ABB AC 800M, Руководство пользователя

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PROFIBUS DP/PA Linking Device LD 800P Section 2 Transmission Technology
40 3BDS009029R5001 B
• Telegrams with a variable data field (0 to 244 data bytes and 9 to 11 control
bytes)
• Brief acknowledgement (1 byte)
• Token telegram for bus access control (3 bytes)
With all data transmissions, the parity and block checking of the telegrams is used to
reach a Hamming distance of HD=4, so that up to three errors can be detected with
certainty.
A transmission rate of 31.25 kbit/s results in transmission times of 0.4 to 8.2 ms per
telegram so that per user data byte an average of 0.4 ms and 34 ms is required.
This data transmission rate is sufficient, for example, to serve 10 control loops -
including 10 sensors and 10 actuators respectively - within a control cycle time of
approx. 210 milliseconds.
During the evaluation, it was assumed that only one cyclic value (5 bytes user data)
must be transmitted per device. With each additional value, the minimum cycle time
increases by (5 x 8 bits)/(31.25 kbit/s)
=
1.3 ms.
For a first estimate, the following formula can be used:
cycle time
≥
10 ms * number of devices
+ 10 ms (for acyclic class-2 master services)
+ 1.3 ms (for each additional cyclic value)
PROFIBUS DP/PA Linking Device LD 800P
Linking Devices are needed to connect PROFIBUS DP to PROFIBUS PA and vice
versa. The PROFIBUS master module CI854(A) is designed exclusively for the
connection of PROFIBUS DP nodes in RS485 technology. To link a PROFIBUS DP
line to a PROFIBUS PA line, it is recommended to use the Linking Device LD 800P.
The LD 800P Linking Device converts the physical bus characteristics of the RS
485 interface for PROFIBUS DP into PROFIBUS PA physical bus characteristics
MBP according to IEC 61158-2, enables connected PROFIBUS PA devices to be
supplied with power via the bus, and allows use in hazardous areas if so required.