APPARATUS FOR MEASURING THE AMOUNT OF A SUBSTANCE THAT IS ASSOCIATED WITH A BASE MATERIAL

• US 3,614,450 A
• Filed: 02/17/1969
• Issued: 10/19/1971
• Est. Priority Date: 02/17/1969
• Status: Expired due to Term

• Current Assignee: John M. French, Richard E. Toepfer, Robert Curtis Hill
• Original Assignee: John M. French, Richard E. Toepfer, Robert Curtis Hill
• Inventors: Hill, Robert Curtis, French, John M., Toepfer, Richard E.
• Primary Examiner(s): Lawrence, James W.
• Assistant Examiner(s): Leedom, C. M.
• Application Number:
  US04/799,784
• Time in Patent Office: 974 Days
• Field of Search: 250/83.3IR,204,205,210,43.5 162/263 356/199 350/311
• US Class Current: 250/205
• CPC Class Codes: G01N 21/314 with comparison of measurements at specific and non-specific wavelengths dual wavelength spectrometry G01J3/427
• CPC Class Codes: G01N 21/3554 for determining moisture content
• CPC Class Codes: G01N 21/3559 in sheets, e.g. in paper
• CPC Class Codes: G01N 33/346 paper sheets
• CPC Class Codes: Y10S 162/06 Moisture and basic weight
• CPC Class Codes: Y10S 162/11 Wet end paper making variables

Abstract

A moisture gauge for paper material includes an infrared source and two detectors one of which is responsive to a wavelength of 1.94 microns which is sensitive to moisture in the paper; the other detector is responsive to 1.8 microns which is not affected by moisture. The operating point of the detector not sensitive to moisture is maintained constant by a feedback system. AT the same time an impedance ratio of the two detectors provides information as to absolute moisture content. Automatic standardization of the system is also provided.

Claims

1. In apparatus for measuring the amount of substance that is associated with a base material said apparatus including a radiation source that emits a first spectral band of radiation that impinges on the material but lies outside of an absorption band of the substance and that emits a second spectral band that lies within a resonant absorption band of the substances, detector means responsive to the intensities of said spectral bands which are reflected from or transmitted through said material to produce an electric signal proportional to the amount of the substance which is present, and control means for maintaining constant the received intensities of said first spectral band by controlling the intensity of said radiation source said control means including electrical bridge means having four legs, one of said legs including at least a portion of said detector means and the other three legs including identical reference means and also including two operational amplifiers each having a pair of inputs coupled across said detector means and an adjacent reference means respectively, the other two legs of said bridge having one end coUpled respectively to an input of said amplifiers and the other ends to subtracting amplifier means, said operational amplifiers having respective outputs coupled to said other ends of said legs.

2. Apparatus as in claim 1 in which said detector means portion is a first detector responsive to said first spectral band.

3. Apparatus as in claim 2 in which said reference means are three resistors of identical value.

4. Apparatus as in claim 2 together with amplifier means coupled to said first detector to provide a virtual ground.

5. Apparatus as in claim 1 in which said detector means includes a first detector responsive to said first spectral band and a second detector responsive to said second spectral band said detectors having similar response characteristics and together with beam splitting means for directing radiation from said radiation source to said first and second detectors and including automatic standardization means comprising means juxtaposed between said radiation source and said beam splitting means for simulating said material in a condition having substantially none of or a known amount of said substance, means for juxtaposing between said second detector and said beam splitting means attenuation means simulating substantially at least one known amount of said substance to be measured, means for normalizing to a standard value said electrical output signal caused by said known amount of substance.