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Signal generator question.

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allegro

New Member
Hello.
I use my S.G. (signal generator) in order to calibrate a chip I own which performs measurements.
I connect the S.G.'s pins to my chip and I need to know exactly what voltage is inserted into the chip by the S.G.

I measured the S.G.'s pins with fluke (multimeter), and the fluke showed unstable results.
I disconnected the S.G. pins from the chip, and the fluke still showed unstable resutls.
For example, when I set the S.G. to output 100mVp, the fluke's results were moving between 70.1mVrms and 73.2 mVrms - it stays a few moments on 73.2mVrms, then went down for a few moments to 70.1mVrms, and so on.

Did someone experience it and could tell me what is the problem?
It means that the S.G. is not ok?

Thank you.
 

allegro

New Member
It means that you don't use a multi-meter to measure the output from a signal generator - you also give no idea what frequency you're talking about.
Hello.
The signal's frequency is 50Hz.
Could you explain please why its not good to measure S.G.'s output voltage with a multi-meter?
And what is the correct way to measure it?

I also own a oscilloscope, but I assume that Fluke is much more accurate than oscilloscope.

Thanks.
 

Externet

Active Member
I do not see a problem with your readings. The multimeter shows what it should, and a couple of millivolts variation can come from radio stations, the blender from the neighbor, ot that compact fluorescent bulb.
The SG seems stable to me.

Miguel
 

Sceadwian

Banned
Why would you assume that?? If the oscope is calibrated you'll see the wave form on the screen.
It also depends on what type of wave form you're sending.
Use the scope see what it displays.
 

Leftyretro

New Member
Also, a signal generator is designed to work into a specific impedance not the very high input impedance of your DVM. Find out what the rated output impedance of your signal generator is and wire a resistor to it's output as a load then then take a reading to see if it's more stable. However I agree that your present reading don't sound bad to me.
Also if you could give the brand of your SG and model we might have more insite for you.

Lefty
 

allegro

New Member
Thank you all.
First, I'll connect tomorrow a 1K resistor to the S.G. output and see if its being more stable (I'll also pick up the SG's type and model).

What makes these variations of 2mVrms on output?
Is it the fluke's fault or the S.G.'s?

I'd really like to know how can radio stations, blender from the neighbor, or compact fluorescent bulb affect the voltage at the S.G.'s output?
 
Last edited:

Nigel Goodwin

Super Moderator
Most Helpful Member
Hello.
The signal's frequency is 50Hz.
The Fluke should be OK at 50Hz.

Could you explain please why its not good to measure S.G.'s output voltage with a multi-meter?
Because they only work on a VERY limited frequency range.

And what is the correct way to measure it?
With an AC millivoltmeter. or an oscilloscope.

I also own a oscilloscope, but I assume that Fluke is much more accurate than oscilloscope.
Stick the scope on it, and see if you can see it varying.
 

Sceadwian

Banned
50hz sine sure, square probably not though, the OP never mentioned the wave shape. Sine is assumed so far.
 
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