AC Bridge vs. DC Bridge: Key Differences & When to Use Each
AC Bridge measures impedance using alternating current, balancing unknown components against known ones. DC Bridge measures resistance using direct current, comparing unknown resistors to a calibrated ratio.
Engineers grab the wrong bridge when rushing at the bench: “I just need a quick value—any bridge will do.” The frustration hits when an AC Bridge gives a drifting reading on a carbon resistor or a DC Bridge sees an inductor as an open circuit.
Key Differences
AC Bridge uses an oscillator and phase-sensitive detector, handling L, C, R with frequency dependence. DC Bridge relies on steady voltage, nulling a galvanometer for pure resistance. One balances imaginary numbers, the other balances ratios.
Which One Should You Choose?
Need inductance, capacitance, or frequency-dependent behavior? Use AC. Pure resistor networks, strain gauges, or thermistors? Go DC. Match the source to the component, not the other way around.
Can I measure a speaker’s voice coil with a DC Bridge?
Yes, but you’ll only get its DC resistance. The actual impedance at audio frequencies requires an AC Bridge.
Why does my AC Bridge drift on a carbon resistor?
Carbon resistors have temperature coefficients; the AC signal heats them slightly, shifting the reading. Use a low-level source or let the part cool between sweeps.