Fieldbus & Industrial Networking


Reliable distributed control of motor starters

March 2001 Fieldbus & Industrial Networking

Allen-Bradley's Modular DeviceNet Starter Auxiliary (MDSA) is available from Rockwell Automation. This modular communication system can be directly mounted onto cable flange panels and has been specially developed for efficiently incorporating motor starters into distributed structures.

The device complements the existing range of DeviceNet Starter Auxiliaries (DSA). In and output devices, like sensors and magnetic coils, can be directly connected at this point. This type of system extension, however, requires no increase in the number of DeviceNet nodes. This simplifies network planning considerably, making data transfer more efficient.

Rockwell Automation says that the MDSA is the only additional starting device that can be directly mounted onto the cable flange plate. As part of the distributed Allen-Bradley starter system it simplifies the connection of sensors and magnetic coils to the field bus. Direct fixing onto the flange or onto the casing wall and the M12 standard plugs on the casing (which substitute terminal blocks on the DIN rails) results in a considerable reduction in the wiring effort required for sensors and actuators.

The MDSA's electrical features, for instance, 5 A relay outputs or 2 A transistor outputs and software filters to eliminate fault signals during contact bouncing, enhance the field of application. Due to its increased temperature, shock and impact resistance, the device is well suited to harsh industrial operating conditions.

The MDSA system consists of a range of modules that can be combined depending on the actual configuration required. A configuration can consist of up to 16 modules, which can be addressed via one single DeviceNet node. The starter module with 2 inputs and 1 output is equipped for controlling one motor. Further modules for connecting sensors, actuators, frequency converters, inputs or outputs complete the available range.

Fewer terminals, faster assembly

More and more, distributed starters substitute conventional motor control centres with their complex, hardwired controls and cables to the motors. The distributed starter concept allows looping power cables from one motor to the next. The control inputs and outputs as well as communication are routed through one single DeviceNet cable with standardised M12 micro connectors. The MDSA is suitable for installation in casings protected to IP66. It reduces the number of terminals required and, thus, cuts down on installation time and reduces the probability of wiring errors. It also simplifies project-planning and subsequent changes, reduces space requirement, improves system monitoring and diagnosis and permits a comprehensive system test in the factory, which reduces the commissioning time on site.



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