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OBS Resolver Information

pczar3

pczar3

Well Known Member
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Not sure which area to post this in but here goes. I am looking for the ARINC Standard that specifies the interface for the OBS Resolver. All I'm looking for are the typical impedances and d.c. resistances, etc. I'm sure those are in the standard. Any help would be appreciated. I'm working on a DIY project and need this information to move forward.

Thanks for all the help.

Paul
 
I believe the Mil ID-249 indicator meets ARINC specs. Airlines used the same. I just looked on ebay. There is one for $175. One could measure it and get some real numbers. It has ILS display, a donut needle and a course selector knob with resolver. 3 1/8 inch

Might help for your research.

I do not remember those specs being in any mil manuals. Getting tech from ARINC could be expensive.

Ron
 
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Thanks Ron,
this has been like looking for hen's teeth! I have chased down a number of RCTA DO - xx manuals but all of them are big dollars. I suspect the ARINC standards would be no different! I might take your advice and just buy a junk unit on ebay and measure the parameters.

Thanks again for the help,

Paul
 
You might check with Kim or Jerry at Techaidproducts.com. They manufacture test gear for avionics and instrument shops. I’ve known them for years. Tell them I sent you.

Jim Butcher
 
Thanks Jim,
I have been in contact with them and they gave me a great lead. It turns out one of the resolver manufacturers is only about 10 miles from me. I made contact with them and one of the engineers who designed many of the aviation resolvers sent me an invitation to visit the facility and also said he could give me the information.
I also found out it is ARINC 407 that has all the information. Of course it it very $$$$
Thanks to all for the suggestions.

Paul
 
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OBS

Looking at a Garmin 430 manual, it sure looks to me like these are rotary windings not resistors. Resistors wouldn't be reliable enough, so coupled windings makes sense. There's a 500Hz drive output from the Garmin. The returns are "phase and amplitude shifted" from the drive.

I have an old Collins ID-1347 / ARN-82 CDI in my pile if you want to rip one open. Yours for whatever it costs me to box it up.
 
blaplante said:
This manual http://www.mikeg.net/hobbies/aviation/avionics/maintenance/King KI-204 Maintenance.pdf

gives a pretty good explanation of how the OBS works, and the circuitry that they use.
I'm not too confident that King, ARC, Narco, Garmin all used the same OBS standards.
Click to expand...

I think that you’re correct, not all obs boxes work with all nav receivers. I know the needles have about 1K dc resistance, and need about 0.15 volts to deflect full scale, but that’s not what the OP asked. The resolver circuit is fed the 30 Hz directional signal, and RC phase shifters shift the phase as the obs is rotated, and compare it with the 30 Hz reference signal, but I don’t know the details, nor do I know the impedance. There are other outputs that are shifted 90 deg to run the to-from indicators. And of course, the SL30 is all digital. It just uses the reference signal to start a timer, the directional signal stops the timer, and knowing 1 cycle at 30Hz corresponds to 360 deg everything is calculated. The obs does nothing except to send a digital radial to the radio as part of the calculation.
 
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