Experiences in designing a low-cost temperature controlled variometer enclosure

Magnetic observatories have traditionally used small buildings or huts to provide a stable, protected and temperature controlled environment to accommodate the sensitive magnetic instruments. As instruments have evolved they have reduced in size and become less reliant on absolute mechanical stability but still require good temperature stability. Maintaining a stable temperature in large older buildings can be difficult and expensive due to their volume, the substantial thermal losses and undefined thermal properties of the construction materials. This report describes a modern instrument housing comprising a small-scale enclosure and low-power, non-magnetic heating elements controlled by a proportional–integral–derivative (PID) temperature controller. Operating magnetometers in a compact environment with other equipment requires careful selection of heating elements and minimising any sources of local interference. The specifications and calculations for the enclosure design, materials and temperature control system are presented with results of long term temperature stability performance in comparison with traditional observatory housings. The disadvantages and benefits of operating instruments in small enclosures are also discussed.