Ratio type infrared thermometer

• US 5,815,410 A
• Filed: 05/03/1996
• Issued: 09/29/1998
• Est. Priority Date: 05/03/1996
• Status: Expired due to Term

• Current Assignee: Raytek Subsidiary Incorporated
• Original Assignee: Raytek Subsidiary Incorporated
• Inventors: King, Steve, Carlson, Paul, Ysaguirre, Jose, Heinke, Thomas
• Primary Examiner(s): Voeltz, Emanuel Todd
• Assistant Examiner(s): COLE, TONY MITCHELL
• Application Number:
  US08/643,222
• Time in Patent Office: 879 Days
• Field of Search: 364/557, 324/115, 340/584, 340/600, 374/126, 374/128, 374/129, 374/130, 374/100, 374/133, 374/131, 374/121, 250/338.1, 250/338.3, 250/346, 250/339.01, 250/339.02, 250/339.04, 250/353, 250/340, 250/339.14, 250/341.5, 250/341.8, 250/345
• US Class Current: 702/135
• CPC Class Codes: G01J 5/22 Electrical features thereof

Abstract

An improved ratio type infrared thermometer utilizes integrating amplifiers for each waveband having the integration time automatically set so that the output voltage utilizes the full range of an analog to digital convertor. The gain and offset of the amplifiers is not ambient temperature dependent so accurate digital representations of the signal for each waveband are provided. The linearized output of each detector is optionally provided so that special or proprietary algorithms for computing the temperature of colored objects can be utilized. A special feature for downloading of updated new programs utilizes a "programming jumper" and an attenuation warning signal is provided for selected levels of attenuation.

Claims

1. A measurement circuit comprising:

an integrating amplifier, having an input coupled to receive an input current signal, an output for providing an output voltage signal, a RESET input for receiving a RESET signal, said integrating amplifier for halting the integration of said input current signal when the RESET signal is asserted and for initiating the integration of said input current signal when said RESET signal is negated and for providing an output voltage signal having a magnitude equal the product of a constant, a time of magnitude T, and the magnitude of said input current signal, where T is time of integration;

a sample and hold circuit, having an input coupled to the output of said integrating amplifier, a strobe input coupled to receive a strobe signal, and an output for providing a sampled voltage level having a magnitude equal to the magnitude of said output voltage signal when said strobe is asserted, for sampling and holding the output voltage signal when the strobe signal is asserted;

an analog to digital convertor, having an analog signal input and a digital output, and characterized by a dynamic range, for converting the magnitude of said sampled voltage level to a digital representation;

a comparator, having a first input coupled to receive said output voltage signal, a second input for receiving a reference voltage signal having a magnitude in the upper range of the dynamic range of said analog to digital converter, and output signal for providing a COMP signal, said comparator for asserting said COMP signal when the magnitude of the output voltage signal is equal to the magnitude of the reference voltage signal;

a counter, having a clock input for receiving a clock signal consisting of a series of clock pulses separated by selected constant time duration, having a count output for providing a count signal, and having a start input for receiving a START pulse, said counter for counting said clock pulses when said START pulse is negated so that the count signal has a magnitude encoding the number of pulses counted and for terminating counting when said START pulse in asserted;

a flip-flop having a clock input coupled to receive said clock signal, a data input coupled to receive said COMP signal, and an output coupled to the RESET input of said integrating amplifier, the strobe input of said sample and hold circuit, and the START input of said counter, for asserting an FF output signal as said START pulse in coincidence with a first clock pulse received after assertion of said COMP signal to stop said counter to generate measured count signal and to sample and hold the output voltage signal so that the magnitude of the measured count signal precisely indicates the magnitude of T to facilitate accurate scaling of the digital representation of said output voltage signal to generate a digital representation of the magnitude of the input current signal; and

a scaling unit for utilizing the magnitude of the count signal, the constant, and the digital representation of the magnitude of said sampled voltage level to generate a digital representation of the magnitude of said input current signal.

