Kitfox Aircraft Stick and Rudder Stein Air Grove Aircraft TCW Technologies Dynon Avionics AeroLED MGL Avionics Leading Edge Airfoils Desser CPS Parts EarthX Batteries
Results 1 to 4 of 4

Thread: 912 ULS Tach wiring

  1. #1
    Birdseyeview's Avatar
    Join Date
    Sep 2017
    Location
    Oregon, Ill
    Posts
    37

    Default 912 ULS Tach wiring

    I've got a twisted pair of 18 gauge wires coming from my engine rev-counter that I'm running over to a UMA brand 912 specific 3 1/8" diameter tach. The UMA literature talks about hooking up one of the twisted pair wires coming from the engine speed "output coil" (Rotax calls it the rev-counter) to an input pin on the tach connector and grounding the other line of this twisted pair to the same ground used by the tach. There are two grounding pins on the tach connector, both internally connected to each other and one of which should be connected to the engine ground. My engine ground is short coupled to a common ground bus behind the firewall and I'd probably use this as the grounding point. Does it make sense to run the second wire in the twisted pair to a ground, such as via the second ground pin in the tach? I had the impression that the rev-counter signal coming from the engine's tach sender is a once per rev DC voltage pulse (on one or both wires?). To ground one of these two wires, either directly to the engine ground, or common ground bus via the internal tach ground, just doesn't seem right somehow. I guess a DC signal has to be grounded somewhere but my Kitfox build manual schematic only shows one signal wire coming into the tach and the other is apparently not connected. I realize that the build manual schematic is somewhat generic and may not be applicable to specific instruments and UMA's wiring hookup description is cryptic at best. As a result this has got me a little confused. I may be off base in my limited understanding of what these two wires are actually doing. I plan to call UMA as well to confirm all this but I thought I might need to get some ideas and clarification from the forum experts so I can ask UMA more intelligent questions. Any thoughts?
    Last edited by Birdseyeview; 04-29-2019 at 07:02 PM.
    Larry Olson
    Kitfox Series 6 - building
    Tri-gear, smooth cowl
    912 ULS

  2. #2
    Senior Member Dave S's Avatar
    Join Date
    Oct 2008
    Location
    St Paul, MN
    Posts
    1,444

    Default Re: 912 ULS Tach wiring

    Birdseye,

    Did you ever get the information to resolver your tach hookup?

    If it is of any value to you at this point, the attached document is an excerpt from a Lockwood article which includes some information on the Rotax tach hookup - I found this a bit clearer than the UMA instructions - see page 4 of 7 and disregard the document page numbering as this is an excerpt.

    The hookup for the 2 1/4 and the 3 1/8 are essentially the same - while it might not seem logical - the two tach wires can be hooked up either way as this is a pulse signal. The tach has to have 12 volt power and it has to have the signal input in order to work.
    Attached Files Attached Files
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  3. #3
    Senior Member Dave S's Avatar
    Join Date
    Oct 2008
    Location
    St Paul, MN
    Posts
    1,444

    Default Re: 912 ULS Tach wiring

    I missed one possible thing - not sure; but, there may be an additional lead that can feed a hobbs meter - not sure if they all have that.
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  4. #4
    Birdseyeview's Avatar
    Join Date
    Sep 2017
    Location
    Oregon, Ill
    Posts
    37

    Default Re: 912 ULS Tach wiring

    Dave,

    Thanks for the link to the article which was helpful. I called UMA and they also were good to explain the wiring to their tach. I believe I'm good to go.
    Larry Olson
    Kitfox Series 6 - building
    Tri-gear, smooth cowl
    912 ULS

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •