«+»
«-»
Car battery
Fuse
(1A)
«GND»
Devices Rx
Devices Tx
FLS
Sensors Tx
Sensors Rx
RS232
4
2
3
1
14
7
13
6
12
5
11
4
10
3
9
8
2
1
6
5
4
3
2
1
Figure 50. Connection diagram for fuel level sensor by RS-232 interface to the device
Periodic data output mode must be enabled in the sensor and the network address and data transfer rate
must coincide with those which are programmed in the device itself.
Note:
Some manufacturers of additional devices (FLS, CAN bus adapters, etc.) connected by the RS-232 interface
change the physical meaning of the designations of the TX and RX interface lines. That is why in this connection
these devices do not function, and it is required to reconnect them by swapping the RX and TX contacts.
If there is any doubt which sensor line is Tx and which Rx , it is possible check this with a multimeter in the
voltage measurement mode. The measured voltage on the sensor Tx line which is not connected to the terminal will
be in the range from -5 to -12 V relative to the sensor supply “-”. On the Rx line, the voltage will be close to “0”.
2.12 RS-485 interface connection
The digital interface RS-485 is designed to connect devices transmitting and receiving information via this
interface, for example, fuel level sensors, CAN bus adapter, tachographs, RFID, MODBUS-devices, etc.
As a rule, the interface is used to connect up to 16 digital fuel sensors. It is supposed to use digital LLS-
compatible sensors.
The RS-485 + interface line of the device should be connected to the RS-485 + line of the sensor, usually
designated as "A", and the RS-485 line of the device should be connected to the RS-485 line of the sensor, usually
designated as "B". The RS-485 interface specifications practically do not limit the length of cables on a land vehicle
(100m or more), since the interface is a differential bus and is well protected from the influence of external
interference.
«+»
«-»
Car battery
Fuse
(1А)
«GND»
FLS
Line A
RS485
Line B
FLS
Line A
RS485
Line B
FLS
Line A
RS485
Line B
4
2
3
1
14
7
13
6
12
5
11
4
10
3
9
8
2
1
6
5
4
3
2
1
Figure 51. Connection diagram of fuel level sensors by RS-485 interface
