Light Sensors0 pages

Active Infrared Detectors
Functional principles
An Active Infrared Detector always comprises one transmitter and at least two receiver chips with high-quality optical systems. These are housed on the sensor
PCBs (modular system) or in the preassembled housings (individual sensors).
The scanning range is set by means of a
mechanical mircro-speed unit by changing
the angle between the transmitter and
receiver. This optical procedure is called
triangulation or optical differential measurement. Active Infrared Detectors are
static, i.e. they only detect persons and objects if these are actually in the beam.

Advantages of background
suppression
■

Almost constant scanning range for
reflective objects with diffuse reflectances which vary greatly

■

Reliable detection of dark objects
against light backgrounds

■

Insensitive toward undesired reflection
from objects in the background (aluminum channelled plates, marble floors
etc.)

■

Very high operating reserve

■

Mobile installation possible (e.g. on
elevator doors)

System variants
Available variants include autonomous
Active Infrared Detectors with separate
housings or systems in the form of a PCB
with profile housings which can be assembled as desired (modular system).
Autonomous Active Infrared
Detectors
Available as single-beam sensors with point
detection beams, as four-beam area sensors
or as count sensors also with four beams and
intelligent evaluation electronics (see Fig.2).
Fig. 2

The detection area consists of points and
depends, to a large extent, on the optical
centre-to-centre distances of the transmitter and receiver lenses. Several beams can
be combined in the modular system (e.g.
RMV/RMT) to form lines (vertical Light
Curtains without counter-sensor) or a defined area (area Acitve Infrared Detector
FLT 2800 or count sensor CLS 2000).

Background suppression
The following comparison determines
which of the two receiver chips receives
more light.

Receiver

Transmitter

Element in foreground
receives more light;
the object is detected
Receiver

Transmitter

N F

Sacanning range

N F

Object in
background

Background

1

2

2
1

In contrast to Active Infrared Detectors
with background suppression (the signal
changes when an object enters the scanning area), the systems with background
analysis require a signal from the background in order to deactivate the output.
The Detector will thus continue to function
even in the event of vandalism, e.g. if the
optical surface is partially or completely
covered.

Important information for Active
Infrared Detectors with background
analysis
Object in scanning range

Scanning area
boundary

S

Background analysis

The choice is yours

Element in background
receives more light;
the object is masked

E

a) Direction of movement 1
b) Direction of movement 2

1.

Scanning area
boundary

The sensor is installed and requires a
background (floor/wall) – the output is
deactivated.

2. The desired scanning range is set
mechanically within the predefined
possible distances.

Light
background

Fig. 1

As only the position of the object within
the optically active range and not its reflectivity determines whether the element
in the foreground or the element in the
background receives more light, light and
dark objects can be detected with the same
degree of reliability. Only in the cross-over
area between the foreground and background is there a difference between the
scanning ranges for white and very black
objects of a few percent of the nominal
range.

3. Each object within the set scanning
range is detected statically (see Fig. 2).
Advantages of background analysis
■

As points 1–3 for background suppression

■

Testing possible – contact-free protection alignment with test

■

Ideal for safety locks as the optical system cannot be covered and it is not
possible to push even flat objects (e.g.
envelopes) between the floor and
scanning field.

2. Line of
light

a
1. Line of light

scanning
field b

Background

2600
2800

Two light bundles are combined in each
case to form one line of light. The movement signal is determined from the sequence in which the person passes
through the lines of light.
Modular Active Infrared Detectors
These Active Infrared Detectors are designed as PCBs – each PCB has one detection beam. Versions with power supply
units and output stages (master) are suitable for controlling and evaluating up to
eight further PCBs without power supply
units and output stages (slave). Detector
PCBs can be installed directly behind covers (pay attention to the lens apertures,
tightness, vibrations, contamination etc.)
or can be mounted in the various aluminium support extrusion which we offer as a
mechanical housing package with the sensor window and side caps for installation
by the user.

Typical applications
Please refer to the individual product
brochures.