Postive Acting Interlock

[AlliedAuto]

What exaclt does the term "Positive Acting Interlock" mean?

I'm using interlocks on 2 of the doors of machine. If a door is openend power to the machine is cut off. Does this mean they are positively acting interlocks?

 

[gepman]

I haven't heard that term before but it may mean the same thing as "fail safe". To be "fail safe" if the wire to the interlock sensor was cut or if you lost power to the interlock sensor the power to the machine should be cut off. Of course there are other ways for the interlock system to fail but if you get beyond the above you need to start looking at SIL (Safety Integrity Levels).

 

[Blackcountryman]

By 'positive acting' I understand this to meant that for example if a guard limit is operated the switch contacts are positivly opend.
In many limit switches when the pressure is taken off the actuator arm the contacts are opened by a spring.
A 'positve acting' switch contact is pulled apart by the operating mechanism.
Telemecanique, Square D and many other manufacturers make safety switches with this type of action.

Regards
Blackcountryman

 

[cdevine]

Spot on Blackcountryman. That is my understanding.

The need for positively guided interlocking often suggests the need for safety rated relays using dual channels with test and reset functions. This is a specialist area and is covered by BS 5304 Code of practice for safety of machinery. In Australia we use AS 4024. IEC 61508 is titled "Functional safety of electrical/electronic/programmable electronic safety-related systems". This standard also discusses concepts like positively guided interlocking.

Chris Devine

http://www.icande.com.au,

http://www.redbusbar.com