Differential Probe x10/x100 (700v) or x20/x200 (1400v)

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I've decided to bite the bullet and purchase a differential probe.  I'm looking at the Cal Test CT2593-1 and CT2593-2.

The CT2593-1 is a x20/x200 probe with a 1400v capability and the CT2593-2 is a x10/x100 probe with a 700v capability.

As I live in the U.S. and I'm interested in troubleshooting SMPS safely, I would think the CT2593-1 is the best pick for me.

My understanding is that both have a switch, so for the CT2593-2 it's 70v/700v and for the CT2593-1 it's 140v/1400v.

If I'm going to be probing 120vAC, I would think by using the low range on the CT2593-1 which is good upto 140v I'd have better resolution/less noise/better result vs the CT2593-2 where I'd exceed the 70v in the first range and have to use the 700V range by default.

Am I correct in my understanding?

Thanks!

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Any advice?

[Paul Moir]

If I'm going to be probing 120vAC, I would think by using the low range on the CT2593-1 which is good upto 140v I'd have better resolution/less noise/better result vs the CT2593-2 where I'd exceed the 70v in the first range and have to use the 700V range by default.

No great advice, but the second set of eyes can be worthwhile:  the 140v range is peak-to-peak while 120v RMS is 170 peak to peak.  So for anything where you expect to see line voltage you're going to be on the high range.  Besides, 120VAC ends in a SMPS the moment it goes through the bridge rectifier.  It's not a particularly relevant number.

Personally if I couldn't see myself ever wanting to probe over 700v, I would get the 700v/70v version.  Otherwise the 1400v.  Another way of looking at it is you're only doubling your resolution with the 700v/70v.  A third way of looking at it is you could setup a resistor divider if you really wanted to look at 1400v. 

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Thanks Paul.  I wasn't thinking about this, you are right, but just one clarification actually.   120vAC is the rms voltage, so 170v is the peak, but the peak to peak would be 340v.  So I guess I'll get the 70/700v version.

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But maybe not...I think I was correct at first.  The specs of the probe are rated in RMS.  -

Differential Range   +/-140V(DC+ AC Peak) and 140Vrms@1/20
+/-1400V(DC+ AC Peak) and 1000Vrms @1/200

[Paul Moir]

Ah yes you're right.  +- 140V is 280V peak to peak, so you could measure 120V RMS no problem.  Sorry about that!