Power supply
The T640 has two supply options — universal MAINS and DC. The DC option has a redundant input which allows two sources of supply. Information concerning the status of both inputs is available within the control strategy. Instruments with MAINS and DC options look the same. However, protection against plugging a T640 into the wrong sleeve is provided both physically, through keying in the connector, and electrically, through the use of different connector pins.

Communications
The peer-to-peer network is supplied as standard. However, a serial communication port can be supplied as an option, and can be configured for RS422 (5-wire) or RS485 (3-wire) operation. Two protocols are supported on the serial port: TCS Bisynch (Binary) for integration with TCS S6000 instruments and Modbus RTU. Selection of the protocol is made via the internal switches.

Input/Output
The T640 has two I/O sites and in principle any option can be selected for either site. There is one restriction in practice and that is a high level option Hx cannot be used in site 2 if the high level option is not selected for site 1. Details of the options currently available are given later in this document. One option is targeted at high level process plant signals (HI, HG, HIB & HGB) and the other at direct thermocouple inputs (TC).

Memory module
This option selects the level of functionality of the T640. Memory modules can be ordered on their own using the code T901.

M006 is the Fixed-Function T640. This will only run the preconfigured standard strategies supplied:

• Single control loop
• Dual control loop
• Dual loop in cascade
• Dual loop with ratio station

The strategies are selected using the internal switches. This is the lowest cost option but it has other advantages. The strategies have already been developed and tested, and so engineering and maintenance costs are also minimized. The I/O is pre-defined, so only the high level options may be used. This is the only restriction. Although T500 LINtools is useful, in particular the view mode, this option has been specifically designed to make this tool unnecessary. The Fixed-Function T640, M006, is provided with its own set of documentation.

The M001, M002 and M004 are provided with the preconfigured standard strategies listed below, which may be used directly or as a starting point for more complex configurations:

• Two simple loops
• Two cascade pairs
• Two simple loops with raise/lower outputs
• Two loops governed by a ratio station
• Two flow loops with temperature and pressure compensated flow measurements
• Two loops with heat/cool outputs
• Two loops, simple or cascade, with high or low level input

The way the standard strategies are implemented allows your own configurations to be selected in place of the strategies provided.

M001 is the simplest of the configurable T640s. This supports the full range of function blocks but is limited to two control loops. This means it will run all the preconfigured strategies except 2 and 6 which use four control loops in their implementation.

M002 is the same as the M001 but supports all four control loops

M004 also supports all four control loops and it will also run SFC sequential control. From the second quarter of 1994 all T640s, whatever option, were shipped with enough memory to run SFCs and therefore upgrading is merely a question of ordering the M006 memory module. Prior to this date T640s with M001 and M002 memory modules were shipped with less onboard memory. If an M004 is fitted to one of these it will behave like an M002.

Sleeve
The T640 may be ordered with a panel mounting sleeve, T710. The T710 sleeve has no active components but has all the I/O termination. This is likely to be the most usual option.

The T750 sleeve allows the T640 to be plugged directly into a 7950 rack wired for 6000 instruments. The I/O has been chosen to match the controllers: 635x, 636x, 637x and 638x. Because these controllers were powered from 24 volts, only T640s with the DC option can function in a T750 sleeve.

The ordering structure of the T640 allows sleeves and controllers to be ordered separately. However, a sleeve is always required for a T640 to be used.