DIY_EFI Digest Sunday, 4 August 1996 Volume 01 : Number 220 In this issue: Re: DIY_EFI Digest V1 #219 Re: DIY_EFI Digest V1 #219 Re: Circuits for magnetic pickups Re: Circuits for magnetic pickups 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: Sat, 03 Aug 1996 02:13:28 -0700 Subject: Re: DIY_EFI Digest V1 #219 - ------------------------------ > > From: Erie Patsellis > Date: Sat, 03 Aug 1996 00:50:02 -0400 > Subject: re: Proper Mixture. > > Donald, > Bosch uses an accumulator to eliminate this very problem, while I don't > have may manuals in front of me you should be able to find one out of a > rabbit/scirroco or for that matter any VW/Audi product, as well as > volvo, MB.... The accumulator acts as a damper and resevior, using a > pressurized diapraghm. I would guess you need only find one with the > approx. pressure rating you need. > > erie patsellis 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. ------------------------------ From: "Clinton L. Corbin : Backgrind/Gold : Pager 0544" Date: Sat, 3 Aug 96 06:07:16 PDT Subject: Re: DIY_EFI Digest V1 #219 >> Donald, >> Bosch uses an accumulator to eliminate this very problem, while I don't >> have may manuals in front of me you should be able to find one out of a >> rabbit/scirroco or for that matter any VW/Audi product, as well as >> volvo, MB.... The accumulator acts as a damper and resevior, using a >> pressurized diapraghm. I would guess you need only find one with the >> approx. pressure rating you need. >> >> erie patsellis >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 ------------------------------ From: Darrell Norquay Date: Sat, 3 Aug 96 11:14 PDT Subject: Re: Circuits for magnetic pickups At 09:16 PM 8/2/96 -0700, Sandy wrote: >Do I need to ground the - on the sensor at all? If I do, don't I lose any of >the balanced input benefits that I'm trying to get? If I grounded the (-) at >the opamp, I would guess that I would lose ALL of the benefits of the >balanced inputs. Ideally, you don't want to ground either side of the sensor unless the sensor requires a return path to ground (ie a Hall effect sensor as opposed to a magnetic reluctor type pickup). Your assumption about losing the common mode rejection is correct. >Also I messed around with some input voltage limiting, and found that zeners >won't work, as they are too slow. I think however, that the TVS's will work >like a champ, with only a few ns to clamp. I don't agree generally that Zeners are too slow, the are only a few percent slower than tranzorb type devices. Zeners should be more than adequate for automotive use. Make sure the voltage is high enough to prevent shunting your signal, though. > > |----------------*---------()()()-------*---*------>>> OpAmp + > | | | / > [pickup] [TVS] Inductors | \ Gain > | | | / > |----------------*---------()()()---*---|---*------>>> OpAmp - > | | > --- --- > --- --- Small Caps > | | > --|-- > GND > >This is what I was thinking, with some hysteresis on the opamp side, should >do the trick, but again this is just a guess. What do you think, and what >problems will be caused by not have a GND in the pickup side? This circuit should work well, with a couple of mods. You don't really need inductors, a couple of resistors will work nicely. Move your tranzorb device to the opamp side of the resistors, to provide some current limiting if the device goes into conduction, this will prevent blowing out the tranzorb (or Zener). You may also want to use a pair of diodes to clamp the input voltage to the supply rails. Place one cathode to +V, anode to + signal, and the other cathode to - signal, anode to ground. This will prevent high common mode voltages from killing the opamp. The standard noise filtering for differential lines usually includes a cap across the two lines, in addition to the two you have shown from each line to ground. Calculate the values of the caps from the f = 1/(RC) equation, and make the frequency cutoff point at least twice your maximum sensor input frequency. This will give you good noise filtering without affecting your signal. The resistor you show as "gain" in the above will serve to attenuate the signal in combination with the two series resistors, eliminate it if possible. The classic differential amp configuration usually uses 4 resistors, as below: RF1 |-----/\/\/----| GAIN = RF/R1 | | R1 = R2 R1 | | \ | RF1 = RF2 ---/\/\/---|--| - \ | | |------|------- ---\/\/\---|--| + / R2 | | / | \ / RF2 \ / | --- If you use this configuration, just hang your circuit on the circuit of above, using R1 and R2 as the series resistors. If you use a single supply opamp running off 5 volts, and make the gain high enough, you will get a rail to rail square wave out of the circuit (you could also just eliminate RF1 and RF2 and run the circuit open loop, like a comparator, but you may find that this is TOO much gain). You can also add some positive feedback by tying a high value (several Mohms) resistor from the output to the + in terminal of the opamp. This will give the circuit some hysteresis. regards dn dnorquay@xxx.com ------------------------------ From: Sandy Date: Sat, 03 Aug 1996 15:36:56 -0700 Subject: Re: Circuits for magnetic pickups > >I don't agree generally that Zeners are too slow, the are only a few percent >slower than tranzorb type devices. Zeners should be more than adequate for >automotive use. Make sure the voltage is high enough to prevent shunting >your signal, though. I tried some zeners in my circuit simulator, and I 'think' they didnt work well at the high frequency that could be comming in from 60 tooth wheel, at say 12,000 rpm would be in the range of 12khz. Will that be a problem? Also, I included the inductors to keep out other high frequency noise. 100uh R1 |-------------()()()-------*---*------/\/\/\--*----*->>> To Balanced amp + | | | | | | | --- | \ [pickup] Inductors | --- [BiTVS] / Attenuate | | | | \ | | | R2 | | |-------------()()()---*---|---*------/\/\/\--*----*->>> - | | --- --- --- --- Small Caps | | --|-- GND A bi-directional TVS is nice, in that it is fast and available. One problem, is that if the voltage gets to trigger the TVS, it effectivly will be a short across the inputs to the amp, and the system should still work, for example if the sensor is too close to the gear. So I am going to guess that the TVS will also need a resistor inline, so to just provide a 'clipping' function. Does this sound plausable? As I remember the P-P voltage can be > 100 volts, but, way down to the mV range. As for testing the circuit, this is still a problem, but, I can easily test for noise rejection, by just string wire to a VR sensor, and see what type of noise shows on the output of the VR, and then finally the opamp. Thanks again for the help, I'll be off to the parts store to get a couple of sensors. Sandy ------------------------------ From: john carroll Date: Sat, 3 Aug 1996 21:35:58 -0600 Subject: magnetic pickups The June, 1996 of _SENSORS_ magazine has an excellent article about solid state magnetic gear tooth sensing by Ed Ramsden, Senior Engineer at Cherry Electrical Products. I reccomend that everyone find a copy. john carroll jac@xxx.us john carroll jac@xxx.us ------------------------------ End of DIY_EFI Digest V1 #220 ***************************** 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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