A tristimulus colorimeter employs a multiplexed dual slope integrator digital voltmeter wherein unknown and reference light beams are compared by sequentially applying unknown and reference electrical signals representative of the two respective light beams to the non-inverting and inverting inputs, respectively, of the integrator amplifier. Moreover, a compensating circuit provides for compensation of the colorimeter output signals with respect to reflectance error encountered in the optics portion of the colorimeter.

BACKGROUND OF THE INVENTION 
The present invention relates generally to a tristimulus colorimeter and, 
more particularly, to such a colorimeter that is adapted for measuring the 
color of teeth. Moreover, the invention relates to improvements in such a 
colorimeter with these improvements also being useful in other types of 
systems, such as, for example, those having optical or non-optical 
transducers for detecting particular phenomena and measuring circuitry 
that measures the electrical output of the transducer to provide a visual 
display and/or a control function. 
Although the invention will be described with reference particularly to a 
reflection type tristimulus colorimeter that produces a digital display 
indicative of the red, green and blue color components of a tooth, it will 
be appreciated that the various features of the invention may be employed 
with other types of color or non-color reflection or transmission types of 
optical measuring systems, non-optical transducer input measuring systems, 
and the like. 
Related U.S. patent applications which include subject matter pertinent to 
the invention of this application and are commonly assigned are as 
follows: Ser. No. 499,479, filed Aug. 22, 1974, now U.S. Pat. No. 
3,986,777; Ser. No. 696,787, filed June 16, 1976, now U.S. Pat. No. 
4,055,813; Ser. No. 698,143, filed June 21, 1976, now U.S. Pat. No. 
4,080,074; and Ser. No. 721,107 filed concurrently herewith for 
"Comparison Type Colorimeter." 
In the first application a colorimeter is disclosed employing a multiplexed 
dual slope integrator type of digital voltmeter to provide a digital 
display of red, green and blue components of light reflected from an 
object. In the dual slope integrator a first electrical signal derived 
from a photosensor is compared with a reference electrical signal from an 
electric energy source, and the visual display of digital color values is 
related to the results of that comparison. A color filter wheel cyclically 
sequentially interposes red, green and blue filters in the unknown light 
beam reflected by the object to the photosensor, and the multiplexing 
circuitry is synchronized to the wheel and is reset on each complete 
cycle. The synchronized multiplexing circuit then automatically controls 
operation of the dual slope integrator to place respective calibrating 
circuits therein and to deliver electrical output signals therefrom to 
respective red, blue and green visual displays. 
In the second and third applications there are respectively disclosed a 
"Single Adjustment Multiple Function Calibration Circuit" to facilitate 
compensation for drift in a multiplexed amplifier having plural feedback 
channels selectively coupled thereto and an "Automatic Zeroing Circuit To 
Compensate For Dark Currents or the Like" to eliminate inaccuracies in 
measurements due to commonly experienced dark current or other leakage 
current in the transducer. 
In the last application an arrangement of the optical elements, including 
light pipes and color filters for illuminating an object and for 
sequentially directing unknown beams of colored light reflected from the 
object and reference beams of corresponding colors to a common 
photosensor, is disclosed. This as well as other optical measuring and 
testing devices may experience optical error, whereby a known portion of 
incident, reflected or other light passing through one or more optical 
elements of the system is diverted, for example, by reflection from one to 
another of plural light paths or is simply attenuated by the optical 
elements. Since such optical error is usually due to internal reflection, 
for example, within a bifurcated light pipe or other optical elements 
through which two or more light beams simultaneously pass, such optical 
error will be referred to hereinafter as reflectance error; however, it 
will be understood that reflectance error also means other types of 
optical error as well. 
SUMMARY OF THE INVENTION 
In the present invention an improved tristimulus colorimeter employs a dual 
slope integrator type digital voltmeter that compares unknown and 
reference light beams and produces a digital output indicative of such 
comparison. In one embodiment a single light source, which includes an 
enclosure about a lamp to shield the same from dust and, thus, to enhance 
the stabilization of the light output therefrom, directs light via 
respective light pipes to illuminate an object to be optically measured or 
examined and to provide a reference light beam. Light from the object in 
an unknown light beam and the reference light beam are intermittently or 
sequentially directed onto a photosensor. Further, color filters of the 
colorimeter are mounted in a movable support, such as a color filter 
wheel, that sequentially and cyclically moves one color filter in the path 
of the unknown light beam and subsequently moves the same color filter to 
position in the light path of the reference light beam, thereby to assure 
that the color filtering effected of each light beam is the same. 
Measurement of each color of the unknown light beam relative to each 
corresponding color of the reference light beam is then effected by a 
measuring circuit, whereby in a preferred embodiment the color values 
ultimately evolved and preferably displayed represent respective ratios of 
each color component of the unknown light beam to each corresponding color 
component of the reference light beam. Therefore, importantly, the 
colorimeter is substantially independent of the absolute intensity of the 
light source, which with aging may produce a light output of reduced 
absolute intensity but of substantially constant color temperature or 
spectral distribution. Similarly, the color and/or transmission 
characteristics of the several color filters may change with aging of the 
filters; however, the invention preferably assures that the unknown and 
reference light beams both pass through each color filter so that the 
mentioned ratios will remain substantially constant. 
An unknown electrical signal produced by one color component of an unknown 
light beam impinging on a photosensor is normalized by calibration 
circuitry or the like and then is integrated for a predetermined duration. 
Subsequently, a reference electrical signal produced by the photosensor 
when the same color component of a reference light beam impinges thereon 
is integrated in the relatively opposite polarity direction, and at some 
time during the latter integration the electrical output of the integrator 
passes a predetermined signal level detected by a comparator that triggers 
the displaying of a digital value indicative of the elapsed time of the 
latter integration. The displayed value is representative of the intensity 
of that color component of the unknown light beam, and similar 
measurements are made to obtain displays of other color components. 
In one form of the invention a common circuit is employed in the measuring 
circuitry whereby the unknown electrical signal is directed to a 
non-inverting input of the integrator and the reference electrical signal 
is directed to an inverting input by such common circuit which eliminates 
the need for additional inverting or like circuitry. Therefore, except for 
switching those unknown and reference electrical signals to the respective 
inputs, those signals are substantially developed in common channels; 
accordingly offset drift and similar discrepancies between the inverted 
and non-inverted circuit channels of prior art devices are appreciably 
reduced and/or eliminated. 
