How to measure waveform at the primary side?

[infinia]

Originally Posted by motbuddy

so where should i clip my black wire of my probe to?


I had got some advice which ask me to use an isolating-transformer. But it seems like not possible for me to buy it.so what else can i do to have a look on the waveform at the primary side?

thank you.

If you cant get an isolation transformer (note for floating the DUT only) connect oscope gnd ONLY to earth. Otherwise STOP untill you get one or find out Y u need one. This thread is becoming a public hazard.

[infinia]

Originally Posted by Juergen Knoop

with only one isolation transformer, the scopes ground set other parts of the DUT to live where you don't expect it, which is not good too.
regards

Yes u are possibly changing the measurement but at least its not a safety hazard.
You are making a PE connection to the DUT circuit when ever u connect the probes common so what.

[Juergen Knoop]

using two transformers is no safety hazard as the floating voltage is earthfree.

You are making a PE connection to the DUT circuit when ever u connect the probes common so what.

so what? You may set the case of the DUT to live. Touch it and prepare to be bitten.
regards

[infinia]

Originally Posted by motbuddy

i would like to upload a full schematic for the primary side.below is the attach.

Attachment 154904

Do u mean by measure the ripple in such way?

thank you.

No dont do this unless u have an isolation transformer (note u are only a diode away from the AC primary)
This thread is already become much too dangerous for this level of dialog!

[infinia]

Originally Posted by Juergen Knoop

using two transformers is no safety hazard as the floating voltage is earthfree.

so what? You may set the case of the DUT to live. Touch it and prepare to be bitten.
regards

This is Basic lab safety 101 ( I can't believe this JK I'm having this level of talking here)
Yes u are right but you should advise any persons entering the LAB that touching DUT items under measurement is potentially hazardous.
But most people expect the test equipment to be safe to point at and move dials and such.

[godfrey]

How about:
A) Forget the oscilloscope.
B) Use a multimeter to test DC and AC voltages between various points.
It's simple and safe.

p.s. and check the circuit - those diodes look wrong.

[infinia]

Yes but even some multimeters are connected to the line with no isolation.
Use battery DVMs to be specific

Originally Posted by infinia

Using O-scopes 2 channels for differential measurements is good advice. Using a battery powered DVM is the best advise for novices.