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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the measurement of the depth of
a recess or pocket and more particularly it relates to a probe instrument
used to measure the depth of the gingival sulcus and periodontal pockets.
2. Description of the Prior Art
Chronic periodontal disease is an inflammatory disease typically induced by
plaque formation. A consequence of the disease is progressive bone loss
around the teeth. The resulting increase in sulcus depths in the gums
creates periodontal pockets, which are indicative of the progression of
the disease. To diagnose and treat periodontal disease adequately, the
depths of the gingival sulcus and any periodontal pockets that exist must
be determined accurately.
Pocket depths have been commonly measured by a periodontal probe that has a
thin metal tip that is scored with calibration marks. The probe is
inserted into the sulcus between a tooth and the gingiva and advanced
until resistance is felt, which indicates that the bottom of the pocket
has been reached. A depth reading is then obtained by observing visually
the calibration mark that is closest to the top of the gingival margin.
Six depth readings are taken around each tooth at prescribed locations, as
standard practice. Each of the six readings is recorded. Frequently this
recording is done by verbal reporting of the depth to an assistant, who
writes it by hand on a dental chart.
Clearly, the use of such a conventional periodontal probe is a
time-consuming and hence expensive procedure. Moreover, the depths of the
periodontal pockets recorded during such a procedure are not always very
accurate. Human error results from the need to interpolate between the
calibration marks on the probe, as well as from variations in the pressure
of the probe against the bottom of the periodontal pocket at the instant
that the depth reading is taken. Additional error sometimes arises from
the verbal communication of the measured values and the manual writing of
those values on the record.
A more recently developed technique is to use a periodontal probe that
contains a thin probe of circular cross-section that can be pushed out of
a handle and into a sulcus by the operator of the probe. The handle is
designed to provide a constant frictional force on the probe, to prevent
injury to the gingival tissue.
Another recently developed periodontal probe instrument, invented by Murphy
et al, contains a displacement-sensing probe element and a parallel
force-sensing probe element in a common handle, together with circuitry
for generating electrical signals indicative of the force and the
displacement. This invention of a probe instrument is an improvement of
that periodontal probe instrument.
The following patents contain descriptions of periodontal probes with a
depth measurement structure:
______________________________________
U.S. Pat. No.
Dated Patentee
______________________________________
3,058,225 Oct. 16, 1962
Ward
3,943,914 Mar. 16, 1976
Grenfell et al.
4,203,223 May 20, 1980
Lautenschlager et al.
4,250,895 Feb. 17, 1981
Lees
4,340,069 Jul. 20, 1982
Yeaple
4,665,621 May 19, 1987
Ackerman et al.
4,677,756 Jul. 7, 1987
Simon et al.
4,708,647 Nov. 24, 1987
Pippin et al.
4,791,940 Dec., 1988 Hirschfeld et al.
4,904,184 Feb. 27, 1990
Murphy et al.
______________________________________
In addition, there is a description of a periodontal probe in a paper
entitled "Computerized Periodontal Probe with Adjustable Pressure",
written by E. Sild et al., which was published on pp. 53-62 of The
International Journal of Periodontics and Restorative Dentistry for April,
1987.
SUMMARY OF THE INVENTION
This invention is related to the invention disclosed in U.S. Pat. No.
4,904,184 listed above but is mechanically simpler and hence less costly
to manufacture and more reliable in use. Moreover, the different means
that are utilized to achieve the desired result make it possible to reduce
the size of that portion of the instrument that must be placed in the
mouth of the patient, thus making the instrument easier for the patient to
accept.
Instead of a combination of a stationary force sensing probe and a moving
displacement-sensing probe, this invention utilizes a moving handle that
contains both a force transducer and a displacement transducer. The object
of the invention is a probe instrument that can be used to apply
controllable pressure to the bottom of a pocket and that indicates the
depth of the pocket accurately and automatically. The depth of the pocket
is converted within the instrument to a signal that can be transmitted
automatically to an electronic recording device, which may be a computer,
in response to a signal generated within the instrument when the correct
force is applied to the probe via the handle of the probe instrument or in
response to the activation of a switch by the user of the instrument when
the measured force is acceptable for taking a reading and the probe is
seen to be properly positioned in the pocket. A digital output signal may
be provided by the instrument in preference to an analog output signal to
obtain an improved signal-to-noise ratio and consequently improved
accuracy in the measurement of the depth of the pocket. An analog signal
may be supplied instead of the digital signal, however, to allow a
reduction in the size and the cost of the probe instrument, if that is
desirable. In that case, conversion of the analog signal to a digital
signal may be effected in an external analog-to-digital converter if a
digital signal is desired.
The force is transmitted from the handle to the probe by means of the force
transducer. This transducer embodies an elastic restraint, contained
within the handle of the probe instrument, that is associated with the
means for measuring the force transmitted to the probe by the handle. The
combination of elastic restraint and force measurement may be implemented
by means of a micromachined thin-film resistance strain gauge, for
example. Alternative means are 1) a force-sensing resistor; 2) a
fiber-optic force transducer; and 3) an oscillating type of piezoelectric
force transducer. A simple and inexpensive means for achieving the desired
result is a linear potentiometer with a spring restraint.
