2015 - 02 - Applied Automation

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Applied Automation February 2015 • A3

A4 What does the Internet of Things mean to people who make things?

Think: ‘The connected machine.’

From resource management to intelligent machine devices to predictive maintenance, IoT offers plenty of things to do to make manufacturing automation even more robust.

A11 Selecting and applying VFDs Clear understanding of the application, noise sources, and

configuration parameters ensures peak VFD performance, efficiency, and reliability.

Modern VFDs have made changing the speed of a 3-phaseac motor simple, but it has not always been that way.

Contents

A11

COMMENT

Historically, I have tried to avoid buzz-words. Frequently, word choices defy how some buzzwords are applied. For example, taken literally, what does the

“Internet of Things” (IoT) actually mean?To the author of this issue’s cover story, IoT

means connecting machines—to each other and to the enterprises they serve. “In manufactur-ing, it’s really all about connecting machines to get more actionable information using intelligent devices at lower levels of the system architec-ture…than ever before.”

Perhaps the words are intended to convey that, because of the Internet, we have more ways to connect “things” than we have ever had. “IoT offers plenty of things to do to make manufacturing automation even more robust.”

Is this new? We have had this connectivity for some time. We have also had the infrastructure. But, as the cover story author points out, the

focus of IoT and big data has been CEOs and CFOs. Now that the context is shifting toward manufacturing automation, the costs of imple-menting the technologies behind this buzzword are becoming more justifiable.

The other story in this issue examines vari-able frequency drives (VFDs), which have evolved considerably over the years. While digi-tal displays, comprehensible error messages, and easy configuration are some of the outward manifestations of technological evolution, the internal changes are even more beneficial to those who use and maintain them. Better power electronics help minimize switching noise, bet-ter circuit designs help minimize harmonics, and better quality has helped to greatly increase reli-ability—which is perhaps the most valuable of these attributes.

When manufacturers see opportunities for improvement, they should act on them.

Investing in automation opportunities

Jack SmithEditor

A4

ON THE COVER Manufacturing automation is about connecting machines to obtain more actionable information than ever before, regardless of how you label it. Courtesy: B&R Industrial Automation Corp.

A4 • February 2015 Applied Automation

Figure 1: Manufacturing automation is about connecting machines to obtain more actionable information than ever before, regardless of how you label it. All graphics courtesy: B&R Industrial Automation Corp.


COVER STORY

What does the Internet of Things mean to people who make things?

Think: ‘The connected machine.’

We’ve heard a lot about the Internet of Things (IoT), centering on big business and big data. But what kinds of “things” do we want to do in manufacturing automation?

And what does it take to implement IoT? What about the standards, vision, connectivity, inte-gration, and processes necessary to meet the specific requirements of IoT in industrial automation? Answering the first question will provide reasons to invest in the sec-ond question.

Whether you call it Industrie 4.0 or IoT, in manufactur-ing, it’s really all about connecting machines—to each other, to expert systems, to man-agement execution systems—to get more actionable information using intelligent devices at lower levels of the system architecture (push-but-tons, servo drive auto-compensation, energy monitors, vision cameras, accelerometers, and E-stop buttons) than ever before (see Figure 1) (see “Industrie 4.0 vs. industrial IoT: Take a unified approach,” on page A7).

IoT: Things to doIoT is much more than extending industrial networks to

the device level architecture. It’s even more than distribut-ing safety, motion, machine-to-machine intelligence, auto-mated maintenance resources, and enterprise connectivity to heretofore inaccessible manufacturing intelligence. From resource management to intelligent machine devices to predictive maintenance, IoT offers plenty of things to do to make manufacturing automation even more robust.

Secure remote connectivityIoT promises connectivity for diagnostics, recipe man-

agement, collaborative engineering, and all kinds of data acquisition, from OEE to serialization. IoT will provide access to data we can’t get now because we haven’t deployed the sensors to get it and IT hasn’t allowed it.

