The Medium Temperature Furnace is of a three-zone design. In addition to the main temperature controlled-zone, there are guard heaters at the top and bottom of the block. These zones are controlled by differential temperature sensors, which enable the furnace to operate with only small temperature differences along the whole length of the heated metal block. This is important when freezing cells, since the assumption made is that cells freeze in concentric shells. This is true only if there is a small temperature gradient along the furnace.
The substantial furnace core is machined from aluminum bronze.
The recommended procedure for establishing a freeze plateau requires operator attention until the plateau is realized. Following that, the 3-zone furnace will maintain the plateau essentially automatically for a period of 10 to 20 hours (longer if the heat flux from the cell minimized).