RGS Witt tach filter: Connect in reverse?

[ksoholm]

Gents,

I was chatting about my RGS's optimistic tach reading with a long-time Laverda man; he asked if the bike had the Witt filter, and I said yes. He noted the Witt filter is a low-pass filter but that the bike needs a high-pass, and that the black and brown wires should be switched; brown to earth, black to ignition.

What say you?

Thanks-

Kristian

 

[Rob]

Be interesting to know why your man reckons a high pass filter is required. Uwe Witt and I disagree!

A high pass filter is likely to let more pulses through and increase the reading? The electrical system on vehicles is inherently very noisy.

 

[ksoholm]

Be interesting to know why your man reckons a high pass filter is required. Uwe Witt and I disagree!

A high pass filter is likely to let more pulses through and increase the reading? The electrical system on vehicles is inherently very noisy.

Here's his explanation - which makes sense if there is DC noise: "The tach seemed sensitive to the average voltage. That is high at low rpm and drops at higher rpm. It should not be sensitive, but it is. The solution is to remove the DC component, which is what a high pass filter does. Original configuration is low pass which does not help: it keeps the DC."

 

[Rob]

Interesting theory.  I'll give it a go tmrw and see what happens