I am looking for an absolute linear position sensor that can span a distance of 40 cm with ~5 mm accuracy. My primary concerns are reliability and cost at a production scale of ~10,000 units. Ideally I can find a vendor that provides an off the shelf sensor but modifying an existing design and printing up circuit boards is not out of the question. I need recommendations on which technology to be looking at (LVDT's, optical encoders, magnetic encoders, etc).
The search so far
I have heard that potentiometers and mechanical solutions in general are less reliable than contactless solutions like LVRTs and encoders. Mostly I have focused the search on encoders because I am a bit more familiar with them. Most encoders I find are accurate to within a micron and cost more than I am hoping to pay for them (example). It seems to me like what I need is the insides of a cheap digital caliper just blown up a little (to 40 cm long) but I can't seem to find a vendor that builds and sells all the digital caliper innards.
Things I have already read:
Questions like this one and this one are similar to mine but both have different accuracy requirements and neither were asking about production at scale. Answers like "buy an optical mouse and take it apart" worked for them but they don't for me. I have also looked at comparisons of position sensing technology (example) but they always seem to focus on solutions with significantly higher resolution than I need.
Gory details in case they matter or your are curious
- Mechanical constraints: hardware can't extend more than ~5 centimeters past the stroke length of the sensor.
- Definition of reliability: At least 20-30k cycles before failure.
- Sample Rate: shouldn't be an issue, as low as 10sps would be fine
- Enviromental factors: A sheltered open air environment so temperature can swing ~0-100 degrees C and condensation can exist