The answer to your question- the Limitless™ product will have difficulty functioning in an area where the 2.4 GHz ISM band is completely consumed on a consistent basis. Some examples include high power industrial microwaves and high bandwidth video transmission on 2.4 GHZ. So you are correct, wireless products are not completely immune to interference, but the chances are small that an issue will arise assuming you survey the site before implementation. Also, unless the interference source is constantly on, our system can recover to a large extent due to the retries and acknowledged transmissions that we built into our system. Please contact our technical representatives if there are further questions at 800-537-6945.
Have you ever experienced a receiver becoming "de-sensitized" because of a strong signal nearby? It is a problem in some areas, even with receivers costing hundreds of times more than the wireless switch control units. I am talking about another signal of amplitude high enough to move the first stage or stages out of the intended operating area. It is not an everyday-everywhere problem, but it certainly does happen. It winds up that certain wireless-sensor security systems can be paralyzed this way. So the fact is that they are not interference immune, only interference resistant.
There are diagnostic functions when using a Limitless™ monitor/receiver that can help isolate a problem with a particular switch. Please review the attached Troubleshooting Section in Section 10 which references other sections for review at the attached link: http://sensing.honeywell.com/index.cfm/ci_id/157464/la_id/1/document
In answer to your question regarding interference issues, there are commercially available devices (i.e. packet sniffers) that allow you to look at all of the RF signals in a localized area and this can be accomplished via a site survey; please reference Section 6.5.3 at the same link above. The WDRR Series product also has the capability to provide an RF signal strength indication for each individual Limitless™ input (i.e switch). The IEE802-15.4 protocol that the Limitless™ product uses was specifically designed for wireless product use in the Industrial market. It has many features within it to minimize interference along with our implementation features, i.e., 128 bit encryption key used by each limit switch; automatic channel/PAN ID and energy scanning at power-up. Testing in the actual application against the customer’s particular requirements is also recommended in proving product suitability.
The Limitless™ products are not meant for use in any human safety or fail safe application. Please contact our technical representatives if there are further questions at 800-537-6945.
I have seen literature on wireless switches and transducers for a couple of years now. My concern is maintenance. How do I know that the switch is still working, and how do I troubleshoot? An electrician uses a meter on the contacts of a wired switch to determine if it is active or not. In the installation drawings, I'd have specified that the switch be wired so that ON = OK and OFF = alarm or not OK or cable fault. How is this done with wireless?
The added problem - how do I determine interference issues? Is there a device available that allows me to receive or 'eavesdop' the 'signal' that the switch is transmitting, on a handheld device, and verify good signal? I am not concerned with false positives - I need to know that the X-ray machine in the lab is not intermittently wiping out my switch signal.
You describe using this on a crane application. A crane installation using the wireless switch for man safety would convince me hat these switches are a 'real solution', reliable enough for me to test in a real application.