Pepperl+Fuchs Blog

What is POWER24 for AS-Interface?

Posted by Tim Cicerchi on Thu, Aug 27, 2015

Even though POWER24 has been around for years, nobody really talks about it.  It is a rarely used and little-known part of the latest specification that allows AS-Interface to run at 24 VDC.  It has taken a while for the right number of components to be designed to the POWER24 specification for it really to be considered useful for most modern-day material handling and assembly applications.

AS-Interface POWER24

You might ask, doesn’t everything already run at 24 V?  The answer is simply, no.  The original AS-Interface specification, which was adopted back in 1994, as well as the current one specifies that the network run at 30 V.  The main reason is because the AS-Interface I/O modules are low-cost devices with no DC-DC converter.  This voltage regulator allows a device to have an input voltage of let’s say 10 V- 30 V and an output at a regulated and steady 24 V to power itself and the sensors attached to the module.  This extra component unnecessarily drives up the cost of I/O modules.  It was decided early in the development of the AS-Interface specification that voltage regulation is done once in the power supply, which provides power to the entire network, and not in every device.

Removing the DC-DC converter simply requires that you start at a higher, 30 V, to account for any voltage drop along the network.  By the end of the network, assuming that you have a lot of cable and current, the voltage will typically still be above 24 V, perfectly fine to run all devices on the network.  A normal, non-POWER24 AS-Interface module has an operating voltage of 26.5 V to 31.6 V.  It can’t operate at 24 V.

An AS-Interface I/O module that is POWER24 has a much wider operating voltage of 18 V to 31.6 V vs. one that isn’t(26.5 V to 31.6 V).  These modules can definitely run at 24 V and far less to account for any voltage drop along the cable run.  If you decide to run everything at 24 V, make sure every device on the network supports POWER24.

POWER24 gateways

An AS-Interface POWER24 gateway is typically one that has built-in decoupling coils and allows for a wide input voltage range.  These coils are what allow both the AS-Interface power and communication to be on the 2-wire cable at the same time.  Putting the coils in the gateway allows you to remove the 30 V AS-Interface power supply that you normally use and replace it with a lower cost, maybe more common, 24 VDC power supply.  These gateways also have other features, like current monitoring, resettable and programmable fuses, ground fault detection, and duplicate address protection.  We have single-network gateways for connection to common industrial busses like EtherNet/IP, Modbus/TCP, PROFINET, and PROFIBUS. There are also gateways with two AS-Interface networks with connection to the same upper-level networks EtherNet/IP, Modbus/TCP, PROFINET, and PROFIBUS to reduce the overhead cost further.

Many gateways also have a built-in safety monitor.  There are POWER24 versions of these, too; however, this feature is less important when using a gateway for safety because many safety I/O modules don’t support POWER24.

Do I have to use a 24 VDC power supply with a POWER24 AS-Interface gateway?

Absolutely not.  Many people still use a 30 V supply, and it is always recommended to use a 30 V supply if you can.  If you do, then you are guaranteed that every AS-Interface certified module will work on the network no matter what.  If you use a 30 V AS-Interface supply with built-in decoupling coils, this will also work.  It is just that in this case, it will use the coils in the gateway and not the internal coils built into the supply.

Can I still run my network 100 m?

No. If you run an AS-Interface network at 24 VDC then you are limited to 50 m.  This length reduction is not because it can’t communicate farther but rather to make sure that voltages at the end of the network are not too low due to the already low starting voltage.

POWER24 modules

The second half of the POWER24 equation is the module.  It was already mentioned that not every AS-Interface module is POWER24 compatible because of the input voltage range.  We have two lines of modules that are compatible:

G11 modules – Available as 4-in, 4-in/4-out, or 8-in versions, these modules connect to AS-Interface using flat cable or M12 quick connects. All I/O is M12 quick disconnect.  Modules are IP69K rated for extremely wet environments.

G10 modules – Available as 2-in, 1-in/1-out, 2-in/1-out, or 2-out versions, these modules connect to AS-Interface using flat cable. I/O is connected using various connector styles and pigtail lengths.

In the end, POWER24 makes installing an AS-Interface network cheaper than ever because of lower cost power supplies and more economically priced AS-Interface gateways.

Questions about AS-Interface? Ask an Expert!


Topics: AS-Interface

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