Comparison Of Programmable Devices And PLC Simulators For Industrial Automation | Flow Meter Instrument

Evaluation of Programmable Devices

1. Evaluate PICs and other programmable devices as programmable devices and embedded controllers.
2. Compare the operation, functionality, advantages and limitations of PLC simulators. Your comparison will need to include two types of simulation software.

3. Would you choose to use a PLC or an embedded microcontroller in the instrument? Explain your reasoning.

1. For this task, a comparison has been drawn between the structure and architecture of the PIC, AVR, ARM, and Intel 8051. The reason these four microcontrollers/programmable devices were selected for a comparative evaluation is because they are one of the most commonly used devices in a range of electronics applications. (Emilio et al., 2015). Each carries its own set of benefits and disadvantages which can make it a difficult choice to pick one over the others on the application, but knowledge of the differences between these devices can simplify this choice given the project or application is well understood.

• Intel 8051, PIC and AVR all utilize the Harvard architecture – a rather broad concept but one important feature for this comparison is that it separates the RAM and program memory into different memory spaces.  ARM is classified as an instance of von Neumann architecture wherein the program and RAM reside in the same memory space. This translates into a direct choice between the two architectural styles and their respective benefits. The difference in memory spaces design itself leads to a number of distinctions between the two.
• The ARM family of microprocessors employs either 16 bit or 32 bit instruction sets, whereas Intel 8051, PIC and AVR primarily utilize an 8-bit architecture.
• The stack space in 8051 and PIC microcontrollers is very limited – 128 bytes for the 8051 and 8 words or less for the PIC. This has led to an increased complexity in writing a C compiler for these devices which is evident in the limited choice of compilers available for them. (Mohini, 2015).
• The Intel 8051, AVR and ARM devices are capable of directly addressing all of their available RAM, which is not the case for the PIC. The PIC architecture is only capable for directly addressing 256 bytes of RAM at a time, and relies on bank switching to extend the directly addressable memory space. Usage of a C compiler conceals this limitation on PIC devices but results in an accompanying loss of speed.
• Most instructions in the AVR and ARM instruction set are single cycle instructions, which means that they require only a single clock cycle to execute. In the case of the Intel 8051 and PIC, a large number of instructions are single cycle but they feature many instructions which are much slower, requiring as many as 4 cycles per instruction. Nevertheless, recent improvements in architecture and design have almost eliminated most differences in speed of execution of the instruction set in these devices. (Machine, 2015).
• There are marked similarities between the 8051 and the AVR, going so far as to make the AVR and 8051 almost interchangeable with little or no hardware change. Some AVR devices even contain 8051 pinouts. The main difference between the two devices is in the Reset polarity.
• Apart from their architecture, the 8051 and AVR also have similar instruction sets although some differences exist. Therefore, in case of replacing an 8051 with an AVR, it may be possible with very little changes in the software, except for the timing critical routines. (Kanigoro et al., 2015).
• AVR and ARM have much better compiler support applications, including IDEs, available. This includes the number of free applications, such as the GCC Compiler.

2. Automation Studio: Automation Studio is a software designed by Famic Technologies Inc. suitable for use in the simulation and design of a range of circuits related to Mechatronics, such as electric, electronic, hydraulic and pneumatic circuits, as well as other related design types such as Human Machine Interaction (Control Panels), fluid power, and more. PLC simulation is included in the Electrotechnical Module of the software, implemented as the PLC Ladder Logic Library. PLC programs can be implemented either as ladder logic programs or Sequential Function Charts (SFCs)/Grafcet. The software supports import/export compatibility of the programs with XML and the Siemens S7 PLC. (Dai et al., 2016). The software suite also supports direct hardware control using suitable interfaces, effectively allowing the computer running the software to act as a PLC, or to directly run and monitor a PLC from the computer in real-time, further assisting in testing out newly developed PLC programs. The GUI editor on the other hand allows mixing different graphical programming languages, grid-based positioning and linking, colour coding, etc.

RSLogix 500

RSLogix 500 was designed by Rockwell Software and was intended to operate on the Microsoft Windows Operating System only. It is a 32-bit software package designed for the SLC 500 and Micrologix processors, compatible with any programs for the two devices created using other Rockwell Software programming package. The chief features of the RSLogix 500 include a free-form ladder editor which employs a GUI, project navigator with error listing and linking, an address wizard to help reduce keying errors and make entering addresses easier, as well as SLC libraries that enable ladder logic, wholly or in parts, to be stored and retrieved across other Rockwell Software programming packages. The interface features drag-and-drop functionality for editing data elements across files, subroutines, and rungs, a project tree interface for easily manipulating files and folders in a project, a customizable data monitor, search and replace functionality for code elements, and trend and histogram generation to aid monitoring data. (Saari, 2015). The projects developed can also easily be developed using any desired mix of programming languages without impacting functionality, although this can complicate project management and documentation.

