M2D-Laser-Scanner with Ethernet-Interface
Manual
HB-M2D-Ethernet-E
Page 5 of 39
www.MElsensor.com
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The M2DFL-scanner requires only 4 wires for transmission of data: Tx-; Tx+; Rx- and Rx+. Standard CAT-5e or
CAT-6 cables have 8 wires organized in 4 pairs. For remote power feed, the remaining 4 wires can be used to
supply power to the unit. This wiring will not be according to standard 802.3af
Power over Ethernet
(PoE), but
when adapters* were carefully designed, it will work without problems.
CAT-5e specification for Twisted-Pair-Network-cables requires twisted leads with 100 Ohms Impedance and
shielded cable. Use always cables specified CAT-5e or better!
When a “switch” is used to connect the M2DFL-scanner to the PC, straight (1:1 wired) Ethernet-cables are to be
used. When connected the M2DFL-scanner directly to the network card in the PC, a cross-wired Ethernet-cable
needs to be used. Ethernet Switches should provide „auto-sense“. This means, the unit automatically detects
signal polarity.
The Ethernet electronic system provides two possibilities to make the Ethernet connection:
o
RJ-45 connector at the top cover
o
Dsub-25 pin connector
Both connections will provide the same function.
Both connections can
never
be used in parallel .
When the connection is made at the RJ-45 connector, no Ethernet cable must be connected at the D-Sub-25 pin
connector. Leaving the Ethernet cable hanging “open” from the D-Sub-connector, will cause problems.
The electric waves in the cable are reflected at the open cable end. Depending on the length of the open cable
end, the reflected waves phase shifts. The overlapping of the origin waves and the reflected wave creates a
“chaos”. Overlapping the origin and reflected waves makes the voltage on the cable vary over the location in the
cable – see drawing below!
When the distance of the open cable end is a quarter of the signal wavelength, the signal voltage is zero.
This is the reason, why the RJ-45 connector
will not work
when a open end of the Ethernet cable is hanging at the
D-sub connector. “Open” means: physically unconnected cable end.
The drawing illustrates the voltage over the cable situation.
The small flash (symbol for a short circuit) is the location where the RJ-45 connector is located.
The rule:
a)
when an Ethernet cable is present at the D-Sub connector, only this cable should be used.
Do not use the RJ-45 connector.
b) When
no
other Ethernet cable is at the D-Sub connector, the RJ-45 connector shall be
used to connect the Ethernet cable.
* these adapters are available on request!
