System Description

        The enclosure houses directly the display, voltage and current transformers, the power connectors, the BNC connector, the range switches and the power supply board. A separate assembly contains the Analog and Micro-controller Board, a header for the power supply cable, and a connectors for the display cable and programming/logging.

        The voltage transformer contains one secondary winding for power and a separate one for the voltage waveform. The current transformer is a large (24 oz) toroid intended as a bench isolation transformer. The original primary winding of 1000 turns is used for measurements, the other is used for monitoring. Two primaries were added of heavy-gage wire, one of 4 and the other of 36 turns. A switch selects decade multiplication.

        Shunt resistances of 100, 300, and 1000 ohms select watt and current ranges. Together with the primary switch, there are 5 ranges of 20, 60, 200, 600 and 2000 watts, with corresponding currents. Both switches contain a second pole (not shown) to report their positions to the Micro-controller.

       The power supply board provides + and - 15 volts for the analog circuits, 5 volts for the digital circuits, and 20 MA for the display’s LED backlight. It also houses a SCR-based snubber circuit which protects the shunt resistors from over-heating if the selected range is grossly low.

        The display is installed in the enclosure and has a preset potentiometer on its back for LCD contrast. It connects only to the Analog and Micro-controller Board.