PLCs are definitely changing. At the low end, in the sub-$1,000 price range, nano and micro-PLCs are gaining capability and offering lots of bang for the buck. At the high end, PLCs are becoming more like PCs every day. Sales are soaring and PLCs are here to stay.
Even market analysts, who predicted for years that industrial PCs would eventually replace PLCs, have given up on that story line. "That dog won't hunt," was the universal response to the analysts' PC takeover theories.
"Omron does not feel PCs will ever replace PLCs," says Jon Giardina, PLC market manager at Omron Electronics (www.omron.com). "PLCs are also now applied in applications where they couldn't be applied before. The barriers in cost and programming are disappearing. In addition, PLCs offer platform stability and long-term availability that PCs don't offer."
Rockwell Automation agrees. "So far, PC-based soft control' has not addressed the end user's overriding need for reliability, durability, and ease-of-use," says Mike Miclot, marketing manager at Rockwell (www.ra.rockwell.com). "These are three attributes that PLCs offer in abundance."
You can see some of those new capabilities in the first of this two-part roundup of PLC products that follow.
Duplex PLC Goes Redundant
The CS1D duplex programmable controller has two CPUs. If a problem arises in the primary CPU, the PLC automatically switches control to the second unit within one program scan, enabling continuous operation. The faulty CPU can be replaced while operation continues. Redundant power supply and communication modules can also be removed and replaced without interrupting control operation, and it has hot-swappable I/O and specialty modules. Prices start at $11,500.
The PACSystem RX7I has four times the speed of GE's existing PLC backplanes and up to 10 MB of memory for programming and documentation storage. It is VME64-based, supports all standard VME modules including Series 90-70 I/O, and supports distributed I/O via Ethernet, Profibus, DeviceNet, and Genius networks. Programming is via Cimplicity Machine Edition software, and the control engine is built on standard embedded architecture with commercial deterministic operating systems.
The SixTRAK IP has open-Linux firmware, five Ethernet and three serial ports, HART compatibility, and a 32-bit PowerPC. User programs may be created using standard ISaGRAF IEC 61131-3 programming tools or high-level C++ programming with a free Linux compiler. An embedded Linux web server runs web pages created using any standard HTML development tool. For most applications, no knowledge of Linux is required--the embedded Linux platform is transparent to users.
Logic Module Replaces Switches
The Logo! programmable logic module handles 130 function block and ladder logic operations in any combination, including timers, counters, and others. It has a backlight display that shows values, parameters, and text on the same line. Programming eight basic and 26 special functions is via SoftComfort v. 4.0 software. The module can be used as a replacement for conventional switching devices.
Siemens Energy & Automation
Flow Computer for PLC
The MVI71-AFC flow computer for Allen-Bradley's PLC platform measures hydrocarbon gases and liquids using AGA 3, 7, 8, and GPA 15 and 25 measurement standards, and API 2540 calculation standards. The module uses process data collected by PLC analog I/O modules to calculate flow rates, accumulated volumes, and accumulated mass. The results of the calculations are transferred back to the processor for use in the application ladder logic, or for transfer to a SCADA host.
Controller Gets Connected
The CompactLogix 1769-L35E has 10/100 Mbps Ethernet/IP communications, I/O memory capacity up to 1.5 MB, and a DeviceNet network interface. It can support up to 32 simultaneous HMI and I/O connections over Ethernet/IP and up to 64 devices on DeviceNet. Advanced diagnostic and data monitoring capabilities are available via Ethernet and web interfaces. Applications include material handling, conveyors, and packaging.
Industrial PC Fits In
Rugged TECLA programmable data processors have USB, Ethernet, PS/2, serial and embedded I/O, and allow Allen-Bradley I/O to be directly plugged into the unit. Options include extra serial ports, PCMCIA/Cardbus, and DeviceNet. The PC has a Microsoft Windows CE.NET v. 4.2 operating system. Disk-on-chip storage eliminates shock, vibration, and grit problems, and the PC does not need a fan.
Look for the second installment of "PLCs Change Names and Application the week of November 24.)