Silvanet Wildfire Sensor
The Silvanet Wildfire Sensor is designed to detect forest fires during the early stages (even during the smoldering phase, within the first 60 minutes) and to monitor the microclimate, measuring temperature, humidity and air pressure.
It combines ultra-low-power Air Quality sensing with a precise gas sensing mode. Hydrogen, carbon monoxide and carbon dioxide and other gasses are detected at the ppm level with built-in artificial intelligence to reliably detect a fire and avoid false positives.
To connect with the Silvanet Network, the sensor uses a LoRA-integrated radio to connect to a LoRaWAN mesh network that is robust within a large forest environment. This allows the sensors to connect to distributed LoRaWAN-enabled Silvanet Mesh Gateways and Border Gateways.
It can run maintenance-free for 10 to 15 years without the need of batteries, avoiding the use of lithium and other toxic materials. It obtains its energy source from a built-in solar-panel. As a precaution against the device itself starting a fire, it stores its energy in supercapacitors rather than batteries. A loop allows it to be attached directly to trees using tree nails or crop wire (temporary use only).
For deployment instructions, see Deploying sensors.
Dimensions and weight
The dimensions of the Silvanet sensor are (LxWxH) 19 cm x 9.11 cm x 1.34 cm. The sensor weighs 136 g.
Ingress protection of the housing is IP65. This means the housing is completely protected against dust and water resistance.
Silvanet sensors detect the environment within a range of 80 m to 100 m (260 ft to 320 ft) for 60 min detection of 2m x 2m fire. It can communicate with Mesh and Border Gateways that are 1 km away from the sensor, depending on topology.
BME688 gas sensor
The Silvanet Wildfire sensor uses the Bosch BME688 Gas Sensor to monitor the microclimate of the forest. It is a low-energy hydrogen sensor that detects the presence of a smoldering fire over distances of up to 115m. The gas sensor detects the presence of Volatile Organic Compounds (VoCs) and Volatile Sulfur Compounds (VSC) and detects these compounds at <20 ppm. The Silvanet Wildfire Sensor uses this gas sensor to monitor the microclimate of the forest.
Set of sensors
The BME688 includes a set of four sensors:
- Gas sensor: Outputs the IAQ (Index for Air Quality), bVOC and CO2 equivalents (ppm), Gas scan result (%)
- Humidity sensor: Outputs relative humidity
- Pressure sensor: Outputs pressure in Pa
- Temperature sensor: Outputs temperature in Celsius
This gas sensor has built-in environmental sensing using Artificial Intelligence (AI) to generate a normalized value for the environment in which it has been placed.
The BME688 sensor can detect:
- CO (Carbon Monoxide)
- CO2 (Carbon Dioxide)
- H2, (Hydrogen)
- VOC (Volatile Organic Compounds)
- Air Pressure
In the Silvanet sensor, the BME688 sensor provides measurements under the following conditions:
- Pressure: 300 to 11000 hPa
- Humidity: 0 to 100%
- Temperature: -40 to 85°C
The Silvanet sensor has very low energy consumption which is provided by its built-in solar-panel. As a precaution against the device itself starting a fire, the sensor stores its energy in supercapacitors rather than batteries.
The two key components that consume energy are the BME688 gas sensor and the radio. The gas sensor consumes ~3.9 mA in standard gas scan mode. The radio consumes 7W of energy to operate so it can continue to operate in a shaded location for ~6 hrs.
The sensor requires sufficient energy to support continuous operation over a 24 hr period while still having enough reserve power to support the heating and powering of the BME688 sensor and to send a burst of messages when a fire is detected.
Normally, the Silvanet Sensor Node is in idle mode. It activates every 60 seconds to read the air quality / gas sensor and every 2 hours to read the environment. It then sends a single packet to the Silvanet Server via the Mesh Gateway and Border Gateway. These data packets contain normal (non-fire detection) environmental data - temperature, pressure and humidity internal values. These values can be viewed in the Site Management app.
Built-in solar panel
The sensor includes on its front housing a 60mm x 60mm solar cell. It continuously generates energy during the daytime and recharges the device with sufficient power for the next 24 hours. After sunset, it begins to discharge until sunrise. After sunrise, it begins to recharge to 100% within about an hour.
Sufficient ambient light is available in forests to provide sufficient light for the solar panel. Forests are never entirely dark during the day, even with a thick forest canopy.
Each day the solar panel harvests 7Ws in the constrained conditions of a forest. The required energy can be generated using a 60mm x 60mm solar panel.
Supercapacitor Energy Storage
The Silvanet sensor uses a set of supercapacitors to store energy for use by the radio and BME688 sensor and other components. It stores the energy for day-to-day tasks and has a reasonable amount of reserve power to operate the gas sensor and radio module in case a potential fire is detected. As supercapacitors have an expected lifespan of 10 years or more, the sensors are essentially maintenance free. This allows for an expected lifespan of the sensor between 10 and 15 years.
Supercapacitors have a high capacity but a small maximum voltage of 2.7V so a series of capacitors are loaded to 4V. Capacitors are fully charged to 5.2V.
Power supply is stored in supercapacitors rather than rechargeable batteries as rechargeable batteries can ignite. Using batteries would defeat the purpose of a wildfire detection system.