Measuring Frequency - Fluke 88 V User Manual

Measuring Frequency

The Meter measures the frequency of a voltage or current
signal by counting the number of times the signal crosses a
threshold level each second.
Table 7 summarizes the trigger levels and applications for
measuring frequency using the various ranges of the
Meter's voltage and current functions.
To measure frequency, connect the Meter to the signal
G
. Pressing Eswitches the
source; then press
trigger slope between + and -, as indicated by the symbol at
the left side of the display (refer to Figure 8 under
"Measuring Duty Cycle"). Pressing
the counter.
The Meter autoranges to one of five frequency ranges:
199.99 Hz, 1999.9 Hz, 19.999 kHz, 199.99 kHz, and
greater than 200 kHz. For frequencies below 10 Hz, the
display is updated at the frequency of the input.
Below 0.5 Hz, the display may be unstable.
D
stops and starts
The following are some tips for measuring frequency:
•
If a reading shows as 0 Hz or is unstable, the input
signal may be below or near the trigger level. You can
usually correct these problems by selecting a lower
range, which increases the sensitivity of the Meter. In
the L function, the lower ranges also have lower trigger
levels.
•
If a reading seems to be a multiple of what you expect,
the input signal may be distorted. Distortion can cause
multiple triggering of the frequency counter. Selecting a
higher voltage range might solve this problem by
decreasing the sensitivity of the Meter. You can also
try selecting a dc range, which raises the trigger level.
In general, the lowest frequency displayed is the
correct one.
Automotive Multimeter
Making Measurements
27