LVDT, Magnetrostrictive, ultrasonic, or ?

[paulengr 44]

Which one gives the longest life for a distance sensor? LVDT's? Magnetostrictive (MMI?) Ultrasonic level indicators?

[Peter Nachtwey 15]

LVDTs. It is hard to break a slug io fmetal between some fixed coils. However, you can't find LVDTs with long travel. If you don't shock MDTs ( magnetostrictive displacement transducers) will last a long time. That is what we use for position feed back in hydraulic cylinders. They seem to last forever except in cases where there is high hydraulic shock and were welders induce high currents on the cables and burn them and the motion controller out. I haven't used ultrasonics at all.

[JRoss 84]

Optoelectric Distance Sensors will last quite a long time too.

[kaiser_will 65]

Design criteria to consider are (1) accuracy and (2) distance. LVDTs have decent accuracy (typically fractional-millimeters). LVDTs are limited in distance (and their price goes way up as length grows). With LVDTs, they do wear with time since there are moving parts (rod and donut), are a function of how they are installed (i.e., improper alignment will lead to premature failure) and are sensitive to the elements (i.e., dirt, vibration, ground noise, etc.). Ultrasonic and laser distance sensors, such as Sick optics, are ever increasing in accuracy and durability, but also have limitations, such as light being reflected off of the measurement target. Develop a list of design constraints and objectives, then try to find the best-fit sensor for the application. If you run into a situation where there is not a perfect fit, you will not be the first. Go for the most reliable solution and make sure your program code has features to deal with the short-falls. Remember to design for failure.