cant post in general this is a test

EDIT: sorry I thought I'd be able to delete, only off topic is working. its "500 internal server error" I cannot search the forum either for same reason.
EDIT 2: I can't even make another post here now so this is the only one I have to work with!

I'm trying to construct a 1/1000 voltage divider from a 25kv capacitor to a 0-100v panel meter. The below image shows what I have and the proposed dividers

http://i.imgur.com/1VPnKj8.jpg

What I don't understand is how the resistance of the panel meter is significant? I see people constructing the divider on the left and testing it by measuring across the second resistor, them I see circuits where the meter resistance is used in place of the second resistor.

Which one is correct? the divider on the left is easy for me to do with what I have on hand using 13.5W of resistors, for the one on the right I will have to buy.

http://www.newark.com/tenma/72-6530...4NspxnEk|pcrid|33870076941|plid|&CMP=KNC-GPLA

 

Good catch on the spec Richard O. I missed that. But what does it mean?!?! This isn't an active probe - is it? It doesn't seem like it is from the description. It doesn't say it is either.

It is definitely a passive probe. They would be real proud and say if it were an active probe.

Another thing I've thought about: 10kV/100Mohm = 1mA... at those kind of voltages, won't that load the supply of a CRT pretty good changing what I see on the scope, possibly? What is the cathode current into a typical CRT? I just don't know.

A decimal point is missing. The current into the probe is 100 uA at 10 KV which is 10 K Ohms per volt.

I don't know what a typical CRT current is either. I agree that even 100 uA sounds like a fair amount of current for a high voltage circuit. (100 uA * 10 KV is 1 watt).


A completely gratuitous story:
I worked with an engineer that applied for a job at Tektronix at the time this probe was being designed! They gave him a tour and he met an engineer that was involved in the packaging design. The engineer showed him a barrel (this is the word that I remember my coworker using) of prototype probes and described what little flaw each of the probes had. At that time it was very time consuming and costly to do the design of a custom injection molded part since CAD was not yet good enough.

 

Those Fluke 80K-40 probes are typically 1000 Meg connected to a 1 Meg input impedance meter, allowing a 1000 to 1 divider.

If your just measuring the CRT HV, those probes will do the job just fine.

 

It is definitely a passive probe. They would be real proud and say if it were an active probe.

A decimal point is missing. The current into the probe is 100 uA at 10 KV which is 10 K Ohms per volt.

I don't know what a typical CRT current is either. I agree that even 100 uA sounds like a fair amount of current for a high voltage circuit. (100 uA * 10 KV is 1 watt).

Ah, you're right - I missed a decimal point. I even redid my calculations and forgot to correct my post.

Strantor - you have a PM.

 

Here is a schematic for a high voltage probe taken from an old Tektronix theory book.

In the book they talk about there being freon inside the case! I have never used any of the high voltage probes so I don't know how common this is/was.

 

Here is a schematic for a high voltage probe taken from an old Tektronix theory book.

In the book they talk about there being freon inside the case! I have never used any of the high voltage probes so I don't know how common this is/was.

I'm not sure where you got that document, but it looks familiar. Very familiar. Actually, I think I have that thing. Ah, yes, I do. I have the 40KV version. Older than dirt, Tekronix scope probe, with "High Voltage Electric Fluid" (probably freon). This piece of history will be up for auction on ebay sometime in the near future.

 

In the book they talk about there being freon inside the case!

That is true. Filled the one I had on Attu Island a number of times.