The Base Unit is fitted with the T2550 I/O Controller Module's) plus additional I/O Modules. These modules plug onto Terminal Units, which provide the wiring interface between the plant or machine and the I/O modules. Intercommunication between the I/O modules and the processor is effected by the use of a passive internal module I/O bus running the full width of the base. Each module position is tracked separately for additional security during live replacement of I/O modules.

The base consists of an aluminum extrusion, the internal I/O bus and mounting supports. The base is designed to be DIN rail mounted, within an enclosure. If preferred, however, it can be directly fixed to a bulkhead or mounting plate. Both base and modules can be installed horizontally or vertically.

Bases are available in three standard sizes to suit the number of modules required in a particular system. The dimensions and weights of the three standard bases are detailed in table below.

The I/O modules are mounted on the base using terminal assemblies. Terminal assemblies provide the interface between the input and output signals and the I/O modules. Terminal assemblies and I/O modules are keyed to inhibit insertion of the incorrect module; this prevents damage to both equipment and plant.

Individual termination units provide for easy module replacement leaving the field wiring connected. Modules are inserted and removed from the termination unit using a unique tool-less locking lever system

Test Disconnect Units
Terminal assemblies have an optional fuse or a link (isolator or disconnect). This provides a series of connections between the customer terminals and the I/O module, permitting pluggable fuse or link units to be placed in series with the signal. Fuse and link units are not interchangeable.

Terminal assemblies that do not have “disconnect”, have a dummy cover in the same position, providing space for a label to indicate the circuit or cable tag name.

Foreign devices such as PLCs supporting Modbus RTU can be readily integrated into the ELIN based architecture by direct connection to T2550 control units.

The Modbus RTU communications allows a T2550 to be used as a gateway providing access to database elements in any ELIN node.

The duplex terminal unit supports redundant power supply connection. Two power connectors, OR’ed together on the terminal unit to permit connection of two separate power supply systems, supplying redundant power to both processors. In the failure of a single power supply system both processors are still supplied allowing redundant operation to continue uninterrupted.

In the case of total power supply failure the processors can optionally warm start. Battery support is not required for this normal operation as each processor is fitted with a super-capacitor providing warm start capability up to 12 hours.

Provision has been made for the connection of an external battery to extend this time via a socket sited between the Serial Communication ports on the Duplex Terminal Unit.

A Processor watchdog relay is optionally provided for high security applications. An independent relay unit can be mounted in a separate base assembly or in the I/O rack occupying a single I/O module position. The watchdog relay unit has two separately replaceable relay assemblies (one for each processor) and is connected to the processor termination unit.

The terminal unit provides for the user circuit to be wired for parallel or series connection of the processor watchdog relays.

Live plug-in feature means that processors and I/O modules can be replaced under power without any disturbance to the field wiring or other inputs and outputs, reducing downtime and minimizing disturbance to other signal conditioning strategies.

Simplex or Duplex control of the processor is available for continuous, logic and sequence control.

A pair of processors operates in primary / secondary configuration with a high speed data link between them providing exact tracking of the control, logic and sequence databases. Should the secondary processor take over from the primary in the event of processor or communications failure the transfer is bumpless.

The non-active processor can be replaced while the system is running and on synchronization it loads its strategy from the active primary processor.

During a processor switch over all outputs remain at the last value. The new primary processor begins executing it application from precisely the same point as the original processor.

Each processor has its own Ethernet IP address and each redundant pair uses two neighboring node addresses on the ELIN network. This enables the system to communicate with the primary while still testing communications to both processors continuously. On processor switch over the ELIN node address is dynamically swapped to allow SCADA applications to display and log uninterrupted data. Change over amongst LIN nodes is transparent.

The following conditions can cause the processor to switch over

Hardware failure Failure of primary controller internal health checks.

Hardware removal Removing the primary processor will cause the secondary to take immediate control.

Removing the secondary will have no effect on control but will cause a system alarm on redundant configured systems.

Internal communications Primary and secondary controllers failure to local I/O continually monitor the communications to the I/O on the local base. Should the primary controller not be able to communicate with the I/O a change over will occur if the secondary can still communicate with the I/O.

If the secondary processor observes a fault in the primary communications or can see more I/O modules the secondary processor will request a changeover.

External communications Each processor in a redundant pair failure in the primary continuously monitors external controller communications. Should the primary controller not be able to communicate with other declared nodes on the LIN network, a change over will occur, if the secondary can still communicate with the declared nodes.

If the secondary processor observes that it can see more declared nodes the secondary processor will request a changeover.

Manual request A user can request a change over if a secondary processor is running, synchronized and healthy.

Ethernet The T2550 supports Ethernet LIN (ELIN) protocol that provides secure peer-to-peer communications between bases and to other Ethernet devices over 10/100 Ethernet from each processor.

Simultaneously it can support Modbus-TCP Master or Slave to other Modbus- TCP devices.

Serial Modbus-serial Master or Slave communications are optionally supported.

The storage of the cold start application files, the processor firmware and software licence code is on secure compact flash card to enable easy transfer from one processor to a replacement.

Primary processor and communications diagnostics are available from the LED’s on the front of the processor module, more advanced diagnostics are available remotely using LINtools monitor online over Ethernet to review the diagnostic blocks.

Multiple tasks are available to the user to tune the update rate of I/O response and the control function.