OK Steve, Subtract .37 from the data and 3.3 volts is 150 psi.
Here is the latest and greatest. 1 msec. 6.8 K bottom resistor and
1.2 K top resistor. The resister junction goes to the MM pin 9. The
top of the resistor divider goes to the out put of the .37 to 4 volt
pressure sensor.
Paul Lamar
Hi Paul
Chart is - Average Data - Subtract 0.375 Then Multiplied by 150/3.3
Of all the 3000 data samples, there was only 228 samples of actual
rotor pumping.
Odd! The sample period appears the same as the 10mSec run. MMBasic
Ver 4.5 claims a min tick of 1mSec
Also, the 8 samples are very consistent so taking them and averaging
appears superfluous.
Steve Izett
I have to run the MM program, run around the front of the airplane to
behind the left wing, over to the cockpit and turn on the master
switch and hit the red starter button on the far right of the
instrument panel for 30 seconds. Then run back around the front of
the airplane and stop the MM program :-)
The data file on the MM 32 Gig SD card was then about 229K. Before
I sent it to you I erased over 100K of samples taken at 1000 samples
per second :-)
When Pete is in the hangar he hits the starter button for me just
after the program starts running. That cuts down on the number of
useless samples.
The data looks great. One usually gets about 60 psi when rotating the
engine with the starter. The throttle was still closed. That rotor is
in perfect condition. That is quite understandable with ceramic apex
seals.
Paul Lamar
I’m thinking I’d like to buy a sensor and try this on our engine.
So is my math right here:
If starter RPM was 400 (total guess) then that is 1200 pulses/min. 20
pulses/sec.
So the timing of a complete pulse would be 50mSec from beginning to end.
I was thinking about the rise time required for the transducer.
I can buy 5v 150psi general purpose transducers for oil/water/air etc
for $20 but wondering what their response time is.
They don’t document performance of these transducers as far as I can see.
I was hoping to not have to purchase a lab quality transducer.
Can anyone help me with this?
Steve Izett
The sensor I got was not the best. Free Scale, now NXP, makes
better sensors with out the zero offset. Here is a pdf.
They cost about $12 US.
Thanks for your help on this Steve.
Paul Lamar
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