How to measure temporary drop in voltage with meter
Normally you'd use an oscilloscope with a suitable bandwidth. For example, an inexpensive 50MHz digital scope would reproduce a 1usec drop fairly well. If that DS thing has a 1MHz bandwidth, then you should be fine if the drop is > 50usec.

Most digital scopes allow you to see what happened just before the trigger, so you should look at your manual to see how to do that. That allows you to trigger a single sweep from the drop in voltage and see the entire event displayed.