Stand-alone Loop Controllers Make Connections

It's tough to stand alone—we all need to feel some connectedness. Increasingly, users say that's also the case with stand-alone loop controllers, as more use network protocols to connect elsewhere. Such findings are the result of a recent Control Engineering and Reed Research Group (both part of Reed Business Information) e-mail/Web-based survey asking subscribers about their views and ...

By Mark T. Hoske, Control Engineering October 1, 2003


PID capability is key

More are networked

Panel area austerity

More computing horsepower

It’s tough to stand alone—we all need to feel some connectedness. Increasingly, users say that’s also the case with stand-alone loop controllers, as more use network protocols to connect elsewhere.

Such findings are the result of a recent Control Engineering and Reed Research Group (both part of Reed Business Information) e-mail/Web-based survey asking subscribers about their views and preferences regarding stand-alone loop controllers.

The research also shows that four leading communications methods for loop controllers were used more in 2003 than in 2000. For loop-controller communications to instrumentation, 4-20 mA is still most often used. Ethernet made the largest gains in that area from 2000 to 2003, now leading in both peer-to-peer communications among or between controllers and in communications with enterprise systems (bar graph).

When choosing a stand-alone loop controller, survey respondents said the top three most-important capabilities are PID (72%; see cover story on proportional-integral-derivative control in this issue), external communications (41%), and provisions for simple interlocking (31%).

Other 2003 survey findings include the following.

Nearly all respondents state that less than 20% of their stand-alone loop controllers are presently running open-loop rather than closed loop. One-fifth of respondents check daily if their controllers are running in open or closed loop.

Over half of the respondents say that with most loop controllers they program and configure on the loop controller itself; 38% usually program and configure by connecting to the device locally.

Top three companies for providing loop controllers to respondents in the past 12 months were Rockwell Automation, Honeywell, and Yokogawa.

PLCs vs. loop controllers

Overall, loop controllers are more “talkative” in 2003 than in 2000; Ethernet made the largest gains amoung leading communications methods.

Is it ironic that the company most selected to provide stand-alone loop controllers sells programmable logic controllers (PLCs) for that purpose, rather than loop controllers? Not at all, says Mike Miclot, marketing manager, Logix Controllers & I/O, Rockwell Automation. “We’ve built process functionality into PLCs. PLCs can do one or multiple PID loops and have appropriate analog and discrete interfaces.”

Miclot claims PLCs do a better job of communicating, have tuning and autotuning capabilities, are easy to set up, have great performance, redundancy, and bumpless switchover, and can be adjusted based on feedback.

Steve Miller, product manager for Invensys Eurotherm Controls (incorporating Barber-Colman), thinks otherwise. Miller says customers can get PLCs with PID or get more functionality from loop controllers. Using a loop controller for many process or discrete applications instead of a PLC makes more sense for cost, reliability, communications, and ease of use, Miller contends. Also, “We fall into much lower cost than a PLC solution. You’d probably have to have 12 loops or more to be equivalent in price,” he estimates.

Higher loop-controller processing power at a lower price, adds Jim Cottrell, product manager, controllers, Honeywell Inc., allows “customers to affordably apply PID control to new applications.” For instance, the new DC1000 Family of controllers shows how users benefit from increased functionality “even as prices go down,” Cottrell says. The DC1040 is pictured.

Ease of use is part of the deal, suggests Dennis McManimon, Watlow product manager, who sees an increase in use of system-level software and a single-user interface for several products within the system. McManimon also expects integration of additional communication protocols in future releases.

Loop controller products

The following products include those ranked among highest in reader responses. For more manufacturers, visit . For system integrators, go to . .

Safe use in process

More than 20 ControlLogix products (which can perform loop controller functions) have a TÜV SIL (Safety Integrity Level) 2 certification. TÜV, an accredited test laboratory certification center, assures suitability of ControlLogix products for use in up to a SIL 2 safety application. SIL designations indicate a safety system’s ability.

Rockwell Automation

Four in the controller family

Available in 1/16-, 1/8-, 3/16-, and 1/4-DIN formats, the DC1000 Family of controllers provides standard features of general-purpose controllers and includes advanced features, such as motor position control and heat/cool control. Basic features include PID or on/off control and up to three alarm relays. DC1000 controllers can serve as programmers for basic ramp/soak requirements as they embed two inter-linkable programs of eight segments each. The user interface can be customized to hide unused parameters, leaving only those necessary, avoiding any potential misconfigurations. Applications include dryers, packaging machinery, plastic processing, painting and coating, small ovens and environmental chambers.


Network control stations

CX1000 and CX2000 Network Control Stations are said to be the next generation of process control as they fuse control, recording, and networking into a single, easy-to-use package. They include independent ramp/soak programs, DIO monitoring and control, advanced math capabilities, as well as measurement, recording and networking features. Applications include heat-treating, thermal oxidizers, water treatment, food and beverage, and manufacturing. A combination of menu-driven screens and function keys enables easy entry of control and measurement parameters into the CX. Data from externally wired Modbus-compatible controllers and devices can also be easily monitored and logged through the use of prebuilt screen and built-in serial interface.

