Your fluke should have some features to allow you to see how low the voltage drops either ysing the max/min capture (100ms resolution) or duty cycle (which may have the shortest measurement interval).
Capturing Minimum and Maximum
The MIN MAX Record mode captures minimum, average, and
maximum input values. When the input goes below the recorded
minimum value or above the recorded maximum value, the Meter
beeps and records the new value. The Meter stores the elapsed
time since the recording session was started at the same time.
The MIN MAX mode also calculates an average of all readings
taken since the MIN MAX mode was activated.
This mode is for capturing intermittent readings, recording
minimum and maximum readings unattended, or recording
readings while equipment operation precludes watching the
Meter. The MIN MAX mode is best for recording power supply
surges, inrush currents, and finding intermittent failures.
Response time is the length of time an input must stay at a new
value to be captured as a possible new minimum or maximum
value. The Meter has a 100 millisecond MIN MAX response time.
For example, a surge lasting 100 milliseconds would be captured
but one lasting only 50 milliseconds may not be captured at its
actual peak value. See the MIN MAX specification for more
To activate the MIN MAX mode, press M. As shown in
Figure 6, the Meter displays e at the top of the
measurement page, and the MIN MAX start date and time along
the bottom of the page. In addition, the recorded maximum,
average, and minimum values appear in the secondary display
with their respective elapsed times.
Start : 06/07/07 7:00 pm
VAC 500 VAC
Figure 6. MIN MAX Record Display
To stop a MIN MAX recording session, press M or the softkey
labeled Stop. The summary information in the display freezes,
and the softkeys change function to allow saving the collected
data. Pressing M again or the softkey labeled Close exits the
MIN MAX record session without saving the collected data.
Measuring Duty cycle
Duty cycle (or duty factor) is the percentage of time a signal is
above or below a trigger level during one cycle, as shown in
The duty-cycle mode is optimized for measuring the on or off
time of logic and switching signals. Systems such as electronic
fuel injection systems and switching power supplies are
controlled by pulses of varying width, which can be checked by
measuring duty cycle.