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December 7, 2017
The need to facilitate the manpower work and reduce the overall wiring costs to video door installer companies have been the main driving forces to evolve the market to two-wire systems. Among all range of different type of systems two-wire systems in the market, DUOX from FERMAX is probably the most advanced two-wire system with most capacities on the market. In fact, Duox is the only full digital tow-non-polarized wires system on the market, which gives it a technological advantage over all other systems. Quicker to install and with no margin for error. Allows all types of possible connections: star, easy chain, distributed. No distributors nor switchers are needed by default and standard installations can be done simply with panel, power supply, line termination and home terminals.
WHY A DUOX FILTER IS NEEDED?
The need to supply panels, terminals and additional devices in the entire installation and at the same time manage to design a communication protocol able to coexist on top of the supply medium is a technical challenge that in the case of DUOX is solved by the use of filters. These filters not only stop the digital signal with commands, audio and video information to attenuate from the low pass filter existing at the output stage of the power supply but also allow at the same time to inject power in the bus whenever is needed. The following pictures shows a simplified schematic of the DUOX filter.
HOW DOES THE FILTER OPERATES?
The DUOX filter operates in dual way depending whether we look at the power supply or data point of view:
b. From the DATA point of view:
HOW TO CONNECT THE FILTER TO THE BUS?
The filter needs to be connected in the following manner:
By following rule above, the connection of two power supplies in parallel to the bus will be avoided.
One could also think on connecting directly from PREV_BUS to PREV_BUS, while this is possible we are adding two set of capacitors in parallel, this reduce the total capacitance and therefore the high pass filter, this in combination with the type of cable and the distance of the wire can affect to the data part of the signal.
HOW TO CONNECT OTHER DUOX DEVICES TO THE BUS
These devices are connected to the bus power supply by means of a couple of diode bridges so they can be supplied by both sides and the higher voltage source will be used for the internal supplied but at least they have to be supplied by one side. The following picture shows a simplified schematic.
b. 2W Regenerator
The two-way regenerator includes an integrated filter and therefore, it needs only a power supply 4830 to operate. By default, the regenerator gives power up to 1.5 Amps to each of the risers B1 and B2 and if selected it can also give power to B, B terminals. This is normally used to supply a panel directly from the 2W regenerator. The following picture shows a simplified schematic.
For the reasons mentioned above, if a bus already powered needs to be connected to any of the bus terminals of the regenerator, that is B1, B2, B or B, it needs to be connected with a PREV_BUS of a filter, as shown in the following picture.
Note that if we connect a powered bus to a powered output somehow, we would be connecting two power supplies in parallel and this is one of the things that needs to be avoided.
In this article we have introduced how the DUOX filter operates along with the different methods of supplying the DUOX bus and also the differences between DUOX interconnecting devices in terms of power supply. We hope that this article has been useful for you and helps you to apply this knowledge to future DUOX installations.
Do not hesitate to get in touch with FERMAX’s After Sales Department if you have any doubt or if you require any further assistance about this device.