Detcon 880S-N1R - Manual (Page 5)

880-N1R
880-N1R Instruction Manual Rev. 0.0 Page 1 of 38
1.0 Introduction
The standard Detcon Model 880 is a PLC based graphic control system specifically designed to serve as a host
monitoring and control system for networks of gas detection sensors as well as a wide range of other field
devices. The main unit is programmed as a Modbus master and is available in two versions: Serial (Model
880S-N1R) and Analog (Model 880A-N1R). Both are fully Field configurable and are made to be mounted in
a 19” indoor rack mount cabinet or enclosure.
The Serial unit (Model 880S-N1R) is designed to monitor up to 32 serial field devices, while the Analog
version (880A-N1R) can monitor up to 72 analog devices via Detcon’s DA4 Modules. The unit features a
color touch screen that graphically displays the status of each device, provides three fully programmable
“Banks” of alarm outputs, and provides the ability to log alarm events to a USB Drive. The use of standard
industrial components makes the Detcon Model 880 an easy and practical choice when configuring point-to-
point monitoring and data acquisition. The system can also be used for remote monitoring simply by adding
the 880 Remote Display Unit.
1.1 Serial Systems (RS-485)
Another 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.
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 systems 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.
Typical Sensors
1 2
31 32
ON / OFF
NO COMM
POWER ALARM 1
ALARM 3
ALARM 2
FAULT
Figure 1 RS-485 Network Configuration
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 systems. The Modbus ™ RTU protocol is standard and allows for
a maximum of 32 sensors and/or field devices to be used in this configuration.