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Registered Member #3806
Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259
Hi all,
I recently got a scope and I have no clue how to display/measure a TC output...
I'm looking for something simple (no costly specialized probe). I want to display this small VTTC output.
My first idea is to build a very simple 1:1000 (adjustable up to 1:∞) capacitively coupled "probe", see below schematic.
I would start with the variable resistor (1k) cursor very close to ground and the probe at 2 meters from the coil, then slowly move the probe closer to the coil until I get a good display, then adjust the variable resistor for proper voltage.
Would this work ?
Any better suggestion is welcomed (and I guess there are many^^)
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
that probe is in effect a series capacitance (from TC secondary to probe) with resistance to gnd, so the 'scope would display the differential of the TC voltage.
You need a capacitive divider. e.g guess 0.1 pF TC-to-probe, add 1nF capacitance to ground = 10,000:1 probe. etc.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Sulaiman is right, the input impedance of the scope is capacitive at TC frequencies, so just holding the scope probe near the TC will create a capacitive divider. I've used this method often.
Registered Member #3806
Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259
The Terry Fritz probe looks really interesting ! I'm gonna build it as soon as I get some missing parts.
But I noticed something wrong in Terry's calculations : he used "pi R^2" to calculate the surface area of a sphere, when it is "4pi R^2". We have to take this into account when calculating the probe to coil distance that gives accurate current measurements.
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How to display TC's output on a scope ?
(and I guess there are many^^)
