epc120
In more detail, such a sequential operation is typically like as follows:
1.
2.
3.
4.
5.
The first epc120 element is turned on (active mode).
On a second command this element sends a short light pulse towards his reflector or object, forming the active light beam
➊.
If there is no obstacle between epc120 and his reflector, the element receives this light pulse and stores it into a local memory.
The bus controller reads out the content of the memory in the epc120 chip and stores the status (light beam interrupted or not
interrupted) into its data memory.
Finally, epc120 is turned off (standby mode).
This sequence, which is also called 'scan', is repeated until all beams are checked and their status is stored in the beam status memory of the
bus controller.
The above mentioned sequence is repeated until power is switched off. Because of the fact, that an object can enter into a light beam right
after a beam has been checked with the above mentioned procedure, up to two full scan sequences are necessary to reliably detect an
object. Thus, the overall maximum response time of the system will be
t
R
=2∗n∗t
beam
t
eval
(1)
where
t
R
= response time of the system
n
= number of elements or light beams
t
beam
= time to evaluate one beam
t
eval
= time to evaluate the beam status memory and generate the output signal
For further reference in optical design considerations please refer to the respective application notes available from epc.
+ I
LED
VDD
Element 1
VDD
VDD
Element 2
VDD
Element n
VDD
VDD µC
epc100
VDD33
SI
SO
SCK
CS
GND
VDD33
VDD33
VDD33
µC
GND
- I
LED
GND
GND
GND
R
LED
R
LED
R
LED
Figure 5: epc120 in the light barrier application as receivers and the interface chip to the microcontroller
From the point of view of the microcontroller, the whole system looks like a single device with several addressable sensors: the microcontroller
activates one epc120 element and fetches the results after a predefined time.
In the circuit in Figure 5, the LED current is defined by a common current source in the I
LED
line. The resistor R
LED
limits the current through the
LED and is not needed in non-safety applications. If such a resistor is inserted, a failure mode can be detected, if more than one LED is active
due to a short circuit or a failure in the epc100. It is also possible to have a common voltage supply and to generate the LED current by a
resistor.
© 2011 ESPROS Photonics Corporation
Characteristics subject to change without notice
7
Datasheet epc12x - V2.1
www.espros.ch
100nF
PD
LED
PD
LED
PD
LED
50Ω
epc120
epc120
epc120
Bus Termination
EPC [ ESPROS PHOTONICS CORP ]
