Generally, which type of signals with a very low source resistance are less sensitive to electrical noise from welders and electric motor starters?

• A. Voltage
• B. Current
• C. Resistance
• D. Capacitance

Answer: (B)

Current signals with a very low source resistance are less sensitive to electrical noise from welders and motor starters because noise in these environments is largely voltage-type. When the signal path has a very low impedance, external voltage spikes won’t translate into large changes in the current that the system sees; the current is governed by the load and the low-impedance source, so the reading through a low-value shunt or a current sensor stays essentially stable. In practice, current sensing using a low-impedance path (like a shunt or Hall sensor with good common-mode rejection) handles EMI better, while voltage measurements are more easily disturbed by the same noise because any spurts in voltage directly affect the sensed value.