Ensure cableless control reliability

09/18/2013


RF management strategy

Yes, e-stops can be wireless, as this cableless control e-stop demonstrates. Courtesy: Automation Rangers Ltd.Strategies for management of your radio frequency environment are varied. One example is using the 30-900 MHz range for two-way radio, 902-928 MHz range for control, 2.4 GHz for wireless Ethernet communication, and monitoring inside and outside potentially invasive frequencies to protect against interference. For most applications this requires a small amount of documentation and awareness for system design. This has given birth to the term “RF Police.”

There is little related documentation online, so in many cases it is left up to common sense. There are many documents related to troubleshooting RF problems in an industrial environment, and they will give clues for strategies to prevent interference. Another reliable method for strategizing is to contact manufacturers of the RF-transmitting devices and ask what they suggest.

RF interference control tasks

To control RF interference consider these responses.

1. If RF interference occurs, then a procedure similar to addressing electrical interference needs to be put into action.

a. Interview all people using the area for knowledge of the use of a new RF device.

b. If that doesn’t turn up the problem, then bring in a RF scanner and try to identify the problematic RF device.

c. If the problem comes from an outside source over which you have no control, address the concern with a strategy that negates the problem.

2. If it is determined that there is potential for RF interference, then a course of action must be decided.

a. Contact the manufacturer for recommended solutions.

b. Contact the outside source if not under your control and ask it to filter the device.

c. Use filters to stop or limit transmission of transient RF.

d. Remove offending devices that do not have internal resistance built in.

e. Remove offending devices that are interfering with other devices.

f. Replace offending devices with newer technology that is either resistant or filtered.

3. Most reputable manufacturers offer solid solutions to limit device interference.

Following up

Mobile radios can be intermittent sources of radio frequency interference (RFI), demonstrating the need to police use of radio frequencies in the workplace. Courtesy: Automation Rangers Ltd.Re-evaluate and/or monitor to stay on top of the situation.

After addressing the RF conflict, deciding on the type of technology needed to accomplish control is no different than in any other control project. In general, here are the types of equipment available. Some devices are capable of integration with any system and others are proprietary to a manufacturer and do not play well with others.

1. “Cableless safe control” between PLCs or process control systems

a. Security?

b. Safety rated?

2. Data transmission or bus system? Safety rated?

3. There are systems that address I/O—discrete, safety, and analog. (Some are flexible; some are not.)

4. Mobile control stations (Most are flexible, but watch for the safety ratings, specifically single channel versus dual channel, or the ability to be part of a safety network.)

5. Pendants very similar to enabling pendants or crane control pendants. (Watch the safety rating and application.)

6. Devices like instruments or switches with a receiver monitoring their signal

All systems must have continuous communication with an ID, be one-to-one, and include redundant monitoring of third-party safety circuitry, communication link monitoring, battery monitoring and alarm, along with a method for swapping batteries without causing a stop. A few systems offer repeaters; security; displays; lighting; explosion-proof capability; a built-in safety bus; shock, drop, and roll detection; as well as vibration and audible alarms.

Frequent RF monitoring                                                                                       

A radio frequency spectrum analysis tool helps track local RF use, avoiding conflicts and maintaining reliability. Courtesy: Automation Rangers Ltd.Applications for RF control technology are part of our everyday environment; RF control quickly pays for itself. Elimination of radio interference will become as commonplace as troubleshooting a circuit. It starts with knowing what the environment contains.

A risk assessment performed by certified safety professionals will determine the value of “cableless control” versus other solutions. Many safety professionals do not have experience with “cableless control.”

The author thanks information contributors for this article: Jamie Sanderson at HBC Radiomatic; Stacy Shumpert at Procter & Gamble; Brian Rowell at Fluor Daniels, Lancaster, S.C.; Ted Sberna at White Horse Safety; Steve Leytus at Nuts About Nets; Mike Kunkle at MEK Consulting; and Brian Huber at Machine Safety Specialists.

- Dan Junker, electrical sales for Ohio, Automation Rangers Ltd. Edited by Mark T. Hoske, content manager, CFE Media, Control Engineering and Plant Engineering, mhoske(at)cfemedia.com.

www.IndustrialWirelessSafety.com


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