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Turbine N1 and N2 (Read 685 times)
Jun 12th, 2017 at 3:33pm

lolachampcar   Offline
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Anyone plugged N1/N2 mono polls into a Skyview EMS???  Any tricks or did it just work?
 
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Reply #1 - Jun 12th, 2017 at 4:43pm

Dynon Support   Offline
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Depending on your RPM, the sensor output from the turbine, and if you want it displayed as RPM or %, it doesn't "just work" but can generally be made to by manually editing the config file.
 

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Reply #2 - Jun 13th, 2017 at 4:43am

lolachampcar   Offline
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Its been a while but I've worked with the configuration side of Skyview enough to know there is great flexibility with how information is massaged and displayed.  My interests were more in dealing with the sensor input (pull up resistors needed, frequency adaptive trigger thresholds and the like).  I was hoping someone had already done it so I could learn through their experience as opposed to the ole fashioned way.
 
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Reply #3 - Mar 31st, 2018 at 4:25am

lolachampcar   Offline
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Ok,
So I'm getting close to crunch time and really would like to get both N1 and N2 imported to Skyview so that all engine info can be logged during phase 1 flights (and beyond).

The Garrett TFE731 uses a Variable Reluctance sensor to count teeth passing on a gear tied to either the N1 or N2 shafts.  These sensors produce a zero crossing sine wave with an amplitude proportional to the speed at which the magnetic field is made/broken.  The manual states-

"The SV-EMS-220/221’s Standard Voltage RPM inputs can read frequency-based RPM signals, provided the peak voltages goes at least 5.1 volts above ground, and crosses back down below
2.0V relative to ground. If the peak voltage exceeds 50 volts, use the included 30 kΩ resistors as described in the P-lead pickoff (Lycoming and Continental) Section above."

I can determine the amplitude of the VR sensor's outputs and install series resistance if needed.  Please confirm that Skyview can accept as much of a negative as positive pulse (as will be generated by the VR sensor) or that it clamps the negative side to prevent system damage.

Alternatively, I can signal condition the VR input to a logic level output for the Skyview system if the logic side of the EMS is preferable.

Next, there are two inputs I would like to display and record.  The Skyview documentation states the unit will display the first of the two RPM signals that appears to the EMS then default to the second if the first fails.  Is there a way to display and record both so that N1 and N2 are always available?

Lastly, speeds are high and I would like to display in % relative to 100.  How much can the input frequency be scaled (divided down) to permit this type of display?  What is the acceptable input frequency range for EMS rpm inputs?  Below are the speeds I am dealing with-

N1 (likely pulled from the sun gear reduced fan speed but I will verify this) is 11,502 rpm at 100%.  I’ll assume there are 20 teeth per revolution which yields an input frequency of 3834 Hz @ 100% so the required divider would be 38.34.
Alternatively, if the N1 sensor is on the turbine side of the sun gear, the numbers are 20688 rpm yielding 6896 Hz @ 100% or a divider of 68.96

N2 goes like this - 29692 rpm yielding 9897 Hz at 100% and a divider of 98.97.

I still need to confirm the tooth per revolution count but the above is likely very close.

I'm hopeful I can use Skyview for so many reasons.  Any help would be most welcome.
 
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Reply #4 - Apr 1st, 2018 at 8:36am

kurt Rutkowski   Offline
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I see a few issues that most likely only Dynon will be able to answer :

What is the maximum input frequency to the Tach inputs?  Manual say max RPM displayed is 9,999RPM but you can scale to % to get around this.

What is the max Pulses per Rev you can input in SV? you need 115 (N1) and 297 (N2).

Can you have two independent Tach signals with one EMS?  May need to install 2 EMS modules?

If Dynon does not already do this:  You can install a diode at the SV input (anode-Ground, cathode-signal) to clamp the negative pulses.  May not be necessary, especially if you need to do any additional signal conditioning.

An alternative to using Tach inputs is to install two Frequency to Voltage converters.  These are commercially available but you will need to find some that covers the input frequency ranges of you system and output 0Vdc to 5Vdc.  This will connect to any type "C" input.

I am sure it can be done but it will require some additional engineering...

Kurt
 
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Reply #5 - Apr 1st, 2018 at 2:03pm

mmarien   Offline
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Dynon has a way to display two RPM signals. See here: dynonavionics.com/cgi-bin/yabb2/YaBB.pl?num=1317301951/8#10
 

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Reply #6 - Apr 2nd, 2018 at 1:16pm

lolachampcar   Offline
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Kurt,

A freq to V is very "doable" inclusive of scaling to 100%.  I'm using very few inputs so there are plenty of inputs available.  My only fear with this approach is accuracy (and, to a lessor degree, repeatability).  Usually, speed values need accuracy in the 1% range which is hard to do when you pass through the analog domain.  I'm also not up to speed on drift with temperature associated with F to V chips.

mmarien
Thanks for that find.  That is perfect and very good news!

Bill

« Last Edit: Apr 2nd, 2018 at 1:16pm by lolachampcar »  
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Reply #7 - Apr 2nd, 2018 at 5:16pm

Dynon Avionics   Offline
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SkyView has a way to treat the two RPM inputs independently. See http://dynonavionics.com/cgi-bin/yabb2/YaBB.pl?num=1355638748 for the config file changes. Asking an EE about some of the deeper stuff.
 

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Reply #8 - Apr 2nd, 2018 at 5:42pm

kurt Rutkowski   Offline
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Bill,
I agree with you 100%.  If the SV tach inputs can be split into 2 independent measurements and can accept an Input of 12KHz (9897 Hz + 10% + margin for worst case of N2 ) will be the easiest to accomplish.  This will also be the most accurate hands down. It starts to get complicated if you have to pre-condition sign wave to square; and/or, then divide by X before SV can even see the signal.  This will be over the heads of most aircraft builders.

I would expect a  2.5% to 5% accuracy with a F to V converter. 

Need to get confirmation from Dynon on the true max input frequency.

This is interesting and would be nice if you keep us informed on how you end up solving this.
« Last Edit: Apr 2nd, 2018 at 5:45pm by kurt Rutkowski »  
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Reply #9 - Apr 3rd, 2018 at 12:34am

lolachampcar   Offline
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I talked with Tech Support and they are looking into the issues.  Initial information is that the EMS supports upwards of 100 KHz input frequency.  This is being verified.  Two separate RPMs can be displayed; this involves a custom config file.

I'll post more when I have things fully checked out.

On another note, there are some limitations on airspeed for some of the other Mfg's experimental equipment (think G here) so I was asked what the limitation on Skyview was.  I found this in an old thread-

"We kind of goofed with the high end spec. The highest pressure that we apply in our calibration applies to about that airspeed, but, it will keep on reading accurately beyond that through it's actual visible limit, which just under 500 knots if I remember correctly (For the nerds out there, it's the low airspeeds which are hard to detect. While airspeeds at the very low end are tiny fractions of a PSI, by the time you're up past 325 knots, the changes are large and the errors in measurement (in airspeed terms) very small.)"

I'll be verifying this as well Smiley
 
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