MicroPLCs - more popular than ever
Programmable Logic Controllers (PLCs) have not been, nor will they be soon, completely replaced by personal computers (PCs).
-- Control Engineering Europe, 7/1/2000
The biggest reason for this is the strength of the microPLC. For small, stand-alone control of a single process, microPLCs are more cost effective, more compact, and easier to use than PC-based solutions.
Functions previously reserved for large PLCs are now routinely found in microPLCs. Some examples are floating-point math, high-speed counters, and analogue functions.
Control Engineering s 2000 study focused on the perceptions and attitudes of 384 readers in the U.S.A. who are involved in specifying, recommending, and/or buying PLCs. The study explored:
- Types of PLCs used;
- Major applications for PLCs;
- How PLCs are interconnected with overall control systems; and
- Preferences for programming languages.
PLCs were categorised by number of I/O points supported. Micro has less than 128; medium is 128 to 512; and large PLCs have over 512 points. More respondents (77%) use microPLCs than other sizes. Medium PLCs were used by 70% of readers. Only 40% reported using large PLCs.
New markets for
PLCs
Do
you think PLCs are devices for discrete manufacturing alone? Consider this:
while 8 of 10 reported using them for machine control, two-thirds use PLCs in
process control, and one-third cite batch process applications. Many have both
process and machine control applications in their plants, since the result is
greater than 100%.
Only a few years ago, integrated motion control in a PLC was often considered a tricky application. Now, 40% of respondents are using PLCs in motion applications. PLCs have found a niche in virtually all types of manufacturing.
Automation is heading toward tighter integration of multiple control disciplines, such as high-speed discrete, motion, process, and drive control.
Ethernet leads
connectivity
Almost half (46.5%) of respondents use Ethernet for networking PLCs. This
number is up six percentage points from 1999. Many network protocols received
increased responses over 1999, led by Profibus-up from 4.0 to 9.0% of mentions
and DeviceNet-up by three points to 15.4% of mentions.
Stephan Borres of Schneider Electric explains, 'Seamless information flow has become the key to automation success. The use of open architecture, including the Ethernet, PCs, and the web, is now driving the market. The PLC has become a component of the flow, not the organiser. Customers are shifting to smaller but more powerful PLCs with embedded intelligence and Internet technologies.'
American PLC
programming
Almost all Americans (93%) program PLCs with Ladder Diagram editors,
which has always been the most popular language in the U.S. About one in five
use function block programming, which is an increase of three points. The
international standard IEC 61131-3 gained much publicity in 1999, and some
companies state compliance with the standard prominently in their marketing
programmes. However, respondents were almost evenly split over whether adherence
to the standard is 'somewhat important' (41%) or 'not important at all' (39%).
Only seven percent said adherence was a must.
Wayne King of Siemens sees future software as 'going beyond just programming, to something more like a project management tool. Programmers not only must control the source, but also must see that everything is properly co-ordinated.'
In the future, the survey shows that 35% expect to buy PLCs with more remote I/O modules. About three in 10 plan to purchase PLC I/O modules to network with PCs, and two in 10 expect to replace PLCs with PCs running soft logic. One in 12 (8%) look to add web-enabled PLCs.
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Palm-size comes to PLCs |
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Ultra-slim PLC Measuring just 90 x 65 x 33 mm, CPM2C offers several communication methods, including RS-232, host link, and standard serial devices, such as bar code readers. When used with an Omron NT631/31 HMI, the CPM2C micro PLC can be programmed via a programming console embedded into each HMI. Programming can also be accomplished through a PC using Omron s software, or through a hand-held programming console. Expandable up to 140 I/O points, other specifications include: 14 basic and 105 special instructions, 4,096- word program capacity. Built-in features such as real-time clock, RS-232 port, and synchronised pulse control help reduce system cost by eliminating more costly peripherals. Omron Electronics Ltd., 1 Apsley Way, Staples Corner, London NW2 7HF U.K. |
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Micro has high
performance CPU This smallest B&R PLC is fully compatible to the larger products and supports Ethernet communication as well as deterministic I/O reaction times of less than 10 microseconds. B&R Industrie-Elektronik Ges.m.b.H., A-5142 Eggelsberg 120, Austria |
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More
power, smaller housings |
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Fuzzy
microPLC |
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A cost-effective relay replacer The FX0S is a controller for users who are familiar with the advantages of a PLC, but whose application requires less than 30 I/O. It allows you to replace the functions of discrete control relays costing several times that of the PLC by using a comprehensive array of timers, counters and data memory. The FX0S works with AC (100-240 V), DC (12 or 24 V), transistors or relay switching (up to 2.5 A). It includes a 200 mA power supply, allowing you to remove the hidden cost of a separate sensor power supply in most cases. You can even implement closed loop control by tracking encoders or other pulse generating devices at up to 7 kHz, while simultaneously generating a 2kHz pulse output and hardware interrupts. Mitsubishi Electric, Gothaer Str. 8, D-40880 Ratingen, Germany |
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A
family of 14 microPLCs |
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MicroPLC with built-in MMI The newest feature, to be released in autumn 2000, is SMS messaging. A GSM-based cellular phone can receive or send data to an M90-run machine or process, thereby providing remote control from any location. Unitronics, POB 733, 71103 Lod, Israel |
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This
microPLC likes it rough |
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Compact process control The PCD1 (shown here with a D16 control terminal, a small MMI device, attached) has a base unit with 4 slots which can be equipped with digital or analogue modules, or with counting, measuring, and motion control modules. The maximum I/O capacity is 64. The base memory is 17kB of RAM which can be expanded to 140 kB. Each unit has two communication ports, one for the programming unit and the other for RS-485. The RS-485 port is most commonly used for SAIA s proprietary S-Bus. There are also network coupling modules for Profibus and LONworks. A real-time clock and an integral watchdog timer are included. SAIA Burgess Electronics AG, Bahnhofstrasse 18, CH-3280 Murten FR |
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New
analogue addition |
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New
series of microPLCs from Hitachi The EH-Micro is an expandable series of microPLCs, offering between 10 and 84 I/O points. The microPLCs were developed with special consideration being given to network capabilities, international standards, and the reduction of EMC noise. The compact package includes pulse width modulation (PWM) and pulse train outputs, interrupt inputs, a 32-bit RISC processor, a high speed counter input and a real time clock. Analogue data processing is also available and the microPLCs can be programmed with Hitachi s PLC programming software Pro-H. HID Ltd., Shuttleworth Close, Gapton Hall Industrial Estate, Great Yarmouth, Norfolk NR31 0NQ, UK. |
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