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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.

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

By James Jowett

By James Jowett

Automation Engineer

Posted on Dec 16, 2019

By James Jowett

Automation Engineer

Posted on Dec 16, 2019

RealPars is the world's largest online learning platform for automation engineers.

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