Shown in meter calibration mode. About 4 foot leads with red lead at battery positive and black lead at battery negative ( this is 100% dwell setting). Adjust wiper on variable resistor to zero 1 milliamp meter at full scale. Can be used on 6 or 12 volt car system.
Ignition points signal is like square wave and we can count bottom time with dwell meter. Diode 1N1518 to hold at 3.9 volts is used.
Conversion to 1 mA. meter scale
8 cylinder engine full scale is 45 degrees
6 cylinder engine full scale is 60 degrees
4 cylinder engine full scale is 90 degrees
Our example is a trip down memory lane. Or news to youth about days of conventional auto ignition.
Think about an eight cylinder 1969 Plymouth Roadrunner with 426 hemi engine that does 0 to 60 in 5.3 seconds @ 105 m.p.h.
Dual point sets in this distributor. Block one set of points open with cardboard, jog engine starter to put point lobe on distributor directly under rubbing block on points we are setting. Insert feeler or thickness guage of .017 thousandths under point contacts and carefully tighten screws to hold points in correct setting. Remove thickness guage, connect dwell meter red lead to distributor connection of ignition coil with black meter lead to ground connection, and crank engine with STARTER motor and check meter for 27 - 32 degree dwell range.
Calculation: 8 cylinder engine full scale is 45 degrees we want 27 degrees = 27/45 = 0.6 ratio. So, 1000 times 0.6 = 600 on meter scale
32 degrees = 32/45 = .71 ratio. So, 1000 times .71 = 711 on meter scale
Remove cardboard to use holding set points open and set second points using above instructions. After setting both sets of points remove cardboard and put distributor together to start car. Running range is 37 - 42 degrees of dwell which is why dual points was used to give more spark build up time. Calculation like above: 37/45= 0.82 and 42/45= 0.93
Dwell with engine running is 822 to 933 on milliamp meter.
