Dupline operating principle. Channel Generator. Transmitters. The 2-wire cable. Transmission of analog signals, страница 3

·  Flexibility: Multiple digital inputs or outputs can be coded for the same address

The same address can be assigned to several inputs. The bit-value ”1” is transmitted if one or more of the inputs are activated, otherwise the bit-value ”0” is transmitted. This feature provides a high flexibility, e.g. in many building automation applications. When it is desired to control a light from multiple light-switches at various locations, it is simply a question of assigning the same address to the light output and all the relevant switches. This also means that an additional light-switch for control of an existing light can be installed without reconfiguring the system, and an existing light switch can be coded to control a different light simply by changing the address.

When multiple outputs are coded for the same address, they all update the output status according to the bit-value received on that address. This feature can e.g. be used in an alarm monitoring system to display the same alarms at various locations, or it can be used for a LED display panel indicating the status of the lights in a building. Again, this functionality is inherent in Dupline, and no reconfiguration of the entire system is required to make use of it.

·  Easy coding and testing

In most Dupline systems, the pulse-trains have a fixed length of 128 pulses, no matter how many addresses are actually used in the system. This eliminates the need to configure the central unit to output the exact number of used addresses and facilitates future expansions of the installation, since there are usually unused addresses available.

The only configuration required in a basic Dupline system is the coding of an address for each I/O used. The handheld coding unit is plugged into the I/O-module or sensor/actuator, after which the existing addresses can be read and changed if desired. This process is not more complex than dialling a telephone number. The coding unit can also be used to pre-define the status of the outputs in case of loss or short-circuit of the bus-cable.

The bus-powered Dupline test unit is far more user-friendly than the protocol analysers used by many other fieldbuses. It can be connected to the bus at any point at any time, either through the coding plug of an I/O-module or directly to the two wires. The continuous updating of the Dupline outputs enables the test unit to read and display the real-time status of all 128 addresses. Also, the test unit can be used to activate any Dupline address. These functions enable easy testing of the I/O-modules as they are installed, and this can save hours of searching for a faulty wiring in a big network.

·  Noise-immune and robust transmission system

Dupline can operate in environments with heavy electrical noise. The low carrier frequency of 1 kHz enables powerful filtering of the Dupline signal both externally (analogue filtering) and internally in the ASIC (digital filtering). Furthermore, the central unit generating the carrier signal has a high CMRR (Common Mode Rejection Ratio) resulting in high immunity against induced noise provided the two wires are ”floating” (none of them connected to ground potential).

Also due to the low frequency, reflections from open cable endings have no effect on the data transmission when the cable length is less than 2.0 km. The “ringings” on the Dupline carrier signal, after a negative transition, die out before the Channel Generator starts sampling for pull-down pulses. Installation is easier when there is no need to worry about where to install - and where not to install - cable terminations.  For distances longer than 2.0 km, a termination unit is required in the far end of the cable seen from the central unit.