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2TLC172001M0211_A
9.1.3 Optional protection against conducted disturbances
Conducted disturbances may cause problems with the Pluto bus communication. This problem
might be solved by connecting a capacitor between 0V on Pluto Supply and earth.
Please note that this connection is optional. It shall only be tried if there is a problem with the
bus communication!
9.2
Response time over the bus
As default the system works with the Baud rate set to 400 kbit/s and CAN-cycle to 20 ms. CAN-
cycle 20 ms gives 10 ms extra response time for data over the bus (10-40 ms under fault
condition). The records under Technical data for response time over bus etc. are related to this.
To enable the use of longer cable lengths it is possible to change the baud rate to a lower
value, but care must be taken as the bus can be overloaded. To avoid this overload there are
two solutions: either to limit the amount of Pluto units connected on the bus or to increase the
Bus cycle time which also increases the response time.
Note that “Bus cycle time” is individually set for each Pluto unit which means that it is possible
to give variables of some Pluto units, better response times than others. It is also important to
note that if an input in one unit controls an output in another, it is regarding the response time
only relevant where the input is located. If the “Bus cycle time” in the unit with the output is
changed it has no influence on the response time.
The table below is a guideline for selection of bus parameters.
Baud rate
Bus cycle time
100 kb/s
125 kb/s
200 kb/s
250 kb/s
400 kb/s
500 kb/s
800 kb/s
10 ms
3..4
4..6
8..10
12..14
18..25
25..32
32
20 ms
6..8
10..14
20..32
22..32
32
32
32
30 ms
12..18
15..21
20..32
25..32
32
32
32
40 ms
12..23
20..30
28..32
30..32
32
32
32
Possible number of units connected to the bus.
NOTE 1:
The exact value for number of units can not be established since it depends on the
application. If I/Os in a Pluto unit changes state often it produces more CAN telegrams.
NOTE 2:
The prolongation of response time for I/O over the bus is equal with the Bus cycle
time.
0V +24V
4-15nF
K
Q2
I6
IQ10
Q3
IQ11
I7
I5
I3
I1
C H
I2
C L
I0
I4
+24V
ID
0V
IQ17
IQ15
IQ13
IQ12 IQ14 IQ16
Q0
Q1
PLUTO
Capacitor between 0V and earth.
Example of terminal block with capacitor.