What is differential measurement, and why is it used in sensor interfaces?

• A. Differential measurement reads the difference between two signals (positive and negative inputs), reducing common-mode noise and improving accuracy.
• B. It uses a single-ended measurement.
• C. It measures the average of two signals.
• D. It amplifies common-mode noise.

Answer: (D)

Differential measurement focuses on the difference between two signals, using a positive and a negative input. By subtracting one from the other, noise that appears on both lines—the common-mode noise—tends to cancel out, while the actual signal (the difference between the two voltages) is preserved. This makes sensor interfaces much more accurate, especially when cables run long distances, sensors are high impedance, or the environment is electrically noisy, because it tolerates ground potential differences and external interference. Instrumentation amplifiers are a common way to gain the differential signal while still rejecting common-mode content, boosting the desired signal without amplifying the noise. The opposite approach—measuring with a single reference, or trying to amplify the noise that appears on both lines—would degrade accuracy and reliability.