Installation manual

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Verify Network Voltages
It needs to be understood that DeviceNet is actually a three wire Differential Voltage
network communication is accomplished by switching the CAN-H (White wire) and
CAN-L (Blue wire) signals relative to the V- line ( Black Wire ). The CAN-H swings
between 2.5 VDC (Recessive State) and 4.0 VDC (Dominant State) while the CAN-L
swings between 1.5 VDC (Dominant State) and 2.5 VDC (Recessive State)
Without a network master connected to the DeviceNet, the CAN-H and CAN-L lines
should read between 2.5 VDC and 3.0 VDC relative to V- and the voltages should be
identical. (Recessive State). Measure these voltages right at the SDN scanner. Use a
voltmeter in DC mode.
With a network master connected and polling the network,
the CAN-H to V- voltage
will be around +3.2 VDC. The CAN-L to V- voltage will be around 2.4 VDC. The
reason these values appear a little different than the ranges shown on the scope trace, is
that the signals are switching, which slightly affects the DC value being read by the
VOM.
If Can-H to V- and Can_L to V- are too low; less than 2.5 V dc and 2.0 V dc respectively
the issue is probably a bad transceiver or bad wiring. To find a bad transceiver remove
one node at a time measuring Can-H and Can-L to V- each time a device is removed.
To check a transceiver (rough test) with everything removed from a device use an ohm
meter to measure resistance between V+ and Can-H V+ and Can-L V- and Can-H V- and
Can-L. These impedances should all be greater than 1 M ohm.
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