Comments on: Some notes on force sensitive resistors (cont’d) http://groklab.org/handhygiene/2010/02/18/some-notes-on-force-sensitive-resistors-contd/ Just another Groklab.org weblog Mon, 28 Nov 2011 02:43:21 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: gthomas http://groklab.org/handhygiene/2010/02/18/some-notes-on-force-sensitive-resistors-contd/comment-page-1/#comment-121 gthomas Fri, 19 Feb 2010 15:51:24 +0000 http://groklab.org/handhygiene/?p=607#comment-121 The way I interpreted the passage is that the position of the book on the acrylic block would be expected to change the reading, possibly because if the book was balanced on the block towards so that it's center of mass was towards the top of the block, then the top row of cells would receive more pressure than the bottom row. Apparently this would give a different result than if the book was exactly centered or shifted slightly downward. At least that was my interpretation. Clearly it is saying that you can't expect a deadweight test to give repeatable results. The way I interpreted the passage is that the position of the book on the acrylic block would be expected to change the reading, possibly because if the book was balanced on the block towards so that it’s center of mass was towards the top of the block, then the top row of cells would receive more pressure than the bottom row. Apparently this would give a different result than if the book was exactly centered or shifted slightly downward. At least that was my interpretation. Clearly it is saying that you can’t expect a deadweight test to give repeatable results.

]]> By: tdecker http://groklab.org/handhygiene/2010/02/18/some-notes-on-force-sensitive-resistors-contd/comment-page-1/#comment-118 tdecker Fri, 19 Feb 2010 05:10:20 +0000 http://groklab.org/handhygiene/?p=607#comment-118 I must not be understanding this passage. Does distribution refer to the actual physical location of the weight distribution over the area of the FSR? In that case, 5psi in the top right corner will not give the same resistance as 5psi in the bottom right corner, test to test. Or does it mean that a five separate 1psi areas will not give the same resistance as one 5 psi area? Or both of these things? In my case, I would think that there would be little variation of the weight distribution between tests: I placed the acrylic block on the FSR, added a 500g weight, removed the weight leaving the block in the same location, and added the next weight, and so on. Undoubtedly the block shifted while I lifted/placed the weights, but I would think it would be a negligible amount. (Or does that passage say that even a negligible amount would have a disproportionate effect on the output?) I must not be understanding this passage. Does distribution refer to the actual physical location of the weight distribution over the area of the FSR? In that case, 5psi in the top right corner will not give the same resistance as 5psi in the bottom right corner, test to test. Or does it mean that a five separate 1psi areas will not give the same resistance as one 5 psi area? Or both of these things?

In my case, I would think that there would be little variation of the weight distribution between tests: I placed the acrylic block on the FSR, added a 500g weight, removed the weight leaving the block in the same location, and added the next weight, and so on. Undoubtedly the block shifted while I lifted/placed the weights, but I would think it would be a negligible amount. (Or does that passage say that even a negligible amount would have a disproportionate effect on the output?)

]]> By: gthomas http://groklab.org/handhygiene/2010/02/18/some-notes-on-force-sensitive-resistors-contd/comment-page-1/#comment-117 gthomas Fri, 19 Feb 2010 04:27:25 +0000 http://groklab.org/handhygiene/?p=607#comment-117 From page 8 of the integration guide: Provide a consistent force distribution. FSR response is very sensitive to the distribution of the applied force. In general, this precludes the use of dead weights for characterization since exact duplication of the weight distribution is rarely repeatable cycle-to-cycle. A consistent weight (force) distribution is more difficult to achieve than merely obtaining a consistent total applied weight (force). As long as the distribution is the same cycle-to-cycle, then repeatability will be maintained. The use of a thin elastomer between the applied force and the FSR can help absorb error from inconsistent force distributions. I'm not sure your quick test is completely valid. From page 8 of the integration guide:

Provide a consistent force distribution. FSR response is very sensitive to the distribution of the applied force. In general, this precludes the use of dead weights for characterization since exact duplication of the weight distribution is rarely repeatable cycle-to-cycle. A consistent weight (force) distribution is more difficult to achieve than merely obtaining a consistent total applied weight
(force). As long as the distribution is the same cycle-to-cycle, then repeatability will be maintained. The use of a thin elastomer between the applied force and the FSR can help absorb error from inconsistent force distributions.

I’m not sure your quick test is completely valid.

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