Fig. 1
From: NetPICOmag: A low-cost networked magnetometer and its applications
The NPM internals appearing from left to right, GPS antenna/engine, microcontroller and electronics, Power-over-Ethernet (PoE) terminal unit, polyurethane foam thermal insulation plug, three orthogonally oriented pulse-counting magnetic sensors. The white-colored polyurethane foam plug located between the PoE unit and the magnetic sensors thermally insulates the temperature-sensitive magnetic sensors from heat emanating from the electronics and the upper portion of the enclosure pipe that is exposed above ground. The lower image shows the instrument enclosure, constructed from 100 mm (4-inch) diameter ABS pipe. A threaded lid on the top of the unit (far left) allows the instrument board to slide out.