H. Kuhnke Ltd, Romsey, UK
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Airbox. The Kuhnke Asi Pneumatic Slave Module

AS-i Safety at Work & Airbox

Kuhnke Airbox is not a "safe" module. It can however be used as part of systems up to EN954-1 Categories 1 and 2 and IEC62061. Users will know that it is the system which must be assesed, rather than the individual components. These notes are intended as a guide to the designer and specifier of AS-Interface systems using Airbox. In combination with other components a Kuhnke Airbox can provide safe operation up to category 4, and SIL 3.

Kuhnke can advise you on a system by system basis. If you need help or advice just contact us.

Notes on use of Airbox in Safety applications.

• Removal of power in the event of stop / emergency stop is defined in safety terms as including removal of compressed air power.
• You will need a separate valve which disconnects air supply to your system in the event of e-stop (pneumatic dump valve).
• Consider immediate or delayed dump. You may need a separate pilot supply for your Airboxes that is not dumped. Category 4 requirements also include the need for an external monitoring device, probably a pressure switch, to confirm dump has occured.

 

• You must consider the safe function of compressed air actuators in the event of compressed air removal. Will loads act dangerously? You may need to consider a valve combination that always returns an actuator to it's safe condition. You may need to fit blocking exhaust valves to lock the position of an actuator.
• Airboxes can be specified with or without black cable (EEMS or auxiliary power). Removal of black cable power in the event of a stop condition can be done with AS-Interface (yellow cable) live, for status & input monitoring.
• Consider re-start carefully. Airboxes require a supply of compressed air (internally or via external pilots) to be able to switch. Allow delay time for compressed air to be re-established before changing node output status. This principle also applies to all start conditions.
• Airbox is no different to any other pneumatic valve, other than its integrated control when assesing safe operating practice. The application of intrinsically safe working, restrictors, pilot valves, dump valves and safe re-start applies to pneumatics generally.
• Remember that Airbox K is suitable for soft start. Use a seperate pilot air supply which will remain live on e-stop. The pilot air supply in this case is control air.
• Consider that after an e-stop your actuator or load may continue to move sufficiently to activate a sensor. This may lead to a changed output instruction on restart. If compressed air is not available in the time the software operates, then a fault condition will occur.
  

Never work on machinery where compressed air is live. Ensure only competent personnel install and maintain automation systems.