wi fi network

What protocol are you using between your CPU and RIO? What equipment do you have? Distance?

Installing a wireless system capable of supporting the realtime, deterministic requirements of a control system is very difficult. If there is any way to use a physical ethernet cable instead of wifi, I would suggest you use the wired method instead.

That said, there are a lot of vendors that focus on wifi for automation. I've had good experiences with the Scalance W products from Siemens, using iPCF to handle rapid roaming. It definitely isn't at the cheap end of the spectrum, though. I would recommend using equipment intended for industrial automation use, and not some random consumer grade equipment.

Things to consider in a wifi install:

1) What radio interference is currently in the plant? Are there other wifi systems? Are there devices like microwaves that emit interference on wifi frequencies?

Doing a site survey to check for existing interference is probably THE MOST IMPORTANT thing you can do to ensure success. If there is interference in the channel, the wifi communicaiton will not be reliable, and there is not much you can do about it.

2) How big of an area must be covered? Different types of antennas are designed to cover different types of areas. If multiple Access Points are required, it will probably be necessary to plan which frequency/channel will be used by each AP.

3) How many clients and access points will there be? Will the clients need to roam between access points, or will they always be attached to one AP?

4) How much data will there be? How often will it be sent?

The first and most important is can the application tolerate response times of 20+mS? If not then don’t bother it will be very difficult if not impossible to achieve and if you can achieve it the cost will be very high (Siemens radios might get the job done in the right environment).
If it’s anything other than a long range application (more than 2 miles) and has good line of sight then I’d look at this (http://www.data-linc.com/fastlinc/fastlinc910e.htm). The nice thing about the FLC910E is that it operates like an 802.11g device except that it’s in the 900MHz band rather than the very crowded 2.4GHz band. Also because it’s not using the WiFi spectrum IT departments tend not to care about it.
If it is a medium range application without line of sight or a long range application (with or without line of sight) then you’re looking at a Frequency Hopping Spread Spectrum device like this (http://www.data-linc.com/srmfamily/srm6230.htm). Keep in mind that the throughput on something like that is going to be very low compared to something like WiFi or the FLC910E. Some basic laws of physics come into play and to gain distance you sacrifice speed (at least with current technology).
One other thing to note, you’ll see a lot of other equipment out there some of which simply won’t do the job (regardless of what they say) some of which will work but may require a lot of “tweaking” to get there. When you work with equipment from Data-Linc, Siemens or ProSoft you’re working with companies that live in the Industrial Automation world and know how to get the job done.

Firejo said:

The first and most important is can the application tolerate response times of 20+mS? If not then don’t bother it will be very difficult if not impossible to achieve and if you can achieve it the cost will be very high (Siemens radios might get the job done in the right environment).
If it’s anything other than a long range application (more than 2 miles) and has good line of sight then I’d look at this (http://www.data-linc.com/fastlinc/fastlinc910e.htm). The nice thing about the FLC910E is that it operates like an 802.11g device except that it’s in the 900MHz band rather than the very crowded 2.4GHz band. Also because it’s not using the WiFi spectrum IT departments tend not to care about it.
If it is a medium range application without line of sight or a long range application (with or without line of sight) then you’re looking at a Frequency Hopping Spread Spectrum device like this (http://www.data-linc.com/srmfamily/srm6230.htm). Keep in mind that the throughput on something like that is going to be very low compared to something like WiFi or the FLC910E. Some basic laws of physics come into play and to gain distance you sacrifice speed (at least with current technology).
One other thing to note, you’ll see a lot of other equipment out there some of which simply won’t do the job (regardless of what they say) some of which will work but may require a lot of “tweaking” to get there. When you work with equipment from Data-Linc, Siemens or ProSoft you’re working with companies that live in the Industrial Automation world and know how to get the job done.

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I agree with the 20ms benchmark. If your IO needs to be updated faster than that, wireless will probably not be a good solution. Using wireless for motion control (servos, etc) is definitely a bad idea. It may be acceptable for digital IO or basic VFD's.

One thing to note about the 900mhz band: it is typically a lot less crowded than 2.4 ghz, but a lot of the devices that use it tend to be hogs. 900mhz walkie talkies are very common in industrial environments, and they will often shut the wireless data network down while they are in use.

The 5ghz band is typically better to use than 2.4ghz. 5-10 years ago, most consumer devices didn't support it, and it was essentially empty. Nowadays, many consumer devices support 5ghz, and office IT environments typically use both 2.4 and 5ghz.

The main push behind the ISM band (900MHz, 2.4GHz and 5.8GHz) is that it’s an open non-licensed spectrum. With that, part of the compliance rules dictate that any device that operates in it must not cause harmful interference (within reason) and can deal with “non-harmful” interference. I say that because the walkie talkie’s that use the 900MHz band shouldn’t interfere with ISM devices. Now the real world; I low quality 900MHz radio modem will more than likely not like most 900MHz walkie talkie’s and vice versa but the opposite is also true in that a high quality 900MHz radio modem won’t be bothered (too much depending the type) by a 900MHz walkie talkie. The FLC910E will likely see a minor slowdown in throughput but it should still run at a pretty good speed (assuming other conditions are good). Data-Linc’s frequency hopping radios will most certainly not have any noticeable performance loss in the presents of any 900MHz walkie talkies. All of this is based off of the premise that the radio modems have good antenna installations and any walkie talkie repeaters (if any) also have good antenna installation practices.