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Radio remote control: demystifying the wireless box.

The science fiction writer Isaac Asimov once said, "Any sufficiently advanced technology is indistinguishable from magic." Of all the advanced materials handling technologies out there, radio remote crane control systems are among the least well understood and seem the most like magic. And that lack of knowledge leads to all kinds of questions and misconceptions about the technology.

Can a transistor radio interfere with the signal transmitted by a remote crane control system? Does a radio control system actually change the operating characteristics of the crane? What are the effects of a thunderstorm? Can a radio remote control unit cause cancer?

That such questions even arise indicates that most potential users don't take the time to learn enough about radio remote technology to understand how it works, and what it can-- or can't--do for them. To help you avoid falling into that trap, this article provides answers to the ten most frequently asked questions about radio remote control.

But don't stop here. The more you understand about a technology, the more effectively you will be able to evaluate it, compare competitive products, make your purchasing decision and--most important of all--use it.

Can someone talking on a

cellular telephone while

driving by my plant

interfere with my radio

remote control system?

Interference in radio signals occurs when two or more signals occupy the same radio channel, or frequency, simultaneously. Most people have experienced this when listening to music on a car radio. When interference occurs, an unwanted signal overrides the music, usually in the form of unintelligible noise.

Although all radio signals are subject to some type of interference, it is unlikely that cellular phones or transistor radios are sources. These types of equipment operate on a frequency band that is far removed from the FCC-approved frequencies used by radio remote control for industrial applications.

Because of the potential for interference from non-intentional radio transmissions, it is important that a radio crane control system be designed to minimize outside noise and not allow any interfering signal to cause false commands or motions. To ensure this level of security, high quality radio remote control systems use a highly secure digital coding scheme that makes each valid signal unique. They use repeated transmission of these digitally coded messages--typically four complete messages per second. In the event that this message is lost or interfered with by any source, the crane control output will automatically stop in less than one second, causing the crane to stop in its current position.

Another safety feature to look for is an automatic safety override, which monitors the verifying commands from the transmitter and disables the system if a fault is detected. The system should also feature some type of sophisticated error checking code of the digital data, which ensures that no more than one error in every 100,000 data transmissions will occur.

Can a thunderstorm affect

my radio remote control

operations?

While thunderstorms often produce lightning, which is classified as an unintentional radio signal, high quality radio remote control systems are engineered to filter out this type of interference (see the preceding question).

If lightning should strike the power source to the building, a radio remote control system is actually much safer than a pendant control. Because the operator is not touching the crane or pendant and there are no wires or direct connections to the power source, he or she is isolated from potentially fatal electric shocks.

While the building structure will protect indoor cranes from a direct lightning hit, all outdoor operations, radio or otherwise, should cease and power removed from the crane until the storm has passed. At that time, the operator should conduct all the normal start-up safety checks before operation resumes.

In the event of a power failure in the plant, a radio remote control system is no different than the motors, lights, and other electrically powered systems on the crane--it cannot operate without the proper voltage present. When the power goes off and comes back on, crane operations can resume after normal startup procedures. To avoid problems during a power "brown-out" condition, good radio remote control designs also feature special circuits that provide under/overvoltage detection, extended hold up, and reset functions.

What happens if the

operator accidently drops

the transmitter while

controlling the crane?

High quality radio remote control systems feature spring-loaded control levels that go back to a neutral position if the operator should trip and fall or accidently drop the transmitter. All crane commands then automatically stop. To prevent accidental activation of the control commands, either a protective handle is mounted over the motion switches on the transmitter or a palm operated, push-to-operate enable switch must be held down at all times for the motion switches to operate.

What is the price of a radio

remote control unit?

Radio remote control systems for overhead cranes are available in a broad range of prices, depending on such factors as the number of motor functions, the number of speeds for each motor, and the crane control voltage. The number of auxiliary functions to be controlled, such as hook rotation, braking, magnet, and lighting, also determines the cost of a system.

While prices do vary considerably, a "custom," five-motion radio control systems sell for about $7000. In contrast, a standard, "off-the-shelf" system, which controls fewer functions and does not need a license to operate, is priced in the $2500 to $3000 range.

In general, a radio remote control system provides a quick return on the initial investment. Conversion of a cab-operated crane to radio remote control, for example, reduces labor requirements by a factor of two. Further savings may be realized through productivity improvements that result from the ability to operate multiple cranes simultaneously; the elimination of travel time to fetch the crane; and the additional ease in observing and safety controlling the load with remote control.

Do I need an FCC license

to operate a radio remote

control system in my

facility?

Until recently, most radio remote control systems for overhead cranes required an FCC (Federal Communications Commissions) license to operate. However, some manufacturers now offer systems that do not require licensing, provided that they conform to certain FCC restrictions.

Available as an "off the shelf" product that can be installed in a matter of hours, non-licensed systems have become a popular choice for controlling overhead cranes and account for a growing percentage of the units sold. A distinguishing feature of these non-licensed systems is that the transmitter power level is considerably less than that of licensed systems. While this lower power output limits the control of the crane to shorter distances, many applications do not require long distance control.

What is the typical

operating range of a radio

remote control system?

Several factors, such as receiver sensitivity, the type of antenna, and the type of transmitter power, affect the operating range of a radio remote control system. Licensed units can be operated at a range of between 100 and 2000 ft without special antenna equipment. Because of a lower power output, the range for non-licensed systems is typically 100 to 400 ft.

In some applications, however, a more limited range of operation may be desirable. Manufacturers now offer systems designed to automatically shut down the crane if the operator goes beyond a specified distance (figure). One manufacturer has recently introduced a new system that has both controlled range and longer operating range capabilities.

Can I retrofit a radio

remote control system to

my overhead crane?

Absolutely! In fact, approximately half of the radio remote control systems sold today involve retrofits to installed electric overhead travelling cranes. Although the radio remote control manufacturer will help you select the optimum system, some of the things to consider are the frequency to be used, the number if motions and auxiliary functions to be controlled, and the type of operating environment.

Whether a radio remote control system is applied to an installed system or a new one, it does not change the operating characteristics of the crane. Radio remote controls are simply a replacement for the manual controls. The steel structure, the wheels, the motors, and the control panels of the crane are still the same.

Who can I buy a radio

remote crane control

system from?

Radio remote control systems can be purchased directly from the manufacturers, as well as from crane manufacturers, who purchase these systems and sell them under their own private label.

Can I get cancer by using

a radio remote control

unit?

While nobody knows for sure the potential effects of radio frequency fields, a common, two-way radio transmits significantly more power than a radio remote control transmitter. The transmitter's power source is also directed away from the operator during use. Proper operation of a radio remote control system will result in the exposure to a level of electromagnetic radiation that is substantially below the FCC recommendation for two way radios (FCC General Docket 79-144, 3-5-85).

We generate a lot of dirt

and dust in our facility. How

will that affect a radio

remote control system?

Like any electronics equipment, the components of a radio remote control system are susceptible to dust, dirt, moisture, and other contaminants. The weakest points in most transmitters are the motion switches. New designs, however, use an offset switch fitted with sealed O-rings that effectively prevent moisture or dirt from getting down into the circuitry. Similarly, the receiver/decoder/interface unit is enclosed in an environmentally and tamper-resistant, NEMA (National Electrical Manufacturers Association) type enclosure. If the system is to be operated in the vicinity of explosive gases or combustible dust, advise your vendor so that Factory Mutual approved transmitter equipment can be specified.
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Title Annotation:crane controls
Author:Augustin, Karen A.
Publication:Modern Materials Handling
Date:Apr 1, 1992
Words:1611
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