Infrared thermometer in making stress-degree measurements for irrigation purposes

In an apparatus for measuring the temperature of an object through the use of infrared radiation from the object, said apparatus including infrared detector means responsive to relative infrared radiation levels to provide a radiation level indicating a signal which is proportional to the temperature of said object, circuit means for converting said temperature indicating signal into an output signal capable of being indicated as a numerical value and meter means for indicating the numerical value in accordance with said output signal;

• the improvement comprising:
• temperature detector means for providing a temperature indicating signal which varies in accordance with the ambient temperature adjacent to said apparatus,
• switch means connected in series with the output of said temperature detector means for enabling both said radiation level and temperature indicating signals to simultaneously reach said circuit means,
• said circuit means connected to said switch means and to said infrared detector means, and being capable of providing said output signal to said meter means so as to indicate the temperature difference between the temperature detected by said infrared detector means and the temperature detected by said temperature detector means when said switch means is closed,
• said infrared detector means comprises a thermopile means responsive to infrared radiation for providing an intermediate signal to said switch means and said infrared detector means in said circuit means, said intermediate signal corresponding to the difference between the relative infrared radiation levels of said object and said thermopile means and linearizing means for converting said intermediate signal into said radiation level indicating signal so that said radiation level indicating signal varies linearly in accordance with differences in said radiation levels, and
• second temperature detector means for providing a reference signal which varies in accordance with the ambient temperature adjacent to said thermopile means, said second ambient temperature detector means being connected to said circuit means,
• said circuit means being capable of providing an output signal to said meter means in response to said radiation level and said reference signal which indicates the temperature of said object when said switch means is open.

An apparatus for measuring the difference between the temperature of an object and the temperature of ambient air adjacent the object, the apparatus comprising:

• an infrared detector for receiving infrared radiation including infrared radiation emanating from said object, said detector generating a first electrical signal indicative of the intensity of said received radiation,
• first temperature detector means in close proximity to said infrared detector and generating an infrared reference signal indicative of all infrared radiation received by said detector and not emanating from said object,
• a sensor circuit substantially identical to said first temperature detector means to provide second temperature detector means for generating a second electrical signal indicative of the temperature of ambient air adjacent said object,
• circuit means connected to the respective outputs of said infrared detector and of said first and second temperature detector means for receiving said first and second electrical signals and said infrared reference signal and for generating an output signal indicative of said temperature difference, and
• means connected to said circuit means for displaying a numerical value indicative of said temperature difference,
• said first and second temperature detection means each comprising a thermistor network.