Dupline operating principle. Channel Generator. Transmitters. The 2-wire cable. Transmission of analog signals, страница 4

The robustness of Dupline is also reflected in the non-restrictive cable demands. A non-shielded twisted pair of cables is recommended, but many Dupline networks have been implemented on non-twisted cables without any problems. Large cost-savings have been achieved in Dupline installations where existing cable has been used.

·  Free topology

There are no restrictions for the routing of the Dupline cable. Line-, star-, ring- or combination-topologies can be implemented. A branch can be made at any point in the system and there is no restriction on the length except for the limitation in total transmission distance. Free topology is an important feature for e.g. alarm/security- and building automation- applications, since the ”routing” of gangways, stairs and rooms in a building represents a ”free topology”.

·  Bus-powered products

Some Dupline input modules, light switches and sensors, are powered via the bus. These components are typically positioned outside installation cabinets, where power is not available or difficult to access. A typical use of bus-powered components is gathering of alarm signals that are widely distributed in a building, factory hall or along a conveyor belt, e.g. in a mine. No power is available in the individual points, and bus-powered components are the only solution.

Interfacing Dupline to the control level

The basic peer-to-peer operation of Dupline described earlier can be used for simple wire-replacement solutions where no PLC or PC is involved. Up to 128 signals can be transferred point-to-point on the same two wires over long distances.

The most important function of Dupline, however, is to operate as remote I/O system for PLCs and  PC-based SCADA systems, or as sub-system for other fieldbuses, in applications where the key characteristics of Dupline match the application requirements. In order to accommodate this, a range of Serial Interfaces (RS232, RS485) and Fieldbus Gateways have been made available:

General-purpose serial interface

This product is a Channel Generator with built-in serial RS232- and RS485- interface ports. It operates as  MODBUS slave and is thereby compatible with many PLC protocols. Up to 32 Dupline networks can be linked to the same MODBUS master, which can either be a PLC or PC.

Fieldbus gateways

Gateways between Dupline and the fieldbuses Profibus-DP, DeviceNet, LON and Ethernet are available. The Dupline gateway, which also performs the function of carrier signal generator, always operates as one address (node) in the relevant device level fieldbus. This means that several Dupline systems can be linked together via a high level fieldbus.

Interfacing Dupline to the process

The Dupline field modules used to physically interface Dupline to the process can be divided into the following categories:

·  Modular digital I/O-modules

Interfaces between Dupline and various types of digital sensors and actuators

·  Modular analogue I/O-modules

Interfaces between Dupline and various types of analogue sensors

·  Digital sensors with Dupline integrated

Bus-powered units like inductive sensors, PIR sensor, magnet proximity sensors and lightswitches

·  Analogue sensors with Dupline integrated

Bus-powered temperature sensor

·  Central units with integrated control functions

Smart house controller, temperature controller

·  Other devices

Repeater, text-displays, panel meters, infrared remote control units, dimmers

App. A

Dupline ASIC-based transmitter

 

App. B

Channel Generator Output Stage

(The second circuit from the top. The third one is the pull-down detection)