What included in Measurement Category I?

[khtwo2002]

Got my Rigol ds1045z for days, so far very satisfied. Thanks for those who convinced me to buy this oscilloscope.

In its manual, it said that this DS1015Z can only used on Measurement Category I. And there's descriptions about Measurement Category I:
"Measurement category I is for measurements performed on circuits not directly connected to MAINS. Examples are measurements on circuits not derived from MAINS, and specially protected (internal) MAINS derived circuits. In the latter case, transient stresses are variable; for that reason, the transient withstand capability of the equipment is made known to the user."

I'm not fully understand the classification. For example:
Is pc belong to Category I? Specifically the circuits behind the power supply?
Are the power supply circuits behind the AC/DC conversion belong to Category I? Is there any difference when the DC ground link to the MAINS ground, and when their grounds are separated?

Can anyone explain why the classification is like this. Is it related to the voltage or the current, or something else?



Another question about the testing voltage of Rigol ds1045z. It's marked as 50V. If I use a 10x probe, can I test the signal voltage up to 500v?

[Wirehead]

I see you're new to using scopes (looking at your other thread) - please take a look at the following before blowing things up 

[khtwo2002]

Yea, I have looked at that one. So basically you should not connect your probe's ground pin(which connected to MAINS ground) to  something that has voltage related to MAINS ground. But, if I avoid that situation, can I still use probe head to test the circuits that have common MAINS ground with the scope?

[dom0]

Yes

But you can / will get ground loops.

[khtwo2002]

Yes

But you can / will get ground loops.

If I connect the probe ground to the equipment's MAINS ground, then there will be no ground loops. Right?

If this can be done, why the scope limit it to category I ? To prevent accident from beginners? Or are there other considerations?

[dom0]

Uh, yes, there will be a ground loop, because the scope input ground is connected to PE (I assume you mean PE by "MAINS ground").

[Kleinstein]

If specified for it, the 1:10 probe could be used for voltage up to 500 V. You also gain a little safty marging if the voltage is a little higher, as the probe is a rather high impedance source to the scope - so chances are good the scope might even survive if 1000 V are probed.

[khtwo2002]

If specified for it, the 1:10 probe could be used for voltage up to 500 V. You also gain a little safty marging if the voltage is a little higher, as the probe is a rather high impedance source to the scope - so chances are good the scope might even survive if 1000 V are probed.

Thanks for the info. I'd better play safe I guest I won't have chance to probe any 500v stuff recently.

[Paul Moir]

Better description of categories:
http://faculty.riohondo.edu/jfrala/fluke_multimeters_-_abcs_of_multimeter_safety_multimeter_safety_and_you_application_note.pdf

(Pg 2).

From that you'll see that CAT 1 is after the transformer in a PC power supply for example.  The rectified AC fits with CAT 2, since overvoltages are not really controlled there.
The risk is from high energy events occurring along the power distribution system.  These can cause very violent arcing due to the available current.

[khtwo2002]

Uh, yes, there will be a ground loop, because the scope input ground is connected to PE (I assume you mean PE by "MAINS ground").

Ok,  I kind of get what you mean. There are two paths connected to PE when interconnected.

So, which is better?
1. Connect probe ground to the equipment PE, then the probe would handle part of current from the testing equipment to Earth. Will this be a problem?
2. Don't connect probe ground to the equipment PE, directly use probe head. There could be several uA of current go through scope Earth. Will this be a problem?

Or, should I ignore probing such equipment at all?
Hm, think about it for a minute. Many equipments thich use home power system could connect their DC part to the Earth. Should I avoid probing them all? A huge waste?

[khtwo2002]

Better description of categories:
http://faculty.riohondo.edu/jfrala/fluke_multimeters_-_abcs_of_multimeter_safety_multimeter_safety_and_you_application_note.pdf

(Pg 2).

From that you'll see that CAT 1 is after the transformer in a PC power supply for example.  The rectified AC fits with CAT 2, since overvoltages are not really controlled there.
The risk is from high energy events occurring along the power distribution system.  These can cause very violent arcing due to the available current.

Ok, that's much clearer. Thanks!