ABB AC 800M, User Manual

Page: 54 / 118

Calculation of transmission delay time TTD Section 2 Transmission Technology
54 3BDS009029R5001 B
Calculation of transmission delay time T
TD
In case of a large PROFIBUS network with numerous optical link modules and long
lines, allowance needs to be made when setting the monitoring times for the delay
caused by network components and lines (transmission delay). This involves
determining the transmission delay time (T
TD
): The transmission delay time is the
maximum time which elapses when transmitting a telegram on the transmission
medium from transmitter to receiver.
If the planning software being used to configure the PROFIBUS network does not
support the PROFIBUS parameter T
TD
, then the two times min. T
SDR
and max.
T
SDR
are to be extended instead by 2 x T
TD
(reaction time of responder is extended
by the outward and return transmission delay time).
The first step is to determine the transmission link with the longest transfer time
between telegram transmitter and receiver. No allowance is made for PROFIBUS
users which do not communicate with one another (for example DP slave with DP
slave).
Indicators of long transfer times are:
• Long optical fiber or copper lines
• High cascading level of active components
In connection with the AC 800M and CI854(A) the T
TD
delay time shall be added
to the slot time (TSL) in the CI854(A) settings tab.