Horizontal Thermobalance

Thermobalances are available in two different designs, i. e. a horizontal construction (Fig. 5-1) and vertical construction. For the vertical construction there are two different versions the top-loading balance, which has the oven above the balance (Fig. 5-2), and the thermobalance with the sample tray hanging on a thin hangdown wire into the oven below the balance (Fig. 2-4). The suppliers claim some advantages for the horizontal arrangement such as complete lack of buoyancy, the avoidance of condensation in the balance cabinet, and the reduction of sensitivity to vibration. However the last two points cannot be confirmed by the author s experience. Despite an efficacious gas flow, a diffusion of condensates was observed opposite to the flow direction of the gas. The sensitivity to vibrations seems to be comparable with the vertical design. Of the vertically constructed balances, the top loader is more convenient to manipulate. 

All thermobalances effectively utilize baffling to reduce the thermal convection currents that would otherwise disturb the measurement of mass and heat the balance compartment. Optimization of the atmospheric flow pattern and the baffling are critical to reduction of thermal noise and drift in the measurement of the mass. Many models will impose a water-cooled plate between the balance compartment and the furnace. When long-term stability is required, it is advisable to consider actually thermostatting the balance compartment. Since heat normally rises, vertical configurations are most susceptible. The horizontal arrangement leads to less interference from the flow patterns arising from control of the atmosphere. 

Figure 15.9 Arrangement of thermobalances showing the furnace (shaded), sample position and casing (a) and (c) suspended (b) top-loading (d) horizontal. The magnet position for Curie point calibration is shown in (c).

Based on this principle, different types of thermobalances are available top loading balance, bottom loading balance, horizontal balance. 

Figure 3.2 Thermobalance designs showing tbe top loading, hang down and horizontal arrangements.

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