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How do I know if my sensors will have enough range where they are placed?

Keywords: sensor placement, placement sensor, site survey, RF range


How Sensor placement effects how far apart you can place the sensors from the gateway.

Monnit wireless sensors incorporate a 900MHz/868MHz bi-directional chipset designed to transmit data (and notifications) from the sensor to the MonnitLink wireless gateway. Being able to create a reliable link between the two points is key to creating and maintaining a functioning wireless sensor network (WSN).

Environmental Factors                                                               
The environment between the sensor(s) and the MonnitLink gateway greatly increases or decreases the range in which your sensors can "talk" to each other. As most sensors deployed in a commercial, industrial or home setting will have obstructions between the sensor and the gateway, Monnit will only focus on optimizing non-line-of-sight (N-LOS) in this tech tip. (Should you achieve line-of-sight (LOS) between the gateway and sensors, you should expect up to 1,000 ft communication distance.)

Physical obstructions limit the range the sensors can successfully communicate to the MonnitLink gateway. Simple obstructions such as vegetation, vehicles, doors, office machinery and furniture to complex structures inside of a building such as walls of various materials (wood, drywall, concrete, steel), ventilation duct work and building wiring can all reduce the range the sensors can be deployed from the gateway. It is in your best interest to conduct a site survey of the area prior to deployment to find the optimal communication path for the sensors.

In additional to physical obstructions, other RF interference (often referred to as "noise") in the same bandwidth can decrease the range of a wireless sensor deployment. Fortunately, Monnit has selected the 900MHz frequency – a license-free ISM band frequency – for its sensor network, reducing interference often found in other commonly used frequencies.

Placement of Sensors
For optimal communication the higher the sensor and/or gateway can be placed for the application the stronger the RF link becomes and the greater distance the sensors can be placed from the gateway. If at all possible, do not place your sensors on or near ground level, as it affects the Fresnel zone of the antenna. (For more information about Fresnel zones and antennas, see this related article.)

For sensors that are to be located several feet from the area to be sensed (such as water on the floor or the temperature of a cooler), make sure your sensors have the appropriate lead lengths in place.

Conducting a Site Survey
Before deploying your sensors, conduct a site survey. If you are preparing to install a larger wireless sensor network, you can purchase a Monnit button sensor to check for signal strength before placing the permanent sensor. The button Sensor is set-up to communicate with the gateway when the button is pushed. To evaluate if a location is good for placement of a sensor, follow the steps below:

  • When you first receive the button sensor, add it to the online account, and then insert the batteries.
  • Plug-in the MonnitLink USB gateway to your PC if not already in place.
  • Once the sensor list has loaded, press and hold the Button Sensor button for five seconds to link the sensor to the gateway.
  • Once the sensor is linked, you will see the button push logged into the "History" of the iMonnit software.
Proceed to the location where you would like to place a sensor and push the button on the Sensor. If you receive a green flash confirmation, you have good RF communication. If you receive a red flash, the sensor could not establish a link with the gateway. Position the button sensor about one foot away from your last spot and repeat the process. Once a green flash is received, attach your sensor to that location with one of the included Monnit mounting options.

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