Ensure cableless control reliability

Industrial wireless, or using ANSI’s term, cableless control, requires reliability. Don’t let radio frequency interference lead to downtime; follow these policing precautions.

09/18/2013


A cableless mobile control station can provide mobile industrial wireless control, allowing users full view of the equipment under control, such as this crane application. Courtesy: Automation Rangers Ltd.Prepare your manufacturing production area or facility for industrial wireless applications for control, or as ANSI now says, “cableless” control. Radio frequency (RF) interference can lead to downtime, but can be virtually eliminated if proper precautions are taken. Several significant solutions exist among certified ANSI “cableless control” manufacturers. Conducting an RF audit on a machine or process area follows the adage, “An ounce of prevention is worth a pound of cure.” Reducing or eliminating wireless interference can help keep your area shutdown free. Attention to the design of cableless control systems can help.

ANSI: cableless control

Cableless enabling pendant is secured to the user. Courtesy: Automation Rangers Ltd.Recently “Cableless Control” was adopted into the ANSI standards from NFPA 79-2012 and RIA R15.06-2012. Cableless control has long been recognized by the European Standards including ISO EN 10218, EN 13849-1, and EN62061. Wi-Fi and other uses for RF have been around for a long time and often are not considered critical. Basically, cableless control is wireless or remote control that is considered control reliable or fail safe. NFPA 79-2012 Cableless Control Functions 9.2.7 is a good start for the requirements necessary for a safe, reliable control system. “Cableless Control” controls until a fail-safe actuation of an e-stop or a signal failure. So it is important to make sure any possible interference is kept to a minimum, much the same as protecting against noise with proper electronics design.

“Cableless Control” is being applied in start-up, installation, testing, operation, and maintenance of machine and process systems. A cableless system should be easy to design, install, and operate with little in the way of maintenance necessary over its lifetime. Start with a basic cableless e-stop or enabling system. Once that is accepted, work your way up to a mobile control station as a good way to get everyone comfortable with the technology.

Many legacy systems are well over 10 years old. Cableless control systems are much more robust than typical standard wireless Ethernet switches or routers. “Cableless” devices or systems being applied are directly integrated into mission critical automation and safety systems. Many Fortune 500 and Fortune 100 companies and their original equipment manufacturers (OEMs) are starting to install these devices globally.

Assessing, auditing RF

A radio bus repeater helps ensure strong wireless signals where needed. Courtesy: Automation Rangers Ltd.Begin management of potential interference from RF devices or systems by auditing your plant environment for all radio frequency sources. A check list of items for an RF audit follows, along with what to document when installing an RF transmitter/receiver on-site. Standard design considerations for electromagnetic interference or radio frequency interference (EMI/RFI) are advised. Inexpensive RF spectrum analyzers are available through most RF system providers.

Most customers have not done this. Very few who do this have signal problems. One customer that did have an issue fixed it with a quick, easy manual adjustment to a new frequency. The reason for implementing an RF policing effort is that RF devices populate the environment more often, and regularly. At some point, unmanaged, they could become a problem. Obviously, addressing the potential for a problem now is better than dealing with an unknown problem that causes downtime later.

RF audit checklist

1. Device audit information necessary to build a RF write map for RF management.

a. “Cableless control” application:

i. New or retrofit?

ii. Interface to an existing or surrounding system?

iii. How many cableless devices in an area or facility?

iv. Control

1. Mobile control station

2. Pendant

3. Network

4. Device or instrument

v. Safety

1. Level of safety

2. Single or dual channel

3. Safety network

b. Manufacturer:

c. Model number:

d. Description or specifications:

e. Configuration:

f. Parameters:

g. If installed with software, get copy of file.

h. Operating frequency:

- Country (This is important because Europe and North America have different frequency ranges available for commercial use, so ensure the specification includes FCC-compliant equipment.)

i. Encryption:

j. FCC ID:

k. RF emissions:

l. RF power:

m. Operating range:

n. Antenna type and specification:

o. Antenna cable and specification:

2. Conduct a radio frequency scan of your facility.

a. Be aware, similar to electrical noise, RF may occur based on events and often is inconsistent, so a scan may need to be conducted for 24 hours or more.

b. Some manufacturers of RF equipment will scan your facility for you, but you may need to buy or rent a scanner to do a thorough longer-term analysis.

3. The easiest way to determine success for a device is to start with one unit and monitor on/off performance over a week or even a month. If the device never turns off, then you are reasonably sure you don’t have a conflict. This is how most customers do it.

Evaluation recommendations

1. Group the frequencies and determine if there are overlaps.

2. Determine if the technology overcomes the overlap. Frequency shifting technology will tolerate much greater population than standard units without shifting.

3. Determine the ability of the device or system to overcome RF interference. This will determine if a device will adjust to interference, if it needs its own band, or another design consideration. Look at:

a. Width of frequency signal (broad and flat versus narrow and sharp)

b. Manual frequency shifting

c. Automatic frequency shifting

d. Frequency-hopping spread spectrum

4. Component design for electronic based control systems should always be evaluated for EMI/RFI, and the proper designs for wiring, cabling, and termination should be followed to keep interference to a minimum.

Click to next page for an RF management strategy, followup, and RF reliability tip, along with more cableless photos, including a wireless e-stop.


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