Analog I/O Serves Real-World Control

When Users Require Large Chunks of Complex Data and Need It Fast, They Still Turn to Analog I/O Hardware

By Jim Montague, Executive Editor

Sometimes ones and zeroes in their tiny time slices aren't enough. Sometimes a manufacturing process, machine application or production line just needs a nice, fast, old-fashioned, undivided analog signal.

Of course, most of today's signal data moves from sensors through digital I/O components, following the lead of digital networking and higher-level computing functions, which have reached ever further down into the device and I/O levels in recent years. Still, the visible world remains an analog environment, so temperature, power, pressure, flow and other physical variables must sometimes be measured closer to the undiluted form in which they were generated — and not in the series of snapshots in which digital data is typically captured and transmitted.

SEE ALSO: All About Analog I/O

Analog Update
Integrated Industrial Systems (I²S) in Yalesville, Conn., builds cold rolling mills and control systems for ferrous and non-ferrous applications and long has used PLCs to control its mills, as well as a gamma gauging system to accurately control metal thickness. To update its gauging system's outdated hardware and software, I²S required a custom measuring device with accurate analog I/O and advanced processing to convert sensor signals into accurate thickness measurements, but the usual PLCs didn't have enough speed and signal processing capabilities.

So I²S adopted CompactRIO programmable automation controllers (PACs) from National Instruments, and used NI's LabVIEW graphical programming tools and real-time function blocks to program its field-programmable gate array (FPGA) and real-time processor.

Each rolling mill contains three networked CompactRIO systems, which are intelligent nodes that communicate with myriad controllers using Modbus/TCP, TCP/IP and UDP protocols. The three CompactRIO systems are connected via Ethernet and use UDP Ethernet messaging
protocol to transmit thickness measurement calculations in less than 20-ms intervals.

"CompactRIO's analog I/O and digital I/O modules connect to the mill's gamma-based thickness sensors, and its embedded FPGA allows us to customize the I/O rates and synchronization," says Clark Hummel, senior development engineer at I²S. "The data received from the sensors then is processed in the real-time processor using real-time, floating-point function blocks to convert data from the sensors to accurate thickness measurements. LabVIEW real-time performs deterministic, advanced logarithmic processing on the data received from the FPGA to calculate thickness measurements. The CompactRIO systems perform all of the I/O and signal processing in the FPGA and real-time processor, and transmit high-accuracy thickness measurements to connected PLCs without slowing down existing PLC control loop rates. With this performance, we were able to add this custom measurement and analysis for our gamma-based sensors without compromising our control rate speed."

More, Faster Signals = Better Control
Similarly, test-rig builder Sitia in Nantes, France, has to deal with a widening range of I/O signals required by the equipment it builds. It manufactures standard and modular, turnkey, automatic test rigs for simulating mechanical, physical, hydraulic, pneumatic, climatic and electrical parameters. These devices are used by industrial and technical laboratories to test material fatigue, quality measurements and parts characterization, hardware in the loop (HiL) and quality in the automotive, aerospace, railway, bicycle, wood and furniture, civil engineering and other industries (Figure 1).

Tests are defined by the equipment users, and Sitia's engineers design rigs for each based on a precise spec sheet, which they and the customer develop together. Lately more clients request machines that go beyond meeting their test requirements in order to give them more flexibility to exchange sensors, actuators and related I/O points for subsequent tests.

"Industrial laboratories need machines tailored precisely to their tests," says Fabien Arignon, Sitia's managing director. "However, at the same time, they also demand independence, which means they don't want to constantly rely on their supplier if sensors or actuators have to be added to or removed from the machine, or if settings have to be changed and parameters entered. We had to come up with a solution that would allow us to offer this flexibility."

These considerations ultimately led Sitia to the concept of a modular, universal test rig. "Modularity and the standardization of components form the matrix of our new machines," Arignon says. "This modularity exists on several levels and extends from the mechanical components to the controller. With respect to the controller, test systems differ from most other automation applications in that they encompass a large number of sensors and actuators in various versions. On the one hand, we wanted a higher degree of modularity, but on the other, the configuration of the hardware and software had to be simple to adapt."

As a result, Sitia selected EtherCAT analog I/O terminals from Beckhoff Automation because they acquired measured values with 0.01% accuracy, enabled the modularity and scalability of Sitia's equipment, and covered the wide range of I/O signals the test rigs needed to handle. Also, Sitia uses Beckhoff's TwinCAT PLC as the new test rig's universal programming and automation software and NI's LabVIEW software as the operator interface. Data is exchanged between TwinCAT and LabVIEW via Beckhoff's communication DLL.

"With EtherCAT terminals, we can acquire measuring signals directly in the standard I/O system, which considerably simplifies the control architecture," Arignon explains. "In addition, we and our customers know LabVIEW well, and it's particularly interesting for us because of its software libraries for the visual representation of measurements in diverse formats, such as digital or dial displays, curves, tables, etc."

