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

One trick you might use is to have the program running in a loop, not
saving anything, and at the first significant voltage rise, start
saving data. After a period of no voltage increase, stop saving and wait
for the next event.

This way, one person can easily run the tests.

Gary Knutson

Real good idea Gary. I'll give it a try.

Thanks.

Paul Lamar

Took only a few minutes.
Worked like a charm.
As soon as you move the prop it starts taking data.

Thanks Gary.

Here is the new program.

The second half is a bit harder to implement.

Paul Lamar

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