August, 2016
www.us-tech.com
Page 53 The Case for PC-Based Machine Control over PLCs Continued from previous page
isolation, which eliminates the ground loops that commonly plague other field buses. Many control sys- tems employ solid state relays to con- trol devices such as motors, solenoids and lights. The ability to control these
relays by Ethernet is highly desir- able, because it adds a layer of fail- safe operation to that control. Relays often control devices that must be turned off in a fail-safe manner for safety reasons (for example, to pre- vent injuries to people or equipment). When such a situation arises, the relay must turn off, even if the relay rack has malfunctioned. In order to accomplish this, the relay rack must work in harmony with interlock and/or emergency stop contacts. Controlling solid state relays over Ethernet enables this control.
Programming. PLCs are pro- grammed using either one of the lan- guages specified in IEC61131-3 (lad- der logic, instruction list, etc.) or some proprietary vendor language, whereas PC-based controls can use programming languages, including C, C++, and .NET. These languages offer unparalleled flexibility and easy integration.
For some applications, the dif-
ference in cost between a PLC and a PC solution may be quite significant, depending on the requirements for performance, expandability, environ- ment, and development work. When the application requires the control system to fulfill demanding calcula- tions, handle complex network loads and process a lot of data, the PC- based solution will most likely be the best choice even though the initial cost of a PC might be higher. The advantage is that it provides a very powerful system for which the cost increases only incrementally when more performance is required. Although PLCs generally start at a lower initial cost, they can quickly become more expensive than a PC when high performance is needed.
Today’s PC Controllers Today’s PC controllers continue
to advance dramatically in terms of power and capacity, as well as robustness. This makes them excel- lent products for integration into today’s increasingly complex manu- facturing lines and workstations with their high demands for process and control capability, data collection and analysis, complex operating sys- tems, and user-friendly GUIs. The Sensoray Model 626 PCI,
which is an integral part of the above-mentioned OEM’s glass prod- uct inspection systems, is an exam- ple. This higher level of control increases efficiency and reduces costs by allowing glassmakers to configure only the functions they need on a modular platform. To reduce capital expenditures while maintaining flex- ibility, the manufacturer can add additional inspections on the existing platform as the need arises. Such configurability and expandability is possible with the capacity provided by the PCI. Product inspection parameters can be pre-programmed for easy recall, thereby reducing downtime for job changes. The 626 combines several popu-
lar interface functions on a half-size card. It has six, versatile 24-bit coun- ters that support incremental encoders as well as single-clock sources, 48 bidirectional digital I/Os (40 with edge detection), 16 differen- tial analog inputs, 4 analog outputs, and a watchdog timer.
Enabling Advanced Technology The 626 PC controller has pro-
vided expanded capabilities for the OEM’s multi-functional inspection systems; but the Sensoray model 826 has enabled the launch of a new tech- nology advantage for the OEM’s flag- ship inspection system line, due to the added capabilities of this next- generation PCI. The Sensoray 826 is
a versatile analog and digital I/O sys- tem on a PCI Express board. It has 48 digital I/Os with edge detection, sixteen 16-bit analog inputs, eight 16-bit analog outputs, six 32-bit counter channels, a watchdog timer with fail-safe controller, and a signal router. The board’s high perform- ance, compact size, and abundant resources suit it for a wide range of measurement and control applica- tions, including tracking and process verification, and identification of trends.
Both the PLC and PC have the
ability to control a multitude of devices using familiar industrial communication networks and more cutting-edge Ethernet-based coun-
terparts, but the PC is equipped with a more open and flexible array of interfaces that give the user access to more off-the-shelf devices to handle tasks that a PLC could not usually handle. Overall, the PC is a better
choice for complex control tasks and particularly for advanced processes requiring considerable memory. Robust and reliable, they excel espe- cially in applications where a PLC would have limited storage and pro- cessing capabilities. Contact: Sensoray, 7313 SW
Tech Center Drive, Tigard, OR 97223 % 503-684-8005 fax: 503-684- 8164 E-mail:
info@sensoray.com Web:
www.sensoray.com r
Some devote their lives to
SCIENCE and some to
HELPING OTHERS. The fortunate few get to
DO BOTH.
Dr. Mike Bixenman, CTO
At KYZEN we go way beyond just getting the CLEANING SCIENCE right. We care enough to thoroughly understand your unique process and needs first, so we create the most effective cleaning technologies for your specific situation. When science and care converge, it makes all the difference.
WORLDWIDE ENVI V RONMENTALL LY RESP PONSI S BL LE CLEA E NING TECHNOLOGIES
KYZEN. COM See at NEPCON South China, Booth 1P01 and at MD&M, Minneapolis, Booth 1112
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88