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Thread: AFS 3500 rpm drift

  1. #1

    AFS 3500 rpm drift

    I just installed 2 Pmags. The rpm at medium to higher rpm is drifting up an down 200 rpm from what it really is. The engine is running very smooth and the AFS worked fine prior to switching to Pmags. I changed the rpm wire to pin 33. Not sure what the problem is. These are new Pmag model 114s. I am not sure if it is the AFS, Pmag or noise being picked up on the wire. Anyone have any ideas?
    Ric

  2. #2
    Ric, please send me your e-mail address and I'll forward you an FAQ document to install a filtering circuit. Your mag is generating noise that is causing that erratic indication.
    ---
    Trevor Conroy
    Technical Support
    Advanced Flight Systems
    Support@Advanced-Flight-Systems.com

  3. #3
    I received your email, but it discusses mags not P mags. I tried the filter with no luck. The email dicusses the mag sensor, but I am using pin 33 for an electonic ignition with 12v tach signal. I have sheilded p leads and also added sheilded tach lead. It worked fine before using the mags with a tach sensor on it, but it jumps up and down now using pin 33 direct to the p mag. I have plugged my laptop into the p mag to get the correct rpm which works fine but I am totally confused what to try next and don't want to fly around with my laptop for rpm. I changed the number of pulses to half as many with my laptop and changed the tach setting to 2 with no real change to the steadyness of the signal. Another option might be to convert my 12v signal to 5v and go back to the other rpm sensor input. Have you any other ideas that I can try. I have just got my AFS3500 back from fixing my AHRS and am hoping it doesn't need more repair.

  4. #4
    Do you have dual p-mags? Have you tried it in the other pmag? The filter should work on a pmag as well, going into pin 33.
    ---
    Trevor Conroy
    Technical Support
    Advanced Flight Systems
    Support@Advanced-Flight-Systems.com

  5. #5
    Yes, I have tried both Pmags with the same results and tried turning them off one at a time as well with no change. I should double check, the capacitor value is .47uf 50V and a 500 ohm resistor. The diagram is not real clear for the capacitor value on my computer. I installed the filter at the pmag end. Is it possible it would work better at the AFS end. The other thing is they send a diode to change the pulse if needed to 5V, do you think using the diode and filter with the 5v input would be better? I hope to get time tommorrow to try and solve this again.
    Ric

  6. #6
    Ric, a few more questions. Do you have both p-mags connected to the RPM input at the same time? When you have a chance, please give us a call so we can get some more information about your install and help diagnose the problem.
    ---
    Trevor Conroy
    Technical Support
    Advanced Flight Systems
    Support@Advanced-Flight-Systems.com

  7. #7
    No, I just have one tach wire hooked up at a time.
    I will give you a call.
    Ric
    Last edited by ricgc; 06-11-2010 at 06:40 AM.

  8. #8
    To bring this thread to a conclusion, and to help anyone that ends up having the same problem, it turned out to be the AFS 3500. It was a problem they had never seen before, and after sending it back to advanced they were able to replicate the problem. It is very good to here they have admitted to the problem and were very honest about the fact that is was their problem now. The support was excellent from both Pmag and Advanced. Both companies did not think it was their product so they were both trying to solve the problem for me with out sending their products back. I tried making two different filters to solve the problem with no luck. Advanced sent me an inline cirrcuit board that they thought should solve the problem which didn't work either. I hooked up an old oscilliscope and it showed no noise on the line and a nice square wave coming from the pmag. All the wires were sheilded and in the end seperated from the harness and it was still not changing. Many other things were tried and checked but it still appeared to be the AFS3500. I had only run it once to check the pmags before I had sent it in for an AHRS repair and some updates. These should not have had anything to do with the RPM but I had not noticed anything unusual before I sent it in for the repair, so either something had got shacken loose in shipping back and forth or something happened doing the update anyway it is to be shipped back to me today and hopefully I will be back in the air soon. This whole process has cost a lot of time(about a month) so far and a lot of shipping during the prime float flying season in our area. Again I would like to thank Trevor for his help.
    Ric

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