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Old 12-14-2011, 05:41 PM   #1
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Default speed sensor in tranny, how many pulses per mile

Anybody know how many ppm the speed sensor in the tranny outputs? 4000ppm?
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Old 12-16-2011, 04:49 PM   #2
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anyone, anyone, ... , Bueler?
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Old 12-16-2011, 05:31 PM   #3
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uhhhhh...x?
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Old 12-16-2011, 05:38 PM   #4
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Are you trying to get VSS working? I can give you a screen shot of my VSS settings for my MS3x. I have no clue what ppm stands for.
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Old 12-16-2011, 05:39 PM   #5
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pulses per mile.
Sorry I don't know the answer.
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Old 12-16-2011, 05:46 PM   #6
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Quote:
Originally Posted by shuiend View Post
Are you trying to get VSS working? I can give you a screen shot of my VSS settings for my MS3x. I have no clue what ppm stands for.
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Old 12-17-2011, 06:00 PM   #7
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Originally Posted by shuiend View Post
Are you trying to get VSS working? I can give you a screen shot of my VSS settings for my MS3x. I have no clue what ppm stands for.
I have VSS working, but I want to use the VSS output to control a S2000 instrument cluster. It expects a 145000ppm pulse so I'm trying to figure out what multiplier to use.
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Old 12-17-2011, 09:03 PM   #8
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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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Old 12-17-2011, 09:15 PM   #9
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Quote:
Originally Posted by baron340 View Post
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.
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.
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Old 12-17-2011, 10:25 PM   #10
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NB's have VSS instead of a cable? I didn't know that. Cool now i can go to bed.
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Old 12-17-2011, 10:44 PM   #11
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http://forum.miata.net/vb/showthread.php?t=417819

Happened to come across this, looks like 8200ppm?
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Old 12-17-2011, 11:28 PM   #12
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Quote:
Originally Posted by Joe Perez View Post
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.
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:
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Originally Posted by Joe Perez View Post
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/

from this: https://www.miataturbo.net/showthrea...&highlight=vss
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Last edited by baron340; 12-17-2011 at 11:42 PM.
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Old 12-18-2011, 02:29 PM   #13
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Quote:
Originally Posted by baron340 View Post
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
Yeah, the terminology can be a bit confusing I suppose. It is an AC waveform rather than the squarewave which the VSS inside the speedo of the '90-'97 cars produces, so referring to this signal in terms of "PPM" might seem awkward, however from the computers point of view, either one can be considered to be a "pulse."

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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Old 12-18-2011, 06:50 PM   #14
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Quote:
Originally Posted by Joe Perez View Post

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.
not interchangable, 1 Hz = 2 zero-crossings; 1 from positive to negative, and 1 from negative to positive
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Old 12-19-2011, 12:12 PM   #15
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not interchangable, 1 Hz = 2 zero-crossings; 1 from positive to negative, and 1 from negative to positive
Ya might wanna stop right there. The word he used was "terms". Hz and ppm are interchangeable in the same way that Celcius and Fahrenheit are interchangeable.
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Old 12-19-2011, 11:46 PM   #16
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Eh; that is like saying the terms positive and negative are interchangeable
just follow that and reverse polarity on your battery and you will be interchanging your ECU/EMS
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Old 12-20-2011, 11:15 AM   #17
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This is going to be like explaining radar to a goldfish isn't it?
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Old 12-20-2011, 12:15 PM   #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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Old 12-20-2011, 09:21 PM   #19
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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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Old 12-21-2011, 12:17 AM   #20
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Quote:
Originally Posted by Joe Perez View Post
(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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frequency = the number of occurrences of a repeating event per unit time; e.g., a positive-negative sequence; so both are 1 Hz [1 cycle per second]

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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