Experiences in designing a low-cost temperature controlled variometer enclosure

Magnetic observatories have traditionally used small buildings or huts to provide stable and temperature controlled environments for housing sensitive magnetometer instruments. As magnetometer technology has developed, instruments have reduced in size and become less reliant on mechanical pier stability, whilst still relying on adequate temperature control. Temperature control in large, older, buildings can be challenging and expensive due to their volume, thermal losses and undefined thermal properties of construction materials. This report describes a modern instrument housing comprising a small-scale enclosure and low-power, non-magnetic heating element controlled by a proportional–integral–derivative (PID) temperature controller. Operating magnetometers in a compact environment requires careful selection of heating elements and minimising any sources of local interference. The specifications, thermal calculations, materials and temperature control system for the enclosure are presented with results of long term temperature stability and overall performance in comparison with traditional observatory housings. The disadvantages and benefits of operating instruments in small enclosures are also discussed.