ETI MAC-21 Controller Monitor Ammeter

Advanced self-contained microprocessor-based metering and control package for primary injection circuit breaker testers

• PIC microprocessor core unit
• Contains a regulated power supply
• Software contained in the PIC

The heart of the MAC-21 consists of a PIC microprocessor core unit, It is connected to a motherboard, which contains a regulated power supply, some support circuitry,. Software contained in the PIC, (also known as "firmware"), performs the required real-time data collection, measurement, user interface, and output control functions.

The keyboard / display PC board contains virtually all of the hardware for the user interface (LED displays and keyboard), as well as contact sensing and output initiation circuitry. The eight LED digits are multiplexed, and have limited alphanumeric capability for more flexible indication of such conditions as overrange. The keys are scanned at roughly 60 times per second, and incorporate LED's to indicate status. An audible indicator (beeper) sounds when a key is pressed. The contact sensing circuitry uses the key scanning system, with a transformer for isolation. The sensing signal is a repetitive pulse of low voltage and low current, and contact sensing leads may be handled without fear of shock. Two separate optically isolated signals are provided for output initiation with an electromechanical contactor or SCR. All functions of the keyboard / display PC board are handled by a single PPI.