Oscilloscope Usage: What to Avoid?

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I've got my first "real" oscilloscope (an Agilent) on order and am looking forward to using it to debug some of my analog and digital designs.

What kind of things should I avoid? I'm thinking here of circumstances that may damage the scope or blow the input amplifiers of one of more of the channels if I do something stupid.

I'm assuming this is a valid concern, so if you have any war stories of things to avoid, please share.

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The only thing that can really "blow up" anything is excessive voltage. Common thing: trying to look at AC line on a millivolt scale.

If the input has a switchable 50 ohm terminator, make sure that it is off, unless you really are connecting a 50 ohm coax from a 50 ohm signal source. Note, particularly, the max input voltage limit when it is on (both AC & DC components of the signal).

Be very careful trying to "look at" AC line voltage. The third wire of the power cord (assuming U.S. power outlets) is safety earth ground. This can be several volts different from line neutral. So, if you connect your input ground to line neutral, you can have some substantial currents flow. Even worse (bigtime worse) if you connect the input ground to the AC "live".

Less of a hazard to the scope than a hazard to your mental health: watch out for the ground that you use on your scope probe. First, where you connect it matters. Second, if you use a probe with the ground near the back end of the probe, you can get anomalous step responses. Much cleaner if you can make the ground connection with as short a wire as physically possible connected near the nose of the probe.

Folks often overlook probe compensation. It IS important!!!!

Jim - a former Tek scope design engineer

 

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