AS-Interface "Safety at Work" - Contact Units (Slaves)

The Working Principle

AS-Interface Safety at Work is based on the standard AS-i log. Together with a connected AS-Interface safety monitor the system is designed for the transmission of safety-related informations. As base serves the transmission of dynamic code sequences which are stored
in each safe AS-Interface slave (8 * 4 bit code table). Through a “teach in” function the safety monitor reads in these code sequences when starting up the machine. During operation the safety monitor permanently compares the nominal and actual sequences of the safe slaves. If the safe slave (e.g. an E-stop) supplies a wrong code sequence, the safety monitor reacts immediately by switching off the machine.
When developing this concept it was attached great importance to an easy handling of the system. Same as on AS-Interface, each safety-related slave has to be assigned an address. The safety monitor identifies and registers these slaves automatically . This configuration must be acknowledged, printed and countersigned in order to ensure clear allocation of the safety-related signals to a cutoff-circuit.

Advantages of the AS-Interface”Safety at Work”

  • Cutback of conventional wiring
  • Reduction of wiring and mounting costs
  • Failure safe PLC not necessary
  • High system flexibility by easy and quick extension of existing systems, easy retrofitting of Safety at Workk
  • Easy system installation by standardised AS-Interface technology
  • Combination of Safety at Work and standard AS-Interface system in one network
  • Grouping of safety signals possible
  • Approved for Safety Category 4 acc. to EN 954-1 and SIL3 acc. to IEC 61508
  • TÜV and BIA certifications

Schlegel E-Stop as Safe AS-Interface Slave

Functional Description

When connecting an emergency-stop pushbutton to an ASInterface network, the integrated code generator permanently produces 8 different 4-bit codes which are set up according to the S-7.B.Eprofile. Each E-stop has its own code sequence which is unique. When the E-stop button is pressed a case of emergency is signalised to the safety monitor by the code sequence “0000”. Should one of the two contacts of the E-stop fail, or should the E-stop actuator be separated from the contact unit, this fault is signalised to the safety monitor by a special sequence enabling precise diagnostics (defective hardware). The actual operating/diagnostic status of the E-stop can be indicated via the external connector (standard output DO), e.g. by an external 24V LED.

Slave Characteristics

  • Type references: ASI_SAW16A, ASI_SAW16E (16mm), ASI_SAW22A, ASI_SAW22E (22mm)
  • AS-Interface profile: S-7.B.E or S-0.B.E., standard address mode
  • Permanent monitoring and safety shutdown on separation of contact unit from actuator*
  • External IDC connector as standard output D0 e.g. for the individual control of a LED 24V/max. 15mA*
  • Safety integrity level: SIL 3
  • Norms and Standards: IEC 61508, IEC 62026-2, IEC 60204-1, EN ISO 13850, EN 60947-5-5
  • Easy connection via 2-pole IDC connector and standard strand
  • Output with short-circuit and overload protection*

*) refers only to the types ASI_SAW16A, ASI_SAW22A

Data Bits of the Outputs and Inputs

data bit info (Interface 3) state
D0 0 off
  1 on


data bit info (Interface 3) state
D0 ... D3 acc. to profiles S-7.B.E*, S-0.B.e

*) refers only to the types ASI_SAW16 and ASI_SAW22

Norms and Standards

  • IEC 62026-2
  • Complete AS-Interface specification, version 2.11 rev.1
  • IEC 60204-1
  • IEC 61508
  • EN ISO 13850
  • IEC 60947-5-5
  • TÜV Type Approval
  • UL/CSA Certification


Addressing of Slaves

The safe AS-Interface slaves are assigned a complete address. The easiest way to assign the addresses is to use a hand-held addressing device, which is directly connected to the slave via the Schlegel programming cable „ASI_PK500M12“. Individual addressing can also be done at the connected AS-Interface master which is supported by different manufacturers.