Equipment Accuracy: Explaining Micro-Amp & CRO Results

[dagg3r]

hi all, can someone explain to me if i were to theoretically calculate current using an ammeter in small units eg micro amp's 10^-6 and physically use an ammeter to obtain results why do they differ greatly?

and also when i am using a cathode ray oscilloscope (CRO), when i am measuring voltage peak-peak values what equipment\limitations\techniques are causing the results to differ greatly then the theoretical results.

 

[Ouabache]

You may be encountering a small internal impedance, inherent in your power supply and also the ammeter, that can cause your readings to vary from theoretical values. If your are finding large variations in your measured values from theoretical.. You may be loading your circuit. You can read more about accuracy and meter loading at this http://www.elexp.com/t_elec.htm (see parts 1 and 2).

hi all, can someone explain to me if i were to theoretically calculate current using an ammeter in small units eg micro amp's 10^-6 and physically use an ammeter to obtain results why do they differ greatly?

For the scope, there is a certain amount of error inherent in the instrument at each setting. Look at the scope manual and find its accuracy measured in percent, at various settings.. Using probes (designed to work with your scope) will also effect accuracy.
There are different http://www.optics.arizona.edu/Palmer/OPTI380B/lablec05.pdf (and settings) for different conditions. Passive probes are the most common and a 10x setting tends to improve accuracy but also attenuates the voltage of signal you're measuring. Besides passive, there are also active and current probes. Each used for different applications. Using the wrong probe, will certainly impact accuracy of your measurement.

Also when i am using a cathode ray oscilloscope (CRO), when i am measuring voltage peak-peak values what equipment\limitations\techniques are causing the results to differ greatly then the theoretical results.