Yet, in large part, the sensors exist today. They just haven’t been cost justified before. Therefore, they aren’t in RFQs yet. A common rationale has been, “Why spend an extra $100 on a smart sensor that is going to get hit by a fork truck?”

The big security breakthrough in 2014 has been the growth of secure virtual private network (VPN) serv-ers and cloud services to address IT’s concerns (see “Standards for industrial IoT,” page A8). The trend in 2015 will be to seamlessly integrate the secure server into the control software suite.

Networked safetyPerhaps the biggest shift in mind-set for industrial

automation users is moving from hardwired safety PLCs and relays to networked safety. It just plain scares people to move from tightening down copper wires with

a screwdriver to consulting a software display. Yet, we get on fly-by-wire air-liners without a second thought. We take driverless shuttle trains to the air-port terminal. We don’t think about it because we can’t see it, but even the car we drive to the terminal depends on networked devices, such as anti-lock brakes, airbags, and cruise con-trol.

Networked safety holds perhaps the greatest potential for improving pro-ductivity, along with functionality that

prevents workers from attempting to circumvent safety systems. Networked safety has many advantages, includ-ing installed cost, testing, and diagnostic capabilities.

The concept is simple. Keep control and line power on while ensuring that operating speeds, torques, directions, and positions can cause no harm. Implementation is in keeping with traditional safety implementations, compar-ing the primary control system status with a checksum on an independent controller.

But instead of E-stops dropping out all power, net-worked safety calls for continued operation in safe mode. Safe-mode operation is intended to prevent an operator from being tempted to defeat a door interlock to clear a jam, or to operate with machine guarding removed to save steps. Instead, nip rolls can’t turn in an

By John KowalB&R Indus t r ia l Au tomat ion Corp . , Roswe l l , Ga .

IoT offers plenty

of things to do to

make manufacturing

automation even

more robust.


unsafe direction. A robot arm can’t push hard enough, fast enough, or far enough to put a maintenance worker at risk.

Where does IoT come in? Safety is networked over deterministic industrial Ethernet, and every state change, every instance of operation in safe mode, is logged and can be transferred to management via the Internet. The interlock or light curtain can communicate the nature of the breach, time, and interval to help management ana-lyze root cause.

Safe motionOf the networked safety functions, safe motion is the

most powerful. Using intelligence and software embed-ded into servo/inverter drives with hardware, such as safety encoders, it is possible for networked safety to maintain operation of production lines, printing presses, robots, and more in safe mode. This intelligence provides not just the now-familiar safe torque off information, but safe limited torque, safe limited speed, safe position, safe limited acceleration, and much more.

Now, the machines on a line can continue to run in safe mode when in the past an E-stop or a controlled shutdown would be initiated to clear a jam, make a repair, or replenish materials. The productivity potential is enormous.

Networked E-stopsSpeaking of E-stops, the E-stop button no longer

needs to be hardwired. Yes, E-stop buttons are now available on the Ethernet network and integral to the control panel. Enough said.

Predictive maintenanceKey to predictive mainte-

nance is monitoring based on actual machine conditions, not just cycles or hours. And key to monitoring machine conditions are mechanical disturbances. Use of net-worked sensors, such as accelerometers, can detect frequencies of bearings, shafts, couplings, and other mechanical devices indicating a trend toward failure that can be interpreted and analyzed to schedule preemptive main-tenance (see Figure 2).

The more critical the pro-cess, the better the cost justi-

fication. But the failure of even a simple device can have a catastrophic result in a process.

Frequency analysis can also lead to identification of root cause before a device is damaged beyond recogni-tion. If conditions such as lubrication, spalling, or corro-sion can be documented, preventive maintenance mea-sures can be taken.

Resource managementThink energy monitoring—and not just electrical power

but water, steam, compressed air and vacuum, natural gas, temperature—and you will recognize the immense potential for improving sustainability.

