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
R
R
E
E
C
C
E
E
I
I
V
V
E
E
R
R
7
7
O
O
F
F
2
2
4
4
1
1
2
2
0
0
-
-
2
2
0
0
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
-
-
R
R
X
X
4
4
A
A
U
U
S
S
E
E
R
R
M
M
A
A
N
N
U
U
A
A
L
L
I
I
s
s
s
s
u
u
e
e
:
:
0
0
4
4
as a digital signal on any valid configurable SILBUS channel address. Compliance is when
the SILBUS-RX4A can generate sufficient voltage to force the required signal current into
the connected load. Loss of compliance can occur when the input resistance of the load
and the signal cable resistance are too high for the required output signal current or when
the SILBUS-RX4A power supply voltage is reduced because of resistance in the power
supply cable. The following formula calculates the maximum load resistance given the
SILBUS-RX4A power supply voltage.
R
L(MAX)
= (U
i
– 3.8) / 0.02
Where R
L
is the maximum load resistance and U
i
is the voltage at the power supply
terminals of the Analogue receiver.
It is important that all installations be checked for output signal compliance using the above
formula to ensure correct functionality. Assuming a power supply voltage of 12.6 volts the
maximum R
L
is 440
Ω. If the power supply voltage is at the operating minimum of 7.5 volts
the maximum RL is
185Ω. If the analogue receiver is at the end of long power supply
cables then the power supply voltage will alter as a function of cable resistance and
influence the compliance of the SILBUS-RX4A.
Should the analogue receiver receive an ANALINK or FASTLINK message that indicates
that the analogue transmitter sending the message has detected an out of range input i.e.
less than 4mA, then the SILBUS-RX4A will output less than 4mA as well, to indicate to the
final monitoring equipment e.g. PLC that the entire signal path from the sensor has a fault
that should be rectified.
Should the analogue receiver loose SILBUS communications with an analogue transmitter
or source device transmitting using the FASTLINK protocol or if the FASTLINK marker fails
or if FASTLINK CRC errors occur, then the SILBUS-RX4A can be configured to carry out
one of the following actions using the FSTFLT command;
•
Leave the analogue output at the last correctly received value until communications
are re-established or,
•
Drive the analogue output(s) to zero (0mA) to indicate an open faulty loop or,
•
Drive the analogue output(s) to full scale (20mA).
Should the SILBUS be experiencing CRC errors due to noise interference then the FSTFLT
command can be used to configure the number of consecutive CRC errors that must be
received before the failsafe action is implemented. The failsafe action can be individually
configured for the four analogue output channels. The selection of failsafe modes is not
available when the ANALINK protocol is selected.
A common alarm or quality digital output can be configured to transmit on any valid SILBUS
address whenever something is wrong with an ANALINK or FASTLINK received message.
Whenever the FASTLINK protocol is selected a FASTLINK marker channel or SILBUS
channel must be specified. The FASTLINK marker is generated by the Dual Port Channel
Generator type GSW1.
