galvanometer - a simple device used to measure currents. This device is similar to a simple DC motor.

gamma rays - high energy electromagnetic waves resulting from atomic fission or fusion.

gate - 1. a circuit that performs on of the Boolean algebra function (i.e., and, or, not, etc.) 2. a connection between a runner and a part, this can be seen on most injection molded parts as a small bump where the material entered the main mold cavity.

gateway - translates and routes packets between dissimilar networks.

Geiger-Mueller tube - a device that can detect ionizing particles (eg, atomic radiation) using a gas filled tube.

global optimum - the absolute best solution to a problem. When found mathematically, the maximum or minimum cost/utility has been obtained.

gpm (gallons per minute) - a flow rate.

grafcet - a method for programming PLCs that is based on Petri nets. This is now known as SFCs and is part of the IEC 1131-3 standard.

gray code - a modified binary code used for noisy environments. It is devised to only have one bit change at any time. Errors then become extremely obvious when counting up or down.

ground - a buried conductor that acts to pull system neutral voltage values to a safe and common level. All electrical equipment should be connected to ground for safety purposes.

GUI (Graphical User Interface) - the user interacts with a program through a graphical display, often using a mouse. This technology replaces the older systems that use menus to allow the user to select actions.