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Old 6th June 2010, 02:43 AM   #1
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Default Reading HP339A scale

I am playing around with my HP 339A and I have a question about reading the scales.

If i am on the .01% scale and I am reading .4 on the 0-1 portion of the meter, this corresponds to .004% correct?

Likewise if i am on the .03% scale and and am reading .8 on the 0-3 portion of the meter this corresponds to .008% correct?


Zc
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Old 6th June 2010, 04:22 AM   #2
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If I'm understanding you correctly:
1) Correct on the 1st account (.01% setting, if corresponding 0<THD<1 was (for ex 1.0) that would be a full .01%) ; but with a .4 reading : .01% x .4 = .004%THD

2)Wrong 2nd, same math....with a setting of .03% a reading of say 1.0 means a full .03%
but with a reading of .8 on (0-3range) is still .8 (units are .03% & you have .8units)
.03% x .8 = .024%THD

Look at it this way; each unit is 3xbigger in 2nd example and your multiplier is twice as big in 2ns ex. so 2nd answer is 3 X 2 =6 times larger than the 1st answer
So: .03% x .8 =.024%THD

Rule of thumb: never pull the % out of equation, just leave answer in %
Equation should have only one unit with a (%) sign on left side of '=', the other has to be a numeric multiplier (no units).....% X % really makes no sense (%)**2?

Common confusion....when yanks say 10% of 50% of (A quantity(no units))=10% of 1/2......same as 5% of quantity.

Charles.....
PS. Its certain if I'm wrong......we'll both know here very quickly !
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Last edited by cowboy99; 6th June 2010 at 04:25 AM.
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Old 6th June 2010, 04:30 AM   #3
1audio is offline 1audio  United States
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If you are reading on the 0-3 part of the scale you don't need any math beyond scaling by range. .8 on the 0-3 scale is .8 on a 0-3 range. You were correct.

This stuff is obvious for those old enough to have started with analog meters. I work with people today who have never seen an analog meter.
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Last edited by 1audio; 6th June 2010 at 04:32 AM.
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Old 6th June 2010, 05:16 AM   #4
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Zc,
Mid fifties here....Must of been that HP calculator I bought years back being a TI'er ...I'm always having to double-think HP's numerical methods.
....I know:To SF Bay folks Texans are the backwards 'ones'.....but, better than the LA bunch, huh....?
Thanks,
Charles
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Old 6th June 2010, 05:29 AM   #5
1audio is offline 1audio  United States
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I must be careful about Texan's, my significant other is also.
I still use a slide rule once in a while. . .
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Old 6th June 2010, 05:45 AM   #6
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Guess we both know what the best thing Texas has to offer ..... If you don't cross 'em that is.
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Old 6th June 2010, 06:39 AM   #7
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I lived in Dallas for 12 years myself so!...

I wasn't sure if the 0-3 scale was read directly or if you multiply the scale by the meter reading.

For example. If the scale is set to .03% I would naturally think that if the needle is pointing to the 3 on the scale, IE FS, that would represent .03%

If the needled pointed to the 2, that would be .02% and if pointing to the 1 would be .01% and likewise if pointing just below 1 at .8 that this would then be .008%

BUT, the manual which is NOT very clear and others have suggested that you multiply the meter reading by the scale knob setting. so that if the scale knob is on .03% and the needle is pointing to 2 on the 0-3 portion. then you multiply 2x.03 = .06% distortion.
and that a full scale reading, when the needle is pointing to 3 that would then = 3x.03 .09% distortion?

Its the difference of what full scale means. when on .01% is full scale .01% and when on .03% is FS .03% or .09%?


Zc
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Old 6th June 2010, 07:43 AM   #8
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You have it, but drop the Full Scale? Too, vague. Call it what it is; Scale Reading.
Yes :
3 that would then = 3 x .03%=.09% distortion

Which scale to use is a confusion point: For argument say the
The upper graduations (0-1) is like a base(10) vernier/evenly dividable by or a factor of 10 (1,2,5,10).

And the lower (0-3) is a base(10/3) vernier/evenly dividable by or a factor of 3 (1,3) Simply, Use it for all the '3' settings.

Evenly is the key word........ Just like a 'slide rule' its the same answer only different by the decimal place location.....
It's some significant figure Egyptian thing. Full scale!zig-zags? Click the image to open in full size.
CK
PS Ever have a Campisi's Pizza in D?
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Last edited by cowboy99; 6th June 2010 at 07:47 AM.
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Old 6th June 2010, 12:27 PM   #9
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Thank you for the explanation. At work i have a Tek AA501 that reads dist in direct % so that when it says 1% it's 1% no mucking about with calculators LOL!




yes to Campisi's, but preferred the lunch platter there. lasagna, spaghetti, meatball, ravioli all smothered in red dead meat sauce mmmmm! $9.99
Now the Pizza from prego's ohhhhhhhhhmmmm
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Old 6th June 2010, 03:27 PM   #10
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Zc,
Cool,..... I have a AA501A opt1 myself paired with an SG5010 in a TM5006 that's got a PSU problem that I haven't got around to isolating yet. The programmable SG5010 is an odd match for the manual AA501 but it makes no sense to downgrade the SG (which is a top-notch ultra lowTHD unit) and I don't see myself springing for a prog. A5010.
I am curious how that pairing will compare to my fully restored/calibrated HP339A Opt-001 cuz the Opt-001 has the 2 additional .1mV & .3mV VM input ranges ......but became almost a $550. investment: about what I 'scored' all 3 Tek pieces for...

More to the issue of 'confusion' which woke me early!
...... Yea, HP defines the Opt001; "..... allows voltage ranges of .1mV "Full-Scale" to 300V "Full-Scale" verses 1mV 'FS' to 300V 'FS' ",
Accuracy is given as a % of the voltage 'range setting' which relates to a 10-fold increase in total accuracy for measurements taken below 30kHz.

.....In my mind this increase in 'accuracy' is actually only a 10fold increase in meter sensitivity (ie. 'sweep').
......All one has to do is read HP's tech-speck to be confused.

Now, I'm very accustomed to thinking of an analog VM's internal impedance being logically in units of ohms/volts measured ....higher impedance relating to less adverse measurement error due to the effect of the meter itself.....which seems more of a 'real effect' on accuracy than a 'FS' multiple ...........ENOUGH !
I believe it's time to sell my other HP339A and give the TEK's a go.

I will get back in touch for your insight on the AA501 which I'm assuming is paired with a SG501 or 505 ? Especially interested in what your preference will be. I don't need 3 THD sets, time to choose.
CK
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