Thunderstorm Detector BTD-350

The Biral BTD-350 Thunderstorm Detector is a standalone sensor that reliably detects the presence of all forms of lightning (Cloud-to-cloud, cloud-to-ground and intra-cloud lightning discharges) to a range of 83km. The detector has a very low false alarm rate and the ability to warn of the risk of overhead lightning. Detects charged precipitation and provides information for enhanced CAP437 reporting of thunderstorms. Meets FAA performance requirements for aerodrome use and is certified for marine operation both on and offshore.

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The Biral BTD-350 Thunderstorm Detector operate on quasi electrostatic principle that gives higher sensitive detection of the storms presence than devices that rely on radio detection. The electrostatic operating principle allows the sensor to warn of the risk of overhead lightning before the first discharge occurs.

The sensor thunderstorm warnings bases on the detection of electric fields (frequency changes in the band 1 -47Hz) and electrically charged precipitation, occurring at the installation site before the occurrence of the first flash; electric field disturbances associated with lightening flashes, allow monitoring of the thumderstorm intensity and their proximity.

The operating principle of the BTD-350 is based upon sensing changes in the atmospheric electric field in the frequency band of 1-47 Hz. Such low frequency means that the sensor is most sensitive to slow-varying electrostatic fields associated with charge transfer (from lightning flashes, turbulent movement of strongly-charged aerosol, etc.). In addition, charge transferred to the antennas by precipitation is analysed and used to determine whether the overhead cloud has the potential for thunderstorm activity. Radio emissions (both natural and man-made) are associated with considerably higher frequencies so do not produce interference on the sensor. Noise associated with mains power distribution (typically 50 or 60 Hz and harmonics) are removed by both analogue and digital filtering.

Virtually maintenance free in operation, the BTD-350 can either interface directly to an integrated system or be operated using the supplied PC compatible display and logging software. The optional warning relay module allows the sensor to automatically sound alarms whenever a storm approaches.

The range information supplied by the sensor can be augmented with a Direction Finder module. The Direction Finder module detects electromagnetic waves produced by lightning discharges in a band from approximately 3kHZ to 1MHz. The direction from sensor to discharge is reported to the nearest degree in the BTD-350 data output. The BTD-350 can be configured for either Ethernet or RS422 serial communication. The data is output as an ASCII coded data string for easy integration with other data processing systems. For standalone use a comprehensive PC compatible software application is supplied which provides data visualisation, sensor control and data logging.


Cloud-to-cloud, cloud-to-ground and intra-cloud lightning discharges

Measurement principle

Passive, quasi-electrostatic. No moving parts

Detection range

83 km

Detection efficency
(for flashes within 56 km)


95% for single lightning flash (any type)

99% for storm with 2 flashes

99.9% for storm with 3 flashes

False alarm rate

< 2 %

Measurement error

0 to 20 km ± 5 km

20 to 83km ± 10 km

Max flash rate

120 per minute

Time of flash

Nearest 10 ms (internal clock)


Ethernet or serial data (RS422)

Sensor power

110 - 240 VAC 50-60Hz

Operating temperature

-40  to + 60 ° C

Operating humidity

5 to 100 % RH

Mass (sensor head)

25 kg

Protection rating


Certification and compliance

CE Certified, EMC – General (EN 61326:2013), EMC – Marine (

EN 60945:2002, Sections 9.2.2 & 9.2.3), Corrosion resistance (

EN 60945:2002, Sections 8.12, EN 60068-2-52:1996 Test Kb),

Virbration (EN 60945:2002, Section 8.7, EN 60068-2-6:2008, Test Fc).

Compliance with EN50536:2011+A1:2012 for a Class 1 detector

Performs in accordance with IEC 62793 for a Class A detector

RoHS and WEEE compliant


Direction finder module, Early warning module on upcoming storm


Datasheet BTD350  BTD_350_DS_DOC101469_03A.pdf 
Thunderstorm Detector BTD-350
Thunderstorm Detector BTD-350
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