Explosion Protection Circuit with Impedance Matching

An apparatus for monitoring at least one physical or chemical process variable,comprising:

• at least one transformer;
• at least one sensor unit;
• an electronics unit for signal registration, evaluation and/or feeding;
• and
• an explosion protection circuit, wherein:
• said at least one sensor unit is operated with alternating electrical current and/or communication between said electronics unit and said at least one sensor unit occurs with alternating electrical current and/or alternating voltage;
• said explosion protection circuit with intrinsic safety, which includes a safety barrier, which has at least one unit for electrical current and/or voltage limiting, and,
• there is provided within said explosion protection circuit a unit for impedance matching, which unit for impedance matching includes said at least one transformer.