speed sensor in tranny, how many pulses per mile
12-17-2011, 08:03 PM
#8
I seem to recall reading somewhere that the miata vss is not that type of sensor. I believe it is a frequency signal instead of a pulse. I can't remember for the life of me where I read that though, so take it for what it's worth. An O-scope on the signal wire should tell you conclusively though.
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12-17-2011, 08:15 PM
#9
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The NB VSS is a VR sensor which outputs an AC waveform, and yes, the frequency does increase with speed, however it can still be defined to have "X" number of zero-crossings (pulses) per mile. I simply have no idea what X is.
Hold the vehicle at 60 MPH and measure the frequency of the signal. Then do the math.
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12-17-2011, 10:28 PM
#12
Frequency is simply a measure of the speed of pulses. (massive oversimplification, but sufficient for this context.)
The NB VSS is a VR sensor which outputs an AC waveform, and yes, the frequency does increase with speed, however it can still be defined to have "X" number of zero-crossings (pulses) per mile. I simply have no idea what X is.
Hold the vehicle at 60 MPH and measure the frequency of the signal. Then do the math.
The NB VSS is a VR sensor which outputs an AC waveform, and yes, the frequency does increase with speed, however it can still be defined to have "X" number of zero-crossings (pulses) per mile. I simply have no idea what X is.
Hold the vehicle at 60 MPH and measure the frequency of the signal. Then do the math.
Edit:
Ah ha, I have discovered why I was under that impression:
This.
I can absolutely guarantee you that the NB speed sensor is a cylindrical VR sensor, with an internal magnet. If you hook it up to a scope and spin it by hand, it generates an AC waveform.
Thus, it requires no pullup.
You could try using the MS's VR input circuit (sans pullup), or if you want something that doesn't suck, do this: https://www.miataturbo.net/megasquirt-18/max9924-47243/
I can absolutely guarantee you that the NB speed sensor is a cylindrical VR sensor, with an internal magnet. If you hook it up to a scope and spin it by hand, it generates an AC waveform.
Thus, it requires no pullup.
You could try using the MS's VR input circuit (sans pullup), or if you want something that doesn't suck, do this: https://www.miataturbo.net/megasquirt-18/max9924-47243/
Last edited by baron340; 12-17-2011 at 10:42 PM.
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12-18-2011, 01:29 PM
#13
Boost Pope
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Maybe I just expressed that poorly. I was under the impression that it output a sinusoidal type form instead of a typical square waveform signal seen in most automotive sensors. But according to that m.net thread, I'm wrong anyway, so it's a moot point.
Edit:
Ah ha, I have discovered why I was under that impression:
from this: https://www.miataturbo.net/showthrea...&highlight=vss
Edit:
Ah ha, I have discovered why I was under that impression:
from this: https://www.miataturbo.net/showthrea...&highlight=vss
Think of it this way- if we were talking about a VR crank sensor, would you say that the ECU is measuring the frequency of the signal? I suppose you could argue that it is eventually deriving the frequency of the signal in the form of the RPM computation, but essentially it's just looking at zero-crossings of the waveform and considering each one to be a unique event.
When dealing with a signal like this, the terms PPM and frequency are essentially interchangeable, as they're just two different ways of looking at the same thing.
Computational philosophy? Too deep for me.
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12-20-2011, 11:15 AM
#18
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(asks self if he really wants to get dragged into this...)
mx594m, let's pretend we're back in middle school physics class. I'm the teacher, and this is a pop quiz.
Here is a sine wave. Describe this wave to me in terms of its frequency.
Now, here is a square wave. Describe this wave to me in terms of its frequency.
Finally, define for me what the term "frequency" means, in this context, in 25 words or less.
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mx594m, let's pretend we're back in middle school physics class. I'm the teacher, and this is a pop quiz.
Here is a sine wave. Describe this wave to me in terms of its frequency.
Now, here is a square wave. Describe this wave to me in terms of its frequency.
Finally, define for me what the term "frequency" means, in this context, in 25 words or less.
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
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12-20-2011, 08:21 PM
#19
Pop quiz aside, I think a better question is this: what is the s2000 cluster or aftermarket speedo, or whatever else you need this signal for actually looking for when it tries to interpret the signal and turn it into a read out so you know how fast you are going? Here is where my knowledge of electrical engineering is extremely limited. Is it looking for the signal to cross zero a given number of times per second? Or is it looking for X volts, and then ground and counting the pulses that way?
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12-20-2011, 11:17 PM
#20
(asks self if he really wants to get dragged into this...)
mx594m, let's pretend we're back in middle school physics class. I'm the teacher, and this is a pop quiz.
Here is a sine wave. Describe this wave to me in terms of its frequency.
Now, here is a square wave. Describe this wave to me in terms of its frequency.
Finally, define for me what the term "frequency" means, in this context, in 25 words or less.
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
mx594m, let's pretend we're back in middle school physics class. I'm the teacher, and this is a pop quiz.
Here is a sine wave. Describe this wave to me in terms of its frequency.
Now, here is a square wave. Describe this wave to me in terms of its frequency.
Finally, define for me what the term "frequency" means, in this context, in 25 words or less.
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
in post #9 you stated:
"The NB VSS is a VR sensor which outputs an AC waveform, and yes, the frequency does increase with speed, however it can still be defined to have "X" number of zero-crossings (pulses) per mile. I simply have no idea what X is."
so if you count zero-crossing and compare that to the "frequency" [or number of positive-negative sequences], you will have twice the number of zero-crossings
perhaps it would be better to state that you are defining frequency as the number of zero-crossing and not an alternating cycle
PS - don't eat the goldfish
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