Bring these monitoring activities into individual machines and down to process units—not just branch circuits or incoming power meters—and the data become much more actionable. Why does one shrink tunnel or one shift use more energy than another? What is the optimum line speed to balance energy costs with throughput?

AutocompensationPushing more intelligence down to the device level

isn’t just about communicating in the IoT. It’s about inher-ently improving performance while removing the need for human intervention. Leading-edge servo drives are a good example.

Autocompensation within the drive lets it respond to anomalies, predictively smoothing out disturbances with-out a technician fine-tuning the drive. No need to bring up the oscilloscope function; no need to plug in a laptop.

COVER STORY

Figure 2: Condition-based moni-toring uses networked sensors to detect trends that could indicate possible machine failure.


AutoconfigurationThe same holds true for replacing an older component

with one that has a newer firmware version. In the past, this has required manually resetting the new compo-nent, which often required software loaded on a PC. Now it’s automatic, requiring no intervention on the part of the user.

Onboard intelligence and Ethernet communications between a controller and device today means that the controller can query the new component and automati-cally downgrade its firmware to the version in use.

This means no need for a technician, no maintenance software, no need to upgrade a software license, no faults showing up, and importantly, no preconfigured spares gathering dust on a shelf.

Intelligent I/O slicesAnother example of pushing intelligence down to

the device level is having I/O slices with onboard field programmable gate arrays that allow a direct response between devices and the I/O slice, bypassing the back-plane, the PLC CPU, and the system scan time. The result is a response time as short as 1 microsec.

I recall a trusted German colleague telling me a few years ago that Industrie 4.0 would be a big deal. I scoffed, to be honest, at the obviously promo-

tional messaging. My initial reaction to IoT was the same.

After all, we’ve had the ability to put smart photo-electric sensors on conveyors for decades. Nobody wanted to pay $100 extra for them. But, when the conveyor jammed up, it was okay to waste time walking the line, using human eyeballs to determine the cause of the stoppage.

Today, that smart sensor allows you to pinpoint the problem from the line controller, from the state model on any HMI on the line (PackML, a.k.a. ISA TR88.00.02 helps here, too). Your tech brings the replacement part with him or her, and readjusts or changes out the sensor in a matter of minutes.

It’s the same scenario for Industrie 4.0 and indus-trial IoT. The difference is mind-set.

Germany has a deserved reputation for engineer-ing, applied technology, and advanced machinery. It’s the basis of the country’s export economy, its economic engine that is trying to drag the rest of the EU out of persistent recession, and a lot of national pride. So it’s understandable that Germany would seize on the potential of IoT and focus on industrial applications.

In Germany, and throughout Europe, technolo-gists tend to sell technology to other technologists. That is, as opposed to the U.S., where technologists need to convince financial managers focused on quarterly results that increased investment in tech-nology is required to keep competitive and generate organic growth. I believe this is why IoT proponents in the U.S. tend to emphasize big data instead of the connected machine. They are selling IT solutions to chief financial officers.

Does this mean that 4.0 has a better chance of actually happening in factory automation than industrial IoT? I’ve become convinced that European industry collectively believes in the vision of the connected machine. So perhaps machine builders and technology providers that also believe should target the European market first.

In Europe, call it 4.0, and when the technology becomes established, next approach the overseas subsidiaries of your European customers. There, call the technology whatever they call it in those markets. Don’t let your organization be caught up in the debate between 4.0 and industrial IoT—they’re the same “thing”—an Ethernet/Internet-based strat-egy for connecting machinery to deliver more effec-tive operations than previously possible.

Let’s make sure they use the same standards.

Industrie 4.0 vs. industrial IoT: Take a unified approach

Figure 3: Machine-mounted sealed drives can now communicate over Ethernet and provide onboard I/O.


