Inductive Prox with 'pulse stretching' feature ?

I have a sensor selection challenge I hope the Forum community can help me with.

I have a system where a mechanism goes by a sensing point relatively fast; the sensing target is only 8 inches long and it's moving as fast as 50 feet per second, so it will only be in range for 13 milliseconds.

The control device is an VFD drive; when the input goes true, I have to detect it (and check for complementary-mode failure !) and begin deceleration of a load.

The VFD drive suggests that it only scans the inputs with its embedded logic solver every 10 milliseconds. That's uncomfortably close to the time that my input will be on.

Are any of you aware of a proximity switch that has a built-in "pulse stretcher" feature ?

Ideally this would be a long-range (40 mm or more) sensor with complementary outputs (one N.C., one N.O.) and a built-in pulse stretching feature rather than using an external signal conditioning relay.

Physical packaging doesn't matter; while I prefer "limit switch" style, a tubular device is OK as well.

I'm Googling furiously and looking through my Banner and A-B catalogs, but I figure there might be a Forum member who has a favored device they are familiar with.

Can it be a retro-reflective or diffuse type photo sensor?

I have used a lot of the A/B (Microswitch) sensors with built in timing features for the same reasons you describe (pulse stretching).

http://ab.rockwellautomation.com/Se...ose-Photoelectric-Sensors/Series-9000-Sensors

I cannot say I have ever used an inductive sensor with a usable range greater than about 12mm.

Turck has a pulse stretcher I have used in the past - goes inline with your signal wiring.

The only issue is that I ended up using a PLC to do the timing setup as a manual teach button would not work for the 40 mSec timing I wanted.

http://www.clrwtr.com/PDF/TURCK/TURCK-Programmable-Timers.pdf

It's got to be inductive; the environment has too much debris and weather to use anything else. The customer won't even allow a physical limit switch because of the risk of false triggers from debris that isn't has heavy and metallic as our moving component.

Thanks for the Turck link; I've seen similar in-line and DIN-rail mounted products from Baluff.

I'll keep on looking, and appreciate any other input.

Aside; It's very cool that PLCTalk posts become themselves Google search results within an hour.

+1 for the Turck pulse stretcher. I've used these before and they work as advertised.

Another option might be the Eaton iProx:
http://www.eaton.com/iprox

I've used these in the past because they have a fairly high sensing range compared to the package size, although it may not be enough for your application (seems to top out at 29mm for the 30mm barrel type). The literature claims they have a configurable on/off delay but I don't have experience with this. The 4-wire DC models have complementary NO/NC outputs.

Sick seems to have a series (Triplex-series with triple sensing range)that goes to 40 mm (IM Triplex - IM30)

https://www.mysick.com/eCat.aspx?go...ist=1&Category=Produktfinder&Selections=55565

I think I'm going to recommend the Allen-Bradley flat puck-style 871F sensor.

They have an 871F0N65BP80-N4 that includes all the features I need other than a pulse stretcher; complementary outputs, a 65-mm sensing range, and 100 Hz speed are all sufficient for my application.

I'm going to ask the mechanical engineer for a slightly longer target, and test the heck out of it.

Gasp! You're turning the world upside down by solving an electrical problem mechanically Ken!

Another way to do that would be to mount two sensors about 6" apart with the NO contacts wired in parallel and the NC contacts wired in series.

Balluff has inline sensor adapters that will do what you want. I've attached a cut sheet.


-rpoet

I have been looking for a Wire Stretcher for years. Any luck on one of those?