2
INTRODUCTION
The LCT-485 is an RS-485 network interface module for the ExTemp infrared temperature
sensor.
This unit, when connected on the safe side of an Intrinsically Safe isolator or barrier, allows
the measured temperature to be read from the ExTemp sensor via the open Modbus RTU
protocol. The sensor’s configuration parameters may also be examined and changed.
Each LCT-485 unit allows communication with one ExTemp sensor. The chosen isolator or
barrier must be compatible with the transmission of digital data superimposed over an
analogue 4-20 mA signal. This allows the LCT-485 to communicate digitally with the ExTemp.
The LCT-485 is a Slave device; up to 224 devices may be connected to a third-party Modbus
Master.
IMPORTANT INFORMATION FOR USE:
The LCT-485 is not suitable for use in a hazardous area. It MUST ONLY be connected in the
safe area, and protected by a suitable Intrinsically Safe isolator or barrier.
Do not attempt to repair a faulty unit. Contact the vendor to arrange a return.
MODEL NUMBERS
LCT-485
RS-485 network interface module for ExTemp sensor
SPECIFICATIONS
Mounting
DIN rail (35 mm)
Communications
Isolated RS-485 Modbus RTU Slave
Dimensions
114(d) x 18(w) x 107(h) mm approx
Connections
Screw terminals for RS-485, power, and sensor loop
(suitable for conductors 0.2 to 2.5 mm²)
Supply voltage
24 V DC (6 V DC min / 28 V DC max)
Max current draw
50 mA
Baud rate
1200 bps to 57600 bps, detected automatically
Bit format
Parity: Odd / Even / None
Stop bits: 1 or 2
Ambient temperature
-20°C to 70°C
Loop resistor
270 Ω, built-in
EMC Conformity
BS EN 61326-1:2013, BS EN 61326-2-3:2013
Max. No. of Devices
Up to 224 x LCT-485 Slave devices per Modbus Master
Reply Delay (at 9600 baud)
ExTemp registers: 1 s max
LCT-485 registers:
30 ms (single register)
50 ms (whole address space)
PREPARATION FOR INSTALLATION
Ambient Temperature
This network interface is designed to operate in ambient temperatures from -20°C to 70°C.
Electrical Interference
To minimise electromagnetic interference or ‘noise’, the network interface should be mounted
away from motors, generators and such like.
Wiring
Check the distances between the Intrinsically Safe isolator or barrier, the Modbus Master, and
the LCT-485 network interface. The LCT-485 conforms to industrial standards for
electromagnetic compatibility with up to 30 m cable attached on the RS-485 side, and 30 m
cable on the 4-20 mA side.
Power Supply
Be sure to use a 24 V DC power supply.
