SYSTEM THREE

A single printed circuit card, designated the Intelligent Input-Output Card, IIOC, forms the heart of the system. It supports a CMOS microprocessor and all associated integrated circuits required to perform:

Multiplexing and demultiplexing

A to D and D to A conversion

Communications control and error detection

Operator interfacing

Data processing and storage

The IIOC is supported by a family of other cards including:

Radio/Modem card

Voltage regulator card

Plant interface cards

Operator interface modules

These cards are common to all three units in the system, namely the Main Terminal Unit (MTU) the Remote Telemetry Unit (RTU) and Portable Unit (PU). This minimises spares holdings and results in a simple and economical system.

Expansion

Unlike other single card telemetry systems, OTS System 3 permits almost unlimited expansion both in numbers of Remote Telemetry Units (RTU's) and in the number of inputs and outputs accommodated at each RTU. The IIOC and associated plant interface card or cards, forms an intelligent modular building block from which almost any size outstation or network can be constructed.

Architecture

A unique feature of System 3 is that the modular building blocks communicate via 'SERIAL' links rather than the parallel bus used in conventional telemetry systems. The use of serial transmissions down to individual input-output module level in each outstation brings important benefits for the user including:

Security

Error correction can be performed down to intercard transmission level and errors rejected or corrected.
This architecture permits graceful degradation of the system. Failure of individual modules need not cause loss of a complete terminal.
Dual redundancy may be easily implemented using the dual serial ports on each IIOC.

Reliability

As the microprocessor bus does not leave the individual IIOC cards, the number of interconnections within a terminal is significantly reduced thus increasing MTBF.

Maintainability

Maintenance is simplified. The fast serial transmissions are checked by the system itself, and faults can be automatically pin-pointed to a particular link. The remaining interconnections are plant input/output lines usually carrying relatively 'slow' signals. These can be checked using straightforward test equipment by technical staff without specialist microprocessor training.

Software

System 3 software utilises state of the art software design and analysis techniques. The software design has been approached with the same careful planning and attention to detail that is manifested in the hardware. A modular building block approach is adopted based on standard field proven modules easily tailored to individual user requirements. Custom software is developed for each RTU from these modules using computer-based structural design techniques on our mini computer based 'in-house' development system. Software is comprehensively checked and documented using computer aided system analysis which generates associated pictorial tree charts. It is then thoroughly tested and emulated before and during integration with the hardware.
Software gives System 3 its flexibility. Most aspects of the system operation can be controlled by simple software changes, including individual channel scanning rates, data conversion to engineering units, command execution procedure, communication protocol, transmission error detection, alarm limits, and diagnostic monitoring.