Oscilloscope doubt

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Lostbrain
Lostbrain's picture
Oscilloscope doubt

I am interested in measuring the noise in my set up. My Clampex software give about 40 pA (yes, I know it is huge) but nothing compared to the reading in my Techtronix digital oscilloscope (several volts!).

Who do I trust? I really doubt the osciloscope reading is right, but I don't know where the problem is. Of course it could be completely out of calibration, but it is almost brand new... Anyway, I plan to calibrate it tomorrow.

Any suggestion?

Thanks

vilsy
vilsy's picture
 What is the gain on the

 What is the gain on the oscilloscope....the same signal can look big or small on the oscilloscope depending on the gain setting u have. Can u calculate the value in pA and then compare with Clampex...

Lostbrain
Lostbrain's picture
Thanks  Vilsy

Thanks  Vilsy

That's the thing, my oscilloscope does not have any gain knob to my knowledge. In any case, if I am not wrong, an oscilloscope should not need that. The device is precisely designed for measuring voltage/current accurately to test electronic circuits (as long as the scope is correctly calibrated). For example, if you probe a battery, it should give you the voltage of the battery, like a voltimeter. It is true that for a voltimeter you normally have to set a range of expected values, but not sure this is necessary for scopes (at least not for mine). Anyway, I am sure I have some missunderstanding somewhere. Please help.

vilsy
vilsy's picture
 Hi,

 Hi,

The oscilloscope gives the read out in volts and yet u r measuring current. Either the output from the amplifier (to the scope) or the oscilloscope should have a gain setting so that you can get an idea of how big the current is...

Also, the oscilloscope should have a knob for gain...otherwise how will the same machine be able to give u a clear enough resolution when u r reading signals in the range of micro amperes versus nano amperes?

I am really bad at explaining technical concepts at times.

Lostbrain
Lostbrain's picture
Will have a look to it

Will have a look to it tomorrow and let you know. Do you mean by gain the volts/division knob. Changing that does not the noise amplitude (it just scales the voltage as it would do in an amplifier gain...).