Today's Message Index:
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1. 06:24 AM - Re: Serial Data Logger (Robert L. Nuckolls, III)
2. 06:21 PM - More MGL Enigma issues (Richard Girard)
Message 1
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| Subject: | Re: Serial Data Logger |
At 08:40 PM 6/27/2014, you wrote:
I've used the analog inputs on that item with vibration sensors and
strain gauges recording at up to 1500 sps mounted on a prop hub but
you need to be a tinkerer to set it up and condition the sensor
inputs. Biggest issue is probably how to analyse the data. I've used
gnuplot and octave which are free but it can be very time consuming.
If a lower sample rate is acceptable, for most folks I'd recommend a
more plug and play type recorder that includes analysis and display
software. Bob has mentioned a starter unit for around $50. that
looked much simpler to use.
http://www.dataq.com/products/startkit/di145.html#ordernow
Ken
I am always pleased to see discussions on the art
and science of data gathering. Had a discussion
with some folks yesterday about a woodruff key
failure in a flap drive system . . . when I asked
if anyone had deduced the moment of inertia for
the equipment downstream of the motor . . . I
got this blank stare.
The ability to go measure and record things for
a very few dollars has been growing by leaps and
bounds. I introduced PC based DAS to Beech in 1999
with a program to characterize pitch trim vs.
autopilot performance on the Beechjet.
At that time, the 'tall boy' in DIY data acquisition
was a $100 'dongle' that plugged into the serial
port of a Win95 laptop. It gathered 8 channels
of 12 bit analog data at 1000 samples per second
for every channel!
I had to limit data gathering runs to 16 minutes
each due to a file size limitation on the application
that supported the hardware. Nonetheless, for
a few hundred dollars and 1 week of fixture building,
I was able to gather very high quality data on a
par with legacy instrumentation that occupied
a 100 pound rack bolted to the floorboards and
took a crew several days to install and wire to
the aircraft.
In later years on the same program, I built
a qualification test fixture for those same pitch
trim motors
Emacs!
This time, a combination of both data gathering
and test control was orchestrated out of a PC using
the two dark green Weeder Technology boards seen here.
$70 each as I recall.
Yeah, that's a cake pan chassis.
Today you can purchase 6 channels of 10 bit
input complete with graphical user interface
software for $12 shipped to your door.
http://tinyurl.com/kd2gb4g
Equipment for fast and accurate measurement and
recording is no longer the bottleneck . . . doing
the interface between the airplane and the DAS
becomes the problem to be solved. That light
green interface board took a day to lay out and
another day to stuff it. Then I spent about a week
instrumenting the motors and getting them into the
chamber.
Emacs!
Emacs!
If that screen looks a bit like PC-DOS, you're right.
I keep a DOS laptop around just for the purpose of
quickly firing up a bevy of test tools to go-get-numbers.
That Weston transistorized "VTVM" has been in my toolbox
for 40 years . . . still works fine.
Emacs!
Emacs!
As owners/builders/designers of systems on OBAM aircraft,
we have 100 times the opportunity to get numbers on
the things that define how our machines function.
This List probably represents one of the greatest
concentration of experience, talent and lessons-learned
in OBAM aviation for things electrical. Our brothers
in the CAFE organization pick up the slack on power
plants and airframes.
If anyone has both curiosity and opportunity to explore
the numbers on their airplane . . . bring it up
here on the list. The talent to assist you is
right here . . .
Bob . . .
Message 2
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| Subject: | More MGL Enigma issues |
To avoid brownout during start up we installed a Mitchell oil pressure
gauge as a supplement to the MGL. The tech folks at Mitchell helped us get
the right gauge for the VDO single wire pressure sender (VDO p/n 360-004)
and everything seemed to be working fine until they weren't. We traced the
problem to a failed sender and installed a new one today. Per VDO the
sender was installed dry to ensure it has a good ground. It seems to work
fine with the Mitchell gauge, but won't produce a steady reading on the
MGL. I've tried every setting in the setup menu for the oil pressure sender
and the only one that works is for a 0 to 5 volt sender (the other three
options are for automotive resistance style, Rotax 5 to 20 mA, and .5 to
4.5 volt). All the others lock up at somewhere between 133 and 139 PSI.
With the menu set for the 0 to 5 volt sender the pressure varies between 62
and 80 PSI at 2200 RPM. When I go into the menu that allows me to see the
raw data coming into the RADC unit it shows the sender is putting out .32
to .39 volts at 2200 RPM. If I decrease the RPM to 1850 the sender output
goes up to .35 to .41 volts. This corresponds to 65 to 85 PSI on the Enigma.
The part that truly makes my head hurt is that at VDO's website;
http://www.vdo-instruments.com/sensors/pressure-sensors-switches/pressure-sender-150-psi-1-8-27npt-29-12.html
The sender is described as sending a signal from 10 to 180 ohms yet, as I
said, using the automotive resistance style setting in the setup menu
causes the Enigma reading to lock up at 133 PSI.
Last, does anyone know where to get current documentation on the Enigma?
What the owner has appears to be an early revision that bears little
resemblance to the current software version installed in the EFIS. On MGL's
website I get a 404, page not found error when I try the documentation page.
Rick Girard
It isn't necessary to have relatives in Kansas City in order to be unhappy.
- Groucho Marx
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