In the context of indirect connection interfaces, which device provides signal isolation between two machines?

• A. Relay
• B. Transformer
• C. Capacitor
• D. Inductor

Answer: (A)

Galvanic isolation is created when two circuits transfer a signal without a direct electrical path between them. A relay achieves this by using a coil on the control side to magnetically actuate a set of contacts on the load side. The coil and the contact circuit are separated by an air gap, so no current flows from one machine into the other; the signal is transferred only through the switching action of the contacts. This protects both machines from noise, surges, and grounding differences and allows different voltage levels on each side.

A transformer can provide isolation by coupling signals magnetically, but its primary use is energy transfer and level/impedance changes rather than simply switching a machine on and off. Capacitors and inductors don’t provide true galvanic isolation; they either couple signals or store energy but maintain a conductive path that doesn’t reliably isolate the two circuits.