Does this unheard-of speed serve a practical purpose? Think of firing a glue gun on a case packer more accurately, high speed registration mark sensing, or shrinking the dis-tance between sensor and reject station on a flow wrapper.

The I/O slices are programmed in the IEC 61131-3 lan-guages, in the same project as the rest of the machine. They just execute down at the slice level.

Distributed motionIt’s not uncommon to see machine mounted, inte-

grated motor/drives today, communicating over Ethernet and providing onboard I/O. This concept has been extended to machine mounted, distributed, sealed drives operating conventional motors to meet higher torque and speed requirements (see Figure 3). Meanwhile, small drives, such as steppers used for format changes, are taking the form of IP67-rated dis-tributed I/O blocks.

Intelligent push-buttonsEven the lowly push-button is now a network node.

Instead of old-fashioned, hardwired, dedicated push-buttons, push-buttons now plug into the same industrial Ethernet cable as the I/O. They are multifunctional and programmable, with multicolored LEDs indicating their

modes and removable legends making them easy to customize. And they are available with E-stop buttons and IP65 sealing.

Typical applications include conveyor modules, where long runs of wire get expensive and complicated.

Autonomous maintenanceThis kind of onboard intelligence, combined with inex-

pensive solid-state memory, leads to another big cost saver that can make machines more efficient. The benefits of using animation and video to walk operators and techni-cians through work instructions are well documented.

Why not tie those animations into the fault codes in the control system, and walk the operator through first-echelon troubleshooting? Using virtual network computing (VNC) and Wi-Fi, the animations can run on the operator’s smart-phone or tablet and they can walk around the whole line if necessary, connected to their interactive troubleshooting aid (see Figure 4).

This is known as autonomous maintenance. It means that a maintenance technician may not be required to bring the machine back on line because less experienced operators can handle problems on their own, and that lan-guage and literacy barriers can be overcome.

Of course, if the problem cannot be resolved, the con-

Cover Story

The following paragraphs explain the standards nec-essary for the success of IoT, and why.

Ethernet to InternetFundamental to IoT is the continuity of TCP/IP, HTTP,

FTP, and other universally accepted Internet commu-nications standards across Ethernet-based industrial networks to intranets and the Internet. Today, even a low-cost controller is expected to provide a Web serv-er and one or more Ethernet connections.

Network securityISA/IEC-62443 (ISA 99) provides a comprehensive

overview of cybersecurity measures for industrial con-trol systems. This is a complex topic requiring subject matter experts. Suffice to say that just as IT has secu-rity standards, so does automation.

Secure VPN servers and hosted cloud services are now widely available. Emerging now are secure services catering to the specific needs of industrial automation. Secure VPN capabilities are also being built into automa-tion software suites. Large users and integrators with extensive IT resources can apply their own solutions across these interfaces. Machine builders and users can source software-as-a-service solutions without investing in additional IT infrastructure.

Services are available from third parties, control sup-pliers themselves, and machine builders and integrators.

Secure services include turnkey remote data acquisition, monitoring, data storage, reporting, and diagnostics.

The bottom line is simple: Security concerns—exem-plified from Stuxnet to Sony—are real, but the counter-measures are out there.

VNC accessVirtual network computing epitomizes the IoT. VNC

is an open-source sharing system that allows remote access to an IoT-enabled controller without the ven-dor’s software suite. No licenses and no dedicated communications software or hardware are required. All you need is the controller’s IP address.

Open networked safetyWithout standards, IoT will fail. IoT can’t tolerate

closed systems because it’s about connecting every-thing. And contrary to popular belief, networked safety does have an international standard. The openSAFETY protocol stack is an implementation of the openSAFE-TY specification according to IEC 61784-3-13 and is licensed free of charge.

Also, openSAFETY has been tested and proven to run on the application layers of the major industrial networks: Profinet, EtherNet/IP, Modbus TCP, SERCOS III, EtherCAT, and POWERLINK. However, it will be up to control users to specify openSAFETY from their suppliers.

