Powercom 485
11
Description and operating instuctions
10
VAH
L
E
P
O
W
ER
C
O
M
®
,K
om
.-
N
r.
00
000nn
nnn
0
6P
C
-E
N
-009_
23-
0
9-
20
14.
fm
,
S
tand:
2
3.
09.
2014
If all indications are without fault but communication is nevertheless disturbed
(e.g. no acknowledgement is received, unexpected telegrams), check the moni-
toring times set on the PROFIBUS subscriber devices (e.g. the slot time). For
further details, please consult the description in the PROFIBUS terminal device
documentation.
1.1.11
Instructions for parameterisation
In large PROFIBUS networks with many modules and long line lengths, the trans-
mission delay caused by network components and lines must be taken into ac-
count when setting the monitoring times.
For this purpose determine the transmission delay time TTD:
–
The transmission delay time is the maximum time which elapses for the trans-
mission of a telegram on the transmission medium from the transmitter to the
receiver.
Note
If the project software you are using to configure your PROFIBUS network does
not support the PROFIBUS parameter TTD, increase instead both two times min.
RSDR and max. TSDR by 2 x TTD in each case (the reaction time of the respon-
der is extended by the transmission delay time for the outgoing and return path).
Calculation of the transmission delay time TTD:
–
First of all determine the transmission path with the longest propagation time
between the transmitter and the receiver of a telegram.
–
PROFIBUS subscribers which do not communicate with each other (e.g. DP
slave with DP slave) should not be taken into consideration.
Indications for long transmission times are:
–
Long fiber optic or copper lines.
–
Great cascade depth of active components
–
Delay time of RS 485 lines The delay time is approx. 5
:
s per km line length.
Converted to bit times this gives:
To calculate the line delay time, multiply the maximum line length in km with the
delay time corresponding to the transmission rate as read from the table.
1. The delay time of the VAHLE POWERCOM
®
485 devices is 1.5 bit times.
2. The total transmission delay time is given by the number of modules passed
through from the transmitter of a telegram to the receiver, multiplied by 1.5 bit
times.
Transmission rate in kBit/s
Time delay in tBIT pro km
9,6
0,05
19,2
0,10