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Help: What is the PPM rate of the Speed Sensor?

 
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Sexy_Rex
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Joined: 04 Jun 2009
Posts: 429
Location: Redondo Beach, CA

PostPosted: Thu Aug 06, 2009 12:26 pm    Post subject: Help: What is the PPM rate of the Speed Sensor? Reply with quote

I need to know the electronic pulse rate (Pulses Per Mile) at the speed sensor. Thx.
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Phil



Joined: 09 Jul 2009
Posts: 30
Location: Montreal

PostPosted: Sun Aug 16, 2009 2:33 pm    Post subject: Reply with quote

Hi, I haven't mesure the PPM @ 30 MPH but here is how I think it can be calculated:
With the 285/40/17 tire, we have 776 rev/mile. To calculate the rev/min @ 30 MPH of the rear wheel it is: 776 (rev/mine) x 30 (miles) / 60 (minutes) = 388.
To calculate the rev/min of the front sprocket it is: 388 x 50 (rear sprocket) / 15 (front sprocket) = 1293.
Each turn of the front sprocket should generate 4 pluses so you have 1293 x 4 = 5173 pluses/minute @ 30 MPH.
5173 PPM is what you should read at the sensor. This is not the PPM at the speedometer because there is a speed healer in between. On my vehicule there is a .696 correction factor so at the gauge the PPM is 5173 x .696 = 3602 PPM @ 30 MPH.
Hi hope this help!
Philippe
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Sexy_Rex
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Joined: 04 Jun 2009
Posts: 429
Location: Redondo Beach, CA

PostPosted: Sun Aug 16, 2009 8:39 pm    Post subject: Reply with quote

Hi Phil,

There is some errors in your calculations. First, mph (speed) does not effect the number of revolutions of the rear tire per mile. Your revolutions are 776 vs mine at 773.06. My tire is a 295/35rx18. Diameter of my tire is 26.1". It will travel 82" per revolution.

Your gear ration is 50/15. Mine is 48/17. Minor ratio differnce but it still is important.

What is important is how many pulses per tire revoltion is generated. My guess it is somewhere around 17-18 pulses at the speed sensor (VSS - pink wire). I cannot verify this and do not have the equipment to do so. Again, the # of pulses could even be higher than my guess.

Hopefully, someone will jack up the back wheel and rotate the tire one revolution by hand and be able to count the number of pulses and post the answer.

The reason this is so important to me is because I am installing a Rostra electronic cruise control and need to know what switches I need to set.

Note: The Speed-O-Healer does not play into this formula because the pulse rate is at the VSS switch. The Spee-O-Healter follows after this measurement.

The formulas are:

Gear Ratio (GR) = Rear Sprocket/Front Sprocket

Tire Revoltions per Mile (TR) = 5280/((2x3.1416xR)/12) - (R mean radius in inches) - know the true tire diameter via the tire manufacter.

Pulse Rate (PR) per one tire revoltion

PPM = TR x GR x PR
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chicknfeet
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Joined: 04 Jun 2009
Posts: 416
Location: Los Angeles

PostPosted: Mon Aug 17, 2009 1:18 pm    Post subject: Reply with quote

I have a scope and the dyno lets work out a time
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Phil



Joined: 09 Jul 2009
Posts: 30
Location: Montreal

PostPosted: Mon Aug 17, 2009 7:33 pm    Post subject: Reply with quote

Hi Richard, I don't think I have made any mistakes in my calculations. The only thing is that I gave you the pulses per minutes instead of pulses per miles because you told me in a message that it meeds to be tested at 30 MPH so I thought you needed pulses per minute at that speed.

Also because you didn't give the informaiton about your tire size and sprocket ratio, I gave you the calculation with my setup. But as I can see, you can make these calculations by yourself.

So the only thing you need to know, as I told you before, is that the speed sensor generate 4 pulses for each front sprocket revolution. Any mesurements that are made with a different setup than yours will not be accurate.

Note: I have gave you the correction factor of the Speed Healler (for my setup) in case you would like to take the signal at the front of the vehicule.
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Sexy_Rex
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Joined: 04 Jun 2009
Posts: 429
Location: Redondo Beach, CA

PostPosted: Mon Aug 17, 2009 10:42 pm    Post subject: Reply with quote

Hi Phil,

Today, I took measurements for Hertz at the yellow wire on the VSS. The tests were at 30 mph & 60 mph. Readings were 75 Htz & 150 Htz respecfully. The test was done on road conditions and not a dyno. A dyno reading would be ideal. With these readings, Thomas, Rostra's lab tech, made the calculations of 9,000 PPM. How his calculations were made, I do not know, but his answer was the same for both Hertz readings.

If someone has the ability to test a T-Rex on a dyno and measure the Hertz at the constant speeds of 30 mph and 60 mph on the yellow wire at the VSS, we will have an accurate PPM
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2007 T-Rex 1400R - BMW Laguna Seca Blue -Turbo Powered
2003 Honda ST1300 - Candy Metalic Red
2002 Acura MDX
21 Speed Cannondale M300 Bicycle


Last edited by Sexy_Rex on Sat Aug 29, 2009 4:44 pm; edited 1 time in total
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Sexy_Rex
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Joined: 04 Jun 2009
Posts: 429
Location: Redondo Beach, CA

PostPosted: Fri Aug 28, 2009 4:56 pm    Post subject: Reply with quote

Here is the formula in how to calculate PPM:

PPM - Pulses per Mile
Hz - Hertz (Hertz is defined as frequency in a set time period. 1 Hz is defined as one occurance within one second).
MPH - Miles per Hour

PPM = (Hz * 3600) / MPH
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2003 Honda ST1300 - Candy Metalic Red
2002 Acura MDX
21 Speed Cannondale M300 Bicycle
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getmad2009



Joined: 11 Oct 2009
Posts: 668
Location: st colomban

PostPosted: Thu Oct 22, 2009 9:25 pm    Post subject: Reply with quote

whoa...............my head is making strange noises................ Shocked
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