Fluke 287 Fluke 287 and 289 Multimeter Users Manual - Page 55

Measuring Pulse Width, Duty Cycle Display

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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 %. 8:10pm 123.45 VAC 06/13/07 49.75 % Duty Cycle Auto Range 0 100 200 300 400 500 VAC 59.756 Hz Menu Save Setup Figure 26. Duty Cycle Display est24.eps 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 True-rms Digital Multimeters Making Measurements 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. 45

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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
.