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| Home > Help Needed / General Tech Chat > Electronic distance measurement - how ? | |||||||
 696 Posts Member #: 10034 Post Whore Birmingham |
9th Dec, 2014 at 06:46:44pm
I meant drill a hole in the top of the dashpot and leave the damper in place. Does that change things? With the piston in a stable position, surely there's no flow in or out of the chamber, so the piston height must be down to spring, weight, and pressure?
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 (2)[/url] by [url=https://www.flickr.com/photos/150672766@N03/]Rod Sugden[/url], on Fli) 5988 Posts Member #: 2024 Formally Retired Rural Suffolk |
9th Dec, 2014 at 07:32:47pm
The dashpot itself has a hole in the cap so there is no pressure generated - apart maybe from under acceleration when the piston rises fast and the air can't get out quick enough.
Schrödinger's cat - so which one am I ??? |
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696 Posts Member #: 10034 Post Whore Birmingham |
9th Dec, 2014 at 09:16:22pm
On 9th Dec, 2014 Rod S said:
Who wants to give it a go ??? I've just bought the Sharp sensor you linked to. It's a cheap ebay one from China, so most likely a copy, but I expect it will work all the same. Another project the new year. http://www.ebay.co.uk/itm/131317819987 |
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3594 Posts Member #: 655 Post Whore Northern Ireland |
10th Dec, 2014 at 01:44:34pm
On 9th Dec, 2014 Rod S said:
The dashpot itself has a hole in the cap so there is no pressure generated - apart maybe from under acceleration when the piston rises fast and the air can't get out quick enough. It only exists to slow the rate of rise of the piston and that is done by the oil and the one way valve on the rod. So the piston height is down to spring/weight/pressure as you say but the basic principle is to have the pressure above the piston the same as across the bridge/venturi to control the fuel rate to match the size of the open area above the bridge. SU's are crude but I don't see any relationship between pressure and piston height as the piston rises to try and keep the venturi pressure constant. The IR sensor I linked - I'm sure there are better - does read below 100mm (10cm) according to the datasheet but its basic specification is 10-80cm and the graph is really linear beyond 10 which would make calibration easier but I'm sure it could be made to work without the extension tubes as the piston is recessed downwards - IIRC, I haven't taken one of these apart for ages - but even very short tubes (plus glue) would be the easiest way to mount it IMO. Who wants to give it a go ??? I won't be placing another order with iTead for a while (just ordered a load of PCBs a week ago) but I'm sure that sensor could be found on UK arduinos sites albeit at a lot higher price. A turbo SU has no holes in the dashpot, and is sealed. Under boost, if there are any holes, there will be leaks. 9.85 @ 145mph
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5988 Posts Member #: 2024 Formally Retired Rural Suffolk |
10th Dec, 2014 at 02:12:43pm
On 10th Dec, 2014 stevieturbo said:
A turbo SU has no holes in the dashpot, and is sealed. Under boost, if there are any holes, there will be leaks. Good point Stevie, just shows how long it was since I worked on any carb, let alone a carb modified for boost. I can't even remember if it's the sleeve attached to the piston or the sleeve attached to the main chamber, which one is inside or outside the other.... But I still don't think trying to measure pressure in that small chamber is going to give any accurate indication of height. In fact, because the whole carb is sealed, whether the pressure was read at the top of the damper or the suction chamber itself, it would just be a measurement of boost, not piston lift (assuming there is leakage of air between the two sleeves). Optical (IR) or ultrasonics are the only non-contact thing I can think of that would give accurate resolution - as I said, the cheap IR solution should be good for 0.295mm I would prefer ultrasonics but the sensors for use in air are too big, the ones we use for time of flight in metals (weld examinations etc) can be a lot smaller. EDIT - extra sentence added. Edited by Rod S on 10th Dec, 2014. Schrödinger's cat - so which one am I ??? |
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 2909 Posts Member #: 83 Post Whore Glasgow, Scotland |
10th Dec, 2014 at 02:48:11pm
could you not mount the distance sensor suggested through a hole cut in the top of the dashpot (to the side of where the screwy bit is) so it directly measures the height of the piston. and seal it in with epoxy or similar? there may even be room inside the dashpot so just the wires come out? so long as it doesnt interfere with the spring. turbo 16v k-series 11.9@118.9 :)
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