epc111/112
Working principle of the digital filter e.g. for the signal OUTN
int
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 n
V
) and missing pulses (parameter n
M
). 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 n
V
and n
M
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 + (n
V
* 1024)
IF counter > 2
15
(maximum limit) then Counter = maximum limit
IF counter = maximum limit then OUTN = 0
IF Pulse = missing then
Counter = Counter – (2
nM
)
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 OUTN
INT
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 n
V
, 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
epc111
epc112
No. of
Pulses n
M
8
3
Table 2: Filter coefficients
No. of
missing Pulses n
V
8
2
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.
© 2011 ESPROS Photonics Corporation
Characteristics subject to change without notice
6
Datasheet epc111_112 - V2.2
www.espros.ch
EPC [ ESPROS PHOTONICS CORP ]
