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Old 24th Apr 2021, 3:23 pm   #1
pentoad
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Default Heathkit V-7AUK AC readings.

I have a Heathkit V-7AUK but I have never used it for testing AC yet
These meters have an AC range of 1.5v to 1500v, the scale shows both ac volts and dc volts ranges. In AC mode, what exactly is it showing here, is it RMS?
There is another scale showing RMS and Peak to Peak below this.
There is an explanation in the manual on how all this works, but I find it rather confusing, I don't understand how that scale relates to the AC scale.
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Old 24th Apr 2021, 4:01 pm   #2
ms660
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Default Re: Heathkit V-7AUK ac readings

Quote:
Originally Posted by pentoad View Post
I have a Heathkit V-7AUK but I have never used it for testing AC yet
These meters have an AC range of 1.5v to 1500v, the scale shows both ac volts and dc volts ranges. In AC mode, what exactly is it showing here, is it RMS?
There is another scale showing RMS and Peak to Peak below this.
There is an explanation in the manual on how all this works, but I find it rather confusing, I don't understand how that scale relates to the AC scale.
The ACV scales are RMS

The P to P scales are Peak to Peak values of the RMS values

P to P = RMS*1.414*2 = 28.28 for 10 volts RMS

All should now make sense.....eg: 10 volts on the top ACV scale is the same as 28.28 volts on the top P to P scale....10*2*1.414.

Lawrence.
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Old 25th Apr 2021, 9:27 am   #3
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Default Re: Heathkit V-7AUK ac readings

The V7AU uses an AC coupled peak to peak responding rectifier for its AC ranges, so for non sinusoidal signals (eg square waves) the p-p scales will be valid, and are the ones to use.

The RMS scales are, as Laurence points out, 2.8 times lower than the p-p scales and are equally valid where the signal being measured is a sine wave. Since the majority of the usage of this type of instrument will be with sine waves, Heathkit chose to make the RMS AC scales and range switch legends match the DC scales as the default scales and legends.

Itís sometimes useful to have a meter such as the V7AU with a p-p response available for measuring non-sinusoidal waveforms such as measuring p-p ripple on a DC supply rail, the amplitude of a square wave (with or without a DC offset), or tasks such as comparing the output of a solid state audio amplifier on music peaks to its supply voltage. For these tasks, an average responding meter such as an AVO would give misleading results.

Stuart
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Old 25th Apr 2021, 12:15 pm   #4
pentoad
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Default Re: Heathkit V-7AUK AC readings.

Ah! it all makes sense - thank you
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