PLC Simulators

3. First and foremost, we must define the purpose and functions of a flow meter. A flow meter, by itself, is an instrument that is used to measure the rate of flow of a liquid or gas, whether it be linear or non-linear, mass or volumetric. The application environment of a flow meter affects a number of choices that need to be made, depending upon which the choice of controller device needs to be made. If we reverse this, then the choice of controller device will result in differing limitations and advantages for choice of application environment for a given flow meter. (Nielsen, 2016). Before making such a choice, it is wise to enlist the relevant differences between usage of PLCs and microcontrollers.

Firstly, PLCs offer greater flexibility in terms of both hardware and software. The program running a PLC can be modified much more easily than the program on a microcontroller. The same applies for the relevant hardware design differences between devices running on a PLC and a microcontroller.

Secondly, writing a program for a PLC is easier and faster than a microcontroller. This is because PLCs support high-level design languages, such as ladder logic, which is not just standardized but also much more efficient in terms of development time than machine language used by microcontrollers. (Green et al., 2016). On the contrary, machine language provides greater precision and control, resulting in higher operating efficiency, but longer development times.

Thirdly, PLCs can easily be fit into customized applications with minimum effort required for interfacing, especially since a number of important peripheral devices such as display units are pre-installed on a PLC. A microcontroller based device will require custom-built signal interfacing, peripheral device connections, and optimization.

Fourthly, documentation and troubleshooting is easier for PLC based devices than for microcontroller based devices. In most PLC based devices, the user can be expected to carry out some maintenance or troubleshooting functions on their own, but most microcontroller based devices are so tightly coupled that this is almost impossible. (Kok et al., 2015).

Thus, microcontrollers tend to be used in applications that, once installed, will be unlikely to be replaced in the near future or undergo modifications. These applications are custom built designs specific to one purpose and are supposed to be very long lasting. The development costs are higher, the development time is longer, but operating efficiency is also much higher. These devices can function at much higher speeds and achieve much greater levels of precision than their PLC based counterparts. However, testing, maintenance and replacement are all very expensive. Microcontroller based devices are either employed in singular, high cost, customized applications, or extensively tested and standardized mass produced applications.

On the contrary, PLCs are used to design devices that are more flexible and expected to be short-lived. Development costs are lesser, but operating efficiency may be lower as well. PLC based devices are intended to be used in applications where functionality may need to be modified at times by the user, or require slight adjustments occasionally. The base development and testing times are lower, and the application can easily be modified. PLC based devices end up being developed for medium cost applications and are rarely used in mass manufactured devices.  (Ramseyer et al., 2016).

Since the company intends to build a large number of devices, it is advisable to use microcontrollers. The initial development costs will be higher, but the large number of devices manufactured will offset this.

Reference

Mohini, A. (2015, November). Microcontroller based orbital motion shaker. In2015 International Conference on Intelligent Informatics and Biomedical Sciences (ICIIBMS) (pp. 115-120). IEEE.

Emilio, M. D. P. (2015). Microcontroller Design. In Embedded Systems Design for High-Speed Data Acquisition and Control (pp. 33-48). Springer International Publishing.

Kanigoro, B., Lie, R. E., & Kacamarga, M. F. (2015). Overview of Custom Microcontroller using Xilinx Zynq XC7Z020 FPGA. TELKOMNIKA (Telecommunication Computing Electronics and Control), 13(1), 364-372.

Machine, B. (2015). La Machine.

Saari, S. (2015). PLCopen XML-esitystapa sovellusten siirrossa.

Dai, W., Zhou, P., Zhao, D., Lu, S., & Chai, T. (2016). Hardware-in-the-loop simulation platform for supervisory control of mineral grinding process.Powder Technology, 288, 422-434.

Nielsen, S. T. (2016). U.S. Patent No. 9,335,192. Washington, DC: U.S. Patent and Trademark Office.

Green, A., Qi, Z., Park, C., Glaser, M., Maclennan, J., & Clark, N. (2016). Flow Meter Based on Freely Suspended Smectic Liquid Crystal Films. InAPS Meeting Abstracts.

Kok, G. J. P., van der Veen, A. M. H., Harris, P. M., Smith, I. M., & Elster, C. (2015). Bayesian analysis of a flow meter calibration problem. Metrologia,52(2), 392.

Ramseyer, S., Achermann, M., & Zimmermann, H. R. (2016). U.S. Patent No. 20,160,069,717. Washington, DC: U.S. Patent and Trademark Office.