Searching \ for '[OT} Pressure to MPH' in subject line. ()
Help us get a faster server
FAQ page: www.piclist.com/techref/index.htm?key=pressure+mph
Search entire site for: 'Pressure to MPH'.

Exact match. Not showing close matches.
'[OT} Pressure to MPH'
2000\05\11@095540 by

Andy (and list) - I  found my notebook dealing with determining the speed of
my Hobie Cat via a pitot tube.  It seems that most of the information I used
came from SenSym  handbook Applications Note SSAN-7.  The basic formula is:
delta P = p(v*v/2g)
where:
delta P is the difference in pressure between a reference pressure and the
pressure in the tube cause by the flow of water (or air)
p is the fluid density in lbs/square inch (fresh water is 1g/cm cubed or
.036 lbs/inch cubed - sea water is 1.025 gm/cm3 or .037 lbs/in3)
v is the velocity of the stream in inch/second
g is the gravitational constant in inch/second/second (386.088
inch/sec/sec)

In playing what I found was that delta P plotted against velocity would give
what looked like a parabolic curve.  But if you took the square root of
delta P you would get a straight line.  I wrote a quick program that would
give me speed in knots for a given PSI, square root of PSI and slope of
square root PSI.

Since all I was interested in was delta P, I had chosen an absolute
pressure sensor that was one closed chamber and one open chamber.  The delta
P with the Hobie sitting in the water at rest was used as an offset for 0
knots.

SenSym Application Note SSAN-18 shows a low cost precision amplifier for one
of their pressure sensors.  It consist of 4 op amps and a few other
components.

One last comment for those who did not know - knots are used in sea and air
navigation.  It is speed in nautical miles per hour, where a nautical mile
is 6000 feet rather than the typical mile of 5280 feet.  The 6000 feet is
based on an equal division of longitude or latitude.  Gee - I wonder if
airline frequent flyer miles are based on nautical miles?  If so then we are
getting shorted!

Hope this helps.

David V. Fansler
TriPath Imaging, Inc. (Formerly AutoCyte, Inc)
336-222-9707 Ext. 261
dfanslerautocyte.com <dfanslerautocyte.com>
Now Showing! http://www.dv-fansler.com <http://www.dv-fansler.com/>
Updated March 31,2000
Ann's Cancer, David's Observatory, Disney World

#include <stdio.h>
#include <math.h>
main()
{
double sqrt();
double a,b=0.0,c,d,e,f,v;
double k=20.2537, g=386.088, p=.036;
FILE *prtout;

if(!(prtout = fopen("prn","w"))){
printf("\n Cannot open printer!\n");
exit(0);
}
fprintf(prtout,"knots\tPSI\tsqrt(PSI)\tslope\t\t");
fprintf(prtout,"knots\tPSI\tsqrt(PSI)\tslope\n");
for(v=0.1; v<40.0; v=v+.1){
a=p*(((v*k)*(v*k))/(2*g));
c=sqrt(a);
fprintf(prtout," %3.1f\t%5.3f\t%5.4f\t\t%4.3f\t\t",v,a,c,c-b);
b=c;
v=v+.1;
a=p*(((v*k)*(v*k))/(2*g));
c=sqrt(a);
fprintf(prtout," %3.1f\t%5.3f\t%5.4f\t\t%4.3f\n",v,a,c,c-b);
b=c;

if((v<10.05&&v>9.95)||(v<20.05&&v>19.95)||(v<30.05&&v>29.95)){
fprintf(prtout,"%c",0x0c);
fprintf(prtout,"knots\tPSI\tsqrt(PSI)\tslope\t\t");
fprintf(prtout,"knots\tPSI\tsqrt(PSI)\tslope\n");
}
}
fflush(prtout);
exit(0);
}

Just got this in from my brother the physics teacher.  Thought it might be

Andy

Andy,

Thanks for getting this to me.  I was just getting out my thermo book.
Potential problem here though.  Go to the line in the note from the other
guy where is says

p is the fluid density in lbs/square inch (fresh water is 1g/cm cubed or

little p, (actually the Greek letter rho), is density and must be lbs/cubic
inch since square inch is surface area not volume

Also, 6000 feet is NOT one nautical mile.  That's the useful approximation
they teach you in airplane and marine navigation. There are a couple of
exact figures given in the Handbook of Chemistry and Physics.  One nautical
mile (British) is 6080 feet.  In US feet its 6076.1.  Only about 1% but you
might as well program it as accurately as possible.

Mike

"Fansler, David" <DFANSLERAUTOCYTE.COM> on 05/11/2000 08:04:20 AM

Please respond to pic microcontroller discussion list <PICLISTMITVMA.MIT.EDU>

To:      PICLISTMITVMA.MIT.EDU

cc:      (bcc: Andrew Kunz/TDI_NOTES)

Subject: [OT} Pressure to MPH

Andy (and list) - I  found my notebook dealing with determining the speed of
my Hobie Cat via a pitot tube.  It seems that most of the information I used
came from SenSym  handbook Applications Note SSAN-7.  The basic formula is:
delta P = p(v*v/2g)
where:
delta P is the difference in pressure between a reference pressure and the
pressure in the tube cause by the flow of water (or air)
p is the fluid density in lbs/square inch (fresh water is 1g/cm cubed or
.036 lbs/inch cubed - sea water is 1.025 gm/cm3 or .037 lbs/in3)
v is the velocity of the stream in inch/second
g is the gravitational constant in inch/second/second (386.088
inch/sec/sec)

In playing what I found was that delta P plotted against velocity would give
what looked like a parabolic curve.  But if you took the square root of
delta P you would get a straight line.  I wrote a quick program that would
give me speed in knots for a given PSI, square root of PSI and slope of
square root PSI.

