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Special Report: Mission Critical PLCs: Regul RX00

by Arabian Oil & Gas Staff on May 17, 2018

100% mirror redundancy.
100% mirror redundancy.

In today's saturated PLC market, one can find devices and solutions for almost any application and need, comment Elov A, technical director, Department of Industrial Automation, and Dobriyan D, head of engineering, at GP Systems.

PLCs are the most universal instruments for automating proce-sses, and they allow more accurate and transparent management of operations. The segment of the market with controllers for critical applications includes such devices as the Siemens Simatic S400, the Modicon Quantum, ControlLogix, and others. The typical characteristics shared by these types of PLCs are: a virtually unlimited number of I/Os (over 10,000 discrete I/O channels and over 1,000 analog I/O channels); high processing power; support of a wide variety of communication protocols; support of hot-swapping of all the modules; support of hot standby; and redundancy.

While this market segment is full of well-known brands, and it is quite difficult to offer anything new in this area, we at GP Systems GmbH have found the ways to overcome the existing limitations. We have implemented our ideas in the REGUL RX00 line of PLCs. Let us go into step-by-step detail about building a PLC for critical applications.

Internal bus is the key

The base of every PLC is its internal bus, used to exchange data between all the modules of the controller. The bus defines the maximum functional speed of the PLC. Eventually, the processor can be upgraded, but the internal bus cannot be replaced when it reaches 100% capacity, as replacing it would change the design of all the I/O modules and require significant changes to the software. Thus, this would be the same as developing a whole new PLC.

The internal bus of REGUL PLCs not only has an ultra-rapid performance speed, with a typical cycle time starting at just 50μs, but it also operates in strict real time and has a high synchronisation accuracy (a difference of less than 100ns in most cases).

Another advantage of the REGUL internal bus is that the number of nodes does not have any impact on the cycle time. Therefore, a PLC with hundreds of I/O modules will have a speed similar to that of a small controller with just a few I/Os. Also, the internal bus in REGUL controllers can be used in racks and between them; the signal just travels through a different physical carrier, and there is no difference in the module placement.

Whether the module is placed in the CPU rack, or in a remote I/O several kilometres away from the CPU [e.g., the controllers could be used with small form-factor pluggable (SFP) modules for fibre-optic communication lines], the functionality and availability of the modules will be the same.

Another interesting feature of the REGUL internal bus is its ring structure, which allows a redundant communication channel in case of line failure. We should note here that REGUL controllers use two independent internal buses in the ring. When the PLC is running in hot-standby mode, the processors communicate with the modules over independent channels with a bus exchange cycle time of 1ms.

Support different types of redundancy

REGUL PLCs support several types of redundancy: (1) 100% mirror redundancy – In this case, every CPU has its own set of I/O modules and is a full mirror of another CPU (Figure 1). (2) CPU and bus controller/power supply unit redundancy – In this case, both CPUs are located in the same rack and exchange data with the same I/O modules over two independent buses. (3) Mixed redundancy – In this case, options 1 and 2 are mixed (Figure 2).

REGUL CPU modules have high processing power. Their core is a CPU with 1-GHz speed and 2GB of RAM. Moreover, the user can use up to 64GB for application programmes, archives, and databases (on an SSD). Module CU 00 061 supports communication over four independent Ethernet ports, out of which two can be used for fibre-optic connections. Also, the module has onboard RS-485 and RS-232 ports and an internal GPS/GLONASS receiver. The CU 00 071 module has two USB ports and a DVI connection (with touch-display support) instead of the RS-232 port.

We would like to note that all the events and archived data are stored in the internal SSD with time stamps and can be made available to the upper level of the system. All the I/O modules, including the discrete I/O modules, have microprocessors. As such, every module is a microcontroller operating with a 1ms cycle time.

Initial signal processing is performed within this time and includes: signal diagnostics for range overshooting and abrupt value changes; a ‘debounce’ function for digital signals; programmable averaging time; conversion of the signal values into engineering units; support of the redundant network with data transmission over two ports; and the assignment of a timestamp with an accuracy of 1ms to the signal and to the event on this signal. Certainly, in most cases, such speed is not required, but it helps to achieve a high accuracy and stability of the measurements. For example, when an analog input signal is to be measured with a cycle of 100ms, then one can obtain 100 measurements from the module, filter them for surges, and obtain a sliding average.

Other technical specifications

REGUL PLCs use a real-time operating system. Its key characteristics are: predetermined behaviour in the worst external conditions; a typical reaction time of around 5μs for interruptions; a predictable reaction time for events; implementation of the algorithms with pre-emptive multitasking and prioritisation; implementation of memory protection; and microkernel operating system architecture (error in one software module does not lead to a blockage of the entire operating system).

For the configuration and programming, we developed Epsilon LD software, based on Codesys, that supports five IEC 61131-3 languages (IL, LD, ST, SFC, and FBD); outputs machine code; provides tools for project configuration (task managers, PLC configuration, library manager); has an integrated debugger that operates in online mode; supports object-oriented programming; supports network protocols such as Modbus TCP, Modbus RTU, TCP/IP, CAN, etc.; and has a visualisation editor for small stand-alone systems.


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