Fluke 189 user manual Measuring Pulse Width, Duty Cycle Display

Making Measurements	3
Measuring Pulse Width

To measure duty cycle, set up the meter to measure frequency; then press N a second time. You can select the level the meter uses by pressing [ to trigger on the positive slope or ] to trigger on the negative slope. A typical duty cycle display is shown in Figure 3-16.

tc027f.eps

Figure 3-16. Duty Cycle Display

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.

If a duty cycle reading is unstable, press M until the AVG annunciator comes on and the average reading appears in the secondary display.

Measuring Pulse Width

The pulse width function allows you to measure the amount of time a signal is high or low within a given period. See Figure 3-17. The measured waveform must be periodic; its pattern must repeat at equal time intervals.

3-25