RPM problems with EMS 220 and Rotax 912 uls (Carburetor)

[Taigajoe]

Hello,

I am running my Skyview installation (first D700, now HDX800) since about 10 years. Since some flights I have massive problems regarding displayed RPM's.
The problem is: Until 4400 RPM's the displayed RPM's are correct and smooth displayed, above 4400 RPM's the displayed RPM's are starts jumping up and down in the range of + 100...1000 RPM's or more or less. I did not see so often lower RPM's than the current RPM.
Off course the engine is running smooth and I let it run on constant RPM.
Every 2...3 second a wrong RPM is displayed than the current RPM is shortly shown and than some wrongs RPM's are displayed and so on...
Today I checked the cable and connectors and found no hardware problems.

According Skyview manual (SV-EMS-220/221 Rotax 912 ULS) I connected RPM to Pin 32 and the second line I conneted to Pin 5 (ground). And this worked for many years.

Now I am thinking about to disconnect the second line from pin 5 and connect it to pin 34 (low voltage rpm input left). In the pin mapping setup is configured for RPM pin 32/pin 34.

Who has any suggestions?
Thank you!

Best regards,
Harro

 

[Taigajoe]

Hello,

I am running my Skyview installation (first D700, now HDX800) since about 10 years. Since some flights I have massive problems regarding displayed RPM's.
The problem is: Until 4400 RPM's the displayed RPM's are correct and smooth displayed, above 4400 RPM's the displayed RPM's are starts jumping up and down in the range of + 100...1000 RPM's or more or less. I did not see so often lower RPM's than the current RPM.
Off course the engine is running smooth and I let it run on constant RPM.
Every 2...3 second a wrong RPM is displayed than the current RPM is shortly shown and than some wrongs RPM's are displayed and so on...
Today I checked the cable and connectors and found no hardware problems.

According Skyview manual (SV-EMS-220/221 Rotax 912 ULS) I connected RPM to Pin 32 and the second line I conneted to Pin 5 (ground). And this worked for many years.

Now I am thinking about to disconnect the second line from pin 5 and connect it to pin 34 (low voltage rpm input left). In the pin mapping setup is configured for RPM pin 32/pin 34.

Who has any suggestions?
Thank you!

Best regards,
Harro

I found the answer by myself:

Trigger Coil (Rotax 912, except 912 iS)

The Rotax 912 engines have a 5th trigger coil for the purposes of electrically monitoring rev
counts. This trigger coil outputs to a two-wire harness. Connect either of the two wires to
ground; connect the other white wire to SV-EMS-220 Pin 32 (Standard RPM Left Input). If you
observe erratic tachometer readings or momentary “spikes” in the display - particularly at
higher RPM – install a 60K resistor inline (in series) between the trigger coil and SV-EMS-220 Pin
32, White/Green wire). Set Pulses / Revolution (PPR) to 1: SETUP MENU > HARDWARE
CALIBRATION > EMS CALIBRATION > TACHOMETER CALIBRATION > PUL/REV (C37 P32/34

I hope it will help to install the resistor.