Little more details FWIW and if anyone's interested, fairly easy, quick and cheap motorless way to bench check/cal those old Tachs.......
Build this
Go to
http://onlinetonegenerator.com/
Tach sig input signal will look like this ( this was at the 67Hz and 400 Hz, see below examples)
8 Cylinder 4 Stroke Tach Example 1
Engine's coil gives 4 pulses per rev (4 P/R)
Want Tach to Read/Check 1000 RPM (1K R/M)
1000 R/M * 4 P/R = 4000 P/M or 66.67 P/S or 66.67 CPS (C/S) or 66.67 Hz
Set signal generator to 66.67 Hz sine wave for tach reading of 1K RPM
8 Cylinder 4 Stroke Tach Example 2
Engine's coil gives 4 pulses per rev (4 P/R)
Want Tach to Read/Check 6000 RPM (6K R/M)
6000 R/M * 4 P/R = 24000 P/M or 400 P/S or 400 CPS (C/S) or 400 Hz
Set signal generator to 400 Hz sine wave for tach reading of 6K RPM
6 Cylinder 2 Stroke Tach Example 3
Engine's stator has 12 poles and gives 6 pulse per rev (6 P/R)
Want Tach to Read/Check 1000 RPM (1K R/M)
1000 R/M * 6 P/R = 6000 P/M or 100 P/S or 100 CPS (C/S) or 100Hz
Set signal generator to 100 Hz sine wave for tach reading of 1K RPM