15-08-2020, 12:57 PM
Marks, thanks for the thorough explanation. Especially the point about equivalent heating which is automatically assumed by those who know and easily overlooked by those who have missed that bit of education. Not so much "what is RMS" but "why use RMS at all". Please don't get me going on the nonsense of "RMS power".
Video is indeed a special case where RMS has no useful meaning. Noise is another non-trivial case. Here, the voltage depends on the bandwidth of interest. For video signal to noise ratios there are particular customary measurement methods which won't be of interest to most GVR members. Best read about in Weaver's books on video measurement.
Audio s/n ratios can be another can of worms. I'm sure Mark has studied the various weightings etc with more care than I have.
But coming back to the simple case of a sine wave, unless there is a context to indicate some other measuement, it's RMS. This can fool those who are using a scope and a DVM to monitor the same signal. Why is the meter saying 1V while the scope is saying 2.8V? I think it was Mark who reminded me that some modern digital scopes can calculate the RMS voltage of a waveform, something I found useful a few months ago.
Video is indeed a special case where RMS has no useful meaning. Noise is another non-trivial case. Here, the voltage depends on the bandwidth of interest. For video signal to noise ratios there are particular customary measurement methods which won't be of interest to most GVR members. Best read about in Weaver's books on video measurement.
Audio s/n ratios can be another can of worms. I'm sure Mark has studied the various weightings etc with more care than I have.
But coming back to the simple case of a sine wave, unless there is a context to indicate some other measuement, it's RMS. This can fool those who are using a scope and a DVM to monitor the same signal. Why is the meter saying 1V while the scope is saying 2.8V? I think it was Mark who reminded me that some modern digital scopes can calculate the RMS voltage of a waveform, something I found useful a few months ago.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
