PD-9 Phase Detector / Polarity Checker Self-Test Auto-Off Audio Speaker Testing
The PD-9A PHASE DETECTOR is the first system that actually checks itself by reversing every fourth pulse on the software. The PD-9A is only 2.25″ x 3.75″ x 1″ and operates on a 9-volt battery. To maximize battery life, an AUTO-OFF TIMING CIRCUIT shuts the PD-9A off after five minutes.