Moreover, a compensating circuit arrangement is provided for cancelling the 
effect of reflectance error or the like which ordinarily is a relatively 
fixed percentage of the light input to the optical portion of the 
colorimeter and thus of the reference light beam substantially directly 
from the light source. The reflectance cancellation circuit stores a 
compensating electrical signal as a percentage of the reference electrical 
signal for each color and under control of a multiplexing circuit delivers 
respective compensating electrical signals for simultaneous, relatively 
opposite polarity direction integration with the unknown electrical 
signal. 
The multiplexing circuit is synchronized with a color filter wheel, which 
cyclically sequentially filters the respective color components of the 
unknown and reference light beams, initially at the start of the first 
complete cycle thereof and subsequently at the commencement of measurement 
of each respective color light of the unknown light beam. The multiplexing 
circuit also includes an internal synchronizing mechanism associated 
directly with a clock oscillator and output counter, which delivers the 
digital output signals to the display, both to control the respective 
operations of the dual slope integrator and to assure that all amplifier 
circuits in the colorimeter are always maintained under controlled gain 
conditions. This feature prevents the connection of an amplifier in an 
infinite gain condition, for example, which may cause saturation and 
subsequent slow recovery of the amplifier and/or related circuitry and 
thereby maintains the circuitry of the colorimeter in condition for prompt 
operation as each color light is measured. 
With the foregoing in mind, a principal object of the invention is to 
provide a tristimulus colorimeter that is improved in the noted respects. 
Another object is to improve the accuracy of measurements made in optical 
measuring systems, such as tristimulus colorimeters, and non-optical 
measuring systems. 
An additional object is to improve the accuracy of comparisons made in a 
dual slope integrator. 
A further object is to compensate for reflectance and/or other optical 
error in an optical measuring system and, moreover, to provide similar 
compensation for relatively fixed percentage errors in other types of 
detecting and measuring systems. 
Still another object is to assure that in a multiplexed circuit system 
controlled gains are provided respective amplifiers and the like therein. 
Still a further object is to facilitate correction of drift and similar 
calibration of multiplexed circuit systems. 
Even another object of the invention is to facilitate the measuring of 
color of an object, such as a tooth or the like, and conveniently to 
present the measured color values. 
Even an additional object is to maintain the accuracy of measurements made 
by a colorimeter although the light source thereof may age and reduce its 
light intensity output. 
These and other objects and advantages of the present invention will become 
more apparent as the following description proceeds. 
To the accomplishment of the foregoing and related ends, the invention, 
then, comprises the features hereinafter fully described in the 
specification and particularly pointed out in the claims, the following 
description and the annexed drawings setting forth in detail a certain 
illustrative embodiment of the invention, this being indicative, however, 
of but one of the various ways in which the principles of the invention 
may be employed.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now more particularly to the drawings, wherein like reference 
numerals designate like parts in the several figures, and initially to 
FIG. 1, a comparison type of tristimulus colorimeter in accordance with 
the invention is generally indicated at 1. The colorimeter 1 includes an 
optics portion 2 that directs unknown and reference light beams, which are 
cyclically sequentially filtered to their red, green and blue color 
components, to a photosensitive transducer or sensor 3, which produces 
unknown and reference electrical signals, respectively, indicative of the 
intensity of the light of each color light impinging thereon. These 
electrical signals are measured in a measuring circuit 4, which produces 
electrical output signals for display as respective red, green and blue 
color values in digital form at an output display 5. 
The measuring circuit 4 is multiplexed to obtain efficient use of numerous 
portions thereof and for accuracy whereby electrical signals developed as 
the red, green and blue components of the unknown and reference lights are 
measured pass along substantially the same circuit channels. Moreover, the 
multiplexed measuring circuit includes a modified dual slope integrator 
type of digital voltmeter that compares the unknown electrical signal for 
each color with the corresponding reference electrical signal for each 
color and produces respective electrical output signals indicative of 
those comparisons and, therefore, of the intensities of the color 
components of the unknown light beam relative to the color components of 
the reference light beam. The electrical output signals produced by the 
dual slope integrator digital voltmeter preferably are displayed in the 
output display 5, as mentioned, or may be alternatively directed to other 
circuits to provide process control functions or the like related to the 
measured colors. 
In the measuring circuit 4 an automatic zeroing circuit 6, which is 
described in greater detail in the copending U.S. patent application Ser. 
No. 698,143, zeroes the electrical output from the sensor 3 to eliminate 
the effect of dark currents and the like therein and then provides the 
respective unknown and reference electrical signals through to an 
amplifier 7. A calibration circuit portion 8 and a single adjustment 
calibration circuit 9, which is disclosed in more detail in copending U.S. 
patent application Ser. No. 696,787, are associated with the amplifier 7 
to vary the gain thereof, and, therefore, to normalize the respective 
unknown and reference electrical signals with respect to those produced 
when an object of known color characteristics is examined by the 
colorimeter 1. Below the reference to calibrated signals also implies such 
normalized signals. A divider switch 10 directs the unknown electrical 
signal after calibration to a non-inverting input of an integrator 11 for 
integration in one polarity direction and subsequently directs the 
reference electrical signal after calibration to an inverting input of the 
integrator for integration in a relatively opposite polarity direction. 
The integrator 11 accordingly integrates the unknown electrical signal for 
a predetermined duration and at the conclusion of that duration the 
electrical output of the integrator achieves a given signal level; the 
subsequent integration of the reference electrical signal from that given 
signal level causes the integrator electrical output ultimately to return 
to a predetermined signal level. The attaining of the latter level is 
detected by a comparator 12, which then produces a brief trigger or 
control signal for the following purposes. 
During integration of the reference electrical signal electrical pulses 
produced by a clock oscillator 13 are counted by a conventional decade 
counter 14. The trigger signal produced by the comparator 12 causes a 
decoder output logic portion 15 briefly to open one of the three red, 
green or blue latch circuits 16r, 16g, 16b in the output display 5, 
depending on the particular color component then being detected by the 
sensor 3, to receive and to store the instantaneous count then on the 
decade counter 14. The opened latch circuit is then promptly closed and 
the count input thereto is stored and is delivered to one of the 
respective red, green or blue visual displays 17r, 17g, 17b in the output 
display 5. A more detailed description of this display mechanism is 
provided in copending U.S. patent application Ser. No. 499,479. 
A reflectance cancellation circuits portion 18 stores compensating signals 
and delivers one to the inverting input of the integrator 11 when the 
latter is integrating the unknown electrical signal of a respective color 
light detected by the sensor 3. The integrated reflectance cancellation 
compensating signal is algebraically combined with the integrated unknown 
electrical signal for compensation of the latter with respect to 
reflectance error in the optics 2. Each of the stored reflectance 
cancellation compensating signals, one for each of the colors measured by 
the sensor 3, is derived as a percentage of the reference electrical 
signal produced during detection of the reference light beam for that 
color. 
