How to Choose Single-Ended or Differential Voltage Measurement (Differential Focus) – 8501068
Examining Important Aspects of Voltage Measurement
Voltage is a difference in electric potential between two points, and a measure of force for current flow in a conductor or circuit. You can choose to measure voltage single-ended, or you can measure voltage differentially. This whitepaper is part 2 of two in the series, How to Choose Between Single-Ended or Differential Voltage Measurement. It is recommended that you first read part 1 of the series, which focuses on single-ended voltage.
In this part, we consider differential voltage measurement. How you measure voltage is important; because voltage measurement is at the heart of most of your processes that monitor current, temperature, resistance, and strain. Thus, your method of measurement should be well-matched to your application to positively impact your results and avoid error.
Beware of Ground Loops
Because differential inputs can also connect to earth grounded source signals, you need to be aware of your instrument. Determine if its Return connection is also connected to earth ground. This will avoid situations where two separate connections to earth ground may create a ground loop; which can lead to measurement error and equipment failure.
Instrument instructions usually recommend limiting yourself to one earth ground connection in a circuit. This avoids generating a ground loop, which can interfere with your measurement. However, it’s only required if the earth grounds are at different potentials; which would push error current between them. Be aware of where your output and input connect to earth ground. If they each connect separately to earth, how far apart are their connections to earth? If the distance between the output and the input is larger than three meters, or the distance between the earth grounding points is long; you may need an isolation barrier between the signal source and measurement device. The presence of isolation between the output and input circuits “breaks the ground loop” by allowing the earth grounds of each circuit on each side of the barrier to be at different potentials (within the limits of the isolation rating).
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Whitepaper: Why Do I Need Electrical Isolation?
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