Since all I was interested in was delta P, I had chosen an absolute
pressure sensor that was one closed chamber and one open chamber.  The delta
P with the Hobie sitting in the water at rest was used as an offset for 0
knots.

SenSym Application Note SSAN-18 shows a low cost precision amplifier for one
of their pressure sensors.  It consist of 4 op amps and a few other
components.

One last comment for those who did not know - knots are used in sea and air
navigation.  It is speed in nautical miles per hour, where a nautical mile
is 6000 feet rather than the typical mile of 5280 feet.  The 6000 feet is
based on an equal division of longitude or latitude.  Gee - I wonder if
airline frequent flyer miles are based on nautical miles?  If so then we are
getting shorted!

Hope this helps.

David V. Fansler
TriPath Imaging, Inc. (Formerly AutoCyte, Inc)
336-222-9707 Ext. 261
dfanslerautocyte.com <dfanslerautocyte.com>
Now Showing! http://www.dv-fansler.com <http://www.dv-fansler.com/>
Updated March 31,2000
Ann's Cancer, David's Observatory, Disney World

#include <stdio.h>
#include <math.h>
main()
{
double sqrt();
double a,b=0.0,c,d,e,f,v;
double k=20.2537, g=386.088, p=.036;
FILE *prtout;

if(!(prtout = fopen("prn","w"))){
printf("\n Cannot open printer!\n");
exit(0);
}
fprintf(prtout,"knots\tPSI\tsqrt(PSI)\tslope\t\t");
fprintf(prtout,"knots\tPSI\tsqrt(PSI)\tslope\n");
for(v=0.1; v<40.0; v=v+.1){
a=p*(((v*k)*(v*k))/(2*g));
c=sqrt(a);
fprintf(prtout," %3.1f\t%5.3f\t%5.4f\t\t%4.3f\t\t",v,a,c,c-b);
b=c;
v=v+.1;
a=p*(((v*k)*(v*k))/(2*g));
c=sqrt(a);
fprintf(prtout," %3.1f\t%5.3f\t%5.4f\t\t%4.3f\n",v,a,c,c-b);
b=c;

if((v<10.05&&v>9.95)||(v<20.05&&v>19.95)||(v<30.05&&v>29.95)){
fprintf(prtout,"%c",0x0c);
fprintf(prtout,"knots\tPSI\tsqrt(PSI)\tslope\t\t");
fprintf(prtout,"knots\tPSI\tsqrt(PSI)\tslope\n");
}
}
fflush(prtout);
exit(0);
}

Well - I guess "the other guy" has been told! :-)

Your brother is right Andy - but it was easier and foolproof to use a p
rather than r (lower case rho) not knowing if your email reader would handle
it.  Yes it should have been volume instead of area.  Darn - and I thought I
was going to make through the year without a single mistake.

As for the 76 or 80 foot error, I was too lazy to look that one up!

I taught high school physics for a little over 3 years before bailing out
for more money - but that was about 25 years ago.

David V. Fansler
TriPath Imaging, Inc. (Formerly AutoCyte, Inc)
336-222-9707 Ext. 261
dfanslerautocyte.com <dfanslerautocyte.com>
Now Showing! http://www.dv-fansler.com <http://www.dv-fansler.com/>
Updated March 31,2000
Ann's Cancer, David's Observatory, Disney World

{Original Message removed}

<x-flowed>At 08:04 AM 5/11/00 -0400, you wrote:
>Andy (and list) - I  found my notebook dealing with determining the speed of
>my Hobie Cat via a pitot tube.  It seems that most of the information I used

<snip>

David,

How fast did your Hobi Cat go?

Thanks.
Jim

</x-flowed>

2000\05\11@234607 by
Jim - I never finished the project - but after we purchased our 27' sailboat
I received a GPS for an anniversary gift.  Being "waterproof", I strapped
the GPS to the mast to see how fast I went.  Of few days I tried it in the
ocean I hit 18 knots.  I feel I have been faster, but it just takes the
right combination of wind and lack of waves.  A protected bay would be ideal
for speed trials.  It is stated that a 16' Hobie with no sails - just the
mast - will do 8 knots in a 25 knot wind.

David V. Fansler
TriPath Imaging, Inc. (formerly AutoCyte, Inc.)
Dfanslerautocyte.com <Dfanslerautocyte.com>
336-222-9707 Ext. 261
Now Showing!  http://www.dv-fansler.com <http://www.dv-fansler.com>
Last updated March 31, 2000
Ann's Cancer, David's Observatory, Trip to Disney

{Original Message removed}

More... (looser matching)
- Last day of these posts
- In 2000 , 2001 only
- Today
- New search...