Theory of Operation

The LX Series light screen sensing system consists of two self-

contained units: an emitter and a receiver of equal size and

sensing range. The emitter has multiple infrared LEDs spaced at

9.5 mm (0.38 in) increments, and the receiver has corresponding

photodiodes. The emitter sequentially fires each infrared LED.

Multiple photodiodes in the receiver recognize each of the

emitted pulses; the result is a “cross-hatched” optical pattern.

Optical synchronization enables the receiver to recognize light

from each of the emitter LEDs.

The optical crosshatch pattern enables the LX system to detect

targets of very small diameter, and extremely thin, flat objects—

as thin as a piece of paper or an envelope. For small diameter

objects, the sensing resolution is less effective at the exact center

(see the minimum object detection size specification) of the

sensing range and at the extreme edges of the pattern (close to

the emitter and receiver faces); sensing should take place within

the center 80 percent of the range, as shown.

Emitter

Receiver

Sensing is most effective in the

center 80% of the sensing range

Figure 1. LX Series optical crosshatch pattern

LX Series sensors are available in two ranges: short and standard. Short-range emitters and receivers may be located as close together

as 75 mm (3 in), with a maximum separation of 200 mm (8 in). Standard-range sensors may be separated 150 mm to 2 m (6 in to 6.5

ft) apart. Both emitter and receiver must be either short-range or standard models, of the same length. Detection sensitivity varies

somewhat, depending on the distance between the sensors and the position of the target object.

For closer-range applications, the working range of any sensor pair can be reduced by connecting the sensor’s Select wire to 0 to 2 V

dc (see the sensing range specification).

The receiver output interfaces directly with dc loads or circuits up to 30V dc, and offers both sinking (NPN) and sourcing (PNP) output

transistors. Outputs conduct whenever a beam is broken. A 5 millisecond pulse stretcher (OFF-delay) is included to improve

interfacing reliability.

Typical Applications

Typical applications for the LX Series include parts ejection verification and package detection on a conveyor.

Installation and Alignment

Reliable performance of the LX series light screen systems requires a simple alignment process. Mount the sensor in a location as free

from vibration as possible.

Sensors may be mounted using the accessory brackets (available separately) or using the T-slots in the sensor housings. After

mechanical alignment is completed, the sensors can be wired and power applied.

1. Loosely mount the emitter and receiver at their operating locations with their front panels opposite each other, and at

approximately the same level.

2. Adjust the emitter position until the receiver detects alignment (the yellow LED turns OFF). For best alignment, position the

emitter in the middle of the positions that cause a clear receiver condition.

3. Tighten the bracket hardware.

4. Position a pencil or similar object within the sensing area to verify that it can be reliably detected throughout the sensing area.

LX Series Part-Sensing Light Screen

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