Primary control of the multiplexed circuits 20 is provided by a counter 
controller 21, which is reset by a new color reset synchronizing portion 
22 at the start of detection of a new color light by the sensor 3. The 
counter controller 21 directly controls both the integrator 11 for 
integrating, holding and discharging operations and the clock oscillator 
13 for turning the same on and off. Moreover, a decoder logic circuit 
portion 23 responds to the control signals from the counter controller 21 
to effect timed multiplexed and functional control and operation of the 
automatic zeroing circuit 6, the calibration circuits portion 8, the 
divider switch 10, and the reflectance cancellation circuits portion 18. A 
color control counter 24 also provides to the decoder logic circuit 
portion 23 and to the decoder output logic portion 15 color control 
signals indicative of the particular color of light then being detected by 
the sensor 3. When the colorimeter 1 is initially energized for use, a 
color sequence synchronizing portion 25 detects the start of a cycle of 
sequential filtering of the unknown and reference light beams in the 
optics portion 2 to their red, green and blue components and provides to 
the color control counter 24 a synchronizing input which sets the latter 
such that the color control signals are properly indicative of the color 
light beam detected by the sensor 3 at any given time. After this initial 
synchronization of the color control counter 24, continued synchronization 
is maintained by the counter controller 21, which is automatically 
controlled by the decade counter 14 as well as by the color reset 
synchronizing portion 22. 
Turning now to FIG. 2, the elements of the optics portion 2 of the 
colorimeter 1 are illustrated. These elements and their operation are 
described in detail in the concurrently filed U.S. patent application Ser. 
No. 721,107 for "Comparison Type Colorimeter." A light source 30, which 
includes a conventional light producing lamp 31 mounted in a housing 
enclosure 32, provides light to unknown and reference light pipes 33, 34. 
The light pipes preferably are flexible and may be, for example, of either 
the solid or fiber type. Moreover, the unknown light pipe 33 preferably is 
of the bifurcated type including an incident portion 33I which directs 
incident light onto an object 35, such as a tooth, to illuminate the same, 
and a reflected light portion 33R, which receives light reflected by the 
object and directs that reflected light as the unknown light beam into a 
color detector housing 36. 
A color filter wheel 37 in the housing 36 has red, green and blue color 
filters 38r, 38g, 38b at angularly spaced locations thereon and is rotated 
by a motor, not shown, in order cyclically sequentially to position each 
of the color filters first to filter the unknown light beam 39 from the 
light pipe 33R and then to filter the reference light beam schematically 
shown at 40 from the light pipe 34. The color filter wheel 37 otherwise 
blocks the unknown and reference light beams. As illustrated, the color 
component of the unknown light passed by the red color filter 38r, for 
example, is collimated by a first lens 41, and the collimated light is 
then concentrated by a second lens 42 onto the sensor 3, which may be, for 
example, a conventional photosensitive transistor. The sensor 3 then 
produces its unknown electrical signal indicative of the intensity of the 
light impinging thereon. At this time the reference light beam 40 is 
blocked by the color filter wheel 37. Subsequently, after the color filter 
wheel 37 has rotated in a clockwise direction, for example, relative to 
the illustration of FIG. 2, the color filter wheel will block the unknown 
light beam 39 and the red color filter 38r will pass the red color 
component of the reference light beam 40 to an aperture plate 43. The 
portion of the reference light beam passing the aperture plate is directed 
by a prism 44 to the second lens 42 which concentrates the reference light 
beam onto the sensor 3 causing the latter to produce its reference 
electrical signal indicative of the intensity of the red color component 
of the reference light beam impinging thereon. The color filter wheel 37 
operates similarly to pass the green and blue color components of the 
unknown and reference light beams. An infrared filter 45 is positioned in 
the housing 36 to filter infrared light or radiation, which may be 
transmitted by the respective color filters 38r, 38g, 38b, from both the 
reference and unknown light beams. 
A quantity of light from the light source 30 also is received by a pair of 
synchronizing light pipes 46, 47 which direct the received light to the 
color detector housing 36. More specifically, the light pipe 46 directs a 
color sequence synchronizing light beam 25L toward the color filter wheel 
37, and when an opening 48 therein aligns with the light pipe 46 just 
prior to the aligning of the red color filter 38r in position to filter 
the unknown light beam 39, which constitutes the start of a rotational and 
filtering cycle of the color filter wheel, the light beam 25L is passed to 
a photosensor 49. The photosensor 49, which is coupled to the color 
sequence synchronizing portion 25 of the measuring circuit 4 shown in 
FIGS. 1 and 3, then poduces an electrical signal to set the color control 
counter 24 in readiness to control the measuring circuit 4 for measuring 
red light. 
Moreover, three additional openings 50r, 50g, 50b are angularly located in 
the color filter wheel 37 to pass a new color reset synchronizing light 
beam 22L from the second synchronizing light pipe 47 to an additional 
photosensor 51 whenever a respective color filter, such as the color 
filter 38r, is aligned in the unknown light beam, as illustrated. The 
additional photosensor 51 is coupled to the new color reset synchronizing 
portion 22 of the measuring circuit 4 and upon receiving a light input 
produces an electrical signal output to the new color reset synchronizing 
portion which then indicates to the counter controller 21 that measurement 
of the unknown electrical signal from the sensor 3 should commence and, 
accordingly, resets the counter controller. Since the color control 
counter already had been set initially by the color sequence synchronizing 
light beam 25L, as described, the measuring circuit 4 now is ready to 
measure red light, i.e. to make a comparison of the red color component of 
the unknown light beam 39 with that of the reference light beam 40, and 
the following description is directed to making such measurement. The 
measuring circuit 4 would also operate similarly to measure green and blue 
light, as will be outlined briefly below. 
In the measuring circuit 4, the various multiplexed circuits 20 are 
employed both to obtain effecient use of several circuit elements and to 
assure the accuracy of the measurements made by the measuring circuit. In 
particular, a single sensor 3 is used to detect both the unknown and the 
reference light beams, thus eliminating possible variations between plural 
sensors. Moreover, the unknown and reference electrical signals travel 
through exactly the same circuits to the integrator whereat their 
comparison is effected, thus eliminating differential drifting and the 
like between circuit elements of separate unknown and reference circuits 
previously used. Both the unknown and reference electrical signals pass 
through the same circuits of the automatic zeroing circuit 6 and are 
amplified in the same manner by the amplifier 7, albeit the amplifier 7 is 
selectively set up to have different respective gains by the multiplexed 
calibration circuits portion 8; and the unknown and reference electrical 
signals after calibration are delivered by the divider switch 10 directly 
to the respective non-inverting and inverting inputs of the integrator 11. 