The distance to which the probe has entered the pocket is measured by the
displacement transducer, which delivers a signal indicative of the
displacement of the tip of the probe relative to the handle, in
conjunction with the force transducer, which indicates the extent of its
own compression or deviation from a reference state as a result of the
force applied, if that deviation is not negligible. The displacement
transducer may consist of a potentiometer, a combination of a
potentiometer and an analog-to-digital converter, a wire-brush digital
displacement encoder, or an optical displacement encoder, for example. It
is to be noted that the force transducer and the displacement transducer
may be identical in nature, except for the elastic restraint imposed on
the displacement-sensing means in the force transducer.
An interface between the probe instrument and a digital computer may be
used to provide means for storing the depth measurements and to make
possible the use of various computer programs to process stored data on
the depths of periodontal pockets in a selected group of patients as well
as the depths of the pockets in a given patient.
An indicating device, such as a light-emitting diode or a buzzer, may be
used to indicate, when the force exerted by the tip of the probe against
the bottom of the pocket is within a predetermined range of values, that
the depth of the pocket may be read.
The front section of the probe instrument can readily be coupled to and
uncoupled from the handle. The front section consists only of the probe
and a front sheath in which it slides freely, with negligible friction.
Consequently, this front section can be sterilized in an autoclave, which
is an important feature of this invention. Another important feature of
this invention, which is a significant improvement over the periodontal
probe instrument disclosed in U.S. Pat. No. 4,904,184, is the simplicity
of the front section. As a result of this simplification, the manufacture
of the instrument is greatly simplified and consequently it can be
produced at a cost sufficiently low to allow disposal of the front section
after use on a single patient. This disposability provides greater
protection to patients against transmission of disease than even
sterilization in an autoclave.
The rear section of the probe instrument consists of a rod, a rear sheath
in which the rod is free to slide with negligible friction, a handle
assembly in which the rear sheath is free to slide, the force transducer,
the displacement transducer, and a spring coupling the rear sheath to the
handle assembly. The probe instrument is designed so that the front
section can readily be attached to the rear section and removed therefrom.
The rear end of the probe in the front section is held in position against
the front end of the rod in the rear section during use by magnetic
attraction of a small ferromagnetic disk attached to the rear end of the
probe to a small magnet attached to the front end of the rod. The magnetic
force is sufficient to overcome the negligible friction of the front
sheath but small enough to allow the probe to be removed from the probe
instrument easily.
The rear sheath is rigidly coupled to the actuating arm on the displacement
transducer, and the body of the displacement transducer is rigidly coupled
to the handle. Therefore, the displacement transducer measures the
displacement of the rear sheath relative to the handle. The force
transducer is rigidly mounted to the handle and is actuated by force
applied to it by the rod.
When the front and rear sections of the probe instrument are coupled
together, the magnet on the front end of the rod is in contact with the
ferromagnetic disk on the rear end of the probe, and the front end of the
rear sheath is in contact with the rear end of the front sheath. To use
the depth probe instrument, it is necessary to position the front section
so that the front end of the front sheath rests on the edge of the pocket
with the probe outside the pocket. Application of a forward-directed force
on the handle then causes the rear sheath to be forced backward relative
to the handle by contact of the rear sheath with the front sheath as the
handle slides forward over the front sheath. Thus, the spring and the
displacement transducer are actuated. Because the force transducer is
rigidly coupled to the handle, as the handle moves forward, the force
transducer forces the rod forward in the virtually frictionless rear
sheath. The rod, in turn, forces the probe forward in the virtually
frictionless front sheath, causing the probe to emerge from the front
sheath and extend into the pocket. The distance the probe extends from the
front sheath is the distance the rear sheath has moved relative to the
handle, and that distance is measured by the displacement transducer.
Until the front part of the probe contacts the bottom of the pocket, no
significant force is sensed by the force transducer. When the bottom of
the pocket is reached, however, the pressure of the bottom of the pocket
against the front end of the probe causes a resistance to further forward
motion of the probe. This resisting force is transmitted by the probe to
the rod, via the ferromagnetic disk and the magnet, and thus to the force
transducer.
In the preferred embodiment, the output signal provided by the force
transducer is compared with one or more reference values. When the output
signal of the force transducer indicates that the force on the front end
of the probe is appropriate for a reading of pocket depth, a buzzer or
other indicator is actuated automatically. If the operator of the
instrument is satisfied with the positioning of the probe in the pocket at
that time, he actuates a switch that causes the value of the signal
provided by the displacement transducer and the value of the signal
provided by the force transducer, if the displacement of the force
transducer is not negligible, to be entered into a digital computer, via a
program in the computer that then operates to compute the value of the
pocket depth and store it for processing at a later time.
In another embodiment, the value of the signal provided by the displacement
transducer and the value of the signal provided by the force transducer,
if the displacement of the force transducer is not negligible, are
automatically entered into the digital computer when the output signal of
the force transducer indicates that the force on the front end of the
probe is appropriate for a reading of pocket depth.
