Posted to News on 3rd Sep 2008, 00:00
Eliminating the need for duplicate redundancy
Claimed the first product of its type, the new Contactor Monitoring Device (CMD) from Moeller Electric means the expense of using duplicate redundant contactors in motor starters with safety functions can be entirely eliminated. Instead, the same levels of safety can be achieved by using a compact and inexpensive CMD module with each contactor, providing not only large cost savings, but also reducing the amount of space required in the control panel.
The CMD modules operate by monitoring the state of the contactor's main contacts, and comparing this with the voltage applied to the coil. If the coil is de-energised but the main contacts are not open, the CMD opens a normally-closed output contact that can, for example, be used to trip the starter's motor protection circuit breaker via an undervoltage release.
This mode of operation ensures that, even if the main contacts of the contactor weld, the motor it is controlling is safely brought to a stop. The CMD can be used to implement Category 3 and Category 4 safety circuits in line with EN 954-1, as well as safety circuits with EN ISO 13849 Performance Level d.