By thus maintaining the unknown and reference electrical signals 
accurately indicative of the unknown and reference light beams of each 
color that sequentially impinge on the sensor 3, the digital values 
usually displayed in the display 17 will accurately represent the 
intensities of the color components of the unknown light beam. 
In the following description elements designated by reference numerals 
having a suffix of r, g or b, which refer to red, green and blue, 
respectively, are repeated in the measuring circuit 4, once for each color 
ordinarily measured, and the operation of the elements of each such 
grouping is the same. Moreover, the expressions red unknown electrical 
signal and red reference electrical signal implies those electrical 
signals which are produced by the sensor and are subsequently calibrated 
or amplified when the red color component of the unknown and reference 
light beams impinge thereon; similar meanings are attached to the green 
and blue unknown and reference electrical signals, respectively. 
Referring now to FIG. 3 wherein the schematic diagram of the measuring 
circuit 4 is shown in detail, the several positive terminals 60 indicate a 
power input of, for example, 12 volts DC from a conventional supply, not 
shown; the several internal circuit ground terminals 61 indicate a 
connection to the same source at a ground potential relative to the 
terminals 60; and the chassis ground terminals 62 are connected to the 
chassis and external ground of the colorimeter instrument. Ordinarily the 
relative potential of the internal circuit ground terminals 61 would be 
maintained slightly higher than that of the chassis ground terminals to 
assure suitable potential differences across respective circuit elements 
for proper operation thereof. However, if desired, the circuit operating 
parameters may be designed such that the terminals 61 and 62 are coupled 
together and maintained at a common ground potential. 
When the color sequence synchronizing light beam 25L passes through the 
color filter wheel 37 of FIG. 2 and impinges on the photosensor 49, the 
latter causes the amplifier 63 in the color sequence synchronizing portion 
25 to produce a brief positive signal on its output line 64. The signal is 
directed to the reset inputs of a JK flip-flop 65 of the color control 
counter 24 to provide the initial synchronization setting of the latter. 
The JK flip-flop 65 has two stages with the four illustrated outputs 
designated Q.sub.1, Q.sub.1, Q.sub.2 and Q.sub.2. Both stages of the 
flip-flop 65 are coupled by the line 66 to receive a clocking control 
signal periodically from the counter controller 21, such signal causing a 
sequential counting operation by the flip-flop 65 after the latter has 
initially been set by the color sequence synchronizing portion 25. 
The two stages of the flip-flop 65 are interconnected, as illustrated, to 
provide first, second and third count conditions in each of which the four 
respective Q.sub.1, Q.sub.1, Q.sub.2, Q.sub.2 outputs specifically assume 
relatively high or logic 1 signals, say at about 12 volts DC, or 
relatively low or logic 0 signals, say zero volts. Chart I below shows the 
logic signals at the four flip-flop outputs for the three count conditions 
thereof. 
CHART I 
______________________________________ 
OUTPUT Q.sub.1 --Q.sub.1 
Q.sub.2 
--Q.sub.2 
______________________________________ 
First count 0 1 0 1 
Second count 1 0 0 1 
Third count 1 0 1 0 
______________________________________ 
When the flip-flop 65 is initially set by the color sequence synchronizing 
portion 25, it assumes the first count condition, which indicates in the 
preferred embodiment that red light is the next color to be detected by 
the sensor 3 and to be measured by the measuring circuit 4. The next 
clocking control signal from the counter controller 21 causes the 
flip-flop 65 to assume a second count condition, which indicates that 
green light is the next to be detected and measured, and the still next 
clocking control signal causes assumption of the third count condition 
similarly indicative of blue light. The following clocking control signal, 
which normally would occur before the color sequence synchronizing portion 
25 produces a pulse on line 64, causes the flip-flop 65 to assume the 
first count condition again; therefore, after its initial set by the color 
sequence synchronizing portion, the color control counter automatically 
remains synchronized with the color wheel via the clocking control signals 
from the counter controller. 
Upon being initially set to its first count condition, the flip-flop 65 in 
the color control counter 24 produces on logic lines 67, 68, 69, 70 logic 
0, 1, 0, 1 signals respectively. Shortly afterwards the color filter wheel 
37 rotates the opening 48 out of the path of the color sequence 
synchronizing light beam 25L and the opening 50r into alignment with the 
new color reset synchronizing light beam 22L, which passes to the 
additional photosensor 51 that causes an amplifier 71 in the new color 
reset synchronizing portion 22 briefly to produce a reset pulse on the 
line 72 to reset the counter controller 21. This resetting preferably 
occurs when the red color component filtered by the color filter 38r from 
the unknown light beam 39 is impinging on the sensor 3. 
The counter controller 21 may be a conventional decade counter type circuit 
that is reset to a zero count condition by the reset pulse applied to the 
reset terminal 21R thereof. The counter controller has five outputs 
coupled, respectively, to apply to control lines 73 through 77 logic 0 and 
logic 1 signals depending on the count condition of the counter 
controller. In its zeroth count condition the counter controller 21 
applies a logic 1 signal to the control line 73 and logic 0 signals to the 
other control lines and in second, third, fourth and fifth count 
conditions the counter controller applies logic 1 signals to the control 
lines 74 through 77, respectively, and logic zero signals to the remaining 
control lines. The counter controller 21 has a first count condition 
during which all control lines 73 through 77 receive logic 0 signals. 
Upon being reset, as described, the counter controller 21 produces a logic 
1 signal on the control line 73. This signal is inverted by an inverting 
amplifier 78 in the decoder logic circuit portion 23 such that a logic 0 
signal is directed to the electronic switch 79, which, as the other 
electronic switches described herein, may be a conventional transistorized 
bilateral gate switch or the like, to open the same. The logic 1 signal on 
the control line 73 also is directed to the several triple input AND gates 
80r, 80g, 80b in the decoder logic circuit portion 23, for example, to 
reverse bias the diode 81r. Moreover, since the flip-flop 65 in the color 
control counter 24 is in its first count condition, logic 1 signals on the 
logic lines 68 and 70 also reverse bias by the diodes 82r, 83r. Therefore, 
a relatively high or logic 1 signal is provided on the control input 84r 
of the electronic switch 85r closing the same to place the red calibrating 
circuit channel 86r in feedback connection to the amplifier 7. 
