Automation has become increasingly important in today’s context to compete in the global market. Programmable logic controllers (PLC) play a key role in this regard and are used in a variety of commercial and industrial applications. PLC is a digital computer used for controlling electromechanical processes such as machinery on factory assembly lines, amusement rides or lighting fixtures. Unlike general purpose computers, PLCs are designed for multiple inputs and outputs, resist vibration and impact, remain immune to electrical noise and work at extended temperature ranges. Programs to control machine operations are typically stored in battery backed or non-volatile memory.
By Jesus Milton Rousseau S and Sandhya Malhotra
Friday, February 17, 2010: PLCs may include logic for single variable feedback analogue control loop, a proportional, integral, derivative or proporational-integral-derivative (PID) controller. For example, a PID loop could be used to control the temperature of a manufacturing process. Historically, PLCs were usually configured with only a few analogue control loops. But where processes required hundreds or thousands of loops, a distributed control system (DCS) would instead be used. As PLCs have become more powerful, the boundary between DCS and PLC applications has become less distinct.
In India, the market is largely import driven and dominated by international players like Messung, Mitsubishi, Allen-Bradley, Siemens, Modicon, ABB, etc. Most of these manufacturers either have their direct presence in India or have alliance with system integrators and assemblers, who represent their products in India.
The year 2008 was not a bad year for automation. The PLC market grew at a moderate rate in spite of the economic slowdown. While a severe contraction period was expected in 2009, automation demand is expected to start turning around beginning 2010 as manufacturers face increasing global market pressures. Governments of many countries around the world are injecting money through various stimulus packages to prop up their economy. These programmes are expected to create new demand for automation equipment such as PLCs across industries. Manufacturing and infrastructure industries are already reviewing their strategies to employ more automation to reduce the cost of operations, which could help them become more sustainable and survive future economic turmoils, says a study ‘Programmable Logic Controller Worldwide Outlook, Five Year Market Analysis and Technology Forecast Through 2013’, conducted by ARC Advisory Group, a leading research and advisory firm.
Another study by the group titled ‘Programmable Logic Controller Outlook for India, Five Year Market Analysis and Technology Forecast Through 2010’ reveals that India’s growing economy and investment friendly policies are enticing many manufacturers to increase their capital spending, step up capacities to meet growing demand and improve the productivity of their existing manufacturing operations. This situation is propelling the robust growth of the PLC market in India. Besides, manufacturers want to achieve economies of scale and improve their global competitiveness. Thus, the demand of PLCs is increasing.
Commitment to service, technologically superior solutions and low pricing are among the key ingredients that ensure manufacturers’ success in the market. Other significant factors include establishing local manufacturing facilities, expanding distributor networks, working collaboratively, targeting growing industries and leveraging relationships with OEMs. The use of PLCs help them achieve all this. Ambrish Kela, managing director, Scientech Technologies Pvt Ltd, a company that provides technology training systems on PLC, says, “Refineries and automobile industries are in constant and growing need of PLCs.”
In India, companies usually assemble PLC products by procuring components from Siemens, ABB, Omron, etc. Sachin Tamhane, project head, Miranda Automation Pvt Ltd, a company that assembles PLC products in India, adds, “We sell complete systems and PLC is only one of the products. We buy PLCs from companies like Siemens.”
Kanday says, “In India, PLCs are being used for industrial automation to communicate with AC drives through modbus communication, control the speed of motor through encoder feedback, GSM protocol or radio communication. Also, we provide ethernet facilities to monitor motor data by creating specific IP address.”
PLCs with user friendly features, wide range and upgraded modules are the latest in the market. Kela adds, “PLCs with easy configuration, variety of choices and user friendliness are in demand.” Tamhane, “Upgraded modules as per the requirement of systems is the latest trend in the PLC market.”
PLC is mainly categorised from low to high end, depending on automation process, configuration and number of applications or logics of the programme. “The integration of PLCs cost approximately from Rs 14,000 up to Rs 600,000,” says Sushil Kumar Dubey, proprietor, Simatech Automation, a Mumbai based system integrator dealing with Siemens PLCs since 2006.
Scientech Technologies, an ISO 9001:2000 certified company, offers single board programmable controller. These PLCs come with features like ARM7 CPU running at 60 MHz, basic compiler runs >10 million lines of codes/sec and 32K flash memory and 8K SRAM memory, besides 24 TTL compatible digital I/O, 8 10-bit A/D converters, 100 KHz sample rate, 8 hardware PWM channels and internal supplies of 3.3V and 1.8V.
Another ISO 9001:2000 certified company Miranda Automation Pvt Ltd is engaged in manufacturing PLC programming automated systems, which are used to gain a complete control over process and equipment. These systems make the process accurate, yielding consistent product quality and material usage. These acquire process data and parameters and continuously record them batch wise, line wise and equipment wise. These systems generate alarms and can page or send SMSes to the supervising staff on critical process events.
“Components needed for assembling or manufacturing PLC products are relay card, microprocessor chip, ICs, filter capacitor, EPROM, RJ-45, RS-232, RS-485 communication ports, etc,” says Anil Kanday, senior service engineer, Neha Automation, a company that assembles PLC products. It offers complete systems for monitoring and controlling industrial plants.
BCH Electric Ltd, an ISO 9001:2000 certified company, produces and supplies multi-functional PLCs, which are suitable for a small sized control system. These PLCs allow users to expand IO points easily for analogue control or communication and integrate power module, CPU and I/O module without any separation module. These can process high speed operations with a built-in high speed MPU.
