The Model 502 alerts maintenance personnel when a filter must be replaced. It only requires a 1/4" diameter hole to be drilled in a vertical wall to obtain a reference pressure outside the ventilated area. The unit is then fastened to the wall with 4 screws and the actuation point determined by placing cardboard on the filter to simulate a dirty air filter. No electrical wiring is required, for an internal "D" battery can power a flashing visible warning continuously for approximately 2.5 years.

The Model 502 is an excellent low cost backup for clean rooms and ventilated areas to compliment your present method of determining when air filters should be replaced. Using the Model 502 can reduced failure rates of air cooled electronic equipment.