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Author Topic:   Tachometer Frequency Calibration: E-TEC 75-HP
nnglenn posted 01-26-2008 01:25 PM ET (US)   Profile for nnglenn  
I have a 75-HP E-TEC. I am putting in the boat [a SystemCheck Tachometer]. [What is the proper setting of the tachometer frequency calibration setting?] Number 5 or number 6 on the [SystemCheck Tachometer] ? Or 10 or 12 pole?
seahorse posted 01-26-2008 02:00 PM ET (US)     Profile for seahorse  Send Email to seahorse     
nnglenn posted 01-26-2008 06:51 PM ET (US)     Profile for nnglenn    
Thanks for the 6.
jimh posted 01-27-2008 04:19 PM ET (US)     Profile for jimh  Send Email to jimh     
Tachometer frequency calibration adjustments are matched to the number of poles in the alternator, and this is not directly related to the number of cylinders in the engine.

The tachometer pulse output is usually derived from a half-wave rectifier tap in the engine battery charging circuit. For more information, see:

jennyhicks posted 04-30-2009 03:55 AM ET (US)     Profile for jennyhicks  Send Email to jennyhicks     
Have you had your device calibrated at a UKAS accredited lab for example
jimh posted 04-30-2009 08:38 AM ET (US)     Profile for jimh  Send Email to jimh     
Since my boat is in North America, it would be difficult to transport to the U.K. for calibration of its tachometer.

Assuming that I had a frequency generator with known accuracy, I ought to be able to calibrate the tachometer using these principles:

Assume a motor is turning at 1,000-RPM and has a 6-pole alternator. The tachometer circuit will generate

6 pulses/1-rev x 1000-rev/1-min x 1-mi/60-sec = 100 pulses/sec, or

1,000-RPM = 100-Hz

and in a similar manner

2,000-RPM = 200-Hz
3,000-RPM = 300-Hz
4,000-RPM = 400-Hz
5,000-RPM = 500-Hz
6,000-RPM = 600-Hz

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