EPC111 datasheet(6/14 Pages) EPC

6 / 14 page

epc111/112

Working principle of the digital filter e.g. for the signal OUTNint to OUTN Filter:

The aim of this programmable filter is to suppress single pulses, so they cannot trigger the output and generate a false signal.

This filter is based on a counter, which is counting up (increment) the valid pulses and counting down (decrement) the missing pulses in a

weighted manner. There are separate weighting factors for valid pulses (parameter nV) and missing pulses (parameter nM). If the counter

reaches the upper limit (maximum count, response time), the signal OUTN is set to LOW. Similar in the opposite direction, if the counter

reaches zero, the lower limit (minimum count, release time), the signal OUTN is put to HIGH. With the parameters nV and nM the filter has the

advantage of individual selectable gradients of the slopes. Counter will never exceed maximum nor minimum limit. In between it acts as an

integrator of both parameters.

IF Pulse then

–

IF Pulse = valid then

Counter = Counter + (nV * 1024)

IF counter > 215 (maximum limit) then Counter = maximum limit

IF counter = maximum limit then OUTN = 0

–

IF Pulse = missing then

Counter = Counter – (2nM)

IF counter < 0 (minimum limit) then Counter = minimum limit

IF counter = minimum limit then OUTN = 1

ELSE wait for Pulse

Lets assume that the photodiode does not receive light pulses for a long time: This means the light beam is interrupted. Then OUTN is at high

level. If the light beam is not interrupted anymore, the photodiode receives light pulses which are strong enough to trigger the OUTNINT

threshold and the internal pulse evaluation unit (designated in Figure 3 with 'Pulse evaluation') starts to count the received pulses. If the

number of received pulses reach the set level nV, the output OUTN turns to low level. Thus, single pulses cannot trigger the output and

generate a false signal.

The same procedure is used when a beam changes from not interrupted to interrupted. The internal pulse evaluation unit counts the missing

pulses. If the number of missing pulses reaches the level n M, OUTN is turned to high level.

The same principle applies to the counter and signal of OUTH.

The counter limit values are different, depending on the device:

Type

No. of

Pulses nM

No. of

missing Pulses nV

epc111

epc112

Table 2: Filter coefficients

Light Pulse Detection Output OUTN

The epc111/112 contains two digital outputs to indicate that a valid signal of light pulses are received by the photodiode. The first output OUTN

is triggered, when the lower threshold is reached by the input signal (see Figure 3). This output is used usually to drive the output of the light

barrier. This is a fully CMOS compatible digital output.

Characteristics subject to change without notice

Datasheet epc111_112 - V2.2

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