Reed Switches and Pneumatic Cylinders

Sure--proportional valves with temposonic probes and PID loops. Lineal positioning systems.

Check Bosch or Moog for the valves.

Check MTS for probes.

Or http://www.pawtaw.com/ for both.

Nice stuff. You buyin' ?

For how many other positions of the cylinder? Few? Many? With what accuracy do you need to know the position? Must the position information be analog (ie, a voltage, perhaps)? Can it be digital?

Your solution's price depends heavily on how you answer these questions. Think about exactly what you need and why you need it. Beyond that and you could end up spending a lot of money you'd probably rather keep.

(Note. The following is not addressed to you. You may skip this part if you wish: There are always arbitrarily sophisticated, expensive and overly complicated solutions to any problem. I mean, who doesn't have a few hundred thou laying around for just this purpose? Great, helpful response. The OP is now way ahead. )

Perhaps the easiest most reliable way is to use a LVDT with a current or voltage output. One manufacturer of LVDTs is: http://www.schaevitz.com/ another is http://www.macrosensors.com/

There are also magnetostrictive devices like the Temposonics: http://www.mtssensors.com/technology/how-magnetostriction-works/index.html

Possibly the cheapest way is to use a linear potentiometer. Like this: http://www.bourns.com/pdfs/bourns_lmp_apno.pdf

Other solutions which may be acceptable are: Cable actuated like here: http://www.unimeasure.com/

There are many different types of linear sensors suitable for use with air cylinders. It would help to know the environment where the equipment will be operating, the length of the stroke, speed requirements interface desired and any cost considerations.

I have even seen a pneumatic sensor which used a tapered needle in an orfice fed through a flow restrictor. The tapered needle was connected to the oposite end of the air cylinder and the position was sensed by monitoring the pressure of the air up stream of the tapered needle arangement. The position display was a specially calibrated pressure guage. As the cylinder pulled the load (retracted) the opposite end of the piston shaft with the needle entered the variable valve body causing the pressure to rise as the needle blocked the air bleed.

Have FUN!
TT3

Try a feedack valve positioner. Search Google for detailed info. This will give you an exact position relative to a linear motion of your piston.

Bimba and TRD make actuators with LRT's in them providing position feedback throughout the length of stroke.

See http://www.bimba.com/Products/PositionControl/PositionControlSystemPCS/

or http://www.trdmfg.com/Products/Balluff/

Bimba have a new, non-contact probe available which will provide better life expectancy than a contact probe. TRD use a Balluf non-contact probe.

Position feedback is available in Volts or mAmps.

If you are in Canada, we can help. www.cowper.ca

Regards,

Gren Cowper

Sir, try a search of Baluff for a reasonably inexpensive and accurate analog solution to your displacement issue.

Regards