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US 4,150,495 AGranted
LEL (lower explosive limit) control with automatic calibration capability
AssigneeBobst-Champlain, Inc.
InventorNathan Stern
Life of this patent
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AssigneeBobst-Champlain, Inc.
InventorNathan Stern
Estimating the term…
The LEL (Lower Explosive Limit) control includes a gas analyzer normally connected to receive sample gas from the evaporation enclosure of a press dryer section and which, during calibration, is sequentially connected to first analyze solvent free gas and then gas having a known solvent content. Situated with the analyzer is a detector the resistance of which changes in proportion to the temperature within the flame cell of the analyzer. The detector forms a portion of a bridge circuit, which also includes a potentiometer. The output of the bridge is amplified, compared to a selected reference voltage and a signal representing the difference therebetween is processed. The processed signal is combined with a signal representing the web speed to form a resultant signal to control a pneumatically operated damper in the enclosure exhaust conduit. Automatic calibration of the system is initiated periodically and takes place in two phases. During the first phase of calibration, the potentiometer is set in accordance with the difference between the amplifier output derived from analysis of the solvent free gas and a 0% reference voltage. During the second phase of calibration, the gain of the bridge output amplifier is set in accordance with the difference between the amplifier output derived from the analysis of the known solvent concentration gas and a full scale reference voltage. When calibration is taking place, the output of the comparison circuit is inhibited and the damper position is determined in accordance with the web speed alone. Emergency stop of the press occurs when the output of the amplifier exceeds a given level.
An LEL control for regulating the exhaust from an evaporation enclosure through which a solvent laden web passes comprising means operably connected to the enclosure for sensing the solvent concentration therein and for generating a first signal dependent thereupon, means operably associated with the web for sensing the speed thereof and for generating a second signal dependent thereupon, means for combining said first and said second signals to form a control signal, means for regulating said exhaust in accordance with said control signal, and means for calibrating said first signal generating means, said calibrating means comprising means for inhibiting the output of said first signal generating means during calibration.
Dependencies are inferred from the claim text.