Supercharging Your PLC System
What if you didn't have to choose between a PLC-based system and distributed intelligence for a process control system, but could have the best features of both? What if you could supercharge your industrial PLC system for process control?
Here's a way to do just that, by adding intelligent remote I/O to your existing PLC-based system.
EtherNet/IP for Communication
Like a DCS, PLC-based systems used to be closed and proprietary. But today many such systems—for example, Allen-Bradley® ControlLogix® and CompactLogix® PLCs—use a common communication platform consisting of an Ethernet network and EtherNet/IP™, an industrial protocol developed by A-B and currently supported by ODVA (Open DeviceNet Vendors Association).
The major advantage of EtherNet/IP is that it provides a widely used, standard conduit for communication between products from various vendors. So a PLC that uses the EtherNet/IP protocol can communicate easily with devices from other manufacturers. And this interoperability gives you choices.
Like your Information Technology (IT) department, which may use Microsoft® software and Dell® computers but chooses printers and peripherals from other vendors, you as a control engineer can use EtherNet/IP-capable hardware and software, such as Allen-Bradley CompactLogix and ControlLogix PLCs and RSLogix, but choose I/O for specific purposes from another vendor.
PLC systems by their very nature do not include distributed control. As you are well aware, when you add analog I/O, you must also add new ladder logic to process that I/O. But additional logic and more I/O points eat up processing power, impacting overall system performance by increasing network traffic and slowing scan times.
One of the more exciting choices EtherNet/IP presents, however, is the possibility of augmenting a PLC-based system with I/O that's designed for process control. You can choose to add the distributed intelligence of a DCS to a PLC-based system.
SNAP I/O™ from Opto 22 can augment an A-B ControlLogix or CompactLogix system—or another PLC system that uses EtherNet/IP (such as MicroLogix 1100/1400)—by doing exactly that: providing intelligent remote I/O that offloads many I/O functions, especially those involving the heavy analog signal processing required by most process control applications.
With remote I/O that handles such analog control functions as ramping, thermocouple linearization, analog scaling, and proportional-integral-derivative (PID) loop control, the PLC can continue to do its normal job with little impact.
The No-Programming Alternative
In a PLC-based system, communication with most remote I/O is through a bus coupler. In the past, putting intelligence at the I/O level meant buying another PLC and programming it, either in ladder logic or by learning a new programming language. Both require development time and expense.
The advantage of Opto 22 SNAP I/O is that it does not require programming. All I/O functions are built into the I/O, in a device called a brain. The brain provides communications, like a bus coupler, but it also provides automatic I/O processing. As soon as the I/O is configured, the brain immediately begins processing. Compatibility with A-B PLCs is guaranteed because SNAP I/O is EtherNet/IP conformance tested by ODVA.
Built-in Remote I/O Functions
For process control applications, the following built-in analog control functions in SNAP I/O are especially useful:
- PID loop control (up to 96 loops per brain)
- Minimum and maximum values
- Analog scaling
- Engineering unit conversion
- Thermocouple linearization
- Temperature conversion
- Watchdog timeout
- Output clamping
In addition, SNAP I/O offers these serial and digital functions on the same I/O rack:
- Multiple serial device control (RS 232/485)
- Input latching
- Digital filtering
- Quadrature counting
- High-speed counting
- Watchdog timeout
- Pulse generation
- Pulse measurement
- Time-proportional output
- Frequency and period measurement
The ability to add all these functions in remote I/O with no programming and little impact on the overall system may well be the supercharger your system needs to succeed with new process control tasks.