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Machine-safety specialist Castell has developed an ASi-compatible
motor-safety relay capable of monitoring practically all electrical motors, including variable-speed drives (VSDs). The CMM200 now incorporates a filtering system to reject the interference produced by VSDs that can sometimes affect similar relays. A vampire connector on the side of the unit fits a standard ASi cable and provides a Category 4 signal to the ASi master interface.

The DIN rail-mountable CMM200 monitors the back EMF generated by a motor to detect whether it is safely at rest or in motion. It is the only back EMF device to be controlled by dual microprocessors which continually check both the state of the motor and the condition of the relay itself.

The unit comprises two independent channels to which are connected separate windings of the motor being monitored for zero speed. Only when both channels have detected zero speed will the normally-open, forcibly-guided safety output terminals become closed. The CMM200 features local indication of status, zero speed, channel one zero speed and channel two zero speed. The microprocessors communicate with each other via an optically-isolated link and will revert to a fail-safe condition should any faults occur.

The microprocessors also monitor the condition of the sensing cables connected to the motor. If one becomes disconnected, the CMM200 will again revert to a fail-safe condition and provide local indication of any fault detected.

Each monitoring channel is galvanically isolated for protection against voltage transients of as much as 4 kV. A high resistance network allows the CMM200 to monitor motors of up to 600 V (ac or dc). The relay can be used with 24 V dc, 115 V ac and 230 V ac power supplies.

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