Beckhoff AX2040, Сборка, установка, настройка

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10.5.7 Bus cable
To meet ISO 898, a bus cable with a characteristic impedance of 120
W
should be used. The maxi-
mum usable cable length for reliable communication decreases with increasing transmission speed.
As a guide, you can use the following values which we have measured, but they are not to be taken
as assured limits.
General characteristic Specification
Bit rates 125 kbit, 250 kbit, 500 kbit
Distance with larger
bus connections
500 meters at 125 kBaud
250 meters at 250 kBaud
100 meters at 500 kBaud
Number of nodes 64
Signal environment CAN
Modulation Basic bandwidth
Coupling medium DC-coupled differential transmit/receive operation
Isolation 500 V (option: optocoupler on the transceiver's node side)
Typical differential input impe-
dance (recessive state) Shunt C = 5pF
Shunt R = 25K
W
(power on)
Min. differential input impe-
dance (recessive state)
Shunt C = 24pF + 36 pF/m of the permanently attached stub cable
Shunt R = 20K
W
Absolute max.
voltage range
-25 V to +18 V (CAN_H, CAN_L)
The voltages for CAN_H and CAN_L refer to the ground pin of the
transceiver. The voltage is higher than that on the V-terminal by
the amount of the forward voltage drop of the Schottky diode. This
voltage drop must be < 0.6V.
Grounding:
The DeviceNet network must only be grounded at one point, to avoid ground loops. The circuitry for
the physical layer in all devices are referenced to the V-bus signal. The ground connection is made
via the power supply for the bus system. The current flowing between V- and ground must not flow
through any device other than the power supply.
Bus topology:
The DeviceNet medium utilizes a linear bus topology. Termination resistors are required at each
end of the connecting cable. Stub cables are permitted up to a length of 6 meters, so that at least
one node can be connected.
Termination resistors:
DeviceNet requires a termination at each end of the connecting cable.
These resistors must meet the following requirements: 120
W
, 1% metal-film, 1/4 W
104 AX2040/2070 Product Manual
Expansion Cards
06/2007
BECKHOFF