Abstract: An apparatus and method are disclosed for measuring and displaying the percentage of ac voltage ripple present on a direct current input voltage. In addition, the apparatus can be set to activate alarms and trip relays when the percentage of ac voltage ripple meets or exceeds a preset value.

Abstract: An impact absorbing lock apparatus to prevent unauthorized entry through a door by kicking or ramming of the door comprises a mounting bracket attached to the door jamb of the door adjacent a latch bolt used to secure the door, a keeper for retaining the latch bolt and mounted for movement relative to the mounting bracket between a rest position contacting the mounting bracket and a displaced position, and a spring contacting the keeper and urging the keeper toward the rest position, the spring absorbing any impulse forces applied to the latch bolt and keeper and permitting keeper movement to displace the spring to absorb impulse forces and keep the lock apparatus from being torn from the door jamb. In one embodiment of the invention, the keeper is slidably mounted for movement toward and away from the mounting bracket. In a second embodiment the keeper is swingably mounted to the mounting bracket.