TASK DEFINITION: Translate the given Spanish text to English
PROBLEM: Graphite may optionally be employed.

SOLUTION: Opcionalmente se puede utilizar grafito.

PROBLEM: A related testing method is also disclosed.

SOLUTION: También se describe un método de prueba relacionado.

PROBLEM: In addition, a central converter is also connected to the network.

SOLUTION:
Hay un convertidor central conectado asimismo a la red.