Yokogawa Corp. of America

Browser monitoring/control of temperature/process

iSeries 1/16 DIN (48 x 48 mm panel cutout) temperature/process controllers connect to an Ethernet network with an RJ-45 connector and can send and receive data in standard TCP/IP packets. It serves Web pages over an Ethernet LAN or Internet making it possible to monitor and control through a standard Web browser. The device also interfaces easily with popular data acquisition and control programs, and Microsoft Visual Basic and Excel. It has a NEMA 4, IP65 front bezel. Prices start at $295; software and five-year warranty are included.

Omega Engineering Inc.

100 mm-deep controller saves space

E5GN 1/32-DIN-sized controller saves panel space and is 100-mm deep. It accepts thermocouple, platinum RTD, noncontact temperature sensor and analog temperature inputs. E5GN features autotuning and self-tuning functions, which can be used simultaneously. It also has heating or heating/cooling control and is water-resistant (NEMA 4X/IP66).

Omron Electronics

Ethernet enables remote access

Series PD controllers feature embedded Ethernet technology, providing a convenient and economical means for setting and viewing key variables, such as process pressure and humidity, at any location. Embedded firmware serves dedicated Web pages that support key functions, including operation, alarm monitoring, and configuration. Microsoft Windows software displays all functions; the unit can deliver remote alarm notifications via e-mail. Watlow’s newly patented Infosense technology improves sensor accuracy at least 50%.


Wizard helps loop controller setup on PC

The 3216 1/16-DIN controller reportedly achieves excellent control-loop performance and provides user-friendly text messaging feature for plain language help at every step. Detailed configurations can be performed by using iTools and the wizard configuration screens on a PC. Eurotherm/Barber-Colman

View the process with Ethernet card

Users can view the process from the control room or from any workstation on the network using the 353 Loop Controller with an Ethernet communication card. This enhancement enables network connectivity with multiple 353 controllers, HMIs, and other devices that communicate Modbus over Ethernet. Network technology reduces plant costs and learning time and provides easier access to plant data for timely decision-making. Siemens-Moore Process

Universal 535r similar final control element. Also available are models with alarm trip outputs that can be used for on/off control or to warn of unwanted high/low conditions. Optional RS-485 communications allows interface with digital-communicating DCS, PLC and PC-based SCADA systems. Quick and easy setup is achieved using the processor’s large, backlit keys and user-friendly menu prompts. This extra-bright front panel display rates NEMA 4X. The patented PowerTune feature delivers pretuning, adaptive tuning, and powerback anti-overshoot. PowerTune constantly analyzes the process and makes modifications to the tuning parameters to ensure precise, long-term, and stable control. Moore Industries-International Inc.

Temperature, process controllers Temperature and process controllers have. Two new models of temperature and process controllers with PID, autotune and on/off control routines have now been added to the line.The temperature controller has one mechanical relay and one pulse width modulated output. The process controller has two mechanical relays. Prices for the line range from $149 to $229. AutomationDirect

ONLINE EXTRA information on the October Product Focus

More 2003 loop controller findings: PC-based controllers are most widely usedIn recent research from Control Engineering and Reed Research Group—both part of Reed Business Information—subscribers gave their views and preferences about stand-alone loop controllers:

Among those specifying, recommending, and/or buying devices that provide stand-alone loop controller functionality, 75% do so for in-plant requirements and 35% do so for OEM requirements. Continuous processing is the primary application of stand-alone loop controllers for 52% of respondents; in discrete applications, 42%.

PC-based controllers were most widely used. Each respondent, on average, uses 53 PC-based controllers.

Thirty-five was the average number of loop controller units each respondent purchased in the past 12 months, which equated to an average spend of $24,539 per respondent.

Nearly one-fourth of respondents expect their need for stand-alone loop controllers to increase in the next 12 months. Over half of the respondents expect their need to stay the same.

More suggestions for users Users might consider simplifying to a single platform as an option. Any plant using a distributed control system likely uses some PLCs somewhere, says Mike Miclot, marketing manager, Logix Controllers & I/O, Rockwell Automation. Because PLCs are already in use, it makes a lot of sense to employ one integrated environment to apply control logic, Miclot suggests, such as Rockwell Automation ControlLogix and ProcessLogix with a RSView human-machine interface.

Flexibility with loop controllers is greater than with PLCs, says Steve Miller, product manager for Invensys Eurotherm Controls. Miller thinks it’s easier to hot-swap a networked controller than reprogram a PLC. Also, he adds, the loop controller speaks the language of the machine that the operator is using.

Dennis McManimon, Watlow product manager, adds that there’s been an effort to simplify initial and long-term configuration for loop controllers and create a more aesthetic look for system monitoring.

Loop Controller Selection Criteria (% respondents rating as very important)

PID capability

External communications

Provisions for simple interlocking

Continuous self-tuning

Hard-manual control station (process runs while controller removed for service/replacement)

Multiple-loop control

User-initiated self-tuning

User-defined algorithms

Peer-to-peer communications

Adaptive control

Removable configuration modules

Multiple-level alarm priorities

Multiple-configuration memory storage and recall

Fieldbus communications

Cascade control


Fuzzy logic


Source: October 2003 Control Engineering/Reed Research Loop Controller Study

Relate loop-controller readingFor related reading on loop controllers, see: “ Loop Tuning Fundamentals ”“ Product Focus: Staying in the loop ”