Signal Tracing through an amp with a Multimeter.

[pompeiisneaks]

Signal tracing through the amp with a multimeter.


so one odd thing I was wondering about, was why i got significantly lower AC voltage readings on my DMM than I got on the scope?

After finishing the video I'm starting to think it's about how the frequency of my sine wave is 1000hz and the dmm may be expecting 60hz? Maybe that's why it's so 'off'? but not sure? Anyone know why that would be the case?

it still works well to see the 'amplitude change per gain stage' but it's not seeming to be as accurate as the scope is?

~Phil

[wpaulvogel]

How much difference are you getting? .707? RMS meter

[xtian]

There are two amplitude measurements we commonly make: peak-to-peak, and RMS. Peak-to-peak is easy to see on the scope--that's the full vertical excursion of the waveform. To calculate RMS, you multiply by 0.7071 <https://en.wikipedia.org/wiki/Root_mean_square>. Your DSO should have a Measurement display that shows RMS while you're observing the waveform.

Your multimeter may be "true RMS" but it's likely optimized for 120Hz sine waves. So if you were measuring a 120Hz sine on your scope and on your multimeter, I'd expect the RMS values to be close.

To calculate clean amp output power, I input a 1KHZ sine wave and observe RMS output amplitude on the scope. Adjust the gain until clipping, then back off so the sine wave is not distorted. Square the RMS value and divide by the load, and you've got watts.

[wpaulvogel]

Sorry, I just watched the video.

[sluckey]

There are two amplitude measurements we commonly make: peak-to-peak, and RMS. Peak-to-peak is easy to see on the scope--that's the full vertical excursion of the waveform. To calculate RMS, you multiply by 0.7071

That is the relationship between peak and RMS. To convert peak-to-peak to rms you gotta multiply by .707 and then multiply again by .5

[pompeiisneaks]

There are two amplitude measurements we commonly make: peak-to-peak, and RMS. Peak-to-peak is easy to see on the scope--that's the full vertical excursion of the waveform. To calculate RMS, you multiply by 0.7071

That is the relationship between peak and RMS. To convert peak-to-peak to rms you gotta multiply by .707 and then multiply again by .5

Yeah someone else on fb just explained this to me too. RMS = .707 peak, not .707 peak to peak I was getting accurate measurements, and I learned something in the process too! Thanks

~Phil

[Guy77]

Nice looking scope Phil! I ordered the same one except its the 2-channel ver. (Rigol 1052) as a Christmas present to myself. It should be arriving this Thursday.
Can't wait till Santa ( Amazon) arrives!

Happy Holidays!
Guy

[pompeiisneaks]

Very cool! Enjoy.

I found that mine does have the Vrms option, and did some more general testing.

Another thing that seemed to keep the voltages 'closer' was that DMM's often are optimized for frequencies around mains voltage (per what some others have said, not sure that's 100% true always) and found it more accurate at RMS voltages near the 50-120Hz range instead of up at 1kHz.

The RMS voltage of the scope at 1kHz was spot on with my DMM though.

~Phil

[sluckey]

User manual for the Fluke 117 shows AC volts accuracy of 1% for frequency of 45 to 500Hz and 2% for frequency of 500 to 1000Hz.

[pompeiisneaks]

Guess it may help if I read it

Yeah that sounds possible, as mentioned, it was a bit closer at lower frequencies. I guess I could have written down numbers, but I forgot hehe.

~Phil

[wpaulvogel]

Just ordered a Rigol DS1054Z. It’ll be replacing my old analog green screen scope.

[TUBEDUDE]

Greetings Paul,
I have the same Rigol, and there is a free code available online you can enter to extend the bandwidth to 100mHz if you ever do any R.F. work.

[pompeiisneaks]

Greetings Paul,
I have the same Rigol, and there is a free code available online you can enter to extend the bandwidth to 100mHz if you ever do any R.F. work.

It's actually a hack someone did of the specific algorithm they use to generate the keys to unlock the full features of the scope. Pretty funny, they call it 'riglol' Be careful, though, some I'm sure are malware laden nightmares for the codes or attempts to get personal info etc.

~Phil

[wpaulvogel]

I don’t see that I’ll need the extra bandwidth. I’m just doing guitar amps. Thanks though.

[wpaulvogel]

Scope arrived today, just opened it up and fooled around for a minute. I think this thing will bake a cake compared to what my old scope would do. Wow, I’ve never had it so good. Seriously though, I use a Pico scope at work and it has this capability.