Jan Mocha

Popular microcontrollers execute IEC 61131-3 standard operators and functional blocks in simply automatic control tasks

Over the recent decades a common approach seems to be taken for granted that only dedicated Central Processing Unit (CPU) offered as self-contained modules by various manufacturers are the only solution for implementation of Programmable Logic Controllers (PLC). To demonstrate right the contrary authors of this study reveal various CPU solutions of PLCs developed on the basis of some typical microcontrollers, including the ones from the families MCS-51, AVR and ARM with the Cortex M3 core. These CPUs were then employed to run a control program developed in an Instruction List (IL) language that meets recommendations of the IEC-61131-3 standard. The paper demonstrates that the basic operators of the IL language can be used to simplify bodies of the standard defined function and function blocks. The rules are outlined that the authors adhered to at development of commands for the IL language with dedicated examples that explain how these commands can be used to define functionalities for operational modules of counters and timers and a combinational Boolean function - on the example of the LIMIT procedure. It is also suggested to define several new operators that additionally simplify the notation. The scope of investigations includes also comparison between the solutions suggested by stipulations of the standard in question and the own solutions proposed by the authors with presentation of the outcome from the comparison. The disclosed considerations served as the basis to suggest the new architecture for a CPU that is suitable for operation in line with rules imposed by the standard, but on the other hand it can be used for operation with some modifications suggested by the authors and intended to reduce processing time for some operators, Boolean functions and functional blocks.

FPGA-based two-processor CPU for PLC

The paper reveals a two-processor Central Processing Unit (CPU) designed for Programmable Logic Controllers (PLC). The CPU is made up of a 1-bit (bit-type) processor and a 32-bit (word-type) processor. The both processors are operated totally independently from one another and information between them is exchanged via a exchange memory module. The 1-bit processor collaborates with edge detectors whilst the 32-bit processor is dedicated for implementation of timers and counters as well as enables execution of arithmetic operations on 32-bit integers and floating point variables. The both processors have been developed as specialized structures capable of executing control routines developed in the Instruction List (IL) programming language in line with requirements of the EN 61131-3 standard. The study presents a new approach to development of the exchange memory module and edge detectors as well as implementation of timers and counters. It is the approach that combines both software and hardware solutions, which makes them more efficient in terms of time performance as compared to already known solutions. Finally the CPU was designed with use of the hardware description language and then implemented in FPGA resources. This paper discloses results of the synthesis and execution times achieved for both individual instructions and benchmarks routines running on the newly designed CPU. The accomplished results make it possible to conclude that the CPU can be considered as an alternative solution to other units available from the market whilst the capability to execute algorithms developed in strict conformity to EN 61131-3 standard is its advantage.

Immunity of medical electrical equipment to radiated RF disturbances

Immunity of medical equipment to radiated radio frequency (RF) electromagnetic (EM) fields is a priority issue owing to the functions that the equipment is intended to perform. This is reflected in increasingly stringent normative requirements that medical electrical equipment has to conform to. A new version of the standard concerning electromagnetic compatibility of medical electrical equipment IEC 60601-1-2:2014 has recently been published. The paper discusses major changes introduced in this edition of the standard. The changes comprise more rigorous immunity requirements for medical equipment as regards radiated RF EM fields and a new requirement for testing the immunity of medical electrical equipment to disturbances coming from digital radio communication systems. Further on, the paper presents two typical designs of the input block: involving a multi-level filtering and amplification circuit and including a solution which integrates an input amplifier and an analog-to-digital converter in one circuit. Regardless of the applied solution, presence of electromagnetic disturbances in the input block leads to demodulation of the disturbance signal envelope. The article elaborates on mechanisms of amplitude detection occurring in such cases. Electromagnetic interferences penetration from the amplifier’s input to the output is also described in the paper. If the aforementioned phenomena are taken into account, engineers will be able to develop a more conscious approach towards the issue of immunity to RF EM fields in the process of designing input circuits in medical electrical equipment.