TENNEY ENVIRONMENTAL
Tenney Junior Test Chambers: Models TJR and TUJR, W942, or WF4
Page 20
Heating of the chamber is accomplished with the use of open air low mass nichrome wire heating elements.
These elements have low thermal lag and provide rapid response to the controller's demands. The elements
are mounted in the plenum conditioning section. This isolates them from the workspace and prevents direct
radiation to the product. The heater bank is rated 500 Watts, consisting of two 250 Watt elements.
Heater Control:
The heaters are controlled by a time proportioned output from the main controller. This output triggers a triac
to conduct and provide power to the elements.
Note: The Boost Heat option may be provided to increase the rate of heating. Reference the “Boost Heat”
option section for details.
9.1 Overview
A thermal cutoff (labeled as Heat Limiter HL) is provided to protect the chamber against overtemperature
conditions. This is an axial leaded one-shot protection device, which is connected in-line with the mains
power supply Neutral Line, directly to the heater rack. The thermal cutoff will permanently open and remove
power from the heater elements when the surrounding air temperature reaches 240°C. Once the thermal
cutoff opens, it must be replaced.
Note: The thermal cutoff is not used when the Boost Heat option is employed. This option uses a Watlow
147 Limit Controller for overtemperature protection. Reference the “Boost Heat” option section for details.
8.0 HEATING DESCRIPTION
Heater Element Rack
Thermal Cutoff is installed
in the Neutral Line, and is
wrapped in glass cloth
electrical tape.
9.0 CHAMBER OVERTEMPERATURE PROTECTION
Thermal Cutoff
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