Homebrew HV hiZ scope probe

Says so on the schematic in the probe manual.

Probe cables, at least modern ones, use foam dielectric, hence lower capacitance per foot.

I've got some probes with removable cables, I'll TDR one when I get the time. I'll have a go at open and shorted measurements, too, and calculate the complex Zo. With a resistive center, Zo will be significantly complex at higher frequencies than "regular" coax.

He's just taking the pith.

-- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)

Certainly not disagreeing with you Fred. In fact I don't know of any 1000:1 probes that are good at high frequency measurements. But for DC measurements, you would want a 1Gohm probe for best accuracy measurements.

Also, I think I read somewhere that the Freon 114 used in the 6015 probe had a permittivity near to 1. There was some discussion of using F-11 as a replacement but its permittivity is up there and the probe does not work well with it.

There is some good information on the yahoo tekscopes group archives concerning this probe.

Regards

That's just nuts!

I meant to say any 1 G ohm, 1k:1 probes.

the

calculate

complex

Nicrhome is ok for heater uses, but i prefer constantan for electronic purposes. Check out the properties differences, it will be worth it.

?-)

the

capacitor of

as

the

which

of

shield.

Whoosh

?-/

How squirrely is this going to get?

?-))

Correct, except it is 1000:1; all else is OK.

I am purposely using a larger capacitance as i am not mechanically inclined; easy to put plastic tube around resistors, centered with thin sheet, and wrap adhesive copper foil on outside cut for same length as resistor. Easy to calculate capacitance of the resulting coax (resistor / air / inner tube surface / acrylic / outer tube surface = = floating shield.

Thought of a way to (perhaps) make resistive coax with element in the

Acorn't tell you!

Yew guys are knot getting board with these jokes?

("My Tree Puns"... Fred MacMurray?)

Best regards, Spehro Pefhany

Ash me no questions, I'll trellis you no lies!

The discussion is about oscilloscope probes. Thousand meg. DC HV probes are a dime a dozen. Most for use with 10M DMMs, so there's a 1M load resistor in those. I have one. Don't use it much.

Could be. I just looked up the CFC dielectric properties table in Kaye and Laby. All there are around 2. It doesn't specifically mention 1.1.4.

I don't do Yahoo groups.

Whassadifference?

My usual convention for transfer functions is Vout/Vin.

Equal to 1/1000. Or 1:1000

BTW, I would never use a high-voltage probe that didn't have an internal load .

Consider the situation where there is HV applied, and the scope amplifier is inadvertently switched to GND (which means the input socket will be open circuit). Practically the full HV will appear at the amplifier input socket. The insulation won't stand that.

Even worse, a 7A13, switched to "near infinite impedance".

Relying on the scope's input resistance is dangerous. We all make mistakes.

I'm sure that UL, CSA, VDE, TüV, et al. would agree.

You can solder to constantan, for a start!

Cheers

Phil Hobbs

I vaguely one of them can be soldered; which one?

I vaguely remember that one can be soldered; which one is that?

Look at it this way; two coax capacitors in parallel one inside the other. First one from resistor as center conductor and inner surface of plastic tube for "outer" coax and air being the dielectric. Second one has its center conductor as the inner surface of the plastic tube, and the outer coax is the outside that has the conductive foil; the plastic being the dielectric.

In physics, that inner surface would be called a Gaussian surface.