Thermal measuring and testing – Temperature measurement – In spaced noncontact relationship to specimen
Patent
1981-10-26
1984-06-26
Yasich, Daniel M.
Thermal measuring and testing
Temperature measurement
In spaced noncontact relationship to specimen
136225, 330 9, 374124, 374129, 374165, 374178, G01J 516, G01J 526
Patent
active
044563906
ABSTRACT:
A portable, battery operated noncontact temperature measuring device including a lens for collecting infrared radiation and a thermopile for producing a signal indicative of the intensity thereof. The thermopile signal is amplified, linearized and summed with an ambient temperature signal derived from a temperature responsive element, e.g. a diode chip mounted immediately adjacent a cold junction of the thermopile. The resulting composite temperature signal is then processed and displayed. The ambient temperature signal is also utilized to control the impedance of a dual field effect transistor, which in turn controls the gain of the amplifier. Thus, temperature induced variations in the responsivity of the thermopile are compensated by corresponding changes in the gain of the amplifier. An adjustable high impedance bias circuit provides bias current to the input of the amplifier, insuring that the signal at the output of the amplifier will not be affected by temperature induced changes in the internal resistance of the thermopile. A switching circuit alternately connects the output of the thermopile and a resistor having a resistance approximately equal to the internal resistance of the thermopile to the input of the amplifier. When the resistor is so connected, an automatic zeroing circuit reduces the amplifier output to approximately zero, thereby essentially eliminating amplifier drift.
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"Digital and Analog Circuits and Systems," by Jacob Millman, Microelectronics .COPYRGT.1979, pp. 404-406.
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Junkert Kenneth G.
Voznick Henry P.
Wahl Instruments, Inc.
Yasich Daniel M.
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