RPM sensor calibration issue

[jhidley]

I've connected the coil input (through a filter and square wave reconstruction circuit) of a 4 cycle V8 engine with a coil on plug ignition to one of the digital inputs on an ADL3. This generates one pulse per every other engine revolution. When I attempt to calibrate the input in Dash Manager, I need to set it to 0.5 pulses per revolution. This isn't possible to do. The minimum is 1 pulse per revolution. This would be fine for an engine running waste spark, but it doesn't work for an engine with a COP ignition. Am I missing something here?

The only work around I've determined is to choose Custom Calibration, select Count and put two data points in the graph. One at (0,0) and the second at (5,000, 10,000), (Count, rpm). I have yet to test this but I think it should work. Is this the only way to deal with this issue?

[jhidley]

My Custom Calibration technique didn't work so well. The RPM kept incrementing from 0 to infinity, the longer the engine was running. I guess I shouldn't have chosen Count. Dumb.

I changed the selection to Frequency and then entered data points at (0,0) and (75Hz, 9,000rpm). Now it works correctly.

[jhidley]

One other issue that I ran into is this. Some of the cars that I'm logging engine RPM on have multispark ignition at idle (Ford 4.6l V8). This obviously confuses the Motec. The RPM shows up as 40,000 at idle. I managed to come up with a way to program the calibration transfer function to fix this problem. Here is what I put in the table:

Hz RPM
0 0
67.50 8100
67.70 400
1000 400

This way, if the Motec sees an input RPM above 8,100, it assumes the engine is really at idle and multisparking, since the ignition system won't actually ever rev the engine that high. I choose 400 RPM so that I would easily see that this was the result of the transfer function programming and not the real RPM of the engine. The real idle RPM is about 700, but you can pull the engine down this low under high load conditions, and since the engine is not at idle the multispark is disabled and the datalog will show a correct 700 RPM.

[OmarK]

Sorry for the delay in replying... The method you are using to get an RPM signal is not how the dash inputs were designed to work originally...

If you have a trigger disc and sensor to suit, it might be a more accurate way to measure RPM using the ADL3 inputs, do you have any details of specific trigger setups for the motors you are using the ADL3 with?