The AS-interfaceField buses PROFIBUS, INTERBUS, CAN, DeviceNet, MODBUS, Lightbus Sensor/actuator...

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Subject to reasonable modifications due to technical advances. Copyright by Pepperl+Fuchs, Printed in Germany

Pepperl+Fuchs Group · Tel.: Germany (6 21) 7 76-0 · USA (2 16) 4 25 35 55 · Singapore 7 79 90 91 · Internet http://www.pepperl-fuchs.com

Figure 1: AS-interface wiring

The AS-interface

PLC / PCPLC / PC

AS-i

Power supply

Power supply

2 wires each fordata andpower supply

Only 2 wires totalfor data andpower supply

Actuators with integratedAS-i chip

Multiple sensorconnection

Actuators with integratedAS-i chip

Multiple sensoractuator connection

MehrfachAktoranschaltung

Isolation switchamplifier

Explosive area

AS-interface replacesthe cable tree

Power supply

Power supply

Subject to reasonable modifcations due to technical advances. Copyright by Pepperl+Fuchs, Printed in Germany

Pepperl+Fuchs Group · Tel.: Germany (6 21) 7 76-0 · USA (2 16) 4 25 35 55 · Singapore 7 75 10 21 · Internet http://www.pepperl-fuchs.com 9

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Figure 2: Network hierarchy

Unshielded, two-wire cable can be used as theconnecting cable. The AS-interface flat cable isparticularly easy and cost-effective: The newinsulation penetration technique allows buselements to be connected quickly, securely andeasily. Due to the self-sealing ability of the AS-interface flat cable, a bus element (slave) can bejust as easily coupled as it can be disconnected.

The AS-interface is a simple bus!

An additional and decisive advantage of the AS-interface is its transparence and simplicity. Itwas specifically designed for the lowesthierarchical level of the network (figure 2).

The AS-interface

Office,laboratorynetworks

Field busesPROFIBUS, INTERBUS, CAN,DeviceNet, MODBUS, Lightbus

Sensor/actuator busesAS-interface

2.1 AS-interface in production andprocessing

It can be seen immediately in figure 1: the wiringfor processing, a production line or a complexmachine is dramatically reduced to only 2 wiresusing the AS-interface. These two wires transferthe data between sensors/actuators and themaster. At the same time, these wires supply thecomponents with power.Up to 124 single sensors and 124 singleactuators or 31 fully programmable AS-interface sensors/actuators can be connectedto one AS-interface branch.


Pepperl+Fuchs Group · Tel.: Germany (6 21) 7 76-0 · USA (2 16) 4 25 35 55 · Singapore 7 75 10 21 · Internet http://www.pepperl-fuchs.com12

The AS-interface

2.2 Basic specifications of the AS interface

Topology: any of: line, star, tree, ring

Number of users: 31 AS-interface slaves, or248 binary elements

Access procedure:master/slave

Addressing: via master usingprogramming device orautomatically whenexchanging

Conductor: Unshielded installationwiring, 2 x 1.5 mm² orAS-interface flat cable2 x 1.5 mm²

Conductor length: 100 m total length (more ifrepeaters are used)

Transmission rate: approx. 167 kBit/s

Cycle time: 5 ms with 31 slaves

Device interface: data transmission: APMwith sin² pulses,

Auxiliary supply: 30 V DC, max. 8 A totalcurrent

Bit encoding: Manchester

Data permessage: 4 bit bidirectional

Data protection: 1 bit parity + signal qualitymonitoring, correspondingto HD = 4

2.3 Technical information

AS-interface protocol

The user does not normally come into contactwith the protocol of the AS-interface (layer 2 ofthe OSI seven layer model). Nevertheless, itcan be interesting to the user.

There is only one master telegram format andonly one slave response format (figure 5):

The master telegram is always 14 bits inlength and contains 10 information bits.

The slave response is always 7 bits in lengthand contains 4 information bits.

The master serially queries (cyclically) allslaves (polling). Each slave is identified by itsown address (1...31).

The master telegram can perform the followingfunctions:

Data call: The master sends its 4 bitsto the slave or it receives 4bits of information back(e.g. the sensor state).