The unknown electrical signal produced by the sensor 3 in response to the 
red component of the unknown light beam impinging thereon is delivered to 
the non-inverting input 87 of a pre-amplifier 88, which has a rough 
calibration or trimming potentiometer 89 coupled in feedback relation 
thereto for controlling the gain thereof to maintain the various elements 
of the measuring circuit 4 operating in their normal ranges and to obtain 
an optimum signal-to-noise ratio. At this time the logic 0 signal on the 
control line 76 maintains the electronic switch 90 in the automatic 
zeroing circuit 6 opened so that the pre-amplified unknown electrical 
signal is coupled by a capacitor 91 in the automatic zeroing circuit to 
the non-inverting input 92 of the amplifier 7 for further amplification 
thereby. Both the preamplifier 88 and the main amplifier 7 preferably are 
high input impedance operational amplifiers to obtain optimum signal 
isolation and gain control capabilities. 
The red calibrating circuit channel 86r, which is now coupled to the 
amplifier 7 by the counter controller 21 and color control counter 24 
operating through the decoder logic circuit portion 23 to close the 
electronic switch 85r, includes a voltage divider impedance network 93r, 
which is adjustable to establish a basic gain of the amplifier 7 when 
connected thereto, and a potentiometer 94r, which is adjustable to 
establish a range of permissible change of that basic gain. The electronic 
switch 85r couples the red calibrating circuit channel 86r between the 
output and the inverting input 95 of the amplifier 7. 
Moreover, the single adjustment calibrating circuit 9 includes a series 
connected potentiometer 96 and resistor 97, which have a combined 
impedance that is much greater than that of the voltage divider 93r, also 
connected to the inverting input 95. That combined impedance also is 
greater than that of each of the voltage dividers 93g, 93b in the green 
and blue calibrating circuit channels 86g, 86b. Therefore, as is described 
in more detail in copending application Ser. No. 696,787, adjustment of 
the potentiometer 96 will determine the percentage of the ranges of 
permissible change of the basic gains for each calibrating circuit channel 
that the basic gains are actually changed. The electrical signals produced 
by the sensor may drift different respective amounts, for example, due to 
aging, temperature variations, or the like, for each color detected 
thereby. It is the principal purpose of the single adjustment calibration 
circuit to compensate the gain of the amplifier 7 simultaneously for such 
drifting as is described in the mentioned application. 
The basic gain of the amplifier when the red calibration circuit 86r is 
coupled thereto ordinarily would be determined experimentally by optically 
examining and measuring a reference object 35 of known red color 
characteristics and adjusting the voltage divider 93r until appropriate 
red color values would be displayed by the red display 17r while the range 
adjusting and single adjustment potentiometers 94r, 96 are turned to 
present minimum and maximum impedances, respectively. The green and blue 
calibration circuits 86g, 86b would be similarly adjusted. Later, after 
the measuring circuit 4 had substantially fully aged or fatigued, the 
single adjustment potentiometer would be turned to present minimum 
impedance and the respective range adjusting potentiometers would be 
adjusted, while the reference object is still examined, to bring the 
respective displayed color values back to their original values. 
Thereafter, when subsequently using the colorimeter 1, as drifting occurs, 
only the single adjustment potentiometer 96 usually would require 
adjustment to correct the amplifier simultaneously for different amounts 
of drifting with respect to each color measured. 
Thus, the unknown electrical signal is amplified by the amplifier 7, as set 
up to have a gain determined by the impedance of the red calibrating 
circuit channel 86r and the single adjustment calibration circuit 9, to 
provide such signal on the line 98. 
The logic 1 signal presently on the control line 73 also is simultaneously 
delivered to the divider switch 10 to close the electronic switch 100U, 
which coupled the unknown electrical signal, after calibration, on the 
line 98 to the non-inverting input 101 of the amplifier 102 of the 
integrator 11, which additionally includes an integrating capacitor 103 
connected between the amplifier output 104 and the inverting input 105. 
The amplifier 102 also has an offset circuit for adjustment in 
conventional manner. The electronic switch 106, which couples the side of 
the integrating resistor 107 remote from the inverting input 105 to the 
internal ground terminal 61, and the electronic switch 108 in the 
reflectance cancellation circuits portion 18 also receive the logic 1 
signal on the control line 73 and, therefore, close. 
Since the logic lines 68 and 70 are at logic 1 signal levels at this time, 
the diodes 109r, 110r of a double input AND gate 111r in the decoder 
output logic portion 15 are reverse biased so that the positive signal at 
the terminal 60 produces a logic 1 signal on the line 112r to close an 
electronic switch 113r in the reflectance cancellation circuits portion 
18. Also, since the electronic switch 108 is closed, a red compensating 
signal stored in the storage capacitor 114r in the reflectance 
cancellation circuits portion 18 is delivered to the inverting input 105 
of the integrator 11 for integration simultaneously with the red unknown 
electrical signal. The red compensating signal ordinarily would be placed 
for storage in the capacitor 114r during part of the previous cycle in 
which red light were measured, as will be described further below. The 
stored red compensating signal is a percentage of the red reference 
electrical signal on the line 98, after calibration, and the adjustable 
voltage divider 115r determines that percentage. A high impedance 
amplifier 116, which is connected with a unity gain feedback loop 117, 
provides signal isolation to avoid draining the storage capacitor 114r and 
delivers the red compensating signal via the closed electronic switch 108 
and a resistor 118 to the inverting input 105 of the integrator 11. 
Thus, simultaneous integration of the red unknown electrical signal on the 
line 98, after calibration, and of the red compensating signal is 
commenced and proceeds for a predetermined duration, which is established 
as follows. The logic zero signal appearing on the control line 77 from 
the counter controller 21 is inverted by an inverting amplifier 119 and 
provided at a control input 120 of the clock oscillator 13, which turns on 
and produces electrical pulses on the clock output line 121 to start the 
predetermined duration. The electrical pulses on the line 121 are 
delivered via a transistor output 122 to the input of the decade counter 
14, which counts the number of electrical pulses received. In the 
preferred embodiment the decade counter 14 actually counts up to a 
predetermined maximum count of 400 and then automatically resets itself 
back to zero to commence counting the next 400 pulses, for example, in 
conventional manner. Moreover, upon reaching the predetermined count of, 
for example, 400, or other predetermined count level, if desired, a brief 
signal indicative of the achieving of such predetermined count and the 
resetting of the decade counter is produced by the latter in conventional 
manner on the line 123 for delivery via a resistor 124, diode 125 and 
inverting transistor 126 as a clock signal on the line 127 to the clock 
input 21C of the counter controller 21, which would cause the latter to 
switch to its next count condition. Upon switching from its zeroth to its 
first count condition, the counter controller terminates the mentioned 
predetermined duration. 