Harithaa Power Engineers is engaged in supplying a huge range of products related to industrial automation and system integration. As part of its product portfolio, the company offers 16k memory PLCs.
Ascent Automation also manufactures PLCs that can be used for automatically controlling, sequencing, timing and counting logic based applications. These are based on a single chip design, which improves reliability of these controllers. It is compact, low power and maintenance free replacement for conventional relay logic panel.
Dhruva Automation and Controls has introduced a new series of PLCs from IDEC Corporation, Japan. The smart relay series consists of a base unit and expansion units. It also has a built-in LCD display and a real time clock. The basic unit comes with 8 digital inputs and 4 digital outputs.
The requirements of the customers are unique and differ from vertical to vertical and industry to industry. So, the individual requirements and applications have to be considered while choosing a PLC. Kela cites, “Choices for PLCs are endless. It is purely based on the user’s needs and application.” Tamhane adds, “Selection of PLC is purely based on the requirements of the system.”
In any type of automation process, there are multiple third party modules, power supplies and products being attached to the PLC to achieve smooth functionality, interoperability and zero downtime. “Customers should always keep spare configuration of digital input and output status. Out of the whole programming, 70 per cent should be utilised and 30 per cent should be kept as backup. Moreover, the whole ecosystem of PLC should be easily scalable and flexible to incorporate any dejection or upgradation of the product and field instrument without shutting off the program,” states Dubey.
While purchasing PLCs, customer should keep in mind that they are user friendly, its integration and configuration should be seamless and complication free. “Instead of looking for low cost and compromising on performance, customers should go for high performance and low cost PLCs,” says an industry insider.
Similarly, Dubey adds, “We advise our customers to go for quality and trusted brands because any failure of hardware and downtime of the program can cost them thousands of rupees.” Hence, it is essential for buyers to get the PLCs from their local and reliable system integrators, who can also give prompt AMC and on site service support. Moreover, manufacturers and local system integrators offer paid training courses and classes for PLC maintenance to customers’ engineers.
Certain PLCs may not support every type of instruction. Thus, one needs to choose a PLC that supports all instructions for a specific application. For example, built-in PID functions are much easier to use than writing one’s own code to perform closed loop process control. Before choosing a PLC, a customer should determine whether the system will be installed from scratch or are there existing products compatible with it. Ensuring this will save them time and money. A customer should also define environmental issues like temperature, dust, vibration, codes specific to his facility, etc, that can affect the application. This is important because typically PLCs have an operating temperature of 0-60 degree celcius.
Determining number of discrete and analogue devices a customer wants in the system is another important factor as it is directly linked to the amount of I/O that will be necessary for the system. A customer should also keep in mind the specialty feature requirement. Will the application require high speed counting or positioning? What about a real time clock or other specialty feature? These are very important questions that must be considered before choosing a PLC. Specialty functions may not necessarily be available using standard I/O modules. Planning ahead to determine whether or not the application will require any feature can help a customer determine whether or not any additional specialty module is needed.
A customer should also check the type of CPU to be chosen and how much memory will the system require. How many devices will it have (determines data memory); how large is the program; and what types of instructions will the program include (determines program memory) should also be taken note of. Data memory refers to the amount of memory needed for dynamic data manipulation and storage in the system. For example, counter and timer instructions typically use data memory to store set points, current values and other internal flags. If the application requires historical data retention, such as measured device values over a long period of time, the size of the data tables required may determine the CPU model. Program memory is the amount of memory needed to store the sequence of PLC program instructions that have been programmed to perform the application. Each type of instruction requires a specific amount of program memory, typically defined in a PLC’s programming manual. Applications that are basically sequential in nature can rely on the I/O device rule of thumb to estimate program memory; complex applications will be more difficult to judge, but memory has become relatively inexpensive and fairly easy to upgrade if necessary.
A customer should also consider the location of I/O. Will the system require only local I/O or both local and remote I/O locations? If subsystems will be needed at long distances from the CPU, a PLC model is needed that supports the remote I/O.
According to experts, determining communication requirements is another criterion for choosing the right PLC. Will the system be communicating to other networks or systems? Customer need to consider this before choosing a PLC. Communication ports are not necessarily included with a PLC. Knowing ahead of time whether or not the system will be communicating with other systems can help customers to choose a CPU that supports the communication requirements or additional communication modules if necessary.
Does the application require only traditional programming instructions or are special instructions necessary? These considerations should determine the customer’s programming requirements.
For maintenance of PLCs, high level technical skills are required to keep them going. Customers should keep competent engineers with right knowledge of PLC applications, instructions, programming, trouble shooting, interfacing and ability to work on varied brands of PLCs, drives, MMI and SCADA.
Besides, cleanliness of systems, regular checkup of the hardware and software and maintaining room temperature are also very critical to keep the operation hassle free. Essentially, the temperature should be maintained between 30 to 40 degree celcius (throughout the year). “PLCs are highly sophisticated and heavy duty, therefore consistency in temperature should be monitored and controlled to enhance the life cycle of PLCs,” says Dubey.
Amit Dange, branch head, Industrial Controls and Applications, adds, “With regard to PLCs and programming terminals, the maintenance engineer should be able to access specific parts of the program and examine the I/O status. He should be capable of making small changes in the program.”
The other important issues a customers should keep in mind are maintain backup copies of the PLC programs every six months regardless of change status; if a PLC program has been changed, it should be documented in the software copy; copies of the PLC program should be stored on a reliable storage device and; all PLC 110V control voltage should have a line filter on it.
Electronics Bazaar, South Asia’s No.1 Electronics B2B magazine