P54x/EN SC/La4 SCADA Communications
(SC) 13-6
MiCOM P543, P544, P545 & P546
SC
It is possible to use the product’s field voltage output (48 V DC) to bias the bus using values
of 2.2 kΩ (½W) as bias resistors instead of the 180 Ω resistors shown in the above diagram.
Note the following warnings apply:
It is extremely important that the 120 Ω termination resistors are fitted. Failure to do so
will result in an excessive bias voltage that may damage the devices connected to the
bus.
As the field voltage is much higher than that required, ALSTOM Grid cannot assume
responsibility for any damage that may occur to a device connected to the network as a
result of incorrect application of this voltage.
Ensure that the field voltage is not being used for other purposes (i.e. powering logic
inputs) as this may cause noise to be passed to the communication network.
1.2.2.5 K-Bus connection
K-Bus i
s a robust signaling method based on EIA(RS)485 voltage levels. K-Bus incorporates
message framing and uses a 64 kbits/s synchronous HDLC protocol with FM0 modulation to
increase speed and security. For this reason is not possible to use a standard EIA(RS)232
to EIA(RS)485 converter to connect with K-Bus devices. Nor is it possible to connect K-Bus
to an EIA(RS)485 computer port. A KITZ protocol converter needs to be employed for this
purpose.
Please consult ALSTOM Grid for information regarding the specification and supply of KITZ
devices.
As K-Bus is implemented on an EIA(RS)485 layer, however the connection details are very
similar to those described in the previous sections and a typical connection arrangement,
incorporating a KITZ, is shown in Figure 2. As with EIA(RS)485, each spur of the K-Bus
twisted p
air wiring can be up to 1000 m in length and have up to 32 relays connected to it.
To Next Page
Loading...
