RMS

[nanopoylos]

my digital multimeter is a true rms meter
when i am measuring a signal 1khz 1Vpp , it does not show me the peak value , but the rms value
is there any way to read the peak value?

(even with the max feature on , it shows me the max RMS value , not the peak value)

another problem is that with my osciloscope i do not see that the rms value is correct , it has a +/- 5% up or down
why is this happening?

example
when i see 1 volt Vp on osciloscope Vp (not Vpp) in the multimeter i should read 0,707 ? right or wrong .Because i read 0.667 .
where is the problem ?
thnx

 

[audioguru2]

Hi Nanopoylos,
The MAX feature of your meter probably shows the maximum RMS signal level that has occured during the measurement period.

You are correct, if the scope shows a low distortion sine-wave of 2Vp-p, the meter should show 0.707V RMS. Your 0.667V reading is low by only 5.7%, which could be the total of the tolerances of the scope and the meter.
Maybe your meter's frequency response is falling at 1KHz, but was calibrated at the mains frequency. Try measuring a generator.

 

[Kevin Weddle]

square the RMS value. That gives you the average of the function squared. Multiply by pi and that gives you the area. This area is different from the original functions area. Maybe you are getting the average of the original function which .636VP. In which case this is the true DC value of the waveform. To say you are not getting .707 is a little absurd considering the value of .636 is so close to .707.