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I am an undergraduate researcher and I am working at enhancing a calibrating system for a hydrographic surveying system that my supervisor uses on his hydrography course. The rope is used to lower a bar check system, and it comes out of a coil. I want to find a reliable way to measure how much rope has come out of the coil.

Currently the rope has markings on it at every meter so that the person deploying it can know how much rope has been used by counting the number of markings that passed.

I was wondering if there is a more reliable way to measure how much rope has come out of the coil, preferable by some sort of measuring device. The most obvious idea would be some sort of pulley system that records the number of rotations of the pulley, but that is prone to slipping and the error could add up over 30 something meters. Do you know of such a device or idea that could help with that?

(p.s.: this is a very minor aspect of the whole design, and doesn't affect at all my work, it would just be a "nice to have" thing in the design)

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  • $\begingroup$ Use a pulley where you can put a full turn of the rope around the pulley - won’t slip then... $\endgroup$ – Solar Mike May 11 '19 at 6:07
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Depends on how much accuracy and at what cost you're looking for.

There are several manufacturers which make devices like what you are asking. Here is one. Cord meter

Also you can use a basic computer optical mouse and an LED counter attached to an Arduino sensor for around $20-30.

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    $\begingroup$ This reference is a good answer, especially when one considers the mechanism includes a pressure roller to remove slippage. A variation on this specific device would be a surveyor's wheel with a flange to guide the rope, along with a pressure roller. Less expensive than the linked product. $\endgroup$ – fred_dot_u May 11 '19 at 0:17
  • $\begingroup$ Yes, this is what I am looking for. The price of these meters is too steep for me, and the precision is way higher than I need, but I can definitely see a way to make it work with cheaper parts. Thank you. $\endgroup$ – Walther Wennholz Johnson May 13 '19 at 19:37

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