The Blue Ring Tester works on the principle of capacitive coupling. When the tester is brought near a live circuit, the high-impedance resistor (R1) allows a small amount of current to flow through the capacitor (C1) and into the circuit. If voltage is present, the neon lamp (NE1) will glow, indicating that the circuit is live.
\[R1 ightarrow NE1 ightarrow C1 ightarrow VDR1\] Blue Ring Tester Schematic Diagram
Blue Ring Tester Schematic Diagram: Understanding the Circuit and Its Applications** The Blue Ring Tester works on the principle