Re: [TCML] Measuring Amperage in Neon Discharges.

["Shaun Epp" <scepp@xxxxxxx>]

Henry,

It is not recommended to put a DVM (multimeter) inline with high voltage circuits, They weren't designed for that use.  Most multimeters are spec'd at either 600 volts or 1Kv to ground.  This is of course for your safety, to prevent shock hazards but also to ensure accurate meter readings, and continued operation of the multimeter.  The inside of a multimeter is not designed to handle high voltages, there are sharp edges, traces run close together and sharp points (solder connections) in the meter near the input jacks and the rest of the meter.  Corona could form and affect the readings. Electricity could spray off of these edges and points and influence the rest of the meter.  An old analog meter ( just the movement and maybe a resistor) would be a much better choice. 

The negative resistance characteristic of a neon tube occurs at the striking voltage. Before that voltage an increase in voltage produced a proportional increase in current(very low current).  Once you reach the striking voltage the tube turns on, current go way up to it's limit (limited by your NST)  and the voltage decreases allot.  That is the negative resistance effect. 

Shaun Epp

original message
______________________________________________________________________________________________
Date: Sun, 13 Dec 2009 18:33:19 -0800
From: Henry Hallam <henry@xxxxxxxxxxxxxxxx>
Subject: Re: [TCML] Measuring Amperage in Neon Discharges.
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
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<8538a2660912131833h53728bbdx18d35f1c97f9a280@xxxxxxxxxxxxxx>
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On Sun, Dec 13, 2009 at 12:26 PM, Harvey Norris <harvich@xxxxxxxxx> wrote:
> Question; Can I simply put a common multimeter in series with a neon tube illuminated by a 30 ma current limited NST secondary, to record that secondaries amperage output?

Yes.  Obviously be careful and treat the meter as "hot", i.e. don't go
near it when power is applied.

>Do I need a special digital meter to do this?

No, an analog meter may even be better.

> ...but where does the idea of a negative resistance occur, if these parameters show the the neon discharge resistance must be in thousands of ohms?

The "negative resistance" refers to the local slope of the V-versus-I
graph.  That is, for part of the graph, a small increase in voltage
results in a small reduction in current, even though the overall
current and voltage are both positive (and R=V/I is several thousand
ohms, as you note)



-- 
Henry Hallam
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