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AC voltage measurement - why no auto zero

DMM6500 6½-Digit Touchscreen Multimeter
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Anwar Ali
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Joined: August 26th, 2021, 5:21 am
Country: Malaysia

AC voltage measurement - why no auto zero

Post by Anwar Ali » August 26th, 2021, 5:50 am

I purchased DMM6500 last year. Recently I was trying to use DMM6500 for AC ripples measurement of linear power supplies.

I wonder why there is no auto zero for AC voltage measurements - is it due to software or hardware limitations? Without auto zero, it very difficult to measure ripples from low-noise LPSUs.

I know DMM7510 has auto zero for AC voltage measurement. Both 7510 and 6500 have similar resolution for AC voltage.

My workaround is the Statistics screen of Active Buffer. Without auto zero, can I consider peak to peak as the worst case and standard dev as the best case ripple values? If this is incorrect, please suggest other ways.

Thanks you.

Andrea C
Keithley Applications
Keithley Applications
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Joined: October 15th, 2010, 10:35 am
Country: United States
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Re: AC voltage measurement - why no auto zero

Post by Andrea C » October 21st, 2021, 11:19 am

With the DMM7510, it has true RMS converter and output of that is measured with the DCV. The auto-zero feature is really applying to corrections to the DCV aspect of the measurement.

The DMM6500 instead uses AC coupled digital sampling (using the digitizing A/D).

In general, VAC measure functions of a DMM require the signal amplitude to be greater than 5% of the range in use.

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