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FC motor / VLT 2800 response time
The update time via the PROFIBUS connection can
be divided in two parts:
1) The communication time, which is the time it takes
to transmit data from the master to the slave (FC
motor / VLT 2800 with PROFIBUS), and 2) the
internal update time, which is the time it takes to
transmit data between the FC motor / VLT 2800
control card and the PROFIBUS.
System update time
The system update time is the time it takes to
update all the slaves in the network when using
cyclical communication. The drawing below shows
the value which is obtainable in theory at 2 input
and 2 output bytes.
MG.90.A2.02 – VLT is a registered Danfoss trademark
FCM 300 PROFIBUS / VLT 2800 PROFIBUS
Communication time (t
) depends on the actual
com
transmission speed (baudrate) and the type of master
in use. The minimum obtainable communication time
with the FC motor / VLT 2800 with PROFIBUS is
approx. 100 µsec per slave, when using DP
communication with 4 bytes of data (PPO type 3) at 3
Mbaud. More data or lower transmission speed will
increase the communication time.
The internal update time (t
data in question as there are different channels for the
data transfer where time critical data e.g. control
word has highest priority. The internal update time for
the different types of data are stated below.
Data
Control word/Main reference
(part of PPO)
Status word/Actual output frequency
(part of PPO)
Parameter read (PCD 1-8)
Parameter write (PCD 1-2)
Parameter write (PCD 3-4)
Parameter write (PCD 5-8)
Parameter read (PCV)
Parameter write (PCV)
) depends on the type of
int
Update
time, t
int
42 msec
40 msec
40 msec
160 msec
320 msec
640 msec
41 msec
40 msec
15
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