Parameter call: The master sends thenecessary parameter bitsfor remote parameteri-sation or it receives thoseparameter bits back (e.g.sensor is a break switch).

Address call: The slave possessing theaddress 0 is assigned thenew address. The slaveresponds with aconfirmation.

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The master request can also containcommands e.g.:

Read I/O The I/O configuration ofconfiguration: the slave is read using

this call.

Read ID code: The slave responds withits permanent, factory setidentification code.

Delete operating The current slave addressaddress: is set to 0.

Figure 5: Master/slave telegram example



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AS-interface is a communication-friendlybus!

Figure 4 shows that the AS-interfacecommunicates with every connected device. Itcommunicates "above" with the PLC and the PC.It also communicates with the primary bussystems:PROFIBUS, CAN, MODBUS, INTERBUS,DeviceNet, II/O Lightbus...

"Below", via its own network, the AS-interfaceconnects binary AS-interface sensors andanalogue AS-interface sensors, AS-interfaceactuators and - using a coupling module -sensors and actuators which cannot connectdirectly to a bus. Using its special AS-interfaceEx module, the AS-interface can communicate

The AS-interface

with sensors and actuators located in potentiallyexplosive areas.The AS-interface is unsurpassed in its ease ofuse not only during project planning, but alsoduring maintenance and error diagnosis.Integrating the AS-interface with binary sensorsallows the optimal acquisition of additionalinformation concerning diagnosis, early failurewarning or function reserve at no additional cost.For good visualisation of the ASi system,Pepperl+Fuchs ships suitable software tools.

Figure 3: Overview of the AS-interface



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AS-interface cost analysis

The AS-interface offers not only the advantagesof flexible project planning, self-monitoring andeasy maintenance and expandability, but it alsoproves to already have a clear cost advantage inits installation in comparison to conventionalwiring. An example:

High-bay car body warehouse in the automo-bileindustry (e.g. 21 storage racks in 7 levels).

Central unit: S5 135 UInputs: 200 sensorsOutputs: 64 actuators.

The material and installation costs areinvestigated for:

• conventional wiring (CW)• networking using xBux (xBus)• networking using AS-interface (AS-i).

The comparison does not include parts whichare common to all setups (switch cabinets,control panels, sensors, actuators, etc.).Discount rates also have not been taken intoaccount.

The results are displayed in figure 4.

The savings of the bus systems compared toconventional wiring lie in the installation costs.Here the AS-interface shows its superiorityresulting from its insulation penetrationtechnique. Figure 4 shows the potential savingsof the AS-interface in comparison withconventional technology and competitiveproducts. From which one may conclude:

The AS-interface is profitable!

The advantages of the AS-interface achieved asa result of increased functionality duringoperation are not taken into consideration here.

Figure 4: Cost comparison of various wiring techniques

The AS-interface



Data encoding

The customary Manchester-encoding usedwith bus systems is implemented in the AS-interface using alternating pulse modulation(APM).

Figure 7: Transmission of an AS-interface telegram

(falling Manchester edge = negative APM pulse, rising Manchesteredge = positive APM pulse).

Figure 6: Data integrity classes in accordance with DIN 19 244

This scheme has the following advantages:

1. Sin² pulses (instead of square pulses) havea relatively small frequency spectrum. Thisnot only reduces interference radiation intothe surroundings, but also allows for theeffective filtering out of extraneousinterference. Therefore the AS-interfacedoes not require shielded bus cable.

2. Simple error checking is possible because

a) two subsequent pulses must haveopposite polarities (alternation),

b) a pulse must always lie in the secondhalf of the bit.

quality monitoring, the AS-interface achievesHD = 4 without any further measures (figure 6).This error detection factor of HD = 4 iscustomary with field buses.When classifying the AS-interface in terms ofdata integrity classes according to DIN 19244,the following can be seen: When encounteringa typical bit error rate of ≤ 10-³ , the AS-interfacefalls into the highest data integrity class 3. Thisis required for the transmission of particularlycritical information.

