4
4
C
C
H
H
A
A
N
N
N
N
E
E
L
L
A
A
N
N
A
A
L
L
O
O
G
G
U
U
E
E
T
T
R
R
A
A
N
N
S
S
M
M
I
I
T
T
T
T
E
E
R
R
8
8
O
O
F
F
3
3
0
0
1
1
2
2
0
0
-
-
1
1
8
8
8
8
-
-
1
1
2
2
T
T
Y
Y
P
P
E
E
S
S
I
I
L
L
B
B
U
U
S
S
-
-
T
T
X
X
4
4
A
A
(
(
G
G
)
)
U
U
S
S
E
E
R
R
'
'
S
S
M
M
A
A
N
N
U
U
A
A
L
L
I
I
s
s
s
s
u
u
e
e
:
:
0
0
5
5
Photograph 2 Access to console port and programming switch
The black four pin console port connector and the red programming switch are located
behind the lower right corner of the front panel label.
4 THEORY OF OPERATION
The four channel analogue transmitter takes four analogue inputs and transmits them onto
the connected SILBUS network using either the ANALINK or FASTLINK protocols. Each
analogue channel is converted to a sixteen bit (Fastlink) or eight bit (Analink) value ready
for transmission on the configured SILBUS channel. The transmission protocol can be
independently selected for each analogue input. See Austdac document 120-009-10 for a
more detailed description of SILBUS communications.
If the Analink transmission protocol is selected then the input analogue is transmitted as a
stream of 255 on / off bits preceded by a single bit that is asserted if a fault alarm has not
been detected i.e. 4mA offset is present.
If the Fastlink transmission protocol is selected then the input analogue including the 4mA
offset is converted to a 16 bit binary value and transmitted along with a four bit checksum.
In effect the 4mA offset is transmitted to the receiver(s) where the decision in relation to a
4-20mA signal fault should be made. Faults are included in the SILBUS-TX4A(G) to provide
compatibility with the Analink protocol and to provide local warning of a signal fault.
Each analogue input is monitored for under range signal level by comparing it to an input
independent under range fault level; if the input signal is below this configured level then a
