Re: [TCML] Measuring Voltage?

[dave pierson <dave_p@xxxxxxxxxxx>]

> > I have an old KV meter from an x-ray machine with a range of 40kv to
> > 140kv dc.
    Sometimes the 'meter' has other calibration bits elsewhere.

> I'm fairly certain NST's output AC current,
    Yep.

> at least that's what I had always thought... Regardless, reading AC on
> a DC meter would cause grossly over-rated readings.
     Wrong, may be under, may be over....

>> I wanted to ask if whether or not the primary, or secondary,  
> > voltages can be measured with a meter.
     Yes, but it takes great care....
     Meters are not as simple to use, accurately as might appear...

>> Here's what I did, and I don't know if my meter is that far off,
>> or if there is something else affecting the readings that I'm not
>> aware of. I have an old KV meter from an x-ray machine with a range
>> of 40kv to 140kv dc.
    Likely the meter is for a few ma, with a 'multiplier' resistor
    elsewhere.  XRay machines ARE dc, Tesla coils are AC...
 

>> I attached a couple hv diodes to the meter and attached it to the  
> > secondary electrodes on a bi-pole coil.
    Diodes, as noted, have 'frequency response'.  May not be right.

>> The needle was pegged almost immediately when I started to apply power.
>> Then I switched it over to the output on the transformer
>> (9kv, 30ma nst).  With the variac at about 1/4 power, the meter was
>> registering 100kv. Not what I expected.
    as noted, likely the '150kv' meter used an EXTERNAL HV RESISTOR
    as multiplier.

> > So I have a couple questions here; first, why is the primary voltage  
> > reading so high with this meter?
    Likely missing resistor, as above, and accurately noted previously.

>> I'm thinking that the meter is showing the voltage rise due to resonance,
>> perhaps?
    cf as above...

>> If that's the case, is there any way to accurately measure the voltage?
    cf as above.

>> I'm actually more interested in knowing secondary output. How can one go
> > about measuring, even "guesstimating" the approximate output on a  
> > coil? I'd like to have a somewhat more accurate answer for people  
> > when they ask what the voltage is of the arcs. Can my bi-pole coil 
> > be putting out more than 140ish kv at such low power?
    Measure the secondary voltage is REAL Difficult.  For one thing
    most anything at the HV end(s) will corona, loading the coil.

    Guesstimates are as close as one can easily get.  

    best
     dwp
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