Because combined motor-drives eliminate external wiring between the two components, these systems often reduce or eliminate phase wiring and transmission line effects like reflected waves. They also ease installation because much of the work has been done for you.

When the old motor on the exhaust fan finally dies, of course you'll replace it. And you'll do the same when the motor on your winder goes. In both cases, you may also want to replace the drives because of installation hassles and the complexities of matching drives to motors.

In that case, you may consider a combined motor-drive. These devices have been available for a few years and their benefits are fairly well known.

For an exhaust fan, a combined motor-drive turns out to be a good alternative to separate units. For a winder, however, it's a less than ideal choice because of limitations in speed and torque control. The point: Before purchasing a combined package, it's important to understand which applications make sense, and which should be left to traditional fixed speed controllers or individual drives and motors.

Finding the fit

If an application requires simple speed control, such as that needed by the exhaust fan mentioned above, a combined motor-drive would be an appropriate choice. Winders and centrifuges, on the other hand, require more advanced control of both torque and speed, and hence are often inappropriate for combined packages.

After determining torque and speed issues, then consider whether the application is in volatile or potentially hazardous environments. Most integrated drive-motor packages are not rated as explosionproof. In applications such as oil refineries, steel mills, and some food manufacturing that can't permit sparks or suspended particles, these drive packages may be inappropriate.

Horsepower range will also be a factor. Most existing drive-motor packages are available from fractional to about 5 hp, with a few reaching almost 20 hp.

Physical considerations

After settling on the basic application type, the next step is to evaluate the needs for motor-control complexity, panel space, communications, and plant-floor location.

Motor control complexity. Integrated drive-motors handle simple, open-loop requirements. In many cases where you use volts-per-hertz drives, integrated drive-motors can be an alternative.

Combined motor-drives are suited to applications that need simple speed control. Industrial mixers, blowers, and fans are some of the more appropriate applications for these devices.

They are usually easy to set-up, operate without a feedback device, and are low in cost making them a good choice for low-horsepower motor integration. Most units deal only with total motor current. They do not separate flux current from torque current, so torque cannot be regulated.

More complex applications that operate at low speeds yet must maintain high torque (like extruders, winders or web handling), as well as applications that demand high starting or accelerating torque (centrifuges) need a greater level of control that is usually available through sensorless vector drive technology.

Panel space. Saving panel space is one of the main benefits of integrated drive-motor packages. Often, they are a good choice for conveyor applications.

Instead of mounting the drive in the panel and running cables to the motor on the factory floor, integrated packages can be set up directly on the floor. Because the drive is mounted either at one end of the motor or on top of it, there is no increase in motor footprint and no depletion of panel space.

Networking. Some manufacturers offer connectivity to industrial networks in their integrated systems, and most offer basic codes for troubleshooting.

Networking takes an integrated package beyond simple troubleshooting. It enables a drive to communicate to a central automation system. Through this link, you can monitor for such factors as current speed, temperature, and lastknown fault - data that aid both preventative maintenance and troubleshooting.

Operator interface devices let you customize screens to monitor whether a drive-motor accepted messages from a controller, which can help to resolve or confirm process issues. In the process, you can more efficiently monitor the entire process, saving time and gaining greater control over it.

Continue on page 2