Confusing jargons

[Keosintal]

I read Fluke 88V user manual. It states in accuracy specification: "AC conversions are ac coupled and are average responding, rms indicating".

What are the meanings of:
1. AC conversion
2. AC coupled
3. RMS indicating

The model is not a true rms meter

Been Googling for hours and nothing useful. What do they mean? Thanks.

[Nitrousoxide]

1. This just states that it will convert an AC waveform into an equivalent DC RMS value that the multi-meter can display.

2.  AC coupled just means that the AC mode only reads AC values, this is more likely due to a capacitor being in series in the front end.

3. RMS indicating just means the units are displayed in Vrms ( Vrms = 1/sqrt(2) * Vpp).

Because it isnt a true RMS meter, you will only get accurate results with single tone sinusoidal waveform as that (ideally) has no harmonics.

[macboy]

I read Fluke 88V user manual. It states in accuracy specification: "AC conversions are ac coupled and are average responding, rms indicating".

What are the meanings of:
1. AC conversion
2. AC coupled
3. RMS indicating

The model is not a true rms meter

Been Googling for hours and nothing useful. What do they mean? Thanks.

"AC coupled" means that it will block DC, and only pass AC (above a certain frequency which is not specified). So if you have a voltage source with both AC and DC components (e.g. a voltage rail with some ripple), it will measure and display only the AC part, ignoring the DC part. This is actually helpful, if you want to measure the ripple on that voltage rail for example.

"RMS indicating" is not to be taken alone, instead consider: "average responding, RMS indicating". That means that the meter will determine the average of the (rectified) AC component of the waveform, then apply a correction to approximate an RMS value. Note that the average of a rectified sine wave is 0.637 of its peak, but its RMS value is 0.707 of the peak. So when the average value of the AC voltage into the meter is (for example) 63.7 V, the display will show 70.7 V. This is an accurate representation of the RMS value of a sine wave, but if the input is not a sine wave, it will be inaccurate to a varying extent.