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I bought a used signal generator today. I want to check if it works with no problem but I don't have access to an oscilloscope right now. I have a multimeter that can measure dc and ac voltage and also frequency. When I connect it to the generator it shows the exact frequency that the generator is set to, so there's no problem there. I also checked the DC-offset feature with DC voltage measurement, no problem there as well.

But when I try to measure the ac amplitude I get 300mv rms when the generator is set to 20v peak to peak and no logical relation to the value shown on the generator in lower amplitudes. I checked the multimeter with 220vac and there was no problem with it. I also checked it with a dc power supply I have and there was no problem with the multimeter there neither. I connected the output of the generator to a simple half-wave rectifier circuit I made with a resistor, a capacitor and a diode and measured the output dc voltage with the multimeter and it shows ((Vp-p)/ 2 )* 0.68 for the sine wave which is around 30% lower than what I expect. the diode on voltage is 0.55 R=1k and C=470uF. So there is actually a somehow valid output amplitude on the generator but I can't see it directly with my multimeter.

I also tried lowering the frequency but I still couldn't measure the ac voltage directly with the multimeter. It seems that both the generator and the multimeter are working fine but somehow I can't measure the ac output rms value of the generator with the multimeter. What do you think the problem is here?

I have PNP and NPN transistors and diodes if you want to suggest another test with a simple circuit. The generator is an MFG-8306 from MCH Instruments and the multimeter is a Victor VC97.

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  • \$\begingroup\$ Ah I think you added that just as I was typing, what was the (sine wave?) frequency you've tried? \$\endgroup\$ – isdi Oct 22 '18 at 23:59
  • \$\begingroup\$ I tried 50Hz to 5MHz but saw no change on the value shown on the multimeter. \$\endgroup\$ – sadegh satari Oct 23 '18 at 0:08
  • \$\begingroup\$ The Victor shows 1KHz sine as max for true RMS values. I'm going to assume it autoranges. \$\endgroup\$ – isdi Oct 23 '18 at 0:08
  • \$\begingroup\$ Do any of the other amplitude output range settings give reasonable values (if I read what you said you've already tried it at lower frequencies)? I can't find a manual on the generator, so more troubleshooting for me would be stabs in the dark. BTW don't do a sweep, it tends to mess with the integration function on some DMMs as the frequency response rolls off. \$\endgroup\$ – isdi Oct 23 '18 at 0:13
  • \$\begingroup\$ I have the manual, What information do you need? I can add a picture of the relevant page. \$\endgroup\$ – sadegh satari Oct 23 '18 at 0:22

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