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What is AS-Interface?
In
this article, you'll learn about what AS-Interface is, and how you can use
it.

3

The AS-Interface is usually shortened to AS-i, and its full title is
Actuator-Sensor
Interface.

It is a simple networking system for devices found out in the
field.

AS-Interface is an intelligent cabling system that is designed to replace the
discrete wires linking actuators and sensors with a Programmable Logic
Controller or other controlling device.

AS-Interface Master-Slave System

One of the benefits of using AS-Interface products is that it uses a simple
cable system that is easy to wire and easy to operate.

It is built for simple device exchanges that operate in a
Master-Slave system, where a single AS Interface
Master can exchange input and output data with up to 62 AS-Interface
Slave devices, with each AS-Interface Slave device being able to transfer up to
four inputs and four outputs at any time, either analog or
digital.

AS-Interface Devices vs. Traditional Devices

The cost saving implications for AS-Interface devices, along with the
simplicity for location and wiring benefits means that they are an extremely
attractive alternative to more traditional, complex devices.

They are also fast. Very fast.

In fact, the response time of a Slave device on an AS-Interface is typically
much quicker than a single data acquisition cycle of a PLC.

The transmissions between a Master and a Slave device on an AS-Interface are
predefined and cyclic, meaning that determining the time it takes for an output
to switch on or off can be easily calculated with great accuracy.

This can be extremely useful for applications where timing is of the
essence.

No Need for Configurations!

There is a simplicity to AS-Interface devices that makes it stand out from
the competition.

There is no need to program Master or Slave configurations, and no parameters
to set.

All that is required is that the device ID is recognized by the AS-Interface
Master.

AS-Interface
Components

1) AS-Interface
Master

A system built using the AS-Interface typically has three components.

Firstly there is the AS-Interface Master, the head of the network. The
AS-Interface Master provides the connection to the higher-level control
system.

It organizes all of the data traffic on the line and is responsible for
parameter setting, diagnostics, and monitoring.

2) AS-Interface
Cable

Next up is the AS-Interface cable. There are two cables required in an
AS-Interface system;

– a yellow cable to carry the power and data to
sensors

– a black cable to carry 24 volts to
actuators

There is no fiddly wiring to do though because these use a special piercing
technology which means that the nodes can be literally snapped onto the cable,
at any point.

3) AS-Interface Power Supply
Unit

Finally, we have a power supply unit.

The unit provides a constant regulated 30 volts DC to supply power to the
Master and the Slave devices.

It also works as a data de-coupler which means it separates the power and
data as they are both simultaneously transferred along the
cable.

They can be connected directly to a Programmable Logic Controller via an AS
Interface Master in the PLC rack.

Alternatively, they can be part of a larger subsystem and connected to a PLC
via Fieldbus connection, such as Profinet or Profibus.

AS-Interface Range

The range of a typical AS-Interface device is around 100m, or up to 600m
with repeaters and extension plugs, making it extremely useful remote
locations.

All of this, and we’ve just scratched the surface!

AS-I Safety at Work

AS-Interface can also be used in safety systems.
ASIsafe or AS-I Safety at Work is a
standard AS-Interface network, but with special ASIsafe components.

An AS-i bus system is TÜV-certified up to Performance Level e, or PLe or
Safety Integrity Level 3, or SIL 3.

An advantage of ASIsafe is that components can be connected directly to the
AS-Interface network, such as Emergency Stop pushbuttons, or safety door
contacts.

AS-i Power 24V

Then we have AS-i Power 24V. We know that the AS-Interface
can carry both power and data on the same cable, so you might be wondering what
AS-i Power 24V does differently.

Well, what AS-i Power 24V does is utilize standard 24-volt power supplies,
meaning that the 30 volts DC power supplies are not needed. This type of device
works well in small systems because the distance the power and data can go is
reduced to around 50m, but can maximize cost savings by not having an additional
power supply to purchase, and the required space to house it.

Summary

So, let’s try and summarize what we’ve learned today.

– AS-Interface is a simple communications
protocol which is very simple to set up and use.

– An AS-Interface Master can have up to 62 Slave
devices, such as an actuator or sensor, attached to it.

– The AS-Interface Master can then communicate
over a Fieldbus connection to the higher-level controller, most likely in our
case, a PLC, or Programmable Logic Controller.

– They are able to transmit either digital or
analog signals, up to four inputs and four outputs. The standard distance that
the power and data can travel is 100 meters or up to 600 meters with repeaters
and extension plugs.

– The AS-Interface can carry power and data on
one cable, which means less cables need to be wired out in the field. Also,
special piercing technology means that they are able to connect, the devices
just need to be snapped onto the flat cables.

– They are low cost, which means they are a
viable alternative to traditional devices, which can be more complex to wire up
because they need separate power and control cabling.

– Finally, we mentioned ASIsafe and AS-i Power
24V, so all in all, the AS-Interface is simple and versatile!

– Getting the setup of the AS-Interface
configuration correct is also extremely simple. All that is required is that the
AS-Interface Master be configured with the ID of each node device, then the
Master sorts all of the parameters and everything else out.

That’s it for this article!

I hope you have enjoyed learning about AS-Interface. Catch us next time for
another informative article.

Thank you so much for watching, sharing, and encouraging this community with
your voice.

Got a friend, client, or colleague who could use some of this information?
Please share this article.

The RealPars Team

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By James Jowett

Automation Engineer

Posted on Dec 16, 2019

By James Jowett

Automation Engineer

Posted on Dec 16, 2019

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