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Data integrity

Interference rejection during data transmissionis an important judgement criterion of a bus.With the AS-interface, a request is protected bya single data bit. This increases the efficiencyand shortens the cycle time. By using a specialtype of coding (APM, alternating pulsemodulation) and through constant signal



Transmission rate and cycle time

The bit transmission rate is a much-mentioned,but not very telling parameter of a bus. The AS-interface has a transmission rate of 167 kBdwhich is relatively low. A low rate was chosen inorder to also exclude interference due to cablereflections even with complex cableconfigurations.

Since the bus length is restricted to 100 m, theAS-interface does not require a terminatingresistor - substantially simplifying installation.

The important timing parameter of a bus isactually the cycle time. In a full system (31slaves or 124 binary sensors + 124 binaryactuators), the cycle time of the AS-interface is5 ms. This places the AS-interface in the groupof the fastest buses.

No transmission is immune from outsideinterference. Therefore, it is important to knowhow the slave response (i.e. the cycle time) isincreased if errors occur.

Here the AS-interface is unsurpassed in itsdesign: even with a bit error rate of e.g. 83 persecond, a cycle time of 5 ms is still guaranteed.If an interruption of the AS-interfacetransmission occurs (cable breakage), allslaves on the master side of the point ofbreakage can be communicated with withoutdelays.

The universality of the AS-interface

Pepperl+Fuchs offers many possibilities forconnecting actuators and sensors to the AS-interface:

Sensors with integrated AS-interface chipsInductive, optoelectronic and ultrasonicsensors with integrated AS-interface chips offerdecisive advantages:

• pre-failure warning(with optoelectronic sensors)

• remote parameterisation(with optoelectronic, ultrasonic sensors)

• reverse direction of action(break switch/make switch, light/darkswitching)

• readiness indication(e.g. standby with ultrasonic sensors,electrical or mechanical system fault)

31 such AS-interface capable sensors and amaster form an AS-interface net. Thesesensors are connected directly to the AS-interface using a cable, circular connector,terminal compartment or the AS-interfaceinsulation penetration technique.

To connect sensors or actuators withoutintegrated AS-interface chips, one requires:

Modules for the switch cabinet, junctionbox, or field use (IP67).

These modules are optimally modified for theirparticular application: the KF modules for theswitch cabinet are narrow (20 mm) and, thanksto their plugable terminals and Power Rail,afford considerable advantages duringinstallation. The K2 and K3 modules for thejunction box are flat (39 mm) and, therefore,well-suited to the conditions in the junction box.Due to their broad scope of use, the IP67modules for field use are available in varioushousings. At Pepperl+Fuchs the sensors oractuators can be connected with either PGscrew fittings or M12 screw connections. Theadvantage here is the use of PG screw fittings,which simplify wiring and reduce the additionalcost for the necessary cable sockets. Anotherspecial feature available from Pepperl+Fuchsare the coupling modules for explosiveatmospheres. These are designed in such away that they may be installed in explosiveatmospheres and can establish a connectionto sensors in accordance with DIN 19234(NAMUR) or appropriate actuators. Additionalinformation regarding this topic can be found inthe introduction to Chapter 4.8 "Couplingmodules".

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Figure 10: Installing the KF system

Power Rail insert

2 conductorsfor power supply

Top hat rail

End cap

3 conductors for bus system

The cabling

There are various types of cabling possible:

In the switch cabinet

Any copper conductor. We recommendconductors with a 2x1.5 mm² cross sectionalarea. Particularly easy for installation is:Pepperl+Fuchs PR05 (Power Rail) for KFhousing.

The PR05 Power Rail is a 50 cm long insetcomponent in the 35 mm top hat rail inaccordance with DIN EN 50022 (figure 9).

Here, 3 conductors are integrated for a bussystem, two of which are used for thetransmission of AS-interface signals. Externalpower is supplied by means of the two power-supply conductors. The connection to the AS-interface conductor and to the external power-supply conductor is made automatically bysnapping the device onto the top hat rail withintegrated Power Rail (figure 10). The device issnapped onto the rail vertically from above.

