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Motor safety relay has an AS-i link

01 April, 2005

Motor safety relay has an AS-i link

Castell Safety International has developed an AS-i-compatible motor safety relay which can monitor not only AC and DC motors up to 600V, but also variable speed drives. The CMM200 relay incorporates filters to reject the interference caused by VSDs that can sometimes disrupt other protection relays.

An AS-i connector on the relay can transmit a Category 4 signal to an AS-i master.

The DIN-rail-mounting relay monitors the back-emf generated by a motor to detect whether it is safely at rest or in motion. Two separate channels are connected to different motor windings. Only when both channels have detected zero speed, will the normally open safety output terminals be closed.

Castell claims that the relay is the only back-emf device to be controlled by two microprocessors, which check both the state of the motor and the condition of the relay itself. The processors communicate with each other via an optically isolated link and revert to a failsafe condition in the event of a fault.

The processors also monitor the condition of the sensing cables that connect the relay to the motor. If a cable becomes disconnected, the relay enters a failsafe mode and the fault is indicated locally. The relay also indicates when either channel is at zero speed.

The relay can be used on 24V DC, 115V AC or 230V AC supplies.

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