What is the benefit of measuring both direct and reverse current?

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Discussion Overview

The discussion revolves around the benefits of measuring both direct and reverse current in electrical circuits. Participants explore the implications of such measurements in terms of resistance effects, voltage identification, and measurement accuracy. The scope includes practical applications and lab practices related to electrical measurements.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants question the necessity of measuring both currents and seek references or context for the practice.
  • One participant mentions that measuring both currents can help nullify the effect of resistance in connecting wires, although they express uncertainty about how this works.
  • Another participant suggests that measuring in both directions can help identify voltages that are independent of current direction, such as battery offsets, and can serve as a sanity check for instruments and circuits.
  • A later reply proposes that measuring both directions can reveal stray currents, which may affect measurement accuracy, especially in environments with energized equipment.
  • One participant suggests using a 4-wire or Kelvin connection to better account for lead resistance, indicating a more advanced measurement technique.

Areas of Agreement / Disagreement

Participants express differing views on the necessity and implications of measuring both direct and reverse currents, indicating that multiple competing perspectives remain without a clear consensus.

Contextual Notes

Some participants note a lack of adequate context regarding the specific setup and connections involved in the measurements, which may limit understanding of the discussion.

phymath7
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TL;DR
Why do we have to measure low resistance (in method of fall of potential )and galvanometer resistance (method of half-deflection ) for both direct and reverse current?
What is it's benefit?
 
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Who says we do ? Do you have a reference, some context. a link ?
 
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BvU said:
Who says we do ? Do you have a reference, some context. a link ?
I don't have reference from any higher level practical book but from a local writter of my country.So I am not providing reference as I think that won't be considered worthy.But my teacher said that it's done to nullify the effect of resistance of the connecting wires.I am not sure how that works.
 
phymath7 said:
I don't have reference from any higher level practical book but from a local writter of my country.So I am not providing reference as I think that won't be considered worthy.But my teacher said that it's done to nullify the effect of resistance of the connecting wires.I am not sure how that works.
That doesn't make sense to me either. It would be a good way of identifying voltages that don't depend on the current direction, like a voltage offset from a battery, or voltages that depend too much on polarity, like a diode in the circuit. It's also just a good sanity check of the instrument and the circuit being tested. The answer should usually be the same, if it's not, more investigation is needed.

In general, good lab practice is to try and verify your measurements with a slightly (or vary) different setups that shouldn't matter, because sometimes your assumptions, instruments, or measurements are wrong.

BTW, if you do want to correct for the lead resistance, you can just measure "0" resistance by putting the probes on the same conductor and subtract that from your measurement. An even better way is to do a 4-wire or kelvin connection, which requires a bit more than just simple ohm-meter.
 
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phymath7 said:
But my teacher said that it's done to nullify the effect of resistance of the connecting wires.I am not sure how that works.
You haven't given us adequate context to understand what's being said. What connecting wires? What do they connect? Can you show us a diagram?
 
What @DaveE said. The 'both directions' process will also indicate the presence of 'stray current' - that isn't uncommon when measuring grounds in a facility with existing energized equipment - it can significantly skew your result if you don't know that it's there. Once identified, it can usually be dealt with arithmetically (or by turning off some equipment).
 

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