epc111/112

Functional Description

Evaluation of single light pulse

For each single light pulse, received and detected by the LED, the threshold levels are processed according to the following principle to

Signal output OUTN

Light reserve OUTH

I

PD

Threshold levels:

OUTN

INT

Light pulse detection

Light reserve detection

I

PD

OUTH

INT

t

t

t

t

t

t

Figure 3: Pulse evaluation

The epc111/112 chip operates the LED and the receiver path on a pulse modulated concept. Thus, the LED is operated with short pulses

whereas the receiver channel does synchronous demodulation of the received light pulses by reading the current pulses of the photodiode.

This concept allows a very high sensitivity, high speed operation, and a high suppression of input ambient or foreign light (DC currents)

generated by sunlight or other DC light sources like light bulbs.

In order to eliminate interference caused by modulated light, e.g. a flashing light or by other light barriers, the input signal from the photodiode

is amplified, filtered, and processed by an integrated signal processor. If the photodiode signal meets the required frequency, pattern and

amplitude, the output(s) are triggered. The following timing diagram shows the basic concept.

Emitter LED

Beam interrupted

Photo diode current I

PD

no

yes

OUTN

INT

or OUTH

INT

t

R

1

2

n

M

t

F

1

2

n

V

t

Pulse

t

Cycle

OUTN or OUTH

off

on

[V]

Response time

valid (non-missing) pulses

Release time

missing pulses

Figure 4: Pulse modulation concept

It is in fact a digital filter which counts missing and non-missing pulses to change the ou tput state of OUTN or OUTH.

© 2011 ESPROS Photonics Corporation

Characteristics subject to change without notice

5

Datasheet epc111_112 - V2.2

www.espros.ch