read engine rpm from battery/alternator???

[David A. Cooley]

At 02:55 PM 6/19/99 +0200, you wrote:
>Recently I´ve seen that Bosch´s latest rolling road reads the engine rpm from 
>the battery voltage. When connecting my multimeter to the battery I can read 
>different frequencies at different rpm´s caused by the alternator. This 
>seems to 
>be easy but when connecting my 20 MHz-oscilloscope to the battery I can only 
>see 
>a flat line around 14.0 volts. 

Use AC coupling, connect it at the alternator output.  The battery is a
HUGE filter.  Probably have to have sensitivity at 1mv/div or more
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           David Cooley N5XMT           Internet: N5XMT at bellsouth.net
     Packet: N5XMT at KQ4LO.#INT.NC.USA.NA   T.A.P.R. Member #7068
   Sponges grow in the ocean... Wonder how deep it would be if they didn't?!
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