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Old 5th April 2011, 08:17 PM   #21
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Wow, thats nice, I understand the choice was made for me, I get the owon with 600V probes, I simply can't wait.
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Old 6th April 2011, 02:41 AM   #22
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I have measured signals as high 10kv acurately with my scope using a proper resistor divider.

Just some food for thought. jer
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Old 6th April 2011, 02:49 AM   #23
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Quote:
Originally Posted by geraldfryjr View Post
I have measured signals as high 10kv acurately with my scope using a proper resistor divider...
Would you recommend others try this at home without a properly insulated EHT probe?
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Old 6th April 2011, 03:04 AM   #24
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It was ment as an example of how to measure a higher voltage than what the maximum input rating is, inculding the 10X probe.
I am not refering any one to try to measure the output of a neon transformer with this method.

"Also I would like to use the scope to measure some mains voltage LED drivers I put together"

And I supose this would safe for the average noob as well?

Do you know what will happen if one tried to connect the ground clip of the probe to the wrong side of the line? jer

Last edited by geraldfryjr; 6th April 2011 at 03:07 AM.
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Old 6th April 2011, 03:50 AM   #25
gootee is offline gootee  United States
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At any rate, there are proper commercial 100x and 1000x scope probes available.
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Old 6th April 2011, 04:10 AM   #26
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hehehe, but those probes cost twice as much as the scope.... I think i'm lucky getting the 600V probes free too. Yes I believe connecting the ground could bring the scope enclosure up to the rectified mains voltage that I'm measuring. I realy want to learn more about how to possibly issolate things with a transformer if someone can assit, I have a pair of bulky 24V transformers.
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Old 6th April 2011, 05:01 AM   #27
cbdb is offline cbdb  Canada
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[BOOK]I am not refering any one to try to measure the output of a neon transformer with this method.
[BOOK]

I have measured neon transformers (with ufarad caps across the output to boost the voltage even more) with resistive dividers on DVMs as well as scopes. You need to make the dividers with strings of resistors to physicaly spread out the voltage and then cover the whole thing with HV insulation. SAFETY is a major concern, but it is doable.

Quote:
Yes I believe connecting the ground could bring the scope enclosure up to the rectified mains voltage that I'm measuring. I realy want to learn more about how to possibly issolate things with a transformer if someone can assit, I have a pair of bulky 24V transformers.
The ground of the scope probe will probably be connected to the power plug ground (third pin) so the enclosure will not become hot, the probe will ground
whatever you connect the probe ground to. Isolating the scope thru a transformer is lifting its ground and is DANGEROUS. The proper way to measure across a device thats hot on both ends is to use 2 probes and use the A-B function on the scope, which shows the voltage diff between the 2 probe tips.
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Old 6th April 2011, 06:02 AM   #28
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Originally Posted by gootee View Post
At any rate, there are proper commercial 100x and 1000x scope probes available.
This Fluke high voltage probe allows a multimeter to measure up to 40,000V though AC or DC Overvoltage Category I available from Mouser for $172.98
80K-40 Fluke Test Probes
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Old 6th April 2011, 06:22 AM   #29
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Thanks for the advice so far, I know its hard without seeing the schematic. Please ignore the ground, I just used it to pour a plane, to sink heat into. There is only the two ac wires comming in. It can operate from 85 to 265VAC. On the output side it puts out an unisolated 373VDC with no load, and 42VDC with the LED connected.

I would like to safely check the PWMD signal to the FET to see how close it is comming to calculations. I also want to check for noise and osilations if possible. Sadly I'm also waiting for an inductor until May apparently, the one I have now works, but is not very efficient as it drives the frequency up to 100k in stead of the 70k or so I want. I now found the largest inductors that would fit our application without going custom made.... just waiting for it. The scope and inductors should land at the same time, so I want to be ready before the time.
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Old 6th April 2011, 07:37 AM   #30
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It's O/T, but it is easy to make and adequately calibrate your own inductive clip probes that can safely supply isolated,
low voltages for use on a scope in differential or grounded mode. Junkbox tiny ferrite SMPS transformer cores, with just
tens of turns could be ideal. We need to be certain of using sufficient insulation and making sure it can't move or fail by
poor construction. However, it's the same principle as clamp DMMs, so nothing new.

There are, or were, tons of junked network BNC coax cables, dummy loads and adaptors suitable as CRO leads. Keep an eye out.
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