Test Equipment: Oscillocopes

[TinselKoala]

My question is than what setup (1x,10x...) to use when. Currently I have my probes permanently set to 10x.  Any general rule?

Most DSOs default to 10x probe input unless you change the setting in the channel menu (or it detects the probe attenuation from the more expensive probes with that function). Most of the time you will use 10x attenuation on the probe. Obviously the scope setting and the probe setting should match or you will get wrong values on the display. Sometime for very weak signals you might use 1x probe and channel values.

Next question - would it make sense to use de-coupling 1pf capacitor - sometimes I do use 1pF 5% 1KV  - but to be honest I do not see much difference on the screen when using it.

It depends on what you are measuring and just exactly how you have your "decoupling" capacitor connected. Are you trying to get rid of some high frequency noise riding on your signal of interest?

I am planning to buy 100x probe. - yes/no? suggestions?

I recently bought a very cheap Chinese 100x probe and it is very handy, I would not be able to make measurements on some of the current projects I'm working on without it. This is the one I bought
http://www.ebay.com/itm/High-Voltage-2KV-2000V-Oscilloscope-Scope-Passive-Clip-Probe-100MHz-100X-P4100-/301521247426
But there are much better probes available if you want to spend the money. You probably will want a higher bandwidth probe like
http://www.ebay.com/itm/100X-P4250-High-Voltage-2KV-2000V-Oscilloscope-Scope-Passive-Clip-Probe-250MHz-/291119544514
or
http://www.ebay.com/itm/B-K-Precision-PR2000B-200-MHz-2-kV-Oscilloscope-High-Voltage-Probe-/321660974891

I am actually using my 100x probe to make measurements that exceed its rated 2kV voltage rating; I am getting away with this because of the very short duration of the 3.5 kV or higher spikes in the EMJ-Meyer circuit. If I were trying to measure a sine or square wave or DC of that amplitude, like on a charged capacitor .... no way I would risk it.

TK, you was talking about integration MATH function, what is that good for?

Integration gives you the "area under the curve" of a waveform. If you multiply a Voltage trace times a Current trace to produce an Instantaneous Power trace, each point on that trace gives you the instantaneous power of your measurement at that time, in Watts. Now, if you Integrate that trace, your answer is in Watts x seconds, or Joules. So the integration of an instantaneous power trace gives you a measure of the Energy that has passed your measurement point up to that time. It is essentially "adding up" all of the instant power measurements to give an answer in units of Joules, or energy, up to the time of integration.
Here's an EEVblog video where Dave gives a demonstration. Unfortunately he just integrates a Current trace instead of the full VxI trace, so don't let that confuse you.
https://www.youtube.com/watch?v=Dh0xYu8YvaE

50Hz modulation from the main- is it big issue?  any chance to filter it out?

Thanks.

Usually by properly grounding the probe you will not be plagued by picking up the mains frequency. But I'm sure you've seen what happens when you have a "floating" probe that's not connected to anything, and you touch the tip with your finger, you often will see a 50 Hz (or here in the USA 60 Hz) signal that can appear to be very strong in amplitude.  If you suspect that you may have some mains frequency riding on your signal of interest, you can switch the scope's Trigger Coupling (or Source) to "line" (or "mains") and this will cause it to trigger at the mains frequency. Of course you should set your timebase slow enough to see a 50 or 60 Hz signal in this case.  How to get rid of it? Use proper grounding and shielding. As I said, if the probe itself is properly grounded by connecting the probe's ground reference lead to the right place in your circuit you should not have troubles. Don't forget that all the probe grounds (I usually call them "references") are connected together at the scope's chassis and therefore back to the mains cord grounding pin and therefore to any other grounded equipment on the same mains circuit.

I'm sure MarkE will also have some good data and advice, my comments come from my experience mostly but MarkE is much better at explaining the operational theory than I am.

[MarkE]

Here's a couple of pictures of what happens using a scope probe the way it is designed to be used versus the way that most everyone uses them using the 6" ground clip.  The source signal is 5V CMOS that rises in about 400ps:  It's very ordinary stuff.  The TEK probe when used coaxially exhibits a fairly clean result with only a couple % artifacts rms to 15ns and then almost nothing after that.  However, using the ground clip, the artifacts go up to +/-20% peak and don't ring out until beyond 50ns.  This sort of thing can really mess up measurements especially if one is measuring narrow spikes.

[TinselKoala]

Yep. Most cheap probe kits that I've seen don't even include coaxial adapters, but a couple of my better probes did come with them. Unfortunately they only fit those particular probes.

I see that the cheap probes from China are now at least including some of the little spring-point thingies as alternative ground connections.

[TinselKoala]

I guess I should repost this video here. Just moving the ground clip a few inches along a wire in the circuit makes a radical difference in the trace.

http://www.youtube.com/watch?v=KWDfrzBIxoQ

(The current probe used in this video cost over 3000 dollars, new. I wish it was mine!)

[Pirate88179]

I guess I should repost this video here. Just moving the ground clip a few inches along a wire in the circuit makes a radical difference in the trace.

http://www.youtube.com/watch?v=KWDfrzBIxoQ

(The current probe used in this video cost over 3000 dollars, new. I wish it was mine!)

This is the kind of thing that scares me about scopes.  This is why I wanted to get a simple fg to produce known traces on the scope so I could see what they are supposed to look like.  I have learned here that most of the time, you use the 10x settings on the probes.  This is good info but...do we use that in our calculation of voltage and current when reading the traces?

In other words....I am on 1 volt/div. and the trace shows a peak of 3 divs.  I am on 10x probe setting.  Does this mean I am seeing 3 volts?  30 volts?  Or
.3 volts?  My scope (tek 2213) has the manual pouch bolted to the top of the case, which I did not like at first however, the manual did survive with the unit from the 80's so...it was a good idea.  I have read this many times but there are some simple things I can not figure out...the probe setting being one of them.

The other is, and this has been mentioned above by Mark as a possible source for bad readings, is where does the ground clip go in your circuit being tested?
If testing a simple JT circuit, do you probe the + output and clip the ground clip to the minus side of the battery?

If this topic is meant to be o'scopes 101, perhaps I should begin at a remedial level and work my way up from there?

Bill