Image: Daniels and Daniels
Because an electric motor invariably generates intolerable amounts of electromagnetic clutter, you must take several countermeasures. Even the metal shaft gives off such deleterious energy, and if the rotating shield pan were connected directly to the shaft, this radiation would spew out between the two pans, where the instrument is most vulnerable to noise. To avoid such degradation, add to the shaft a nonconducting extension, such as a wooden dowel 2.5 centimeters (one inch) in diameter. Use a drill press to bore a precision hole along the exact centerline of the dowel and then epoxy the shaft inside it. Next, electrically isolate the motor by mounting it coaxially, with Teflon screws and washers, to the inside of an upside-down metal trash can like the ones found in offices and schools. You can capture most of the radiated gunk with two layers of aluminum window screen.
Next, cut off part of a second metal trash can so that it will fit within the first can with the motor attached. Then drill a hole through the centers of the sensor pan and a third cake pan (for calibrating the instrument) that can amply accommodate the dowel. During the calibration process, you will need to charge the third pan, so affix a wire to its outside surface by using a conducting metallized epoxy. Three small rubber gasket spacers wedged between the sides of the sensor and calibration pans will hold them close together without their touching. Bolt them as a unit to the inner trash can by using insulating standoffs and drill a hole in the can to take the wire out.
The circuit must be attached to the inner trash can at a location directly below the sensor pan. To reduce electrical interference, shorten as much as possible the wires that connect the sensor pan to the circuit and the circuit to the inner trash can. Also, completely enclose the circuit with a patch of aluminum screen. Remember that you need to force all the signal current to pass through the amplifier, so make sure that the ground wires are the only electrical link between the sensor pan and the trash can.
Install the entire assembly inside the outer trash can by again using insulating standoffs. Then, from the end of a PVC pipe of 2.5-centimeter inner diameter, cut a spacer that is precisely one centimeter long. Thread the spacer over the wooden dowel and rest it against the sensor pan; epoxy the spacer to only the dowel. (If you bond it to the sensor pan, the shaft will not rotate.) Finally, cut a hole in the center of the shield pan so that you can secure it onto the dowel between the spacer and a second piece of PVC pipe.
To calibrate the instrument, you first need to glue a fourth cake pan coaxially to one end of a dowel and a large pizza pan (for screening out the earth's electric field) to the other end. Insert this implement within the trash-can assembly. A voltage placed between the top and bottom cake pans creates a field that approximates the earth's. With a two-centimeter spacing between those pans, a two-volt difference creates a 100-volts-per-meter field inside the instrument. You can calibrate the device at the low end of its scale with nine-volt batteries and a rheostat. Simulating the field generated by a powerful thunderstorm requires a 200-volt power supply, which you can find at most electronics surplus shops for less than $100. But keep in mind that these devices can deliver enough current to kill, so use extreme care.
Use your homemade field mill outdoors, far away from buildings, either rigidly suspended from a pole or resting level on an insulated ring. Either way,
make sure its opening has an unobstructed view of the ground. If you run the signal into your home through a coaxial cable, you will be able to monitor the
field comfortably in all kinds of weathe
For more information about this and other projects, check out the Society for Amateur Scientists's Web page. You may also write the society at 4735 Clairemont Square, Suite 179, San Diego, CA 92117, or call 619-239-8807.
This article was originally published with the title Detecting the Earth's Electricity.