SPECTROPHOTOMETER FOR MEASURING THICKNESS OR WEIGHT OF WATER-CONTAINING COATINGS

• US 3,661,462 A
• Filed: 04/23/1970
• Issued: 05/09/1972
• Est. Priority Date: 04/23/1969
• Status: Expired due to Term

• Current Assignee: Luc Yves Natens
• Original Assignee: Luc Yves Natens
• Inventors: Natens, Luc Yves
• Primary Examiner(s): Wibert, Ronald L.
• Assistant Examiner(s): McGraw, V. P.
• Application Number:
  US05/031,189
• Time in Patent Office: 747 Days
• Field of Search: 356/51,96-98,204,205,188 250/43.5R,226
• US Class Current: 356/51
• CPC Class Codes: G01N 21/314 with comparison of measurements at specific and non-specific wavelengths dual wavelength spectrometry G01J3/427

Abstract

The thickness and/or weight of a water-containing composition is measured by an infrared spectrophotometer wherein the attenuation of radient energy at a measuring wavelength which is substantially absorbed by the coating composition is compared with the attenuation of radient energy at a second reference wavelength not substantially absorbed by the coating composition.

Claims

1. A spectrophotometer wherein the measurement of the spectral absorption of a medium occurs by comparison of the attenuation of radiant energy at a first wavelength which is subject to substantial absorption by the medium with the attenuation of radiant energy at a second wavelength which is substantially not subject to absorption thereby, comprising a. a radiant energy detector, b. a radiant energy source for directing radiant energy in at least the mentioned first and second wavelengths towards said medium so that said energy after impingement thereon is received on said detector, c. filter means disposed in the radiation path between the source and the detector and arranged to alternatively transmit radiation at said first wavelength and radiation at least at said second wavelength, d. a measuring wedge mounted for movement across the radiation beam while the radiation in one of said wavelengths is transmitted to the detector for progressively altering the amount of transmitted radiant energy as it moves through the radiation beam, e. means for producing a first electric signal of a magnitude proportional to the radiant energy received on the detector at the wavelength which is not attenuated by said measuring wedge and means for stoRing said signal, f. means for producing a second electric signal of a magnitude proportional to the radiant energy received on the detector at the wavelength which is progressively altered by the said measuring wedge, g. means for comparing said second electric signal with said first one and for detecting when the two electric signals reach equal magnitude, and h. means effective when said equality is detected for producing an indication of the position of the measuring wedge at said moment.

2. A spectrophotometer according to claim 1, wherein said filter means comprises a filter holder which is mounted for continuous rotation through the radiation beam and including a first filter transmitting radiation at said second wavelength which remains in the radiation beam for a small angular displacement of the filter holder and a second filter transmitting radiation at said first wavelength which remains in the radiation beam for a substantial angular displacement of the filter holder.

3. A spectrophotometer according to claim 1, wherein said filter means comprises a. a filter holder mounted for continuous rotation through the radiation beam, said holder carrying a first filter transmitting radiation at said first wavelength which remains in the radiation beam only for a minor angular displacement of the filter holder, said filter holder transmitting for the remaining major part of its angular displacement all of the radiant energy of the source, and b. a second filter fixed in the radiation beam which transmits radiation at said second and said first wavelength.

4. A spectrophotometer according to claim 3, wherein the limits of said second wavelength extend almost symmetrically with said first wavelength.

5. A spectrophotometer according to claim 2 wherein said measuring wedge is mounted for introduction into the radiation beam while the first filter, which remains in the radiation beam over only a small angular displacement of the filter holder, is outside of the radiation beam.

6. A spectrophotometer according to claim 2, wherein said measuring wedge is mounted on said filter holder.

7. A spectrophotometer according to claim 1 wherein said means for producing an indication of the position of the measuring wedge at the moment of equality of said two electric signals comprises:

a. a pulse generator, b. a pulse counter, and c. control means controlling said pulse counter to begin counting pulses from said pulse generator at the moment the measuring wedge enters into the radiation beam, to end said counting at the moment of equality of the electric signals and indicate the number of pulses counted as an indication of the wedge position, and to reset the counter to zero prior to reconnection to the pulse generator.

8. An infrared waterband meter for measuring the thickness of a water-containing coating applied to a substrate comprising a. a source for directing radiant energy at a measuring wavelength of 1.96 Mu m and at a different reference wavelength which is substantially not absorbed by the coating composition, b. a detector for receiving the energy transmitted or reflected by the coating after partial absorption thereby, c. a circular filter holder carrying over a substantial angular part a filter transmitting only the 1.96 Mu m wavelength radiation and over a small angular part a filter transmitting only the reference waveband radiation, the filter transmitting the 1.96 Mu m wavelength radiation including a measuring wedge, and the filter holder being mounted for rotation to successively pass said filters through the radiation path, d. means for producing a first electric output signal proportional to the amount of radiant energy impinged at 1.96 Mu m measuring wavelength on the detector, and means for storing said signal, e. means for producing a second electric output signal proportion to the amount of radiant energy impinged at said reference wavelength on the detector, f. means for comparing said two output signals and for triggering a voltage comparator at the moment said output signals are equal, g. a pulse generator, h. a pulse counter, i. and means for connecting said pulse counter to said pulse generator at the moment the measuring wedge enters into the radiation beam, said counter being preset just prior to its connection in the circuit, disconnecting the counter from the pulse generator in response to the triggering of said voltage comparator, and for re-setting said counter prior to reconnection to the pulse generator.

9. An infrared waterband meter for measuring the thickness of a water-containing coating applied to a substrate, comprising a. a radiation source for directing radiant energy at a measuring wavelength of 1.96 Mu m and at a reference waveband from 1.79 to 2.17 Mu m to the coating, b. a detector for receiving the energy which is transmitted or reflected by the coating after partial absorption thereby, c. a circular filter holder carrying over a small angular section a filter transmitting the 1.96 Mu m wavelength, the remaining angular part of the filter holder showing no particular spectral absorption and a measuring wedge of neutral density, said filter holder being mounted for rotation to successively pass said 1.96 Mu m filter and said measuring wedge through the radiation path, d. a stationary filter in the radiation path which transmits radiation from 1.79 to 2.17 Mu m, e. means for producing a first electric signal proportional to the amount of radiant energy impinged at said measuring wavelength on the detector, and means for storing said signal, f. means for producing a second electric signal proportional to the amount of radiant energy impinged at said reference wavelength on the detector, g. means for comparing the magnitude of said two signals and for triggering a voltage comparator at the moment they reach equality, h. a pulse generator, i. a pulse counter, j. and means for connecting said pulse counter to said pulse generator at the moment the measuring wedge enters into the radiation beams, said counter being preset just prior to its connection in the circuit, disconnecting the counter from the pulse generator in response to the triggering of said voltage comparator, and for re-setting said counter prior to reconnection to the pulse generator.