Newbie: I have a signal generator set (I hope!) to output a 60htz, 12v sine wave. When I put a DMM set for AC across the output I measure < 5v?? I expected either 12v peak to peak, or 8.5 RMS. What am I missing?

  • FeelTech FY6800
  • FREQ: 0.050 KHz
  • AMPL: 12.0000V
  • OFFS: 0.00
  • DUTY: 50.00% (not changeable)
  • PHASE: 0.0°

DMM AC 0.421 V RMS

  • 1
    \$\begingroup\$ What signal generator, and how did you configure it? \$\endgroup\$ – Jeroen3 Sep 27 '18 at 6:15
  • \$\begingroup\$ Note that nearly all signal generators specify their output voltage amplitude in Vpeak (not Vpeak-peak and also not Vrms). Also nearly all signal generators specify that voltage when a 50 ohm load is applied. Your DMM is not a 50 ohm load, so then you would get double the voltage. Also most DMMs specify AC voltage in Vpeak (not Vpeak-peak) or Vrms (cheap DMMs might fake the RMS value though). \$\endgroup\$ – Bimpelrekkie Sep 27 '18 at 6:23
  • \$\begingroup\$ Updated question with settings. Strangely 2 x 0.421 is more or less the RMS of 12V peak \$\endgroup\$ – Keith Whittingham Sep 27 '18 at 13:53

There can be two problems:

  1. You don't really know what the signal generator output voltage is supposed to be. You said it is "12v". You apparently mean 12 V, but is that RMS, peak, peak to peak, or something else? Until you know that, you don't know what a perfect meter is supposed to read.

  2. Some meters deliberately reject power line frequencies. Most that do this only reject the 50 or 60 Hz when it is below some percentage of the overall. I've never heard of a FeelTech. Check its datasheet.

Let's see what RMS results from a peak or p-p voltage specification. A sine with 12 V peak is 8.5 V RMS. 12 V peak to peak would be half that, or 4.2 V RMS. Considering your vague 12 V spec, a 4.2 V reading from a good meter is a possibility.

  • \$\begingroup\$ Ah., that makes sense. So, if the dialed in 12 V is peak to peak from +6 to -6 V then the RMS is going to be 4.242 V which is what I'm seeing, Thx \$\endgroup\$ – Keith Whittingham Sep 27 '18 at 19:38

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