Practical Industrial Data Networks:Design, Installation and ...

AS-interface (AS-i) overview 147103.62.50.502bluebrown410Figure 11.2Cross-section of AS-i cable (mm)Each slave is permitted to draw a maximum of 65mA from the 30 V DC-power supply.If devices require more than this, separate supplies must be provided for each device.With a total of 31 slaves drawing 65 mA, a total limit of 2 A has been established toprevent excessive voltage drop over the 100 m permitted network length. A 16 AWGcable is specified to insure this condition. If this limitation on power drawn from the(yellow) signal cable is a problem, then a second (black) cable, identical in dimensions tothe yellow cable, can be used in parallel for power distribution only.The slave (or field) modules are available in four configurations:• Input modules for 2- and 3-wire DC sensors or contact closure• Output modules for actuators• Input/output (I/O) modules for dual purpose applications• Field connection modules for direct connection to AS-i compatible devices• 12-bit analog to digital converterThe original AS-i specification (V2) allowed for 31 devices per segment of cable, witha total of 124 digital inputs and 124 digital outputs that is, a total of 248 I/O points. Thelatest specification, V2.1, allows for 62 devices, resulting in 248 inputs and 186 outputs, atotal of 434 I/O points. With the latest specification, even 12-bit A to D converters can beread over 5 cycles.A unique design allows the field modules to be connected directly into the bus whilemaintaining network integrity. The field module is composed of an upper and lowersection, secured together once the cable is inserted. Specially designed contact pointspierce the self-sealing cable providing bus access to the I/O points and/or continuation ofthe network. True to the modular design concept, two types of lower sections and three