Hi everyone !
I have a circuit which only has two 1ohm resistors in series. And I use a dc power supply to apply a 1mv voltage on them.
and then I measure the voltages across the two resistors using the 2 leads of an oscilloscope. The results displayed in the screen is noisy.
(with the lead connected to the hv side and the black clip connect to the lv side )
And then I apply 50mv to the circuit. Voltage measured Channel 1 is about 30mv and the voltage from channel 2 is quite low(only around 400uV and is not stable). However when I inverse the connection of the lead of the channel 2 (lead---lv, clip----hv),the voltage apperas on the screen are about 25mv of CH1 and -25mV of CH2.....

I cannot figure out what happen. I think the way i do the measurement is wrong. and maybe I need to amplify the samll dc voltage ?

Please give me some advices please ! Thanks !

 

You have a bad scope probe. They tend to get loose at the connector that plugs into the scope.

 

You can measure 400uV with an oscilloscope?

What probe (10:1, 1:1 and model) and oscilloscope are you using and what's the input divider set to?

 

You have a bad scope probe. They tend to get loose at the connector that plugs into the scope.

yeah i changed a probe and the results are much better.
And I think my breadboard is not good

 

You can measure 400uV with an oscilloscope?

What probe (10:1, 1:1 and model) and oscilloscope are you using and what's the input divider set to?

the 400uV is the number calculated by the oscilloscope....and the number jumps between different values....

now I want to use my dc power supply to apply a small voltage to my measurement circuit and then apply a voltage to activate my op-amp to amplify the small dc voltage across it. The dc power supply has outputs as +6, -6, GND, +25, COM, -25.
what is the proper way to connect the power supply and the oscilloscope ?
I did this: (+6)----circuit------(-6), (-6)---GND----Com,
(+25)---Op-amp---(-25),
Op-amp output-----probe of oscilloscope
COM----Clip in the probe

 

Now I learn something form http://www.allaboutcircuits.com/worksheets/scope1.html