DIY_EFI Digest Monday, 5 August 1996 Volume 01 : Number 221 In this issue: Re: DIY_EFI Digest V1 #220 re: AFMs Re: Circuits for magnetic pickups See the end of the digest for information on subscribing to the DIY_EFI or DIY_EFI-Digest mailing lists. ---------------------------------------------------------------------- From: talltom Date: Sun, 04 Aug 1996 04:39:10 -0700 Subject: Re: DIY_EFI Digest V1 #220 > >While I'll go along with the above, one might keep in mind that the > >cars these came off of don't use much fuel and as a result won't > >sized for something that say burns 10 gallons of fuel running the 1/4 > >mile. Might consider bigger or more of them if making any real power. > > Just what kind of car are we talking about? If the engine makes 1000hp and > has a BSFC of only 1.00 (real world closer to 0.5), figure the 1/4 mile run > lasts for 5 minutes at full power (a REALLY big car!), it would burn around > 10 gallons of fuel in the run. And most all cars DO NOT make 1000hp, they are > about twice as fuel efficent as this example, and they are at full throttle for > only 30 seconds or so, counting the burn-out. While I agree with you that you > need to size the accumulator for the application, your example is a bit > extreme. Unless it is for a top-fuel or top-alchol car, in which case it > just may be a bit understated! > > Clint Corbin > ccorbin@xxx.com > ccorbin@xxx.com Isn't one of the things that's supposed to be taught to engineers is that there are no extreems? It's all a matter of degree. Well the figures I saw ran 10-12 gals/pass, approx 3500hp, and the pass takes about 5 seconds. Admittedly I scrimped some on the gallonage because I was thinking of mine, which I doubt I'll ever get that well built, but the cost difference between a fuel sys. that delivers 8gals in 5 sec. and one delivers 12 is slight and I don't ever want to have do it over.(ps. mine weighs 7500) Further, while we're at it, has anybody figured the effect of the g's on where the fuel will be to pick up in the tank under acceleration?(yes, that's the voice of expierience, I goofed) ------------------------------ From: RABBITT_Andrew@xxx.au Date: Mon, 5 Aug 1996 08:02:16 est Subject: re: AFMs >>Is it a MASS FLOW measurement? NO, vortex shedding frequency is a function of flow velocity, therefore it's only volume flow metering. The pressure and temp. sensors are only to do the corrections, which alledgedly leads to messy lookup tables and calculations in the OEM ECU. (yuk!) >>Does a problem occur at low (read idle) flow rates (of resolution)? I shouldn't think so, it should be just a matter of sizing the vortex shedder and minimum flow velocity appropriately. (my opinion only) >>All this stems from me being a little nervous about using Bosch hotwires in a high vibration offroad application. If you're worried about vibration on a hotwire, try using the bosch hot-film sensor (HFM-2) as fitted to many late model BMW's and probably many other European cars. Take a look at the latest 540i (4.4L V8) which should be good for your application Also, the Hitachi bypass meter fitted to most fords (EEC iv) is an analogue output, not frequency. Also, for everyone's info, Bosch has recently started production on a hot-film meter capable of measuring back-flow (properly!) A neat piece of design using micro-machined silicon technology. Andrew Rabbitt Orbital Engine Company ------------------------------ From: Donald Whisnant Date: Mon, 05 Aug 1996 01:49:40 -0400 Subject: Re: Circuits for magnetic pickups >From: Sandy >Date: Fri, 02 Aug 1996 21:16:04 -0700 >Subject: Re: Circuits for magnetic pickups > >Tim and others... > >I was thinking much of the same idea, but was afraid that it was way too >simple. I guess that I have to go out and get a sensor, and a wheel on a car >and see how bad the noise really is. I'm guessing that it is really bad in >some cases, but if I can rid my design of the lm1815, that would be very >good. The circuit that you used on the Direct Ignition looked good, but >again looked like it would be susceptible to noise. > > Actually the noise really isn't bad at all.... I've got a 120v power inverter and have actually put my oscilloscope in the car (had someone else drive :) and looked at the signal under real-time operating conditions. The key factors I found were: be sure to twist the wires from the sensor together, and a simple integrator type filter is more than adequate to remove all noise -- even running it single-ended. ... The LM1815 and HIP9020 both have zero cross detection which eliminates a lot of noise problems that you'll find in op-amp setups (this probably accounts for my "clean" signal -- as I didn't try it with just op-amps) ... So, you may want to look in some data books for zero-cross detectors -- I seem to recall a circuit that employed several diodes in the feedback loop of an op-amp to do zero cross detection. ... ... As for "voltage" limiting, the key factor actually is reducing current flow (for example, the HIP9020 requires a 40K resistor in series with the input lead) --- A well designed voltage divider ladder with resistors but choosing the correct size --- (i.e. a 1k and 2k in series gives a 0.66666 ratio and so does 100k and 200k -- the current flow in the 100k/200k is a lot less than the 1k/2k ladder)... But, all in all, I believe you'll find it simpler just to use either the LM1815 or HIP9020 -- it will definitely be cheaper in the long run (from both time and parts), unless you are pressed for board space... Donald Whisnant dewhisna@xxx.com ------------------------------ End of DIY_EFI Digest V1 #221 ***************************** To subscribe to DIY_EFI-Digest, send the command: subscribe diy_efi-digest in the body of a message to "Majordomo@xxx. 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