When a PLC is not what you expect
Control engineers are very familiar with the concept of the programmable logic controller (PLC). Since its introduction nearly 40 years ago, the PLC has become a standard tool in manufacturing control and automation. Having been around for so long, the PLC now carries with it a certain level of expectations—how big it is, what it can do, how it operates, and etcetera.
Like most other aspects of our world these days, advances in technologies are not only accelerating what our tools can do, but also their form factor. Yet our expectations are often slow to catch up to these realities. The PLC is no exception.
WAGO Corp., a manufacturer of electrical and electronic components for use in automation, recently introduced a its 750 Series Programmable Fieldbus Controller (PFC). Appearing similar to the company's slave I/O hardware, the PFC is often not thought to be what it is—a fully functional PLC.
Programmable Fieldbus Controllers
The PFCs are available with built-in Ethernet or with support for DeviceNet, Profibus, Modbus, Interbus, CANopen, and LONworks fieldbus protocols. Standard features include:
The WAGO PFC offering is an extension to the company's I/O System 750 Series, encompassing bus couplers, ECO couplers, PFCs, and I/O modules/cards.
According to WAGO, its PFC is the smallest, modular, fieldbus independent, programmable I/O system available and it packs the same, if not more, power than PLCs provided by the industry's larger automation suppliers.
Mark DeCramer, WAGO product manager for advanced electronics, says the PFC has two principal uses: 1) as a stand-alone controller talking to local I/O or communicating to other Ethernet or serial devices as an Ethernet master; 2) as an add-on to existing or legacy systems for added functionality, performance enhancement, or to provide data collection capabilities for sharing over an Ethernet network.
One issue that leads many to believe the PFC is just I/O hardware is the price. At less than $600 for a DIN-rail mountable system, the 750 Series PFC checks in at nearly $6500 less than its main PLC competitor.
The PFCs with built-in Ethernet capability, which supports all Internet protocols (including EtherNet/IP), allows the controller to connect with manufacturing execution systems as well as send machine alarms or maintenance notifications via email to PCs, pagers, or cell phones. Other benefits of the Ethernet PFC include:
Use of decentralized control for optimal processing of subtasks;
Dividing complex applications into multiple tasks;
Utilization of existing Ethernet infrastructure and IT standards to reduce commissioning and configuration costs.
Direct communication via local or global networks (LAN, WAN, Internet)
Real time clock for time stamping of events;
Eliminate costly fieldbus scanner cards and cabling systems;
The PFC's broad level of fieldbus protocol support allows machine builders to build their I/O structure as needed and then install the PFC with the protocol capability required by the end customer. All WAGO I/O modules are interchangeable with all WAGO PFCs, permitting communication to the existing plant network and local machine control.
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WAGO I/O cards' interchangeability is an important consideration for both control engineers and machine designers with an eye toward future-proofing their automation purchase decisions in light of increasing Ethernet use. The universal nature of these cards requires only the replacement of the WAGO PFC or coupler linked to an existing node in order to change the fieldbus protocol (for example, converting from DeviceNet to EtherNet/IP). Field wiring to the I/O cards remains intact. For machine builders in particular, this capability reduces machine life cycle and future scalability issues.
The granular I/O card design of the 750 Series allows machine builders to use only the I/O required for the application. Most PLCs require 16 or 32 channel I/O cards. The 750 Series can be configured in 1, 2, 4, or 8 channel I/O modules. DeCramer says, "Whether you use a bus coupler, an ECO Fieldbus coupler, a PFC, or an industrial PC from WAGO, they all connect to the same 750 Series I/O cards. Other manufacturers don't offer this. You have to buy a specific I/O card for specific controllers. We have multiple network solutions with one, universal I/O card system."
WAGO offers more than 100 I/O modules for digital, analog, and special functions such as serial interface, AS-interface master, up/down counters, encoder interface, and pulse interface. The modules, measuring 12mm wide, are recognized as being the smallest in the industry. Because the I/O is DIN-rail mountable, additional I/O modules can be easily added in the field.
The PFC system's software—WAGO-I/O-PRO—supports all six IEC 61131-3 standard programming languages. The software (included in the less-than-$600 list price of the system with a built-in visualization/HMI tool) is provided via site license, meaning that it can be used on as many PCs as desired with no additional charge. "Our IEC 61131-based software allows users to program in one or a combination of all six programming languages," says DeCramer. "Users have the flexibility to create a function block that performs a unique function in one language but use it in a program that's written in another. The programming can also be converted from one language to another based on customer requirements." WAGO also offers a software solution called WAGO-DLL, which allows a machine software programmer to program proprietary automation code in Visual Basic or C.
WAGO-I/O-Check is another provided software application that allows users to read the node (I/O configuration) and display it graphically on a PC. The graphic can be printed out along with a configuration list to provide complete node documentation. Users can also display and determine the process data of the I/O modules, thereby permitting field wiring for devices such as sensors and actuators to be checked before start-up.
Additional features of the 750 Series include:
Cage Clamp spring pressure connection technology. Introduced by WAGO in 1977 for easy and fast wiring (60% faster than traditional screw connections), Cage Clamp provides users a vibration proof, corrosion resistant (stainless steel clamping mechanism and gas tight connection), temperature cycling resistant, and maintenance-free connection; and ease of use.
The ability to mix and match different signal types, power, and special functions in one node;
PLC program is stored on the controller (no battery back-up required)-up to 512KB of program memory;
Built-in diagnostics on the controller; and
24KB of non-volatile memory for data logging.
To read Control Engineering coverage of WAGO, click here .
For more infomation:
N120 W19129 Freistadt Rd.
Germantown, WI 53022
PH: 800-DIN-RAIL (346-7245)
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