Standards for industrial IoT


troller will text the maintenance tech on call, advise him or her of what’s been done already, and even identify a faulty part and submit a purchase order for a new one. And the fault will also be documented and communicat-

ed back to management, the machine builder, and the component supplier.

John Kowal is director of business development at B&R Industrial Automation Corp., Roswell, Ga.

Proprietary safety protocols (those limited to the networks for which they were originally designed) don’t support IoT because they limit connectivity. They may also effectively limit third-party access to develop master rather than only slave interfaces. To be open, safety must allow any automation supplier to develop compliant controllers and devices.

ISA TR88.00.02Better known as OMAC PackML,

this standard describes a state model, modes, and tag naming conventions originally intended to communicate with packag-ing lines typically comprising machinery from many different suppliers using different control platforms.

Developed by the Organization for Machine Automation and Control (OMAC), PackML has been demonstrated to pertain equally well to any discrete control scheme. OMAC has specifically taken this standard through the ISA (International Society of Automation) review process to become an ISA Technical Report, ISA TR88.00.02. OMAC next will initiate the International Electrotechnical Commission (IEC) review process.

TR88 is a key standard for machine programming, as well as machine-to-machine and management data acquisition.

OPC UAOPC UA (IEC 62541) stands for OPC Unified

Architecture, developed by the OPC Foundation to replace the original OPC (OLE for process control,

OLE standing for object linking and embedding, a Microsoft-centric interface based on COM).

OPC UA is based on Web ser-vices and is platform independent. Cooperation is underway between PLCopen (representing IEC 61131-3) and OPC Foundation to map OPC UA to the popular control programing standard. It is antici-pated that the OMAC initiative, ISA TR88.00.02 (PackML) will follow.

This is both a game changer and a necessity for industrial IoT practitioners. Compared with the proprietary data acquisition tools provided by the PLC suppliers and limited to their products, OPC UA is a true international standard. OPC communica-tions fit the need for data handling between Ethernet and the Internet, and between factory and manage-ment systems.

Without standards,

IoT will fail. IoT can’t

tolerate closed systems

because it’s about con-

necting everything.

Figure 4: Using VNC and Wi-Fi, animations can run on an operator’s or technician’s smartphone or tablet to provide work instructions or aid in troubleshooting.

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A wide variety of variable frequency drives (VFDs) are available, and are sometimes referred to as inverters, ac drives, variable speed drives, or adjustable speed drives. Despite the differences in terminology, these components are all VFDs and control

an ac motor’s speed and torque by adjusting the input frequency and voltage to 3-phase ac induction or synchro-nous motors.

Modern VFDs have made changing the speed of a 3-phase ac motor simple, but it has not always been that way. Even though 3-phase ac induction motors were invented in the late 1880s, for almost 100 years, operat-ing an ac motor at more than one or two speeds was dif-ficult. The number of magnetic poles and an ac motor’s physical construction made a variable speed ac motor drive cost prohibitive, so instead, dc motors were used in variable speed applications.

In the 1980s, VFD technology started becoming less expensive and more reliable. Today, the VFD com-petes well with traditional dc motor control, but when specifying VFDs, a clear understanding of the applica-tion, installation methods, and configuration is critical. Common issues with VFD application, operation, and con-figuration include:

� Drive selection� Drive overload� Drive overvoltage� Sources of noise� Electromagnetic interference (EMI)/electromagnetic

field (EMF) problems� Grounding issues� Incorrect configuration and/or parameter settings.

VFD loadingThe main function of a VFD is varying the speed of a

3-phase ac induction motor. VFDs also provide overload protection, start and stop control, and adjustable accel-eration and deceleration. Programmable acceleration and processor-controlled current limiting can reduce motor inrush current at start-up, an important feature for con-trolling a factory’s maximum instantaneous power load and corresponding peak demand, which is often used by the utility company to set rates or surcharges.

