RF interference and security in One-to-One applications - Facility Explorer - LIT-12011663 - Wireless Device - WRZ: Wireless Room Sensing System

FX-WRZ Series One-to-One Wireless Room Sensing System Technical Bulletin

Facility Explorer
Product name
WRZ: Wireless Room Sensing System
Document type
Technical Bulletin
Document number
Revision date

The FX-WRZ Series Sensors, FX-WRZ7860 Receiver, and the one-to-one wireless sensing system are designed to virtually eliminate RF interference with other wireless applications. In most commercial environments, the One-to-One system does not encounter or generate significant RF interference, even in environments that are saturated with cell phones and competing Wireless Fidelity (Wi-Fi) applications.

The FX-WRZ Series Sensors and FX-WRZ7860-0 Receiver operate on multiple discrete channels within the 2.4 GHz ISM band and use multi-frequency Direct-Sequence, Spread-Spectrum (DSSS) technology.

Cell phones do not operate on the 2.4 GHz ISM band, and cell phones do not interfere with One-to-One wireless room sensing systems, except when a cell phone is operated within 3 ft (1 m) of an FX-WRZ Series Receiver. When One-to-One wireless room sensing systems encounter most other Wi-Fi transmissions in the 2.4 GHz ISM band, the transmissions merely appear as noise and do not significantly impact wireless sensing system communication.

Using DSSS technology, the FX-WRZ Series Sensor is designed to transmit a data message to the associated receiver every 60 seconds. When a single data burst is successfully received and acknowledged, the sensor goes dormant for 60 seconds and then repeats the transmission burst sequence.

When the One-to-One wireless room sensing system encounters RF interference, the system changes to a different channel to enhance reliability. The FX-WRZ7860 Receiver establishes the RF network, using one of several channels in the 2.4 GHz ISM band. The sensors then try transmitting on each of the channels until they locate the receiver. Operation continues on that channel until communication problems develop. If the receiver cannot communicate with the sensors, it restarts the network on a different channel. The sensors then locate the receiver on the new channel and continue operating on that channel as long as reliable communications occur.

These data-transmission sequences greatly enhance the success of the wireless room sensing system data transmissions. Transmitting short, high-speed data messages at periodic intervals also reduces RFdata-transmission collisions and interference with other Wi-Fi and Bluetooth transmissions. The DSSS technology also prevents the most malicious RF interference.

RF interference and transmission failures can also be prevented by maintaining an adequate distance between RF transmitting devices. Restrictions to distance between devices are listed in the following examples:

  • FX-WRZ Series Sensor should not be mounted less than 3 ft (1 m) from a FX-WRZ7860 Receiver.
  • Cell phones should not be used within 3 ft (1 m) of an FX-WRZ Series Sensor or FX-WRZ7860 Receiver.
  • Wi-Fi access points should be mounted at least 20 ft (6 m) from any FX-WRZ Series Sensor or FX-WRZ7860 Receiver.
  • Other low-power Wi-Fi transmitting devices should be mounted at least 3 ft (1 m) from any FX-WRZ Series Sensor or FX-WRZ7860 Receiver.
  • 2.4 GHz cordless phones and some older phone headsets can cause interference and should not be used anywhere near a One-to-One wireless room sensing system.
  • Avoid areas where microwave ovens are located between the FX-WRZ sensor and the FX-WRZ7860 receiver.

To secure One-to-One RF wireless messages, the FX-WRZ Series Sensors and FX-WRZ7860 Receiver, use a custom Johnson Controls message protocol that prevents deciphering any One-to-One data transmissions received or intercepted by any other receiving devices.