The above described operation is summarized in part in the Chart of FIG. 4 
commencing at time t.sub.0. Accordingly, at time t.sub.0 the leading edge 
128 of a reset color pulse 129, which appears at line 72 between the new 
color reset synchronizing portion 22 and the reset input 21R of the 
counter controller 21 resets the latter; the counter controller is, 
therefore, placed in its zeroth count condition, as indicated in block 
130; the clock oscillator 13 and decade counter 14 are running, as 
indicated by block 131; the electronic switch 90 is open so that the 
automatic zeriong circuit 6 is disabled, as indicated by the line 132; the 
unknown light beam signal 39 of FIG. 2 is impinging on the sensor 3, as 
indicated by the block 133; and the integrator 11 is integrating the 
unknown electrical signal, after calibration, and simultaneously the 
compensating signal from the reflectance cancellation circuits portion 18, 
as indicated by the block 134. 
In the graph of FIG. 5 the electrical output, as an integrated voltage 
leverl V.sub.0, of the integrator 11 during operation thereof is shown. 
The times t.sub.0, t.sub.1, t.sub.2 and t.sub.3 indicate durations or 
times corresponding to those indicated on the Chart of FIG. 4. 
In the graph of FIG. 5, the solid line 135 illustrated represents the value 
of the electrical output voltage level V.sub.0 of the integrator 11 
without considering the effect of the integration of the compensating 
signal 136, which is shown in phantom; and the dashed line 137 illustrates 
the value of the electrical output voltage level V.sub.0 with such 
compensating signal considered and, accordingly, algebraically combined 
with the unknown electrical signal during integration. 
At the time t.sub.0 on the graph of FIG. 5 the red unknown electrical 
signal is delivered by the electronic switch 100U in the divider switch 10 
to the non-inverting input 101 of the integrator amplifier 102 immediately 
causing the electrical output of the integrator as well as the lefthand 
side of the integrating capacitor 103 instantly to jump to a value 
V.sub.u, the instantaneous voltage of the red unknown electrical signal. 
This is shown by the solid line 135 in FIG. 5. Between time t.sub.0 and 
t.sub.1, the red unknown electrical signal is integrated in usual manner 
and would cause the electrical output to follow the solid line 135 of the 
graph of FIG. 5 over that predetermined duration. Due to the instant jump 
of the output voltage level V.sub.0 at time t.sub.0 the mentioned 
integration will proceed according to the formula 
##EQU1## 
wherein R is the resistance of the resistor 107, C is the capacitance of 
the capacitor 103 and the time constant RC is much larger than the 
predetermined duration between times t.sub.0 and t.sub.1. Without 
considering the effect of the compensating signal, at time t.sub.1, as 
will be described further below, the switch 100U will be opened and the 
red unknown electrical signal V.sub.u will be removed from the 
non-inverting input 101 to stop the integration thereof, and, therefore, 
the output voltage level V.sub.0 will drop by an amount V.sub.u so that 
the resulting value of the output voltage level V.sub.0 after the 
integration of the unknown electrical signal V.sub.u would truly be 
representative of the time integral of the latter over the predetermined 
duration. 
However, during integration of the red unknown electrical signal the red 
compensating signal also is integrated. Without considering the 
simultaneous integration of the unknown electrical signal, the integration 
of the compensating signal would cause the electrical output of the 
integrator 11 to follow the phantom line portion 136 of the graph of FIG. 
5 until a reflectance cancellation voltage V.sub.RX would be achieved at 
time t.sub.1, the end of the predetermined duration. 
The unknown electrical signal and the compensating signal are algebraically 
combined during the integration thereof and, accordingly, the voltage 
level output V.sub.0 of the integrator 11 actually will follow the dashed 
line portion 137 of the graph of FIG. 5. 
At time t.sub.1 ending the predetermined duration for the integration of 
the unknown electrical signal a pulse from the decade counter 14 causes 
the transistor 126 briefly to bring the line 127 to relative ground 
potential, as indicated at the leading edge 138 of the electrical signal 
illustrated in the Chart of FIG. 4. The positive-going trailing edge 139 
of that electrical signal, which is exaggerated in width for clarity in 
the drawing, appears at the clock input 21C as a clock signal to the 
counter controller 21 to switch the latter to its next count condition, in 
this case to its first count condition indicated at the block 140 of the 
Chart. 
This first count condition of the counter controller 21 provides a hold 
time interval between times t.sub.1 and t.sub.2 during which the red color 
filter 38r is rotated out of alignment with the unknown light beam 39 and 
into alignment with the reference light beam 40 so that the light signal 
impinging on the sensor 3 generally follows the lines 141, 142 in the 
Chart. 
Moreover, during the hold time interval all of the control lines 73 through 
77 of the counter controller 21 receive logic zero signals. Therefore, the 
inverting amplifier 78 provides a logic 1 signal to the electronic switch 
79 turning the same on to provide an assured unity gain feedback loop for 
the amplifier 7. Also, the diode 81r in the triple input AND gate 80r is 
no longer reversed biased and, therefore, the electronic switch 85r is 
turned off to uncouple the red calibrating circuit channel 86r from the 
amplifier 7. The electronic switches 100U, 106 and 108 are all opened so 
that the voltage lever V.sub.0 of the electrical output of the integrator 
11 is held constant at its achieved integrated level indicated V.sub.H at 
dashed line portion 143 on the graph of FIG. 5. The hold condition of the 
integrator is indicated in block 144 on the Chart of FIG. 4. The logic 
zero signal on the control line 77 is inverted by the inverting amplifier 
119 to assure that the clock oscillator 13 continues to produce electrical 
pulses on the clock output line 121, and, therefore, the decade counter 14 
will continue counting those pulses. 
When the color filter wheel 37 has properly aligned the red color filter 
38r to pass the red color component of the reference light beam 40 to the 
sensor 3, while the unknown light beam 39 is now blocked by the wheel, the 
decade counter 14 for the second time reaches a count of 400. As described 
above, the decade counter again resets itself and at the same time 
produces a clock signal to switch the counter controller 21 to its second 
count condition, whereby a logic 1 signal is produced on the control line 
74 at time t.sub.2 while the other control lines remain at logic 0. 