When specifying a VFD, it’s important to understand the application and select the drive accordingly (see Figure 1). The operating profile of the load must first be considered. With both constant torque applications, such as conveyors (see Figure 2), mixers, and com-pressors—and variable torque applications, such as pumps, fans, and blowers—careful attention must be paid to overload ratings.

For example, attempting to drive a fan motor faster than its base speed can significantly impact the amount of power required as the fan horsepower varies with the cube of the speed.

Running a fan too fast can thus consume excess power and may overload the VFD,

while running it at half speed can reduce horsepower requirements by 75% or more, per the affinity laws, which apply to pumps and fans.

Many applications can take advan-tage of this reduced power consump-tion at lower speeds to save energy. An example is using a VFD to vary


VFD ISSUES

Selecting and applying VFDsClear understanding of the application, noise sources, and configuration parameters

ensures peak VFD performance, efficiency, and reliability.

By Chip McDanielAutomat ionD i rec t , Cumming, Ga .

Figure 1: VFDs are available to fit almost any application requirement. Understanding these requirements helps ensure optimal operation. All graphics courtesy: AutomationDirect


fan speed to match the load, instead of using dampers to reduce airflow from a fan running at full speed.

To avoid the possibility of drive overload, the VFD should be sized based on its maximum current require-ments and peak torque demand, as sizing by horsepower alone may not satisfy the maximum demands placed on the motor. Although most VFDs can handle a wide range of horsepower, oversizing is advised when limits are approached.

An oversized motor is less efficient than a properly sized motor, but a VFD helps to minimize this inefficiency, reducing the oversizing penalty to little more than the ini-tial cost for oversizing the drive and motor.

Overhauling loadsAnother application that can cause issues is an over-

hauling load—a high inertia load that must be slowed faster than what would occur when coasting, or a load that back-drives the motor during normal operation. When overhauling loads are present, the motor becomes a generator and the energy produced must be dissipated. There are multiple options for handling this type of load.

In some instances, an oversized drive will help, but this works only in marginal cases. A more common solution is to use dynamic braking units with large resistors that

convert the excess energy into heat. While some VFDs can produce up to 20% braking torque with their built-in resistors, adding an external braking resistor can greatly increase a VFD’s braking torque. Larger VFDs typically require external braking units to accommodate overhaul-ing situations.

A common issue in overhauling situations is an over-voltage drive fault during deceleration. However, a prop-erly sized braking resistor can eliminate these overvolt-age faults as the excess energy generated by the motor is simply dissipated as heat through the resistor.

Higher end, more expensive solutions include regener-ative drives that feed excess energy back to the line side of the drive, and common-bus drives. In common-bus systems, each of several VFDs has its dc bus connected to a common bus so other drives can use the excess power generated by the overhauling drive. These two types of drive systems can be very cost-effective when the amount of excess power generated from overhauling is high.

Where’s the noise?As part of a VFD application and installation, proper

accessories must often be specified with the drive to deal with noise issues. Electrical noise can be present at the

VFD ISSUES

Figure 2: The photo shows a VFD installed in a conveyor system—a common VFD application.

line side and/or the load side of the drive from external sources, and it can also be created by the drive. Existing noise on the factory or line side of the drive generally does not affect modern VFDs. However, the drive itself can create harmonic noise on the line side that may affect other devices in the facility.

For most applications, the instal-lation of a line filter upstream of the VFD is worth the expense. At a minimum, one should consider leav-ing room in the control enclosure for filters, reactors, or drive (isolation) transformers—just in case they are found to be needed after installation (see Figure 3).

A VFD and the motor it controls can create EMI that can affect sen-sitive nearby devices, particularly analog wiring and circuits. Using proper grounding techniques goes a long way toward reducing EMI. Ground loops that occur when pieces of equipment are connected to more than one grounding path can be eliminated by using a common power circuit and single-point grounding. Power filters, line filters, line/load reactors, or even isolation transform-ers may also be necessary to mini-mize EMI/EMF from the drive.

