Oscilloscope input limits

[sunil21]

I wish to clear few doubts about an oscilloscope I got last week.
Purpose of this is to use with smps ,, flyback and forward.

spec is 100mhz
channel I -
on the left side - written-- 1Mohm , 20pf , <or= 300vrms

channel 2-
right side written- 400v/ cat II (and an earthing symbol)

as per manual Max. input voltage 400V (DC+AC, PK - PK)

then probe is T5100
X1: <200vDC+Peak AC
X10: <600vdc+Peak AC

So what is truly means .. I can connect a 399volt battery to the scope with out damaging it
with the probe at x10 - can connect a 599 volt battery without damaging it

at x10 ac sinewave - 212v ac can be connected without damaging it.

what about checking a flyback and forward (with 600-800v rated mosfets).?

It is written in the manual not to check ac line becoz of
" from the manual =
When powered by AC power, it is not allowed to measure AC power source
directly, because the testing ground and power cord ground conductor are
connected together, otherwise, it will cause short circuit.
"
Can this be solved simply by removing the ground terminal or should use an isolation transformer
(600v at x10 is okay?)

 

[danadakk]

Ap notes on line operated measurements -

Floating Oscilloscope Measurements ... And Operator Protection

Introduction Oscilloscope users often need to make “floating” measurements where neither point of the measurement is at ground (earth) potential. “Signal common” may be elevated to

www.tek.com

The Three Facets of "Floating" Measurement Solutions

What is a Floating Measurement? A floating measurement reads the voltage between two points, neither of which is at ground potential. Floating measurements of fast AC signals are a challenge for

www.tek.com

Ground of oscilloscope always connected to earth? - Page 1

Ground of oscilloscope always connected to earth? - Page 1

www.eevblog.com

Ground of oscilloscope always connected to earth? - Page 1

Ground of oscilloscope always connected to earth? - Page 1

www.eevblog.com

Regards, Dana.

 

[FvM]

You'll use a 100:1 high voltage probe for the power converter measurements, if the DUT is grounded, or a differential high voltage probe for floating DUT.

 

[treez]

your probe on x1 is for 200v as you say. So you can probe up to 200v with it......best not to ever go above 200v, even if on x10...because you could accidentally switch to x1 and blow it.

Anything above 200v...just use a suitable diff probe or x100 probe as FvM says

 

[danadakk]

Observe the ground problem as discussed in the ap notes posted in #2 above.


Regards, Dana.

 

[sunil21]

Most of the above questions I asked is for " (minimum)things I should know " , not to try risky things.
I am in asia, the unit came with an european pin I think ( with the earthing pin hollow). i swapped its power cord with my HP 1020 laserjet cord which has three pins..

so the earthing of the DSO is why i cannot directly probe the mains.
I will get an isolation transformer.

so with the current setup at 10x I can connect buck ,boost, flyback, forward with input and output upto 100v dc.
I will get a high voltage probe at 100x for mains SMPS;
So it is also risky to probe 120v mains smps with an isolation transformer at 10x

 

[treez]

I am in asia, the unit came with an european pin I think ( with the earthing pin hollow)

..extremely unusual to have an oscilloscope with a 2 pin plug with no earth.
The earth is needed for safety.
Also to avoid potentially overstressing the supply SMPS within the scope...its isolation transformer...its isolation barrier may be compromised.