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Networking the Loop

March 4, 2008
Networked Ethernet, DeviceNet and Distributed Nodes Let Loop Controllers Speak

These days, manufacturers are putting more functionality into smaller-sized loop controllers, making it possible to shrink the the size of machines and control panels and reduce overall cost. However, many applications require more functionality than these tiny loop controllers can deliver. For instance, if end users have a variety of controllers from different vendors, networking is a highly attractive alternative. They can connect single-loop control to high-function networks such as DeviceNet or Ethernet. Then Internet connectivity is easy, which opens up a range of communication possibilities.

Dennis Schneider, product manager at Rockwell Automation says, “Loop controller trends currently include reduced costs and increased connectivity. The price of display technology has gone down, allowing integrated controllers to display more readable configuration and program characters. As the cost of microprocessors diminishes, control is getting faster, allowing  improved intelligence and more  communications with supervisory controllers.”

Paul Sagues, president of Berkeley Process Control, says, “The future direction of loop control is clearly toward more distributed nodes on standard networks. Whereas peer-to-peer architectures have been built as custom software applications, we see these identical, single-part-number, distributed modules using peer-to-peer architectures that are configured, not programmed. On some new semiconductor tools, we see the trend toward hundreds of such modules doing closed-loop temperature, pressure and plasma control control with nodes sharing information seamlessly.”

Patti Pool
Products Editor

FOUR ZONE TEMPERATURE CONTROLAthena Controls800/782-6776EMC 4Z controller offers the control capabilities of four single-loop controllers, plus auto tuning on a control board measuring 4.5 x 7 in. for embedded machine design applications. The board’s basic capabilities include four 16-bit analog inputs that can be standard process types (4-20 mA or 1-10 Vdc), or low-level sensors such as TC, RTD, thermistor or smart sensors that require excitation voltages of 5, 10 or 15 Vdc. The board’s 14 MIPS processor handles the four PID control zones in addition to the two encoder/counter inputs. EMZ 4Z has 256K flash code and 8K RAM memory.

Control-RRR units operate pumps, valves and alarms based on a dual set point control algorithm. Each unit includes up to four control channels, and can display data from up to four sensors. The control is telemetry-ready for spread-spectrum radio, so sensors can be connected both locally and/or at remote sites. Each control output is associated with a sensor that provides feedback information to the controller. The controller compares sensor readings with two set points to determine whether to turn the control output on or off.

UNIVERSAL DIGITAL CONTROLLERHoneywell Process Solutions215/641-3050UDC3500 ¼-DIN universal controller is available as a single loop or dual loop controller. The waterproof NEMA 4X/IP66  faceplate allows it to be used in washdown applications. Software makes controller configuration easy. A wireless infrared communication port enables controller setup from a Pocket-PC or computer. Ethernet communication allows connection to plant-floor networks. Application flexibility is assured with up to five analog inputs, math and logic functions and AccuTune III tuning with fuzzy logic overshoot suppression.
DUAL-ZONE CONTROLLEROMEGA Engineering800/826-6342CN79000 1/32 DIN dual-zone controller offers five thermocouple input types, and each zone offers a single set point. Features include independent fuzzy logic, autotune and peak/valley indication for each zone, plus free software. RS485 Serial communication is optional. The CE compliant controller can be used for food processing, automotive-engine testing, water and chemical tanks, plastic molding, and temperature control applications.
TEMPERATURE CONTROLLERAutomationDirect770/889-2858Solo process/temperature controllers include 22 models, including 11 under $100. Available in four standard DIN sizes (1/4, 1/8, 1/16 and 1/32), each unit is equipped with a dual four-digit, seven-segment display, which is useful for process variable display. Each model offers dual-output control, making it suitable for heating and cooling processes. The built-in autotune function with PID control feature allows easy startups. Control modes include PID, ramp/soak, on/off and manual operation. Universal inputs are standard on all controllers, including thermocouple, RTD, mA, mV and DC voltage. Select models are equipped with three available alarm groups.
ALL-IN-ONE CONTROLBerkeley Process Control510/222-8044Soft-I/O is a palm-sized module that performs loop control and I/O control. Each of 25 I/O pins can be configured by user as an input or output, analog or digital. Thermocouple, RTD, load cells and other low-voltage sensors can be directly connected. On/off, PID and PWM control loops are available. Ethernet connectivity and a built-web server enable configuration using a web browser. Included and downloadable software components ease connection and configuration with no PC software required. A single-loop temperature controller with PID control, autotuning, ramping, profiling and alarms are included in the module.
DUAL LOOP PID CONTROLLERAdvantech, Industrial Automation Group800/205-7940Adam-4022T dual loop PID controller is a serial-based controller with an accuracy of ±0.15% accuracy. The utility software helps users select input and range configurations, and set the operating parameters for the process control needs. The software also integrates the trend chart to help users monitor and debug control settings. The controller can be installed on the standard DIN rail inside the cabinet, and it can  be  powered by unregulated 10-30 Vdc. It also withstands ambient temperatures up to 60 ºC and resists the effects of vibration and mechanical shock.
SINGLE-LOOP CONTROLLERRockwell Automation414/382-2000 Bulletin 900-TC16 and 900-TC8 single-loop auto-tuning temperature/process controllers combine thermocouple and RTD sensing capability with either on/off or analog outputs into a global temperature controller. Both analog input and on/off analog output capability are also available. Configuration is via four sealed, tactile-feedback keys and 11-segment LED display. The keypad and display also allows users to switch from manual to automatic control without system disruption. If PC configuration is desired, the controllers can connect directly to a PC using a single cable. RS485 network can also be used as an option.

