Measuring Rpm - Fluke 88 V User Manual

Measuring RPM

RPM can be measured in either the dc volts or ac volts
function. In dc volts, the measurement is dc-coupled,
while in the ac volts position, it is ac coupled. If RPM
readings appear noisy, you should use the function
setting that provides the most stable reading.
Two RPM functions are available:
RPM o is used for conventional 4-cycle engines.
RPM n is used for 2-cycle engines or waste spark
DIS 4-cycle engines (1 count/revolution).
When RPM is first selected, the Meter is in the 6 V dc
range. (The range is indicated by the number shown at the
right end of the analog bar graph.) If the reading is
unstable, move to the 60 V range by pressing
The Meter comes with an inductive pickup. The inductive
pickup takes the magnetic field generated by the current in
the spark plug wire and converts it to a pulse that triggers
the Meter's RPM measurement. The Meter can also read
RPM directly from appropriate signals (like the camshaft
position sensor or tach signals) using test leads rather
than the inductive pickup.
If the meter reading is too high or is unstable, move
to the next V range by pressing C once.
C once.
1.
2.
Using the Meter for Automotive Applications
On some systems with non-resistor plugs, the pickup
may need to be moved away from plug or use the AC
function.
On DIS waste spark systems, the pickup may need
to be reversed, depending on what side of the coil
the plug is on.
Note
When RPM measurements are displayed, the
last digit on the display might not settle. If you
want a more stable display, use the Smooth
function. In Smooth mode, multiple
measurements are averaged before a value is
displayed. Refer to the Smooth Feature earlier in
this manual.
XWWarning
To avoid personal injury, make sure that the
engine is off before connecting or removing
the pickup. The ignition system can create a
potential shock hazard.
Turn engine off.
Connect output plug of Inductive Pickup in the input
terminals shown. Make sure the (-) plug is in COM
and the (+) is in RPM. See Figure 9.
Automotive Multimeter
35