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High Voltage Test Equipment
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From: Harri Suomalainen [SMTP:haba-at-cc.hut.fi]
Sent: Monday, March 09, 1998 4:02 PM
To: tesla-at-pupman-dot-com
Subject: Re: High Voltage Test Equipment
>From: Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
>The voltage ratings associated with film resistors has to do with
>internal arcing ruining the resistive material, not flashover
>voltages or heating.
That can vary a lot, I think. I think the most usual way to make film
resistors is to apply a film of resistive material over some ceramic
and then it can be spirally cut to make high-value resistor. Then it
is covered with resin. For example Philips makes some resistors
exactly like this.
Surface mount resistors on the other hand cannot be made like this.
They have a film over the block of ceramic material. I guess they
have to be cut in bit different way. I've seen one smd resistor which
indeed did have the film almost cut from one end and next to it a cut
from the other edge and so on. This results a zig-zag like pattern.
They are usually coated with resin too.
Unfortunately too much info on coating is available. The matter of
resisitor internal structure might mean a lot to us. I think Terry has
already proved the usefullness of smd resistor based probe. Getting
scoped images from primary circuits can be a lot of interest to us!
However, I have once pushed a normal 1/4W resistor as a probe
to the extremes. (Way back when I did not exactly understand
everything :) I managed to actually measure flyback output voltage
over a single resistor but it did have a flashover. Unfortunately I
have no idea of the possible arcing inside but no visible damage
was done.
I think the fibre-optic system like Terry has built is a key to many
things including protection of user. It also makes it safe to push
everything to the limit.
--
Harri Suomalainen mailto:haba-at-cc.hut.fi
We have phone numbers, why'd we need IP-numbers? - a person in a bus