During the second count condition of the counter controller 21, as 
indicated in block 145 of the Chart, the logic 1 signal on the control 
line 74 and the logic 1 color control signals on the logic lines 68 and 70 
from the flip-flop 65 of the color control counter 24 cause all three of 
the diodes 150r, 151r, and 152r of a triple input AND gate 153r of the 
decoder logic circuit portion 23 to be reversed biased, whereby the logic 
1 signal on the control line 74 operates through the resistor 154r to turn 
on the electronic switch 155r. The red reference electrical signal 
produced by the sensor 3 is pre-amplified by the pre-amplifier 88, is 
passed by the capacitor 91 since the electronic switch 90 is off, is 
further amplified with unity gain by the amplifier 7 since the electronic 
switch 79 is on and is applied to the line 98. The closed electronic 
switch 155r allows the storage capacitor 114r to be recharged to a voltage 
level that is a percentage determined by the voltage divider 115r of the 
reference electrical signal, after calibration by unity gain amplification 
of the amplifier 7 in this case, on the line 98. That percentage would be 
determined experimentally, for example, by determining the percentage of 
red incident light applied by the light source 30 to the incident portion 
33I of the light pipe 33 that is internally reflected into the reflectance 
portion 33R without actually impinging on the object 35. The same 
experimental compensating type procedure would be followed to determined 
similar green and blue compensating signals for storage in capacitors 114g 
and 114b by adjustments of the voltage dividers 115g, 115b. 
The logic 1 signal on the control line 74 also turns on the electronic 
switch 100R in the divider switch 10 to deliver the reference electrical 
signal, after calibration, on the line 98 to the inverting input 105 of 
the amplifier 102 of the integrator 11. Therefore, the integrator 11 will 
integrate the reference electrical signal in the opposite polarity 
direction relative to that of the earlier integration of the unknown 
electrical signal, as indicated by block 156 in the Chart. The electrical 
output voltage level V.sub.0 of the integrator then will be reduced 
according to the dashed line portion 157 of the graph of FIG. 5. At time 
t.sub.2 ' the electrical output voltage level V.sub.0 reaches a zero 
voltage level, and the zero crossing comparator 12 detects the same and 
produces a trigger signal on the line 158. If desired, the zero crossing 
comparator 12, which is a conventional comparator device such as that 
disclosed in the copending application Ser. No. 499,479, may be adjusted 
to produce the indicated trigger signal when the electrical output voltage 
level V.sub.0 achieves during integration of the reference electrical 
signal a predetermined level other than a zero voltage level. 
The time t.sub.2 " on the graph of FIG. 5 indicates the time, relatively 
later than time t.sub.2 ', at which the integrator output voltage level 
V.sub.0 would reach zero voltage if the unknown electrical signal were not 
compensated for reflectance error. Therefore, without such compensation 
the also realtively later produced trigger signal would cause the latches 
16 to receive and to store incorrect electrical output signals from the 
decade counter 14, as will be described further below. 
The trigger signal from the zero crossing comparator 12 is synchronized 
with the electrical pulses from the clock oscillator 13 in a NAND gate 150 
so that when both a trigger signal and an electrical pulse are provided 
thereto a logic zero signal is produced thereby. The inverting amplifier 
160 then produces a logic 1 signal on the line 161 as an input to each of 
the three triple input NAND gates 162r, 162g, 162b in the decoder output 
logic portion 15. 
As was mentioned above, both diodes 109r, 110r in the AND gate 111r are 
reverse biased by logic 1 signals on the logic lines 68 and 70 from the 
color control counter 24 and, therefore, that AND gate causes a logic 1 
signal to be delivered to a second one of the inputs to the NAND gate 
162r. Moreover, closure of an update control switch 163, which may be a 
finger switch, a foot switch or the like manually operated by the dentist 
or technician who is using a colorimeter 1, will cause the inverting 
amplifier 164 to produce a logic 1 signal on the line 165 as the third 
logic 1 signal input to the NAND gate 162r. Therefore, the NAND gate 162r 
produces a logic 0 output signal to turn off conduction in the transistor 
166r, which permits a logic 1 signal to be provided at the terminal 167r 
coupled to the latch circuit 16r in the latch mechanism 16 briefly to open 
that latch to receive the count then on the decade counter 14 as an update 
of the magnitude of the intensity of the red color component of the 
unknown light beam. As soon as the electrical pulse from the clock 
oscillator 13 on the line 121 is terminated, the NAND gate 159, inverting 
amplifier 160, NAND gate 162r, and transistor 166r remove the logic 1 
signal from the terminal 167r immediately to close the latch 16r, which 
then maintains the updated count stored therein and provides the same to 
the visual display 17r in the display portion 17. By the time the next 
electrical pulse is produced by the clock oscillator, the trigger signal 
from the zero crossing comparator 12 normally will have been removed from 
the line 158 and, therefore, the latch circuit 16r is maintained closed 
until the colorimeter in the next full cycle of the color filter wheel 37 
and measuring circuit 4 measures the red color component of the unknown 
light beam. 
Thus, it will be clear that the magnitude of the count signal applied to 
and stored in the latch circuit 16r is directly proportional to the 
duration of time required for integration of the reference electrical 
signal by the integrator 11 to bring the electrical output voltage level 
V.sub.0 thereof from its achieved integrated level, in this case V.sub.H, 
back to a predetermined level, in this case zero volts, which duration is 
indicated on the graph of FIG. 5 between the times t.sub.2 and t.sub.2 '. 
Although the latch circuit 16r had been opened, updated, and closed again, 
as described, the decade counter 14 continues to count the electrical 
pulses produced by the clock oscillator 13 and when the 400 count is 
attained again at time t.sub.3 the decade counter resets itself and 
simultaneously causes production of a clock signal to switch the counter 
controller 21 to its third count condition, as indicated in block 168 in 
the Chart of FIG. 4. 
When the counter controller is in its third count condition, the control 
line 74 receives a logic 0 signal that turns off the AND gate 153r, which 
turns off the electronic switch 155r so that the red compensating signal 
remains stored in the capacitor 114r, and that logic 0 signal also turns 
off the electronic switch 100R to remove the red reference electrical 
signal from the inverting input 105 of the integrator. Also a logic 1 is 
now provided on the control line 75 to reset the integrator 11 by closing 
the electronic switch 169, which then turns on and discharges the 
integrating capacitor 103. Moreover, the arrangement of diodes 170, 171, 
172, assures that such discharging resetting operation, as indicated at 
the elongated block 173 in the Chart of FIG. 4, will continue during the 
third, fourth and fifth count conditions of the counter controller 21 over 
the time period between the times t.sub.3 and t.sub.6. 
While the counter controller 21 is in its third count condition, the clock 
oscillator 13 continues to produce electrical pulses and the decade 
counter 14 continues to count the same. Moreover, at same time during the 
third count condition the red color filter 38r will be rotated by the 
color filter wheel 37 out of alignment with the reference light beam 40 so 
that substantially zero light will impinge on the sensor 3, as is 
indicated by the light intensity signal representation line portion 174 in 
the Chart of FIG. 4. When the decade counter reaches its 400 count again, 
it resets itself simultaneously and causes a clock signal to switch the 
counter controller 21 to its fourth count condition, as indicated in block 
175 of the Chart. 
