EFIS RPM Indication

Hi All
I have AFS 4500 in my RV-4 and I am receiving incorrect RPM readings between my Emags and my EFIS. Has anyone this problem and what did you do to remedy it.

Dayton, not a lot of data here to help us understand what you are seeing. Is it erratic, or a vastly different number on the RPM guage than what you would expect? The second one is most likely a configuration issue, as in the s/w you have to tell the system how many pulses per revolution. Pretty quick fix, and you can verify with an optical tach.

If it's erratic, it could be wiring or a sensor.

Vic

vic syracuse said:

Dayton, not a lot of data here to help us understand what you are seeing. Is it erratic, or a vastly different number on the RPM guage than what you would expect? The second one is most likely a configuration issue, as in the s/w you have to tell the system how many pulses per revolution. Pretty quick fix, and you can verify with an optical tach.

If it's erratic, it could be wiring or a sensor.

Vic

Click to expand...

It?s steady- not erratic - just reading low. We did a prop balance for Dayton the other day, and when he set it at 2350 by the EFIS, I was seeing 2525 on the Dynavibe. Totally repeatable on each run.

We didn?t run multiple points, so I can?t tell you if its a scale factor or a bias.

If resistors are used between the P-Mag RPM out put and the AF4500, this may be an issue with the sizing of those resistors, such that the P-Mag output is just on the hairy edge of detection by the AF4500. This could result in most pulses, but not all, being counted, thus giving some weird RPM indication of something less than reality but not the usual "zero" or "half" RPM indications that come from an incorrect pulses-per-rev setting.

Did you set up the EFIS properly? The efis/EMS needs to know how many pulses per engine revolution. You should find this in the manual.

Larry

Canadian_JOY said:

If resistors are used between the P-Mag RPM out put and the AF4500, this may be an issue with the sizing of those resistors, such that the P-Mag output is just on the hairy edge of detection by the AF4500. This could result in most pulses, but not all, being counted, thus giving some weird RPM indication of something less than reality but not the usual "zero" or "half" RPM indications that come from an incorrect pulses-per-rev setting.

Click to expand...

The Pmag likely is sending a square wave 12 volt tach pulse and no resistors are needed or desired in that case (they degrade the current of the pulse and create the symptoms you mention) The resistors or for mag setups, where the EMS is looking for the flyback pulse from the collapsing field of the coil (these are much higher currents). Actually, I am not sure if they look for the flyback pulse or the abrupt absence of current flow through the coil once the points open, but it is one of those two.

Larry

Larry - interesting point. I was seizing upon this note in the P-Mag manual:
”6” is a courtesy (optional) connection to provide a digital tack signal – two pulses per revolution (reconfigurable to 1ppr using EICAD). The default tach voltage is 12 volts, although some ignitions were produced with a 5 volt signal. See notes on the Wiring Diagram at the end of this manual for switching tach voltage signal, if needed. Adding a ground wire (pin #1 to the EFIS or tach instrument) will help assure a clean signal.

And then this info:
EICAD allows builders to adjust:
Tach Output - Tach output can be set to either one or two pulses per revolution to match your digital tach instrument. Factory default is two pulses per revolution – 12 volts. Series 114 ignitions change the tach voltage from 12 volts to 5 volts by installing the diode, provided in your kit, between the tach output (terminal #6) and ground (terminal #1) on the Control Plug (see wiring diagram). Alternatively, the diode can be installed on the instrument end of the tach lead.

With all in mind, I still had it stuck in my little pea brain that it was a resistor used to cut down the 12 volt square wave rather than the diode. Note to self... NEVER trust memory! LoL

From our phone call on Friday:

1. Make sure the software is current: Version: Vs8.08.35-MV16

2. Verify which device is wrong using a RC airplane optical tach.

3. How many RPM is it off at idle?

4. How many RPM is it off at 2500 rpm?

If the EFIS pulses per/2 revs setting was off it would be more than 200 RPM at 2500 RPM.

Rob Hickman
Advanced Flight Systems

Not sure if this is valid relating to the problem but when I went from slicks to p-mags, AFS IIRC had me move the RPM wire for the Pmags to different pin on the 4500s than what was used for the slick mags and the tach works well. Verified with another source.

N402RH said:

From our phone call on Friday:

1. Make sure the software is current: Version: Vs8.08.35-MV16

2. Verify which device is wrong using a RC airplane optical tach.

3. How many RPM is it off at idle?

4. How many RPM is it off at 2500 rpm?

If the EFIS pulses per/2 revs setting was off it would be more than 200 RPM at 2500 RPM.

Rob Hickman
Advanced Flight Systems

Click to expand...

I have the most current software update:
I used 3 different optical tach. devises:
EFIS Tach
780 850
1000 1080
1500 1620
2000 2170
2500 2710
It appears to be off a percentage.Can it be adjusted?