Fluke 289 - Manual (Page 55)

True-rms Digital Multimeters
Making Measurements
45
To measure duty cycle, position the rotary switch on one of the
functions allowing frequency measurements shown in Figure 23.
Press the softkey labeled Menu and move the menu selector to
the menu item labeled Hz,%,ms. Next press the softkey labeled
%.
Menu
49.75
%
Hz 59.756
Save Setup
Auto Range
500 VAC 0
123.45 VAC
100 200 300 400
Duty Cycle
8:10pm 06/13/07
est24.eps
Figure 26. Duty Cycle Display
As shown in Figure 26, the duty cycle percentage is shown in the
primary display while the signal frequency appears in the
secondary display. The mini-measurement display indicates the
volts or amps value of the input signal. The bar graph tracks the
volts or amps value of the signal and not the duty cycle value.
The pulse polarity is displayed to the right of the duty cycle value.
J
indicates a positive pulse and K indicates a negative pulse.
To change the polarity being measured, press the softkey
labeled J K. The polarity indicator changes to the opposite
polarity.
For 5 V logic signals, use the 5 V dc range. For 12 V switching
signals in automobiles, use the 50 V dc range. For sine waves,
use the lowest ac or dc range that does not result in multiple
triggering. A manually-selected lower input range will often
measure better than the AUTO-selected input range.
Measuring Pulse Width
The pulse width function measures the amount of time a signal is
high or low, as shown in Figure 27. The measured waveform
must be periodic
; its pattern must repeat at equal time intervals.
The meter measures pulse width from 0.025 ms to 1250.0 ms
ranges.
To measure pulse width, position the rotary switch to one of the
functions allowing frequency measurements shown in Figure 23.
Press the softkey labeled Menu and move the menu selector to
the menu item labeled Hz,%,ms. Next, press the softkey labeled
ms.