Although not typically considered electrical noise, VFDs can also create disturbances on the motor cabling, the most notable being harmonics and reflected waves. Harmonics are caused by the high switching frequencies of the insulated-gate bipolar transistor that produce the pulse width modulated output from the VFD to the motor. Load reactors may be necessary to minimize harmonics on the output side of the drive, as these harmonics can reduce motor efficiency.

Reflected waves on the drive-to-motor cabling can effectively double the voltage that reaches the motor at a given point in time. This can produce potentially damaging volt-age stress on the motor insulation. Installing load reactors on the drive output cables is recommended, par-ticularly if cable distance is greater


than 125 ft. Specifying motors with proper insulation ratings also helps prevent reflected wave problems. For example, inverter duty motors with 1,000-V insulation rating or higher should be used if running at a high

line voltage such as 480 Vac (or 575 Vac commonly found in Canada).

Configuration issuesThere’s no excuse for failing to

enter the correct motor nameplate

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data, but it often happens. Considering that the VFD also provides overload protection for the motor, improperly entered nameplate data can cause a variety of faults or even lead to motor damage.

If there is a problem due to bad nameplate data or other issues, it can often be located by checking the fault code on the drive’s display. Older drives may display somewhat cryptic codes, so quick access to the operat-ing manual is a must for translating codes into actionable information. Newer VFDs usually display fault information as text in English (or other languages if available and if so configured) instead of alphanumeric codes, greatly simplifying troubleshooting (see Figure 4).

There are dozens of VFD configuration parameters that must be understood. Although many parameters work fine at their default settings, it’s a good idea to read the manual and adjust parameters to optimize drive opera-tion. Typically, suppliers can assist in this area because they are familiar with the nuances of their products.

At a minimum, a new VFD should be programmed with the motor nameplate data (full load current, rated volt-age, and speed), desired control mode (keypad control, 2-wire, 3-wire, or network communications), and desired speed reference (0 to 10 V, 4-20 mA, keypad, network communications, etc.).

A common configuration parameter set-ting is activation of the auto-tune algorithm in a vector drive, a

feature that often increases efficiency and improves control. Understanding these configuration parameters and settings, and adjusting as necessary from default values can ensure proper operation, maximum efficiency, and optimal control.

Final checksPerforming a few simple checks can help ensure effec-

tive application of VFDs. For any application, specifying the correct input voltage and understanding the nature of the load are critical. By understanding the load, most overcurrent conditions can be easily eliminated. For most applications, effective operation can be achieved by per-forming the following checks:

n Ensure the input voltage is correctn Understand the nature of the loadn Eliminate overcurrent conditionsn Stretch out acceleration and deceleration time

if possiblen Get/keep the noise out of the VFD—and the

rest of the plant.

Ease up on aggressive acceleration and deceleration ramps to reduce overload or overvoltage faults and save energy. Check the drive display and address any recur-ring faults. Follow good noise reduction techniques.

Careful attention to drive selection, parameter settings, noise sources, grounding issues, overload conditions, and overvoltage conditions will ensure successful drive operation. With proper understanding of common drive issues, the application can withstand changes to the motion profile and motor speed. By following these rec-ommendations, modern VFDs will offer years of trouble-free service.

Chip McDaniel works in technical marketing for AutomationDirect and is a graduate of Georgia Tech. His 30 years of experience in the industrial automation field includes designing, building, and commissioning control systems of all types.

VFD Issues

Figure 4: Modern VFDs show faults by displaying fault names instead of cryptic codes, speeding and sim-plifyingw trouble-shooting.

Figure 3: The photo shows an ac drive mounted and wired in a con-trol enclosure. Oversizing a VFD enclosure aids in heat dissipation, and can also help accommodate additional related components.

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2015 - 02 - Applied Automation