# Best linear position sensor for piston feedback

I have been looking at measuring the extension/retraction of a piston to record and predict the life of the device. What would be the best way to measure the piston strokes?

So far, I have come up with following guesses/ideas:

1. LVDT in parallel. This is cost prohibitive.

2. Linear Pot. I like this idea, but I have not found a decent source for COTS solutions. No idea what price is.

3. Optical sensor on piston, stripe piston (encoder-like feedback and the environment is very clean). I imagine I would need to add limit switches and possibly calibrate this configuration. This seems overly complicated.

I figure there are other solutions out there, but I am currently ignorant to them.

Info for the piston/interface: - 8 inch stroke - Clean environment with some dust intrusion (think home office, not industrial) - Accuracy is acceptable to within 10% of stroke - Maximum actuation time of 1 stroke per second - Ambient temperature is 20C-25C without much variation - Time is not an issue, this is an experiment - The cheaper the solution the better. Ideal price point is $5-$10 though likely unrealistic - My goal is to test to 10,000 strokes - An absolute output is ideal, but not completely necessary

• As always, you need to define what "best" means in the context of your project. We can't read your mind! Oct 17 '16 at 11:39
• "the best linear position sensor" depends on your application: How long is the stroke of the piston? Is the piston constrained to one degree of freedom, or can it e.g. rotate within the cylinder? What level of inaccuracy is tolerable? How rapidly does the piston move? Would the sensor be exposed to dirt/water/grease? Is the environment corrosive? What temperature range is to be expected? How many strokes is the sensor expected to last? Does the sensor have to produce an absolute output? How much money and/or time are you willing to devote to this?
– jms
Oct 17 '16 at 16:43
• The piston stroke is 8 inches. We are indeed constrained to 1 degree of freedom. Accuracy does not matter to me as long as I can I can tell the piston moved. Let's say 10%. The piston moves full stroke at a maximum of 1 second per stroke. There will be minimal dirt and grease intrusion. The environment is clean and ambient is room temperature without much variation (not industrial). Time spent can be about a month, but I have access to a machine shop and usually moves faster than most engis. This is to last ainimum of 10,000 strokes. Absolute output is ideal, but not necessary. Oct 17 '16 at 17:13
• And the final cost of the widget is critical. I was hoping to make a few of these and budget is close to nonexistent, minus my time. Oct 17 '16 at 17:19
• Are there any parametric measurements you could make? For example: if the piston is tied to a crankshaft, could you measure the angle of the crankshaft and infer the position of the piston? Oct 17 '16 at 18:52