MGL Avionics User Forum

I have an EMS-2 that I flew with for over a year. It was a stand alone install on a Rotax 912 ULS engine. Configuration was:
2 EGT thermocouples
2 CHT thermocouples
rpm
oil temp and oil pressure using stock Rotax sensors.
The EMS-2 preformed perfectly.

This year I installed a MX-1 and RDAC XF. I ran all the sensors to RDAC XF per the manual. A really short CAN bus was installed between the EMS-2, MX1, and the RDAC. All engine monitoring readings are nice and stable on the MX1. While the EGTs, CHTs, RPM, are unstable on the EMS-2. The EMS-2, MX1 and the RDAC are all grounded directly to the engine block. The interesting thing is if I turn off the MX1, the readings on the EMS-2 are nice and stable. This occurs with nothing else in the plane turned on. Even with the Rotax not running the thermocouple temperature readings are unstable on the EMS2 with the MX1 on. Turn the MX1 off and the TC temperatures are stable on the EMS-2.

Things I've tried to resolve the issue.
1. Moved ground from my grounding buss to the engine block
2. rerouted the CAN Bus 3 times behind the instrument panel
3. ran a wire from rpm1 directly to the EMS-2 from the RDAC so that I can switch rpm from RDAC to internal on the EMS-2. The rpm is nice and stable when the EMS-2 is switched to internal.
4. Made the CAN bus wiring really short. It is now less than 3 foot total length
5. Moved the termination resistors. Right now there is only one termination resistor close to the RDAC.
6. Increase the number of twists/inch on the twisted pair.
7. Installed the latest firmware on the RDAC, EMS-2 and the MX1

None of the above had any effect on the issue. The only thing that I can think of to do next is to convert the CAN bus from twisted pair to shielded cable.

Any help of ideas of where to go next would be appreciated

Just a short update.

The problem appears to be resolved. During my troubleshooting today, I unhooked the CAN Low wire from the EMS-2 and everything started working. This does not make sense to me. I don't understand how the EMS-2 is working with just the CAN High being connected.

I reconnected the CAN Low and readings became erratic on the EMS-2. Disconnected the CAN Low and readings became stable on the EMS-2. Also ran the Rotax for 15 minutes and the MX-1 and EMS-2 readings were stable and they were the same.

Will test fly tomorrow and see if it still works.
Jerry

There are a few manufacturers who can comply with BS 7273-4, but many systems and installations fail to comply. They will get their come uppance when it all goes wrong.