Have you considered an accelerometer(s)? Don't know if they would be precise enough. Two arranged at 90* from each other and 45* from vertical might do it. Most likely a lot of low pass filtering required to take out vibration etc.
Il 24/02/2010 22.53, BobS ha scritto:
Yes, that is the first alternative. But it requires a lot of work to cabling sensors on the moving structures. I can't explain all the details because I don't know all of them too, but the customer wouldn't use electronics on the moving parts of the plant. I simplify the description of that cylinder but there are other parts in the nearby.
Thanks! Marco
It's a tad exotic, but you could paint a striped target onto the tank, and look at it with a good camera; some 2D FFT work will give you a VERY accurate idea of which direction the stripes are tilted. Strains in the tank support structure might make a bit of trouble for local sensors, but not for a camera on a wallmount.
A simpler option: wrap a string around the tank, and run it to a sensing take-up reel (digital tape measure, in essence). You have to have access to a bit of accurate circumference to do this, of course, and worry about tank-weight causing support sag (i.e. take off the string at an angle that is insensitive to any axis-of-cylinder fluctuation).
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