PBS-RPM & Mag Ignition RFI / EMI

  • Maybe I'm missing something here... If so, somebody please point it out. I posted under another subject in this forum (Erratic PBS-RPM Reading) about using this device on a Zenoah G-62 Magneto Ignition gas engine over a month ago. At first startup, I was seeing an RPM reading of over 12,000 rpm on an engine that was actually running at 6,000 rpm. Throttle response was also erratic. Since then, we tried a maiden flight, during which the engine went into "full throttle" mode, and we lost partial control of the aircraft. We were able to kill the engine and get the aircraft back safely.

    Since then, we have done some bench testing with new servos for the throttle (with the PBS-RPM module still connected), and each time lost all contact with the throttle at anything over 1/4 throttle setting, and the throttle servo went to "full throttle" & locked out. We also lost all ability to control the flight surfaces as well.

    The PBS-RPM unit was removed from the aircraft completely, and the engine was restarted. We regained full use of the throttle servo and all the flight servo operated completely normally.

    It would appear that the use of the PBS-RPM sensor in conjunction with ANY magneto ignition engine will result in SEVERE RFI / EMI interference with the receiver, leading to possible loss of control of the aircraft, unless the sensor is optically isolated from the receiver. All my other gas engines are CDI ignitions, and use optically isolated devices for either telemetry or engine kill switches... so I do not have a problem in this area.

    So, am I missing something here? Should I be using some other device, or connecting the sensor differently, in order to use it safely?

    Any suggestions or workarounds?


  • Hello,

    no one reported this so far. The sensor has no physical contact to the ignition and the inducted voltage for RPM detectiing is some mVolts.

    Of course if your ignition wire is maybe defect and some thousand volts are coming in the RPM detecting wire this will cause issues. But then you may get issues also without RPM sensor

  • Regarding my earlier post. The aircraft I was having problems with is a 1/3rd scale Bucker Jungmeister that is 10 years old, museum quality, and historically accurate that I purchased to re-condition and fly at our local Warbird events. It is the only such aircraft that I have which has a Magneto ignition, and is simply too valuable to test or risk loosing. I will be happy to test the new software, but may have to wait a bit until I line up a suitable aircraft / engine combination for testing.

  • Richard... Tested the new software update on a NEW PBS-RPM sensor, and ran it on the ground on the same G-62 Bucker it was intended for. Sorry Richard, but you still have huge problems with this sensor. I accessed the menu, and used the .5X setting. The RPM read-out numbers were lower (as expected), but still were very erratic and jumped around all over the place.

    Also at first, I was getting good consistent throttle response (with and without a range test) but after 5 minutes or so, the servo went into complete lock-out, and went to full speed. Had I been in the air, I would have lost the aircraft. All other flight surfaces locked up as well.

    The PBS-RPM sensor is simply not ready for Prime-Time yet. I'm pulling what sensors I have out of the aircraft that have this sensor, and will fly without this telemetry data. This sensor not only need to be optically isolated internally, it also needs to be physically isolated as well (preferably by a fiber optic link) so there is no possible way in inducing an RFI/EMI signal back into the Rx.

    BTW... All your components for lower amplitude voltage CDI ignitions work very well, and I will continue to use the.