16-08-2021, 10:22 PM
(16-08-2021, 07:43 PM)Mark Hennessy Wrote: In my experience, just about every RMS multimeter I've come across is AC coupled by default, so measures the AC component of the signal. Which is usually what you want IME. You can measure the DC component in DC mode, and sum them together as appropriate.
Thanks - it's not my imagination then!
The trouble with doing the summing is the DC component has to be added in quadrature to the AC component, the square root of the sum of the squares, so needs calculator or pencil-and-paper. Which is messy.
A moving-iron or hot-wire analogue meter will read true-RMS of course- if the AC component only is wanted, it is simple to connect a blocking capacitor in series. But a meter which claims to read true RMS, yet doesn't, is going to catch somebody out.
