Recent content by Kevinh

You can Google ergonomic chairs. Or "bum-friendly chais" (just kidding) I would just experiment with hardwood chair / your existing chair / find another chair nearby,...It does not have to ne so methodical Do not forget the second paragraph in my original responce

I like to thank everyone for their suggestions and questions. Sometimes a good enduring question sets a framework for new possible solutions. This was my first time using this forum and I am already enjoying it.

Have three different chairs with different cushioning and change every 2 hours or so. That works for me (although I never did 12 hours stretch) If you love reading so much, can you pick up some new reading topics ( arts,sport,...) and leverage your love for reading into going to a new area...

It seems to me that you need to start with "energy in = energy out" equations since you are using a battery. Creating a magnetic field with a winding to overcome a permanent magnet may take more juice than you can afford. Unless the magnet is a weak ferrite which may not have enough force. What...

What do you mean by "Wind the permanent magnet to cancel the permanent magnets field" How do you wind a magnet? Have you looked into magnetic latching solenoids? Company called Ledex sells them (among others), you can buy one and benchmark, or just apply it??

Marcus, The field is radial outside of the barell. I realize that the MRI has a time based wave shaping. In my case, I only have eddy current issues when magnet moves. When it does move, then I should be able to take a derivative of magnetic field with respect to position (time). I would think...

I like the out of the box thinking dlgoff. Unfortunately in this case absolute position sensing is needed. This means that if you loose power and then the piston moves to a new location, upon power up an hour later, you must know where you are.

The piston is carrying a set of magnets and as it moves, it creates a magnetic signature (kind of like sine waves) outside of barell. If you can imagine magnetic field actually goes through the barell (after some of it is shunted). I have an array of magnetic sensors outside of barell(along the...

I need to measure absolute position and not incremental so in the case of loss of power, i still know where I am. Optical encoders will not survive the dusty / nasty enviroment. Putting a magnetic sensor looking at the rod was one of the original ideas but did not work due several reasons...

The rod and piston are attached to each other. If you sense one, you have sensed the other. The magnets are attached to piston since there is more real estate.

Fundamentally all waves can be represented as series of sine waves ( Fourier ). A square wave is no exception and it has its own spectrum. To me the most natural wave is a sine and anything else has been polluted with harmaonics. I am not sure what you are trying to do, but you may benefit by...

Good question. I am trying to measure position of a piston in a hydraulic cylinder that has a steel barell. This is a special project for me and being a magneto-haulic, I am taking this approach. There has been numerous attempts using ultrasonics, microwave,...(not by me, but to my knowledge...

Found the book and ordered it, thanks ( a bit pricy, you should have saved your copy ). The pole spacing is around 50 mm and the entire cylinder is around 700 mm with an inside diameter of 80 mm and a cylinder wall thickness of 5 mm. You can imagine that I am using pretty powerfull Neo magnets...

Thanks Marcus, I know it is eddy current because at higher speeds I get more delay and attenuation. You are correct about hysteresis, but its magnitude (mesuered at very low speeds) is small compared with eddy current effects. The problem is that I do not know speed. If I infere speed from...

Hello everyone. I am trying to measure the position of a magnet moving inside a steel tube using a magnetic sensor on the outside. Eddy currents are causing errors due to phase shifts and amplitude changes. Any ideas? Can eddy currents be re-directed using selective copper paths? Since eddy...