When the counter controller 21 is in its fourth count condition, a logic 1 
signal on the control line 76, in addition to maintaining the electronic 
switch 169 turned on, provides a clocking control signal on the line 66 to 
both stages of the flip-flop 65 in the color control counter 24 causing 
the flip-flop to change to its second count condition, whereby, as 
indicated in Chart I above, logic 1 signals are placed on logic lines 67 
and 70 and logic 0 signals are placed on logic lines 68 and 69. Therefore, 
the AND gate 111r in the decoder output logic portion 15 is turned off, 
i.e. causes a logic 0 to be applied to an input of the NAND gate 162r, and 
the AND gate 111g turns on to provide a logic 1 to an input of the green 
NAND gate 162g to enable the latter to turn off the transistor 166g when 
the next "green" trigger signal is received from the zero crossing 
comparator 12 and the update switch 163 is closed, thereby to update the 
green storage latch 16g and green display 17g in the same manner described 
above. 
Additionally, the logic 1 signal on the control line 76 turns on the 
electronic switch 90 in the automatic zeroing circuit 6 to discharge the 
capacitor 91 through the resistor 176. Therefore, the righthand side of 
the capacitor 91 coupled to the non-inverting input 92 of the amplifier 7 
will be brought to the internal ground potential of the terminal 61 and 
the left side of the capacitor 91 will assume a voltage that is 
representative of the dark current or leakage current through the sensor 3 
since no light is then impinging on the sensor. This operation of the 
automatic zeroing circuit 6 to discharge the capacitor 91 is indicated by 
block 177 in the Chart of FIG. 4. 
The fifth count condition of the counter controller 21, as indicated at 
block 178 in the Chart of FIG. 4, occurs when the decade counter 14 again 
reaches a count of 400 and resets itself as described above. The control 
line 77 then receives a logic 1 signal, which is directed through the 
diode 69 to maintain the electronic switch 169 turned on to continue 
discharging the capacitor 103 to reset the integrator 11. Moreover, the 
logic 1 signal on the control line 77 is inverted by the inverting 
amplifier 119, which provides a logic 0 signal on the control input 120 of 
the clock oscillator 13 to turn the clock oscillator off, thus stopping 
any electrical pulses from being produced on the clock output line 121. As 
is shown by the line portion 179 on the Chart, sometime during the period 
of the fifth count condition between times t.sub.5 and t.sub.0 again the 
green color filter 38g will have been rotated by the color filter wheel 37 
to pass the green color component of the unknown light beam 39 from the 
light pipe 33R to the sensor 3, whereby the latter receives the green 
unknown light beam signal. 
Moreover, at the time t.sub.5 the previous logic 1 signal is removed from 
the control line 76 and is replaced by a logic 0 signal which turns off 
the electronic switch 90 in the automatic zeroing circuit 6 to stop 
discharging the capacitor 91. Therfore, when the unknown light beam again 
impinges on the sensor 3, which will occur relatively promptly after the 
electronic switch 90 has been turned off, the green unknown electrical 
signal will promptly be pre-amplified by the pre-amplifier 88, will pass 
the capacitor 91 and will be provided to the noninverting input 92 of the 
amplifier 7 for amplification thereby. 
The complete operation of the measuring circuit 4 through one complete 
controlled counting cycle of the counter controller 21 from its zeroth 
count condition to its fifth count condition has now been described for 
measurement, for example, of the red color component of the unknown light 
beam with resepct to the red color component of the reference light beam 
to develop a digital output signal indicative of the ratio of the red 
components of those light beams. Similar operation of the measuring 
circuit 4 will subsequently sequentially occur to obtain measurements of 
the green and blue color components of the unknown light beam, 
respectively, thus completing one complete cycle of the colorimeter. This 
cyclical operation ordinarily may be continued, as desired; and as long as 
any change in the intensity of the light source 30, for example, due to 
aging is relatively slow or insignificant as compared to the speed with 
which each complete cycle of the color filter wheel 37 and measuring 
circuit 4 occurs, the output signals will accurately represent the color 
of the object 35 without regard to the absolute intensity of the light 
source. 
Continuing in the cycle to measure the next color, a new color reset 
synchronizing light beam 22L will impinge on the additional photosensor 51 
via the additional opening 50g in the color filter wheel 57 when the green 
color filter 38g is fully aligned to pass the green color component of the 
unknown light beam 39 to the sensor 3. The reset pulse produced then by 
the new color reset synchronized portion 22 resets the counter controller 
21, to its zeroth count condition placing a logic 1 signal on the control 
line 73. The triple input AND gate 80g, which already has been enabled by 
the logic 1 signals provided by the color control counter 24, turns on the 
electronic switch 85g, which couples the green calibration circuit channel 
86g to the amplifier 7. Therefore, the unknown electrical signal is 
approriately calibrated for properly representing the intensity of the 
green color component of the unknown light beam, and that calibrated 
signal is integrated by the integrator 11 which at the same time 
integrates the green compensating signal that had been stored earlier in 
the storage capacitor 114g and is now passed by the electronic switch 112g 
that is enabled by the AND gate 111g. 
After the several above-described operations occur in the measuring circuit 
4 under control of the counter controller 21, as described above, to 
obtain a display of updated green color values, the blue color component 
of the unknown light beam will be measured and displayed in similar 
manner. 
At the conclusion of the measurement of the blue color component the 
production of the fourth count condition by the counter controller 21 to 
place a logic signal on the control line 76 causes the flip-flop 65 in the 
color control counter 24 to revert to its first count condition. This 
first count condition of the color control counter is then maintained even 
though a subsequent signal is delivered by the color sequence 
synchronizing portion 25 when the color filter wheel 37 is about to begin 
its cycle and the opening 48 has passed the color sequence synchronizing 
light beam 25L to the photosensor 49. 
The above-described operation will continue to occur in the cyclical 
manner, whereby the red, green and blue color components of the unknown 
light beam will continuously be measured with respect to the corresponding 
color components of the reference light beam and the values stored in the 
respective latches 16 and displayed in the respective displays 17 will 
continuously be updated. Of course, whenever the update switch 163 is 
opened, the decoder output logic portion 15 is prevented from opening 
respective latches and updating them. Therefore, the dentist may place the 
light pipe 33 to engagement with a portion of a tooth and close the switch 
163 to provide for a displaying of the color components of the tooth at 
the particular area examined. Before the light probe is removed from that 
area, the update switch 163 would be opened so that the measured and 
displayed color values will be retained in the latches and the displayed 
values may be written down. 
It will now be clear that the colorimeter 1 provides for the measurement of 
plural colors of an object and the production of electrical output signals 
that preferably are displayed in digital form as color values indicative 
of the color of such object.