Switch amplifier with 2-channel isolated barrier, dry contact or NAMUR inputs, relay contact output, line fault detection (LFD). It features reversible mode of operation. Terminals 14 and 15-connection. This isolated barrier is used for intrinsic safety applications. It transfers digital signals (NAMUR sensors/mechanical contacts) from a hazardous area to a safe area. The proximity sensor or switch controls a form-C changeover relay contact for the safe area load. The normal output state can be reversed using switches S1 and S2. Switch S3 is used to enable or disable line fault detection of the field circuit. During an error condition, the relays revert to their de energized state and the LEDs indicate the fault according to NAMUR NE44.