Consequently, combining analog I/O with new software and networking helped Sitia achieve its vision for a modular, universal test rig and enables its users to configure their machine independently. "I/O reserves are provided, so users can add or change sensors and actuators, as well as the necessary measuring modules in their machines, depending on needs," Arignon adds. "The changes are specified in a table under LabVIEW and passed on to TwinCAT. Special knowledge isn't required on the part of the user because the software is easy to use."

Black Boxes Join Networks
While analog I/O were traditionally used as stand-alone devices in process applications from oil and gas to textiles, specialized components allow them to do more varied jobs in more integrated, diverse settings, according to Kurt Wadowick, Beckhoff's safety and I/O specialist. "Analog I/O specialty modules now can do power monitoring at the terminal level and examine voltages, currents and analyze three-phase power," Wadowick says. "This is possible because the cost of converting chips inside I/O modules is down, and their availability is way up. Also, analog I/O modules have more channels available now, and they have better integrated circuitry that's come a long way in recent years."

While most analog I/O terminals still only cost a couple of hundred dollars on average, Wadowick adds that their more-capable, less-costly microprocessors allowed them to evolve from stand-alone black boxes with proprietary software to more-capable and connected devices that can handle more different jobs. "This is why we brought analog I/O into our system, so we can eliminate the black box and make its functions less costly to implement," he explains.

"EtherCAT's high bandwidth can work with a high-speed strain-gauge terminal, which used to run stand-alone in a weigh-scale application, and instead use analog I/O devices such as our EL3xxx series terminals to do readings and pass along data to the overall system. Specialty analog I/O terminals can check voltage and current inputs and perform condition monitoring, such as using an accelerometer to establish the baseline frequency on a large bearing, and then using a vibration terminal to pick up bangs and knock as it wears. In classic voltage measurement, as analog I/O terminals can see finer and finer increments of voltage changes, it allows users to do more and more precise control."

Retrofit and Revive
Ironically, bringing in old-style analog can improve the performance of machines with seemingly more modern digital controls. For example, R&B Plastics in Saline, Mich., builds continuous-extrusion, blow-molding machines with wheel-and-shuttle and calibrated, water-cooled neck finishing for high-volume output. They're designed to accommodate multiple parisons, multilayer coextrusion and in-mold labeling of 12-ounce to 2.5-gallon containers (Figure 2).

Tight parison programming and control are needed to maintain production, reduce cycle times and achieve optimum wall thicknesses of continuously extruded profiles, but still minimize raw material waste. Besides programming parison controls, R&B also offers its users scalable control retrofits of their parisons.

To meet its high-speed, high-volume goals, R&B's blow molders must employ equally high-volume data processing. So R&B uses ControlLogix Fast Analog I/O modules from Rockwell Automation, which use on-board data-archiving to increase system throughput by reducing overhead required to collect data. This module also has four archiving inputs and two outputs, which generate fast sample rates, while decreasing backplane traffic for optimized system performance. In addition, Fast Analog lengthens the time between I/O data transfers, relieving R&B's controller of burdensome information and decreasing process disruptions. The analog I/O module's data archiving also helps R&B's users make sure their quality expectations are being met, even though their applications are increasingly complex and fast. Finally, its data archiving feature allows for configuration options, such as data type, tag generation and establishing connection between the controller and the high-speed analog I/O module.

Going System- and Plant-Wide
Just as analog I/O can bring faster, more holistic signals from an individual machine, it can do the same for overall production lines and facilities.

Filtros Tecfil in Guarulhos-SP, Brazil, manufactures 5.5 million automotive filters per month and exports to more than 120 countries. However, until recently, it controlled production data manually with paper forms and Excel spreadsheets, and machine stoppages were communicated through a synoptic panel that didn't provide enough data on time and cause.

To reduce its downtime, Tecfil brought in system integrator GMR Consultoria, which recommended its two-part GMR Olho Vivo solution to acquire analog and digital signals via improved sensors and wireless networking on its filter-assembling machines. The first section includes a rack with an 18-channel, isolated digital I/O with a Modbus TCP networking module and an eight-channel, isolated analog I/O also with Modbus TCP, both from Advantech. This hardware acquires data and passes it to a central server, where the second section, GMR Olho Vivo software, analyzes and converts it to usable information, transmits it to displays at strategic production points and integrates with ERP/MRP managerial systems.

Each display can show different information, so users can see and act on relevant data for their area. The system administrator also can receive data on instability and equipment failures via email or text messages. Tecfil reports its new analog and digital I/O and analysis has saved time by automatically gathering data and recording event times, so technicians can focus on root-cause analysis, identify priorities and develop actions plans much faster.

Likewise, Advantech reports that these analog I/O can help control and coordinate the larger numbers of CNC machines now running in many plants, easily join and participate on existing networks, and help managers quickly understand abnormal events, restore normal functions faster and reduce downtime. While a PLC can acquire CNC signals, this option can be costly and result in poor data immediacy. In this CNC scenario, the digital I/O module can collect all switch data from a plant's CNC machines as states change, while the analog I/O detects current changes on the machines to help control their workloads. Using an Ethernet interface, both modules can be integrated into a plant's original network architecture and transmit on-site signals to its overall distributed network control server via Ethernet switches.