Measuring peak to peak values without an oscilloscope?

Ello.

Is there anyway to measure the p-p voltage of signals without using an oscilloscope?

If it's about audio you could record the signal in your DAW and compare it with the amplitude of a known steady test-signal.

[quote author="clintrubber"]If it's about audio you could record the signal in your DAW and compare it with the amplitude of a known steady test-signal.[/quote]

yeah i've thought of doing something like that. I have an oscilloscope, but its only a cheapy... I figured I could aquire a signal generator and mark the appropriate peak to peak values in.


But I found an answer anyway... DMM's measure RMS values right? I can just use this calculator and my multimeter to determine the peak to peak values. Too easy.

http://www.sengpielaudio.com/calculator-db-volt.htm

But I found an answer anyway... DMM's measure RMS values right? I can just use this calculator and my multimeter to determine the peak to peak values. Too easy.

Click to expand...

As long as you know the waveform of your signal and you're sure it's in the bandwidth of your DMM that could be a solution.

/Anders

[quote author="Sammas"][quote author="clintrubber"]If it's about audio you could record the signal in your DAW and compare it with the amplitude of a known steady test-signal.[/quote]

yeah i've thought of doing something like that. I have an oscilloscope, but its only a cheapy... I figured I could aquire a signal generator and mark the appropriate peak to peak values in.


But I found an answer anyway... DMM's measure RMS values right? I can just use this calculator and my multimeter to determine the peak to peak values. Too easy.

http://www.sengpielaudio.com/calculator-db-volt.htm[/quote]

check your DMMs specs. most measure AC up to 400 Hz only with sufficient accuracy.

steff

[quote author="Sammas"][quote author="clintrubber"]If it's about audio you could record the signal in your DAW and compare it with the amplitude of a known steady test-signal.[/quote]

yeah i've thought of doing something like that. I have an oscilloscope, but its only a cheapy... I figured I could aquire a signal generator and mark the appropriate peak to peak values in. [/quote]

Let's insert a question now first:

Do you want to check the peak-peak value of a steady-state (continuous, repetitive) signal or of a single event ?

In either case even a simple oscilloscope will do (with say some 10% accuracy).

But I found an answer anyway... DMM's measure RMS values right?

Click to expand...

Yes for continuous signals.

No for single events, unless you have a (more expensive) model with 'real peakhold'.

Regards,

Peter

I would not trust a DMM to give REALLY accurate results unless you know for certain that you have unclipped, relatively clean sine wave sources.

The better bet is a "True RMS" model of the Fluke line. Most of them don't have response above about 1k or so, but I have not measured one of those.

The other day, I did measure a Fluke 83 and found its 1V response to be accurate to 1dB up to 10kHz and the 3dB rolloff started about 30kHz or so. I used an Audio Precision System 2 for the generator and calculated the voltages for 1 and 3 dB loss from 1Vrms and just ran up the frequency on the gen up til I got that value on the meter. I'll see about doing that today with on of the 70 series just for fun.


EDIT --> Forget these numbers for the 83 and see new data below for sine wave response...

Peace!
Charlie

Its to calibrate a synthesizer. It includes measuring and adjusting the peak to peak value of a C4 sine wave (262Hz) and the peak to peak value of white noise... both continuous waves well below the specs of my DMM. Shouldn't be a problem should it? These are readings taken from included test points in the synth, and are nice clean unclipped waveforms according to my scope.

Noise is a whole can of worms. We need to know how it is generated---if it is truly random then the peaks are limited only by the limits of the gain stage that sees the highest magnitude ones, and then it's a matter of the observation time---i.e., how long do you want to look?

If it is pseudorandom, generated by a shift register with feedback, then it's not as bad.

The type of meter you use is important. Most cheap ones are average-responding and calibrated to give the right answer for sinusoids; the "true-rms" have a limited peak-to-average ratio they can handle before getting very inaccurate.

You also mention the noise is white, but clearly it has to be bandlimited somewhere.

I'll try to find some references, and anyone who knows some should chime in.

As Brad has pointed out, measuring noise if everthing else than trivial if you need a figure with less than 50% error. Fortunately enough your application is likely to be uncritical and I'm pretty sure that a rough look with your scope will do the trick--I guess it has a calibrated vertical scale? If not, you might reference your reading to a low-frequency sine wave which amplitude you can measure with reasonable accuracy using a DVM.

For the records some notes on the noise measuring problem: I just recently acquired a HP 3400A RMS voltmeter for this task. Most RMS voltmeters use log-based computation to obtain a RMS value which is restricted with respect to bandwidth and crest factor. The mentioned meter is (amongst very few others, mostly obsolete ones I think) based on heating a resistor (or diode) with the measurement signal and referencing the temperature rise to a thermal reference, which results in much higher bandwidth and crest factors.

Linear Technology has several application notes which cover the problem and its solutions pretty well; amongst them, I can only find AN83 right now, but there were more...

Samuel

Okay new data...Keep in mind this is measuring a really clean sine wave from an AP2.

Just to establish how I did this: 1.0Vrms reference at 1kHz, -1dB = 0.89V, -3dB = 0.71V

Fluke 87 - True RMS
1kHz = 1.003V (+0.04dB)
-1dB = ?
-0.2dB = 100kHz
Actually rose to about 1.2V at 200kHz!!

Fluke 83 - True RMS
1kHz = 0.998V (-0.005dB)
-1dB = 95kHz
-3dB = 193kHz

Fluke 79 series III - True RMS
1kHz = 1.000V (+0dB)
-1dB = 8.3kHz
-3dB = 19.2kHz

Fluke 179 - True RMS
1kHz = 0.988V (-0.1dB)
-1dB = 3.3kHz
-3dB = 6.4kHz

Fluke 77 series II
1kHz = 0.981V (-0.15dB)
-1dB = 2.55kHz
-3dB = 4.8kHz

So that tells us for relatively clean signals, any of these meters will do an adequate job. 80-series Flukes are good for the whole audio bandwidth. I can measure square waves too in anyone wants to see that.

Peace!

[quote author="Samuel Groner"]

For the records some notes on the noise measuring problem: I just recently acquired a HP 3400A RMS voltmeter for this task. Most RMS voltmeters use log-based computation to obtain a RMS value which is restricted with respect to bandwidth and crest factor. The mentioned meter is (amongst very few others, mostly obsolete ones I think) based on heating a resistor (or diode) with the measurement signal and referencing the temperature rise to a thermal reference, which results in much higher bandwidth and crest factors.

Samuel[/quote]

The 3400 is still a very good instrument. I wish I had one. LT made a chip for a while that used the same principle.

I wish I had one.

Click to expand...

I think you might pretty easily get one for cheap. Mine arrived in absolutely mint condition, calibrated to specs and with a one-year guarantee from the seller for just EUR 180.- plus shipping, which is a bargain indeed I'd say.

Another application note from Linear covering noise is number 61.

Samuel

You say you have a scope, albeit a cheap one, it's still very useful if you have a known signal for a reference. as an example, measure 60Hz on the secondary of a low voltage power transformer using your true rms DMM. Multiply by 1.414 and this will give you the peak voltage. Now, connect the same transformer to the scope and adjust the vertical amplifier to display the sinewave on the graticule divisions. You now have a reference. Measure the synth waveform, and you can calculate the peak voltage by counting the divisions difference on the graticule. If you're not familiar with this, there is a good booklet published by Tektronix called the XYz's Of Using A Scope. (or something similar to this)

I used an old Eico 460 for years, and it was as accurate as the reference calibration voltage used. (At lower frequencies of course; Outside the bandwidth of the vertical amps was a different story.)