The Oven
The sample may be hung vertically in the oven, but baffles may need to be employed to eliminate convection currents affecting the sample pan and producing mass-signal ‘noise’. The condensation of any volatile substances that are evolved from the sample must also be studiously avoided by careful oven design. Another oven arrangement would be the horizontal form, where the balance-arm projects into the furnace and the crucible is attached to an extended portion of the arm. This design reduces condensation problems but care must be taken to avoid the beam becoming heated resulting in beam expansion, which would result in false mass data.
The furnace is electrically heated and, due to the balance control being magnetic, the windings on the furnace heater must be non-inductively wound. The volume round the crucible must be uniformly heated and have a uniform temperature environment. The heat capacity of the oven system must be kept as small as possible so that the oven temperature will accurately follow the temperature program as determined by the computer even when the program is relatively rapid. The heater material must be carefully chosen to provide the desired temperature range of the instrument (a maximum normal operating temperature of 2800oC, an extreme condition, would require the use of a tungsten heater).