/Y variance of magnet distance to the transducer will never vary and a floating magnet will not work in the application.
Have questions on transducers? Contact us and we will be glad to assist with your application.
