- #1
BlackHole213
- 33
- 0
When using a multimeter, how come the values for the current and voltage fluctuate?
Understanding Fluctuations in Multimeter Readings
- Context: High School
- Thread starter BlackHole213
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- Multimeter
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Discussion Overview
The discussion revolves around the fluctuations observed in multimeter readings for current and voltage. Participants explore potential causes for these fluctuations, including the multimeter's condition and the nature of the measurements being taken. The context includes practical applications in a student lab setting, particularly in relation to verifying Kirchhoff's laws.
Discussion Character
- Exploratory
- Technical explanation
- Debate/contested
- Homework-related
Main Points Raised
- Some participants suggest that fluctuations may indicate a defective multimeter or that the current and voltage are genuinely fluctuating.
- Others propose that the batteries in the multimeter might need replacing as a possible cause of the fluctuations.
- A participant reports specific readings (6.692V and 1.236 mA) with noted fluctuations, seeking to understand how these affect their verification of Kirchhoff's laws.
- One participant notes that the fluctuations observed are small and suggests that they may be acceptable within the context of a student lab setting.
- Another participant emphasizes the importance of considering the last digit of multimeter readings with caution and recommends consulting the user’s manual regarding uncertainties.
- A later reply humorously offers to swap multimeters, implying that the issue may be resolved with a different device.
Areas of Agreement / Disagreement
Participants express varying views on the cause of the fluctuations, with no consensus reached on whether the issue lies with the multimeter or the measurements themselves. The discussion remains unresolved regarding the exact nature of the fluctuations and their implications.
Contextual Notes
Participants mention the need for additional information about the measurements to narrow down potential causes, indicating that assumptions about the stability of the voltage source and the multimeter's accuracy are relevant but not fully explored.
- #2
Bobbywhy
Gold Member
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1. The multimeter is defective, or
2. The current and the voltage really are fluctuating.
I suggest you check your multimeter by reading the voltage and current of a battery-operated device. The voltage and current should not fluctuate.
2. The current and the voltage really are fluctuating.
I suggest you check your multimeter by reading the voltage and current of a battery-operated device. The voltage and current should not fluctuate.
- #3
- 12,178
- 186
orBobbywhy said:
3. The batteries in the multimeter need replacing.
What are you measuring? What is the value of the voltage or current you are reading, and by how much is it fluctuating? That information might help us narrow down the cause.BlackHole213 said:
- #4
BlackHole213
- 33
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I got a voltage of about 6.692V. The digit after the 2 was fluctuating between 2 and 4. For the current, I got 1.236 mA with a similar fluctuation right after the 6. My assignment was to verify Kirchoff's current and voltage laws. Only a few of the calculations actually equal zero. The majority are off by a few milivolts or microamps. I am trying to account for the non-zero values in my discussion.
- #5
- 12,178
- 186
Those appear to be real -- and very small -- fluctuations. Your readings are stable to 4 significant figures, it doesn't get much better than that! 
(At least in a student lab setting.)
As for the cause, it could have been the voltage source, or it could be the meter itself. In hindsight, it might have been good to measure the power supply voltage directly (with the circuit connected to it), and see what level of fluctuations were there.
At any rate, you can use the fluctuations to estimate the uncertainty in the measurements, and add a digit for the meter possible being off. As long as the loop voltage ±uncertainty contains zero, you are fine.
(At least in a student lab setting.)As for the cause, it could have been the voltage source, or it could be the meter itself. In hindsight, it might have been good to measure the power supply voltage directly (with the circuit connected to it), and see what level of fluctuations were there.
At any rate, you can use the fluctuations to estimate the uncertainty in the measurements, and add a digit for the meter possible being off. As long as the loop voltage ±uncertainty contains zero, you are fine.
- #6
Gordianus
- 535
- 148
Welcome to the real world where measurements do fluctuate (I think the multimeter is working well).
The last digit of any multimeter should be regarded with suspicion.
I strongly suggest reading the user's manual as regards uncertainties.
The last digit of any multimeter should be regarded with suspicion.
I strongly suggest reading the user's manual as regards uncertainties.
- #7
cmb
- 1,128
- 128
BlackHole213 said:
Just PM me if you want to swap your multimeter for one of my 3 digit meters - your problem will then disappear!
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