REFLECTANCE METER

• US 3,604,815 A
• Filed: 04/22/1968
• Issued: 09/14/1971
• Est. Priority Date: 04/22/1968
• Status: Expired due to Term

• Current Assignee: Anton Hubert Clemens
• Original Assignee: Anton Hubert Clemens
• Inventors: Clemens, Anton Hubert
• Primary Examiner(s): Wibert, Ronald L.
• Assistant Examiner(s): Sklar, Warren A.
• Application Number:
  US04/723,102
• Time in Patent Office: 1,240 Days
• Field of Search: 356/22,212,226,177,176,179,186,195 250/210
• US Class Current: 356/421
• CPC Class Codes: G01N 21/4738 Diffuse reflection precedence is given to G01N21/55 - G01N21/57 if specular component is taken into consideration, e.g. also for testing fluids, fibrous materials
• CPC Class Codes: G01N 21/474 Details of optical heads therefor, e.g. using optical fibres
• CPC Class Codes: G01N 21/55 Specular reflectivity
• CPC Class Codes: G01N 21/86 Investigating moving sheets G01N21/89 takes precedence

Abstract

A small, portable photoelectric cell-type reflectance meter is described for use in measuring color reflectance values of analytical test devices. Since these analytical test devices have predetermined ranges of color reflectance values, the reflectance meter is preset to read color values within these ranges. The meter has a constant light output circuit, a regulated power supply based on battery power and a battery power check circuit.

Claims

1. An instrument for measuring light reflected from a colored surface having a predetermined range of color reflectance values, said instrument comprising a light source, means for supporting a member having a colored surface the reflectance of which is to be measured in a predetermined position wherein said surface is exposed to light emitted from said source, a measuring circuit in the form of a Wheatstone bridge having four arms and an indicating meter portion, said bridge having variable resistances in three arms and a measuring photoelectric cell only in the fourth arm, said measuring photoelectric cell being exposed to the light reflected from said surface, a reference reflectance surface also exposed to light emitted from said source, a reference circuit including a reference photoelectric cell exposed to light reflected from said reference surface connected to adjustably control the current flow to and thereby the light emitted from said light source in a manner to maintain the intensity of light emission at a substantially constant value, said reference cell being electrically separate from said measuring circuit, and a power source to provide electrical power for said light source and said reference and measuring circuits, said power source also providing a regulated voltage to said measuring circuit.

2. An instrument according to claim 1 employing a battery as a power source and having means for indicating a weak battery.

3. An instrument according to claim 1 wherein the physical relationship between the light source, the color surface whose reflectance is to be measured, the measuring photoelectric cell, the reference photoelectric cell, and the reference reflectance surface being such that the paths of light emitted from said source form an isosceles right triangle, the light source being located at the intersection of the legs of said triangle, the color surface to be measured being located at the intersection of one leg and the hypotenuse of said triangle, the reference reflectance surface being located at the intersection of the other leg and the hypotenuse, and the measuring photoelectric cell and the reference photoelectric cell being mounted back-to-back and being located midway along the hypotenuse with the measuring cell facing the color surface to be measured and the reference cell facing the reference surface, said instrument also having shielding surfaces to prevent light from the light source from shining directly on the measuring cell and the reference cell.

4. An instrument according to claim 1 wherein the indicating meter has a rotary indicating needle movement and a linear indicating scale, the axis of rotary movement of said indicating needle being located offcenter with respect to the linear indicating scale.