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MICRONOR AG
MR340-1 DIN Rail Module Controller
Page 67 of 74
Two light beams are generated by two VCSEL diodes, emitting at 850nm and 980nm. The
light of the two VCSEL diodes is combined using an optical dichroic beam splitter. The two
wavelengths are guided by the optical fiber as parallel information.
Since VCSEL (Vertical Cavity Surface Emitting
Laser) diodes are indeed laser diodes, they
must be electronically stabilized. In the block
diagram, this is depicted within the “VCSEL
Driver” block. A small portion of the emitted
light is measured with an integral
photodiode. The photodiode current is
stabilized to a constant value. Thus, a
constant optical output is maintained.
The micro controller has full control over the
ON/OFF state and the power level of the
VCSEL diodes. During manufacturing, the
optical power level is calibrated to the
desired value. Within ZAPPY® software this level is accessible via Modbus commands 0x144
and 0x145.
The receiver is comprised of a dichroic beam splitter which separates the two wavelengths.
The light of each wavelength is converted into an electrical current by photo diode 1 and
photo diode 2.
The sensor modulates the light accurately.
The scope picture shows the optical analog
signal following a triangular shape as the
encoder disk is blocking the beam
gradually.
The lower two scope traces show the
quadrature output after passing through
the Schmitt trigger circuit.
The microprocessor main function is to supervise the incoming optical signal, regulate the
amplitude and perform other plausibility tests. Based on these tests status codes of various
types are generated.