Principles of Operation

MODEL 2100 OVERHEAD PROJECTOR

Optics (See Figure 1-2)

The light source for the Overhead Projector is 275 watt, 24 volt, Tungsten Lamp listed as ANSI Code FNT and rated at 75 hours. An external reflector is needed with this lamp.

Care should be exercised to prevent excessive vibration or jarring of the projector when the lamp is on. The lamp filament becomes more brittle at the operating temperature of the projector and shocks may cause premature failure of the lamp.

The glass envelope should not be touched by the fingers when inserting the lamp in the lampholder. Oils on the skin may combine with the glass to form blisters which also will shorten the life of the lamp.

The Fresnel lens, located above the lamp and directly beneath the projection stage, is a condensing lens which consists of a series of concentric rings, each of which has a surface curvature similar to that of a thick smooth lens. The Fresnel lens is made of plastic and may be severely damaged if the fan is stopped or the paths of cooling air blocked. Proper alignment and direction of the Fresnel lens is essential in order to maintain the resolution and brightness specifications for the projector.

The stage glass provides a convenient flat surface for placing transparencies and other materials to be projected. Because the light passes through the stage, these projection materials must be transparent.

There are two (2) different projection head assemblies available for the projector. One is an Open Triplet Head with focus correction which has a triplet lens and front surface mirror and the second a closed Doublet Head which has one or two condensing lens(es) and a front surface mirror. The projection head is located directly over the center of the Fresnel Lens. The projector is focused by raising or lowering the projection head.

Proper alignment of the optical components and a clean machine are essential if the maximum operating capabilities of the overhead projector are to be realized. Cleaning and alignment procedures are discussed in Sections 2 and 4 inclusive.

Cooling (See Figure 1-3)

Cooling of the overhead projector is accomplished by a motor-driven fan located next to the lamp housing. The cooling air enters the projector through opening “A” and exits through opening “B.” (See Figure 1-3) It’s important that the flow of cooling air not be restricted either by placing projector too close to a wall (about one foot clearance is necessary) or by leaving foreign objects inside the projector.

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