Invensys, Eurotherm
703 443-0000
Mini8 controller performs PID loops outside the PLC without compromising the benefits of an integrated solution. It has four plug-in slots and can cater for a variety of signals such as thermocouples and RTD inputs and relay, logic and analog outputs. Up to eight discrete control loops can be connected to fieldbuses such as Profibus, DeviceNet and CANopen, which take responsibility for the loops outside the PLC. In the event the PLC is down, equipment pressure and temperature can still be maintained and failures avoided. It also offers Modbus both on RS485 or Ethernet.

Moore Industries-International
Model 555 ¼-DIN controller handles flow proportional control, residual control, compound control with lag times and dechlorination with sulfur dioxide. Designed for the water and wastewater industry, the controller can be used in the chlorination and dechlorination processes. The front panel is NEMA 4X-rated. All menu prompts are in English. The 55 has isolated 4-20 mA or 0-20 mA output for control or retransmission to an analog control system.

ETR-9300 1/16 microprocessor-based temperature controller has universal input, and all thermocouple, RTD, voltage and current types can be selected from the front panel. A universal power supply along with a low-voltage input option provides a wide operating range. An analog input allows the set point to be remotely adjusted. Remote networking of multiple controls is available with serial communications. The NEMA 4/IP65-rated front panel controller has an analog signal that retransmits the process value to a chart recorder, data logger or PLC.

EZ-ZONE ST integrated control loop integrates temperature control, power control, safety shut-down and power disconnect in a single package. It features a PID temperature controller connected to a high-amperage, solid state relay with the option of adding a properly sized heat sink, current measurement, an over/under temperature limit, a definite purpose mechanical contactor and digital communications in one package.

National Instruments
cRIO-9072 and cRIO-9074 CompactRIO systems have an integrated hardware architecture that combines an embedded real-time processor with a reconfigurable FPGA within a single chassis. Using this standardized architecture and LaBView tools, engineers can design and prototype industrial monitoring and control systems. Because engineers can reuse the same LabVIEW code during prototyping and deployment, they are able to shorten time to market.

Control Microsystems
SCADAPack 350/357 combines 32-bit processing with high-speed LAN and USB communications and power-saving features. The controller has an integrated power supply, 12 Vdc to 24 Vdc converter, analog and digital I/O, serial communication and turbine flowmeter counter inputs. SCADAPack 350/357 uses industry-standard Modbus and DNP3 serial protocols as well as Modbus TCP- and UDP-based Ethernet protocols and can be programmed locally or remotely through a choice of programming languages.

Red Lion Controls
Data Station Plus and Modular Controller now come with an XCDN DeviceNet option card. This card enables any connected devices to communicate with DeviceNet products to realize complete system integration and data transfer. In addition, the XCDN option card is isolated, protecting user’s equipment from potential harmful ground loops.

PLC packages include 8 built-in auto-tuned PID loop controllers for $40 to $60 a point, depending on display. An alphanumeric display with 8 in and 8 out is available for approximately $500. The EZPLC also has a PID monitor that allows the auto-tune cycle to be monitored and charted in Excel to achieve the best PID settings. 

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