Skip to content
Extra 7% OFF Everything Over $99 for HANUKKAH Sale | code: HAPPYHANUKKAH | Expires 12/15 Midnight CST
Extra 7% OFF Everything Over $99 for HANUKKAH Sale | code: HAPPYHANUKKAH | Expires 12/15 Midnight CST

Boltek EFM-100C RS485 Electric Field Monitor


Free Shipping US Wide

Easy 30 Day Returns

Best Price Guarantee

Expert Customer Service

Select Power Supply
Select Power/Data Cable Length
why you should buy from weather scientific

Boltek EFM-100C RS485 Electric Field Monitor

Measuring the static electric field generated by thunderclouds the Boltek EFM-100 not only detects nearby lightning but can detect the atmospheric conditions which precede lightning. Electric field data is displayed and graphed on your desktop computer using the included software.

For complete electrical isolation from the field mill outside, the EFM-100 connects to your computer using a fiber optic cable. The EFM-100 features aluminum and stainless steel construction for corrosion resistance, gold plated connectors throughout, and the highest quality ball-bearing brushless dc motor for excellent reliability.

The electric charge contained in a thundercloud also generates an electric field. This field can be measured on the ground.

Electric fields develop wherever there is a difference in electric potential. If the electric field gets high enough you can feel your hair stand on end (if this happens outdoors during a thunderstorm crouch down with your feet together as you are about to be struck by lightning.) An electric field is what attracts your hair to a charged comb or a charged balloon.

Electric field is measured in Volts per meter (3.3 feet) The electric fields which accompany thunderstorms normally measure in the thousands of Volts per meter, usually abbreviated to kV/m.

Lightning is detected as a sudden change in the static electric field.


  • High accuracy lightning detection (0 to 24 miles / 0 to 38km)
  • Monitors and alerts for weather conditions that precede lightning
  • Standard RS485 data output with optional fiber optic package
  • Electrical isolation from the field mill to PC or Laptop
  • Customizable alarm distances and electric field levels
  • SMS text messaging and E-mail alarm notifications
  • Monitor up to four separate locations per computer
  • Aluminum and stainless steel parts throughout for corrosion resistance
  • Free software updates
  • One year parts & labor manufacturers warranty

Parts Included:

  • EFM-100 Electric Field Mill
  • 100 Foot (30m) Cat6 Power/Data Cable
  • 120V/220V AC Power Supply
  • EFA-21 Power / RS485 to USB Module
  • USB Cable
  • DIN rail clip for EFA-21 Module
  • 6 Attenuator Plugs
  • 1 mast (10” x 3/4” NPT)*
  • 1 mounting flange (4” diameter)
  • Windows Software & Manual

Optional fiber optic package includes fiber optic cable, EFA-20 with USB cable, and EFA-10 with DB9 serial cable

*Custom mounting masts available

EFM-100C User Manual
EFM-INV-M / EFM-INV2 / EFM-INV3 Installation Instructions
EFM-100 Product Brochure
USB-RS232 Driver Fix Instructions


EFM-100 V1.33 Software for Windows
EFM-100 V1.27-100kV Software for Windows
USB Adapter Device Driver for EFA-20/EFA-21
USB-RS232 Adapter Driver for Windows 7/8/8.1/10

Shipping is fast and FREE across the USA for all orders $199 or more. For more details about shipping see the full shipping page here.

We offer 30 Day Easy Returns. If you decide you don't need a product we'll take it back so long as it is in original and re-saleable condition. See the full details here.

Please see this page for our Texas Electronics Shipping & Return Policy:

Found a better price online? We'll match it or beat it if we can. 

All you need to do is let us know via phone or email ( and we'll let you know what we can do.

You will need to provide evidence of the better price online and it must include any shipping or taxes charged by that site. i.e. It needs to be the total price.

This only applies to new products, it does not apply to used condition products.