What does (DC + Peak AC) actually mean?

[sijmen]

Hi,

I've been looking at various test equipment specs and see specifications like the following:

Max differential measuring voltage (DC + Peak AC):  ±500V
Common mode voltage (DC + Peak AC):  ±500V

Can someone please explain what the DC + Peak AC means.  Does the Peak rating mean peak to peak on an AC signal, or the 0V to Peak AC voltage?

Also, am I right in assuming that if I had a 400V DC signal, and a standard AC sinusoidal signal sitting on it, then the AC signal can not be more than 100V (measured center to Peak)?

Could the item with the above rating be used to measure mains 230V RMS AC, which is 325V centre to Peak, or 650V Peak to Peak?

Regards,
Sijmen.

[schmitt trigger]

Hi,

I've been looking at various test equipment specs and see specifications like the following:

Max differential measuring voltage (DC + Peak AC):  ±500V
Common mode voltage (DC + Peak AC):  ±500V



Also, am I right in assuming that if I had a 400V DC signal, and a standard AC sinusoidal signal sitting on it, then the AC signal can not be more than 100V (measured center to Peak)?

Regards,
Sijmen.

If in your example you are implying a 200 volt peak to peak AC signal superimposed on a 400 volt DC, then your assumption is correct.

[bdunham7]

DC + AC_PEAK is just an awkward and very slightly incorrect way of saying the peak voltage.  They appear to simply mean the absolute value of the maximum instantaneous voltage.

[David Hess]

Max differential measuring voltage (DC + Peak AC):  ±500V
Common mode voltage (DC + Peak AC):  ±500V

DC + Peak AC means the peak voltage including the DC component.

For a floating input like a multimeter or isolated oscilloscope channel, the common mode voltage is what is applied between the low or common terminal and chassis ground.  This depends on the built in galvanic isolation.  Power supplies with floating outputs have this specification also whether they list it or not.

The differential voltage is what is applied between the high terminal and the low terminal.