MTL MTL4532 Pulse Isolator

Passive Hubs for Zone 1 Fieldbus Networks

Megablocks are DIN-rail mounted passive hubs for Foundation™

fieldbus networks. They connect several field devices to the network

trunk cable and provide short circuit protection to the segment.

Megablocks minimize hand wiring and allow individual devices to be

added to and removed from the segment without disrupting network

communication.

A green power LED on each unit indicates whether at least 9V dc

is present. F2xx-XE Megablocks are available in four, eight, ten and

twelve drop versions. Multiple Megablocks are easily wired to one

another to allow larger segments to be constructed.

Megablocks are available with an integral terminator making

them ideal for a star or “chickenfoot” topology where several devices

are connected at a single field junction box. Separate Megablock

Terminators are also available, whch may be wired easily to any

Megablock. Megablocks having a built-in terminator are clearly

marked (‘T’) for easy identification by field personnel.

Connections to the Megablock are made using pluggable, screw

terminal type connectors. This allows wire terminations to be

made to the individual connectors which are then plugged into the

Megablock. Devices can then be connected and disconnected easily

during commissioning. After commissioning, retaining screws are

tightened to secure each connector to the Megablock.

Trunk connections for the fieldbus home-run/ trunk cable are easily

identified by their black connectors. Separate numbered connections

are provided for each spur drop.

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Megablocks can be mounted vertically or horizontally using 35

mm DIN rail within a suitable enclosure, such as a field junction

box. Megablocks are removed from the DIN rail using a flat blade

screwdriver to release the mounting platform. Use of DIN rail end

stops is recommended to prevent sliding in vertical installations. The

four, eight, ten and twelve port Megablocks have labeling areas so

that segments can be easily identified according to plant standards.

MTL have a wide range of standard junction box designs for use with

Megablocks. See the data sheet for the range of Process JBs.

Shown above is an example of a common Fieldbus segment topology.

Twelve field devices are connected to a twelve-drop Megablock,

which is mounted in a field junction box. The trunk connector on

the Megablock is wired to the segment trunk cable that leads to the

control room or marshalling panel where the power supply and second

terminator are located. The example shows the

increased safety (Ex em) version connected to a general purpose

fieldbus power supply.