Detcon 1640-N4X - Manual (Page 5)

1640-N4X
1640-N4X Instruction Manual Rev. 0.0 Page 1 of 28
1.0 Introduction
The Detcon Model 1640 is specifically designed to serve as a host monitoring and control unit for networks of
gas detection sensors as well as a wide range of other field devices. The NEMA 4X rated enclosure is rain
tight and suitable for mounting in outdoor locations that are deemed electrically non-hazardous environments.
The 1640 Controller is programmed as a Modbus™ master with the capabilities to monitor up to 32 Sensors or
Devices. The unit is capable of monitoring both serial and/or analog Sensors or Devices. Serial devices can
be wired directly to the RS-485 Modbus™. 4-20mA analog devices are monitored via the use of Detcon’s
DA4 Modules.
1.1 Serial Sensors (RS-485)
One method of integration commonly used in industrial applications is the RS-485 serial communications
network, or Modbus™ (Figure 1). RS-485 serial communication is used for multipoint communications and is
a popular choice due to ease of wiring installation. The 1640 is capable of monitoring up to 32 serial devices.
Advantages of using RS-485 serial communication
:
¾
Inexpensive method allowing multiple devices to communicate over a single twisted pair of wires.
¾ More data/information can be sent beyond the simple 4-20mA signal.
¾ Transceiver communication up to 4,000 feet without using repeaters.
¾ Highly resistant to induced noise when proper cable and terminations are used.
¾ Two-way (bi-directional), half-duplex, data bus communication consisting of multiple transmitter and
receiver combinations.
Most Units use the RS-485 master/slave architecture for multiple device communication. Each slave unit has
a unique address and responds to data packets generated by the master. The master periodically polls all
connected slave units.
The protocol used by Detcon for the RS-485 communications is the Modbus
™ RTU, which is compatible with
most PLC’s, MMI’s, and distributed control Units. The Modbus ™ RTU protocol is standard and allows for a
maximum of 32 sensors and/or field devices to be used in this configuration.
Typical Sensors
1 2
31 32
Model 1640-N4X
Gas Detection / Alarm System
Figure 1 RS-485 Network Configuration