Does a DMM calculate RMS at any frequency?

[JustAnotherGuy999]

or there is a certain range that the DMM cant go beyond? if it can't, how do we know the RMS of a very high frequency signal?
(im talking about true RMS multimeters)
the same thing for peak to peak voltage.
to make the question more concrete, can a fluke 87 measure RMS of any signal at any frequency, if it can't what should we do?

[dadler]

Use an oscilloscope.

Edit:

The Fluke 87 (and every other RMS multimeter) is only specified for RMS voltage accuracy  to a particular max frequency.

Here is the Fluke 87 service manual. Check the specs in section 1-3:

http://assets.fluke.com/manuals/83_85_87smeng0500.pdf

[JustAnotherGuy999]

Use an oscilloscope.

oscilloscopes are more expensive than DMM, because they have many and more important features than just measuring RMS, for example imagine you want to measure the RMS of a 2GHz signal, such an oscilloscope ain't cheap.

[Jeroen3]

There is a maximum bandwidth involved. I don't know if the fluke 87 has analog or digital true-rms conversion. I'd say digital, but I would have to review the teardown to confirm it.
Fluke says the 87 does:
AC bandwidth   20 kHz with low pass filter; 3 db @ 1 kHz
According to the freely downloadable spec on fluke's website.

_{Note that fluke does not say this for current.}

[dadler]

Use an oscilloscope.

oscilloscopes are more expensive than DMM, because they have many and more important features than just measuring RMS, for example imagine you want to measure the RMS of a 2GHz signal, such an oscilloscope ain't cheap.

And, in general, they are required to measure accurate RMS voltage at high frequency. They may be more expensive, but that is neither here nor there. A DSO will almost always have better RMS accuracy at high frequency than a given DVM. All physical devices are bandwidth limited, DVMs and DSOs included.

[JustAnotherGuy999]

There is a maximum bandwidth involved. I don't know if the fluke 87 has analog or digital true-rms conversion. I'd say digital, but I would have to review the teardown to confirm it.
Fluke says the 87 does:
AC bandwidth   20 kHz with low pass filter; 3 db @ 1 kHz
According to the freely downloadable spec on fluke's website.

_{Note that fluke does not say this for current.}

mmm so DMM are used to measure RMS of very low frequency signals only, thanks jeroen3

[Wytnucls]

Few portable multimeters go beyond 100kHz.
Vpp is seldom accurate for repetitive transients below 250uS.
Fluke 87V 20kHz and 250uS.

Buy a more sensitive meter or use an oscilloscope.

[retiredcaps]

I'm not sure if I'm interpreting the question correctly, but the Fluke 8060A specs are below.

[exe]

imagine you want to measure the RMS of a 2GHz signal, such an oscilloscope ain't cheap.

Such scope would cost a fortune, but... I don't think there are such multimeters that would do the job. I would say in most cases "true RMS DMM" means "it works for 50/60/120Hz". Dealing with >100MHz requires special equipment, probes, etc.

[rfeecs]

For 2GHz and above, you would be using a power meter, or a spectrum analyzer.

[Jeroen3]

What is the maximum bandwidth of a banana plug?

[tggzzz]

or there is a certain range that the DMM cant go beyond? if it can't, how do we know the RMS of a very high frequency signal?

RTFM, or use google.

For THz frequencies you need instruments like bolometers

Don't use an oscilloscope, except in special circumstances. Their amplitude accuracy and range is limited.

Define what you need to know, including range, accuracy, and repeatability. That requires stating why you are measuring something. If you don't do that you will get correct answers that don't help you.

Here's a general guide that may help you.

[newbrain]

What is the maximum bandwidth of a banana plug?

I defiiteley do not know for the plug, but you could use a very long socket as a waveguide for some tens of GHz