AS-i Bus Actuation0 pages

AS-i Bus System

AS-i (actuator sensor interface) offers many of the
benefits of more complex and costly bus systems, but
does it at a substantially lower cost and with greater
simplicity. The AS-i is ideally suited for controlling valves,
actuators and many other field devices in your processing
application. This interface can be used for stand-alone
process control, or it can be used together with a
higher level bus control system. AS-i does not compete
with higher level bus systems; it should be seen as a
complimentary system that offers low cost, reliable
device control for binary and analog devices. Reliability,
simplicity and interoperability make AS-i a cost effective
connection/control solution, particularly where low
installation costs are imperative. A pair of wires, which
handles power and communications, is used to control
the network by means of “chaining” the actuators with
the PLC. Each actuator (or device) will then have its
own unique address within the system and only that
device with the proper address will respond to system
commands. AS-i is best known for its yellow flat cable,
which is pierced by insulation displacement connectors
so that the expense of tees and complex connectors
is avoided. Devices are simply clamped onto the cable.

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Digital signals are encoded on this cable in a
sinusoidal signal, which has a very narrow frequency
bandwidth. Filtering, which is distributed through the
network, rejects all extraneous frequencies, and, in
this way, AS-i can be operated in electrically noisy
environments without experiencing transmission
errors. The yellow flat cable carries low current (30
VDC) for input devices as well as the AS-i signal.
If power for outputs (such as energizing relays) is
required, an additional black flat cable is available.
Standard networking is capable of 62 units with
a distance up to 100 meters, and a cycle time of
5 ms. A maximum of 300 meters is achieved by
installing repeaters. This system also responds
well with products from other manufacturers, by
installing a gateway to “translate” the commands of
higher level networks. This allows an existing system
to be expanded simply by using the AS-i networking
system. There are various wiring structures that can
be used with this system such as the star, the ring,
the branch, and the tree, etc. All are practiced and
acceptable, but the loop has a distinguished property;
if there were a “break” in the network cable the units
would still cycle and the master would detect the loss
of a node. This feature is unique to the ring structure.

ASAHI/AMERICA

Rev. G 6-14