Frequency Measurements - Fluke 28IIEX User Manual

Frequency Measurements

For frequency measurements, the Product counts the
number of times the signal crosses a set voltage level
each second.
Table 7 summarizes the trigger levels and applications for
frequency measurements in the ranges of the voltage and
current functions of the Product.
To measure frequency, connect the Product to the signal
source. Next push G . When you push E, the
trigger slope switches between + and -, as shown by the
symbol at the left side of the display (refer to Figure 9
under "Duty Cycle"). Push
counter.
The Product autoranges to one of five frequency ranges:
199.99 Hz, 1999.9 Hz, 19.999 kHz, 199.99 kHz, and
>200 kHz. For frequencies less than 10 Hz, the display is
updated at the frequency of the input. Less than 0.5 Hz,
the display can be unstable.
D to stop and start the
True-rms Digital Multimeter
How to Make Measurements
Some guidelines for frequency measurements are:
If a measurement shows as 0 Hz or is unstable, the
input signal can be below or near the trigger level. To
correct these problems, go to a lower range, which
increases the sensitivity of the Product. In the L
function, the lower ranges also have lower trigger
levels.
If a measurement is a multiple of what you expect, the
input signal can be distorted. Distortion can cause
multiple triggers of the frequency counter. Select a higher
voltage range to decrease Product sensitivity to try and
repair this problem. You can also set a dc range to
increase the trigger level as a possible solution. In
general, the lowest frequency shown in the display is the
correct one.
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