Help: Needing to bypass 4-20ma signal in tractor

Discussion in 'General Electronics Chat' started by Big Tom, Oct 3, 2010.

  1. Big Tom

    Thread Starter New Member

    Oct 2, 2010
    Make a long story short, we have a tractor that uses a Elobau 424.A11 series angle sensor for the electronic variable speed control, the tractor dealership believe the sensor is failed/failing and wants to replace it at great cost and zero guarantees it's even the problem, make matters worse they don't have the part and it'll take forever to order it in plus being electronic no returns.

    The problem is something is causing the onboard computer to lock out the electronic throttle controls (all of them...) and we need them to regulate the speed of the motor.

    It's harvest, we need this tractor working ASAP.

    I'd like to try and bypass this sensor and simply inject 5ma or something into the system so the computer thinks the sensor is working properly and see if it'll start up, there are other controls we can use to regulate the speed IF the computer thinks this sensor is working and doesn't lock out the controls. OR if I inject a signal into the system and the tractor acts exactly the same I can call the dealership and tell them to come up with another theory why this $200K tractor won't throttle up properly...

    I don't have my Fluke meter here so I have nothing to inject a current with, can someone come up with a way to output something like 5ma? I don't need it to be variable... all we have for power is the onboard 12V.

    The simpler the better, I'm at the farm not in the city so I can't run to the local electornics depot to gab a handful of parts... likely I'll be scavenging all the parts from busted old electronics kicking around the farmyard. Yes I'm that desperate :)
  2. jpanhalt


    Jan 18, 2008
    Some tractor manuals are on the internet. What brand and model is yours? Do you have the part number for the suspect sensor? John
  3. Big Tom

    Thread Starter New Member

    Oct 2, 2010
    We have the tractor manual and I've gone over the schematics a bit, one issue it's all in German. If we re-start the tractor a piss load of times once in a blue moon it'll work completely fine and as long as we don't shut it off that sensor and everything else works perfect which is one reason why I'm not convinced it's the sensor like the tractor dealership says. Thing is, once it comes up running and I have speed control I drop the schematics and hit the field hard to try and catch up to the other guys :D

    It's a Fendt 920 Vario

    The part number for the sensor I don't know 100%, I took a picture of it since I couldn't find a pen at night and of course it's blurry, but as my original post said Elobau 424.A11 is the type, the rest of the part number I can't read is simply the angle specs etc
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    I think this simulator circuit should work as a substitute for your sensor. R1+R2 would be 250Ω for 5mA. The Short-Open-Range switch was for testing a controller and not needed in your case.