JPI data - Groundspeed

[Bob_Belville]

I wonder if someone here has solved this annoyance:

Most of the time the "groundspeed" captured and stored by my JPI EDM 930 is wrong, too high. When I asked about this a couple of years ago JPI told me it must be the Garmin GTN because the JPI simply stored the info fed to it. It must be more complicated than that. The GTN (and the Aspen) display correct speeds.

Coming home from Summit yesterday the JPI data file has me cruising at 173-206 kts ground speed. I had very little help from the winds at 9000' and was seeing 155 or so ground speeds. (FlightAware shows 148-161.)

This field is not very vital but it would be nice to know climb and final approach speed profiles.

 

[DVA]

1 minute ago, Bob_Belville said:

Most of the time the "groundspeed" captured and stored by my JPI EDM 930 is wrong, too high. When I asked about this a couple of years ago JPI told me it must be the Garmin GTN because the JPI simply stored the info fed to it. It must be more complicated than that. The GTN (and the Aspen) display correct speeds.

So the interface between the GPS and the JPI is a simple serial two wire connection, so nothing there to go wrong. However, you do have some formatting choices on both the output of the navigator and the input to the JPI; they can be incorrect and possibly cause erroneous readings. I have the GTN750 and JPI 830 and my GS on the JPI is exactly what my GTN shows.

What GTN do you have and what JPI? Also, what version of the GTN software is installed, same question for the JPI?

[carusoam]

Could be on to something there!

Hello, JPI customer service....

Best regards,

-a-

[gsengle]

I would sure care, I like to use the NMPG readout... which requires accurate groundspeed


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[Bob_Belville]

11 hours ago, DVA said:

So the interface between the GPS and the JPI is a simple serial two wire connection, so nothing there to go wrong. However, you do have some formatting choices on both the output of the navigator and the input to the JPI; they can be incorrect and possibly cause erroneous readings. I have the GTN750 and JPI 830 and my GS on the JPI is exactly what my GTN shows.

What GTN do you have and what JPI? Also, what version of the GTN software is installed, same question for the JPI?

The GTN 750 main software is ver 6.11; 

The JPI 930 firmware rev 1.20.489 (updated 8/14 by JPI)

The GTN was updated to 6.11 in June, I think you're on to something - gspd has been wrong since then. 

I sent JPI a msg this morning.

[Bob - S50]

2 hours ago, Bob_Belville said:

The GTN 750 main software is ver 6.11; 

The JPI 930 firmware rev 1.20.489 (updated 8/14 by JPI)

The GTN was updated to 6.11 in June, I think you're on to something - gspd has been wrong since then. 

I sent JPI a msg this morning.

If you think it happened when you updated the GTN, I'd be looking at the GTN not the JPI.  I know that the GTN update changed some settings.  For example, it changed the default format for waypoint entry.  I had it set to Lat/Long but the update changed it to UTM.  I had to change it back so I could enter a new waypoint I wanted.

[Bob_Belville]

Just now, Bob - S50 said:

If you think it happened when you updated the GTN, I'd be looking at the GTN not the JPI.  I know that the GTN update changed some settings.  For example, it changed the default format for waypoint entry.  I had it set to Lat/Long but the update changed it to UTM.  I had to change it back so I could enter a new waypoint I wanted.

Interesting. I'll walk the 750 through all the settings and look for a likely culprit.

[DVA]

Here’s a little info - please be careful when you access the Service Pages of the GTN you can change stuff and break things.

There is an RS-232 config page that allows you to set up the format for the input and output, it looks like this:

 

You’ll have a serial port set up for the JPI, it could be any of them so be sure that you are fiddling with the correct one. Take pictures with your camera or write down all of the settings before you futz with anything. Unfortunately I don’t have my airplane handy to look up what settings I have that work for me, hopefully one of the others here can help with that quickly. (I can look in a day or two). You have to have the OUTPUT format set to deliver the correct payload to the JPI, (see below). I **think** I remember that it is Aviation Output 1.

The JPI GPS input should be set to GPS-C7 if memory serves me correctly which calculates destination rather than waypoint data.

Again, I (or someone) can confirm all of this soon, but this should be enough info to get you thoroughly and completely in trouble.

Good luck!

DVA

[Bob_Belville]

6 hours ago, Bob - S50 said:

If you think it happened when you updated the GTN, I'd be looking at the GTN not the JPI.  I know that the GTN update changed some settings.  For example, it changed the default format for waypoint entry.  I had it set to Lat/Long but the update changed it to UTM.  I had to change it back so I could enter a new waypoint I wanted.

I checked my 750 and it is indeed set to UTM. But JPI says it should not matter re the gspd.

[Bob - S50]

15 hours ago, Bob_Belville said:

I checked my 750 and it is indeed set to UTM. But JPI says it should not matter re the gspd.

I wasn't trying to imply that the change to UTM was the problem.  What I meant to imply was that if that setting was changed during the update, some other settings may have been changed too.  It might have changed other settings back to 'default' settings.  I would work with whoever installed your EDM 930.  Have them check any GTN settings they had to make when they installed the EDM 930 for you.

[Bob_Belville]

I can compare GTN settings to original. I'm waiting for JPI's comments.

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[Browncbr1]

I have the hardwire kit for my Aera510 that has all the color coded data wires.   Somwhere, I read that the GPS data output wire is blue and could be connected to the GPS input grey wire on the JPI... I had my avionics shop make the connection, but the JPI still doesn't seem to calculate estimated remaining fuel, etc... and no GPS data is recorded by the JPI..  I assume it is not the blue wire that is the correct output from the garmin...   Does anyone know the correct wire color that should be connected to the JPI?  

[Andy95W]

It is the blue wire for data out of the Aera series.  You have to now tell the Aera to transmit the data, and in which format.

Go to Main Menu> Tools> Setup>Interface

Touch the Serial Data Format button and select the format the JPI requires.

EDIT: BTW, if you ever want to use your Aera with a GDL-39, make sure you buy the GDL-39 with a bare wire connector.  That way you can keep using the data output to the JPI.

Edited October 10, 2016 by N1395W

[Browncbr1]

Thank you Andy!

[carusoam]

The power of MS is endless!

Best regards,

-a-

[Bob_Belville]

Okay, for thread closure I updated the GTN 750 again yesterday from 6.11 to 6.21. We put the GTN in demo mode and set the 327 transponder to display the gspeed info as we entered gspeed into the 750. The xponder displayed the correct speed.

But more importantly, the JPI data on the return trip was correct! (It was not on the flight to the shop before installing 6.21.) 

I'd rather I knew the why but I'm happy to have it working correctly.

BTW, in addition to the 750 main software upgrade we were installing a FS 510. There was another plane in the shop for the same work. We both flew home empty handed. The avionics shop owner spent the entire day in our planes with Garmin tech service on the phone. At 5:00 P.M. Garmin had run out of things to try and concluded we had TWO bad cards. (We got to the point where the tablet and the 750 were communicating wifi & bluetooth but files would not upload from tablet to 750. The other plane was a Rockwell 114 with a 750 and an IPAD. I have Garmin Pilot running on Android.)