Equipment Accuracy: Explaining Micro-Amp & CRO Results

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SUMMARY

The discussion centers on the discrepancies between theoretical and actual measurements of current using an ammeter, particularly in micro-amps (10^-6), and voltage peak-to-peak values with a cathode ray oscilloscope (CRO). Key factors affecting accuracy include the internal impedance of the power supply and ammeter, circuit loading, and the inherent error of the CRO at various settings. The use of appropriate probes, such as passive probes with a 10x setting, is crucial for improving measurement accuracy. Users are advised to consult their CRO manuals for specific accuracy percentages and probe compatibility.

PREREQUISITES
  • Understanding of micro-amp measurements and their significance.
  • Familiarity with cathode ray oscilloscopes (CRO) and their operational principles.
  • Knowledge of measurement accuracy and error analysis in electronic instruments.
  • Experience with different types of probes (passive, active, current) and their applications.
NEXT STEPS
  • Research the impact of internal impedance on measurement accuracy in electronic circuits.
  • Learn about the specifications and accuracy ratings of various CRO models.
  • Study the differences between passive and active probes, including their appropriate applications.
  • Explore techniques for minimizing circuit loading during measurements to enhance accuracy.
USEFUL FOR

Electronics engineers, technicians, and students who are involved in precision measurement and analysis using ammeters and oscilloscopes, particularly those seeking to improve the accuracy of their readings.

dagg3r
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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.
 
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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).
dagg3r said:
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.
 
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