The external supply is connected to the powersupply by means of the feed component KFD2-EB2.B. It provides 24 VDC and 4 A and protectsthe device by means of a fuse. The 24 Vauxiliary power for modules in the KF series canbe supplied either via the Power Rail or via theterminals. The solid construction of the PowerRails eliminates the possibility of a lineinterruption or a short circuit. The plug-interminals of the KF system allow work to becarried out while the system is under voltage.

Figure 9: Power Rail as an inset component in the top hat rail



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In the field

• normal two-wire round cable (figure 11),we recommend flexible power cableH05VV-F2 x 1.5 accord. to DIN VDE 0281.

• yellow and black AS-interface flat cable(figure 12)

The cable offers two major advantages duringinstallation:• coding strip protects against polarity

reversal• connects in seconds via the AS-interface

insulation penetration technique.

With the insulation penetration technique, theAS-interface cable is inserted into two cablebaskets in the coupling module base. Thisensures strain relief. There are two contact pinsper cable lead.

Screwing together the upper part and the basecauses the contact pins to penetrate throughthe cable jacket, the wire insulation and into theconductor, guaranteeing a secure electricalconnection without damaging the conductor.

Figure 11: Flexible power cable H05VV-F2x1.5 in accordancewith DIN VDE 0281

The AS-interface

Figure 12: AS-interface flat cable

Figure 13: External power supply via flat cable

When disconnecting, the contactopening in the cable closes itselfwatertight.

If an additional 24 V feed is required (e.g.for power actuators), this feed can beconveniently done through the black AS-interface flat cable. This cable is runparallel to the yellow AS-interface flatcable via the IP67 Modules.



Principle points concerning installation

• The AS-interface wiring is symmetric, i.e.neither of the two leads may be grounded.

• Terminating resistors at the end of thecables are not required.

• A junction can be established at any point.• The total length of the AS-interface cable

may not exceed 100 m.• The total length of the cable can be exten-

ded beyond 100 m using repeaters.• Power is generally provided by a 30.5 V

AS-interface power supply unit. This canbe connected at any point on the AS-interface net.

• Connect the power supply unit near to highpower slaves to reduce the voltage drop.

• 24 V additional supply for connection ofhigh-power actuators.

• The separate AS-interface masters aresupplied with 24 V or directly with the AS-interface power supply unit.

• A PC or PLC is not required forcommissioning the AS-interface bus.Pepperl+Fuchs masters have a displayand 7 LEDs for on-site diagnosis, as wellas 2 buttons for mode switching andaddress programming.

• Connecting a new slave is Plug and Play:connect, teach-in at the master, finished.

• Connecting and disconnecting slavesduring operation is possible and allowed.

• The sensors and actuators are wired to thecoupling modules via a connector or screwterminals (Bild 14).

Figure 14: Wiring variants of sensors and actuators to the coupling modules

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Analogue transmission

The AS-interface was extended to include aprofile for transmitting digitised analoguevalues for the many measurement points inprocessing technology.

The 4 information bits of an AS-interfacetelegram are divided into 3 analogue bits andone handshake bit H. The master calls theanalogue mode in the first cycle (Figure 15).

Figure 15: Transmission of an 8-bit analogue value

Here is e.g. H = 1. The slave responds withthree status bits S. H is still equal to 1. Duringthe second cycle, the master requests the mostsignificant analogue triplet (H = 0). The slaveresponds with the three most significantanalogue bits (H = 0). This repeats itself until allanalogue triplets have been transmitted. In theexample shown in figure 15, the 8 bit analoguevalue 10010011 = 147 is transmitted. To dothis, 8:3 → 3+2 = 5 cycles are required. For a 12bit analogue value 12:3 → 4+2 = 6 cycles arerequired. Analogue values up to a maximum of18 bits can be transmitted using this method.

This process can also be carried out in thereverse: the master transmits an analoguevalue to the slave.The ultrasonic sensors UC500, UC2000,UC4000 and UC6000 in this catalogue are ana-logue distance sensors with 12 bit resolution.

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Notes

The AS-interfaceField buses PROFIBUS, INTERBUS, CAN, DeviceNet, MODBUS, Lightbus Sensor/actuator...

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