Calex LCT-485 Operator's Manual page 4

Intrinsically Safe Isolator or Barrier
LCT-485 must not be connected directly to the ExTemp sensor. It must only be used in
conjunction with either an Intrinsically Safe isolator or zener barrier.
The isolator or barrier must be capable of simultaneously passing an analogue 4-20 mA
signal with a superimposed digital signal such as Frequency Shift Keying (FSK).
Suitable models include:
• Isolator model MTL5541
• Barrier model MTL7706+
These are manufactured by Measurement Technology Ltd (www.mtl-inst.com).
Connections - RS-485 Modbus Network
All the below connections are on the safe side of the Intrinsically Safe isolator or barrier.
Modbus Master
(e.g. PLC, SCADA etc)
Device
#1
Device
#2
Device
#224
* Ensure the distance between each device and the network bus is as short as possible.
Notes
The LCT-485 conforms to industrial standards for electromagnetic compatibility with up to 30
m of RS-485 cable attached. If the network must be run over a longer distance, the use of RS-
485 repeaters is recommended.
Ensure all connections are correct before applying power.
4
RS+
RS-
Signal Ground
LCT-485
11
12
13 & 14
LCT-485
11
12
13 & 14
LCT-485
11
12
13 & 14
120 Ω
*
COM RS- RS+
*
*
*
120 Ω
Junction
Box
Junction
Box
Junction
Box
Junction
Box