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New product focus: Ultra View Temperature (& Humidity) Chamber
2-2 Anti-fogging viewing window panes
Environmental test chamber not only requires interior lighting and the effective visibility
noted on the previous page, the chamber must also prevent the glass panes from fogging
up due to the temperature and humidity conditions inside the chamber. Fogging occurs
when the moisture in the air condenses on the surface of the glass. The conventional
method of preventing fogging was to install a heater to warm the surface of the glass, but
this approach required maintaining the glass surface temperature above the dew-point
temperature, which was not economical. Also, during tests using such conditions as high
temperature and low humidity, a heater is not required to maintain the glass surface
temperature above the dew-point temperature. These new chambers prevent fogging on
the glass surface using a heater control inside the glass, so instead of merely applying
constant heat to the glass, only the minimum amount of heat required is used, thus
conserving energy. (Patent pending)
Glass using conventional heat-reflecting film or incorporating heating wires required the
chamber design to incorporate upper and lower heat limits that were suited to the
thermal limits of the glass panes. When reach-in ports were added to provide a means of
operating the specimens, the glass surface in the vicinity of the reach-in ports tended to
fog up, and localized hot spots occurred. This fogging was caused by not being able to
place heaters near the reach-in ports (due to the processing on the glass for the ports) so
that the heater current did not flow near the reach-in ports, resulting in a difference in
current density in the vicinity of the reach-in ports. These new chambers are designed so
that the current density is the same in all areas of the glass, including the areas around
the reach-in ports, with no unevenness in current. Even when reach-in ports must be
provided, there is no fogging on the surface of the glass, and the specimens can be clearly
observed and operated. (Fig.1) (Patent pending)
Fig.1 Current flow with viewing window reach-in ports in glass doors
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Espec Technology Report No20