Circuit to detect a pipe wall

[fikseren]

We need suggestions on how to detect the outlet of a 1-inch pipe. A unit will travel in the pipe and detect the wall and we need to detect the pipe end in less than 4 millisecond. The sensor must be electronic and we are thinking of an IR-sensor. The sensor must be insensitive to daylight. Do anybody have a proposal.

 

[joboyd]

If you can mount a strong ring magnet, at the end od the
pipe, you could use a Hall effect sensor to detect the
pipe end. I am not sure how the ring magnet would be affected by the high temperatures, though.

 

[jraef]

"As for now we are back to more or less a micro switch with a leaver sensing the pipe wall."

I would suggest, from a redundancy standpoint as mentioned earlier by others, that you use 3 or 4 "wisker" type switches, somewhat trailing the plug at angles and held closed by the pipe walls. Then set up a voting method of detection by requiring 2/3 or 3/4 switches to be open for ignition, helping to eliminate false ignition from movement of the plug inside the pipe.

"Venditori de oleum-vipera non vigere excordis populi"

 

[joboyd]

About the ring magnet approach, the magnet could be
wrapped in a layer of asbestos.

 

[kevstar]

I have read the posts here. I am very interested in this application. What an earth is it???? However assuming that the pellet can only travel forwards and not turn over "in flight" then the sides of the pellet will always face the inside of the tube. How about mounting a/some proximety switches to the side of the pellet. This way if failure happens inside the tube the sensors will always see the pipe and so ignition will not occur. However when the pellet exits the tube the sensors will then not see the tube anymore and ignition will occur. If necessary a time delay circuit can be added to the pellet to stop instant ignition as soon as the pellet is outside.

 

[sreid]

As I understand it you need to ignite something (gas vapour) near the end of the tube. How about a piezo spark ignitor that is continuously zapping but has nothing to zap until it reaches the end of the tube.