M
M
F
F
W
W
-
-
Z
Z
D
D
-
-
B
B
A
A
-
-
U
U
K
K
-
-
0
0
0
0
6
6
P
P
a
a
g
g
e
e
6
6
o
o
f
f
2
2
4
4
A system from the MFW product family
In the event of
transmission faults
, the system detects the faulty communication and reports it via LED
and relay contact both in the central station and in the respective substation. In addition, a binary
contact can be used to signal availability of all connected stations at any point of the telecontrol system,
if appropriate I/O modules are used. If a serial interface is used, this information can also be evaluated
via this interface. In case of a transmission fault the input and output values of a defective station are
frozen in the state of the last valid transmission. After the cause of the fault has been rectified, normal
operation is resumed automatically.
3.2 2 wire line transmission medium
Any standard signal cable is suitable as transmission medium. The two wire system can be configured
as a line, star or branch system. However the maximum loop resistance, that results from the sum of
the resistance of both individual wires, may not be exceeded. The interference immunity of the 2 wire
data transfer is very high. To avoid undesirable interference through induction of interference pulses
from wires laid parallel to each other, the distance between wire pairs should be selected to as large as
possible in multi-wire lines. The use of cables twisted in pairs is the best solution for this.
To match the MFW to each application (type and length of transmission cable and interference impact)
the transmission level of the input damping of the 2 wire modem can be adjusted by means of a DIP
switch (
“
” section).
The
system transmission rate
(cycle time) depends on the system configuration and the frequency of
the almost simultaneously changing input states. The cycle time is approximately 1 second plus
approximately 250 ms per substation.
The MFW always transmits the current inputs status at the time of query. The minimum pulse
width/pause, that is required for the secure transmission of a status change, depends on the above
mentioned cycle time. Inputs and outputs 1 - 4 of the digital modules can be used for safe transfer of
short pulses. This ensures that the pulses are reliably transmitted even in the case of longer cycle
times.
The MFW data transfer is made via the telegrams with test information. The basic modules reliably
recognise faulty telegrams and reject them. Any faults delay transmission or interrupt the connection
but don’t lead to incorrect output values.
3.3 Inputs and outputs
3.3.1 Digital inputs
Digital inputs are made with the basic or expansion modules. Each module has 8 inputs which can be
switched via DIP switch or parameterisation via PC to one of the following 4 input types:
Static binary input
The current input status is recorded for each transmission. The status must be present longer than the
cycle time to be sure that the status change is transferred.
Binary input saved statically (only for substation basic modules)
Change to a digital input of the substation’s basic module is recorded and saved in a substation until the
master register’s and confirms the change. Only after this confirmation is it possible to record a new
status on the digital input. All status changes that appear in the meantime are not registered.