2. In an infrared thermometer comprising:

a detector assembly including first and second photodiodes, with the first and second photodiodes for receiving incident IR radiation in first and second different IR wavebands and for generating first and second output current signals indicating a magnitude of the intensity of radiation in the first and second IR wavebands, respectively, incident on the first and second photodiodes;

a first integrating amplifier, having an input coupled to receive the first output current signal, an output for providing a first output voltage signal, an RESET input for receiving an RESET signal, said first integrating amplifier for halting the integration of said first output current signal when the RESET signal is asserted and for initiating the integration of said first output current signal when said RESET signal is negated and for providing an output voltage signal having a magnitude equal the product of a constant, a time of magnitude T, and the magnitude of said first output current signal, where T is time of integration;

a first sample and hold circuit, having an input coupled to the output of said first integrating amplifier, a strobe input coupled to receive a strobe signal, and an output for providing a sampled voltage level having a magnitude equal to the magnitude of said first output voltage signal when said strobe is asserted, for sampling and holding the first output voltage signal as a first sampled voltage level when the strobe signal is asserted;

a first comparator, having a first input coupled to receive said first output voltage signal, a second input for receiving a reference voltage signal having a magnitude in the upper range of the dynamic range of said analog to digital converter, and an output signal for providing a first COMP signal, said comparator for asserting said first COMP signal when the magnitude of the first output voltage signal is equal to the magnitude of the output voltage signal;

a second integrating amplifier, having an input coupled to receive the second output current signal, an output for providing a second output voltage signal, an RESET input for receiving a RESET signal, said second integrating amplifier for halting the integration of said second output current signal when the RESET signal is asserted and for initiating the integration of said second output current signal when said RESET signal is negated and for providing an output voltage signal having a magnitude equal the product of a constant, a time of magnitude T, and the magnitude of said second output current signal, where T is time of integration;

a second sample and hold circuit, having an input coupled to the output of said second integrating amplifier, a strobe input coupled to receive a strobe signal, and an output for providing a sampled voltage level having a magnitude equal to the magnitude of said second output voltage signal when said strobe is asserted, for sampling and holding the second output voltage signal as a second sampled voltage level when the strobe signal is asserted;

a second comparator, having a second input coupled to receive said second output voltage signal, a second input for receiving a reference voltage signal having a magnitude in the upper range of the dynamic range of said analog to digital converter, and an output signal for providing a second COMP signal, said comparator for asserting said second COMP signal when the magnitude of the second output voltage signal is equal to the magnitude of the output voltage signal;

an analog to digital convertor, having an analog signal input and a digital output, and characterized by a dynamic range, for converting the magnitude of a provided sampled voltage level to a digital representation and for providing said digital representation as a digital ADC output signal;

a multiplexer, having first and second inputs coupled to said first and second sample and hold circuits to receive said first and second sampled voltage levels and having an output coupled to the analog signal input of said analog to digital convertor, for controllably providing either said first or second sampled voltage level as a provided voltage level to said analog to digital convertor;

a counter, having a clock input for receiving a clock signal consisting of a series of clock pulses separated by selected constant time duration, having a count output for providing a count signal, and having a start input for receiving a START pulse, said counter for counting said clock pulses when said START pulse is negated so that the count signal has a magnitude encoding the number of pulses counted and for terminating counting when said START pulse is asserted;

a flip-flop having a clock input coupled to receive said clock signal, a data input coupled to receive said first and second COMP signals, and an output coupled to the RESET input of said integrating amplifier, the strobe input of said sample and hold circuit, and the START input of said counter, for asserting an FF output signal as said START pulse in coincidence with a first clock pulse received after assertion of either said first or second COMP signal to stop said counter to generate measured count signal and to sample and hold the output voltage signal so that the magnitude of the measured count signal precisely indicates the magnitude of T to facilitate accurate scaling of the digital representation of said output voltage signal to generate a digital representation of the magnitude of the input current signal.

3. In a ratio type infrared thermometer having an imaging aperture, a method for providing a temperature output signal and for generating an attenuation warning signal comprising the steps of:

calculating a calculated temperature of a target object utilizing the ratio of first and second response signal levels generated in response to radiation emitted by said target object in first and second IR wavebands;

calculating a black body signal level that would be generated in response to radiation emitted by a black body in the first IR waveband, at the calculated temperature, that completely fills the imaging aperture;

calculating an attenuation factor being equal to the ratio of the level of the first ratio signal level and the black body signal level;

generating an attenuation warning when the attenuation factor is greater than a predetermined value; and

continuing to provide said temperature output signal after the attenuation signal is generated.

4. The method of claim 3 further comprising the steps of:

providing the magnitude of said attenuation factor as an output of the ratio type infrared thermometer.