Bosch Appliances DS426I, DS422I Application Tips, Perimeter Protection, Beam Stacking

9.0 Application Tips

When using photoelectric detectors for motion detection, there are a few installation techniques that will make the system more versatile.

9.2 Perimeter Protection

When protecting the interior of an installation, a good technique is to mount the units at 90° angles around the coverage area (see Figure R).

9.1 Beam Stacking

Beam stacking gives a wall of protection by stacking several units at different heights and providing an alarm activation on the blockage of only one pair of beams (see Figure N for the correct set-up technique). Note that the system is installed with alternating transmitters and receivers at each end. This eliminates the possibility of a receiver being covered by more than one transmitter.

T1	R1
S
R2	T2
	D

Figure N - Beam stack method

R4	T2
T1	R1
R3	T3

The maximum spacing between receivers (S) can be calculated by dividing the distance between the transmitter and its receivers (D) by 20.

Therefore, if the distance between a transmitter and receiver is 100 ft. (30 m), the maximum spacing between receivers would be 100 ft. (30 m) ÷ 20, or 5 ft. (1.5 m)

S = D/20 S = 100 ft. (30 m)/20 S = 5 ft. (1.5 m)

A potential problem when installing systems in a beam stack is “Near Field Reflection.” Near field reflection is caused when a reflective object is placed in the line-of-sight of the detectors and causes the transmitted signal to be reflected to the wrong receiver (see Figure P).

T4 R2

Figure R- Perimeter protection

Note that the beams are mounted so they cross each other. This way, an intruder can not enter the area by walking between the units. When installing multiple transmitters and receivers, test with all the receivers powered-up, but with only one transmitter powered-up at a time. A transmitter should set up only its receiver.

Receivers physically too close to a different system’s transmitters may be set up even if the transmitter is not pointed at them (see Figure T).

T1 R1

R2 T2

Figure P - Near field reflection

It may be desirable to have more than two sets of beams to create taller stacks. This can be accomplished by adding receivers as shown in Figure Q). Note that the beam from each transmitter is covering two receivers.

T1	R1
R3	R2
R4	T2

Figure T - Close proximity field problem

If a receiver is being set up by the wrong transmitter, the signals can usually be eliminated by masking the sides of the transmitter and receiver. Use electrician’s tape or duct tape inside each enclosure’s window.

When installing these systems, remember that the infrared signal may reflect off objects (e.g. glossy walls or floors) in the coverage area and still set up the receiver.

A thorough walk test performed at several different points within the coverage area will catch this problem. Re-aligning the units should solve this problem.

The only way to insure proper continual protection is to perform regular walk tests of the desired coverage area.

Figure Q - Multi-system stack

© 2004 Bosch Security Systems	03/04
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