Because the front end of the front sheath remains at rest on the edge of
the pocket as the probe enters the pocket, the signal obtained from the
displacement transducer before the front end of the probe contacts the
bottom of the pocket indicates the depth to which the probe has entered
the pocket. Because the spring that couples the rear sheath to the handle
assembly serves only to hold the front sheath in position against the edge
of the pocket and exerts no force on the force transducer, the output
signal of the force transducer is zero until the front end of the probe
contacts the bottom of the pocket. Because this spring contributes in no
other way to the reading, ordinary problems of spring calibration and
changes in spring characteristics over time are irrelevant. When the
operator ceases to push forward on the handle, the spring returns to its
original state, causing the rear sheath to return to its original position
relative to the handle and to the rod in the rear section of the probe
instrument. Because the ferromagnetic disk on the rear end of the probe is
held in position against the magnet on the front end of the rod, the probe
is thus caused to retract to its reference position, in which the front
end of the probe is located just at the front end of the front sheath.
The two sections of the probe instrument can be uncoupled when desired, and
the front section can then be sterilized in an autoclave, if desired.
Alternatively, the front section can be made disposable to provide even
further protection against infection of a second patienty by a first
patient.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other advantages and features of the invention will be
apparent to those skilled in the art from the following description taken
in conjunction with the accompanying drawings, in which:
FIG. 1 is a drawing of the probe assembly, and
FIG. 2 is a diagram of an interface circuit between the probe assembly and
a digital computer.
DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference to FIG. 1, a preferred embodiment of the novel probe
instrument is shown in diagrammatic form and designated generally by
reference numeral 110. A front sheath 6 slides in a handle 10 that serves
as the housing for the rear section of the probe instrument assembly. The
front sheath is prevented from rotating within the handle by a projection
141 on the rear portion of the front sheath that is constrained by a slot
142 in the front portion of the handle 10, which extends to the front end
thereof.
A flexible probe (or first probe member) 2 of round cross-section and small
diameter slides within the front sheath 6. The friction between the probe
and the front sheath is rendered negligible by the use of teflon or a
similar material in the front sheath. The front end 3 of the probe 2 is
smoothed to prevent damage or injury to the bottom of the pocket to be
measured. The rear end of the probe 2 is terminated in a ferromagnetic
disk 14 cemented to the probe at a right angle thereto. In a reference
position, the front end of the probe 2 is aligned with the front end of
the front sheath 6.
A rod (or second probe member) 16 is terminated at its front end by a
permanent magnet 15 that serves to hold the probe 2 in place against the
front tip of the rod by magnetic attraction of the ferromagnetic disk 14.
The rear end of the rod 16 passes through a hole 130 in a cup 11, which
has an integral exterior flange 131, and presses against the actuating
member of a force transducer 20. The force transducer 20 is rigidly
fastened to the cup 11 by two screws 200 and 201. A cap 111 has an
integral interior flange 132, and the handle 10 has an integral threaded
exterior flange 134. The inner surface of the front end 135 of the cap 111
is threaded to mate with the threaded flange 134 that is integral to the
handle 10. The cup 11 is held in position against the rear end 133 of the
handle 10 by virtue of the force applied to the flange 131 integral to the
cup 11 by the flange 132 integral to the cap 111 when the cap 111 is
screwed to the flange 134 integral to the handle 10. Consequently, the
force transducer 20 is rigidly coupled to the handle 10, and
rearward-directed axial force applied to the rod 16 is sensed by the force
sensor 20 if that force is opposed by forward-directed force applied to
the handle 10.
A rear sheath 17 slides over the rod 16. The friction between the rod and
the rear sheath is rendered neligible in a manner similar to that used in
reducing the friction between the probe and the front sheath. The rear
sheath is terminated at its rear end by a projection 18, which is rigidly
connected to the actuator 23 on a displacement transducer 24, which may,
for example, be a potentiometer. The body of the displacement transducer
24 is rigidly fastened to the inner surface of the side wall of the cup 11
by two screws 202 and 203. Thus, the body of the displacement transducer
24 is rigidly coupled to the handle 10 when the cap 111 is screwed onto
the flange 134 on the handle, holding the cup 11 in place, and the
displacement transducer responds to displacement of the rear sheath 17
relative to the handle 10. Rotation of the rear sheath within the handle
is prevented by virtue of the fact that the projection 18 on the rear
sheath is constrained to move within a slot 143 within the handle 10,
which extends to the rear end of the handle. In some embodiments,
additional protection against rotation of the cup 11 when the cap 111 is
screwed in place is achieved by providing one or more pins on the cap 111
that engage corresponding holes in the handle 10.
The rear end of the rear sheath 17 presses against one end of a coil spring
21, contained within the rear portion of the handle 10, the other end of
which presses against the inner rear surface of the cup 11. The function
of the spring 21 is to supply a light force to urge the rear sheath 17 to
return to its reference position relative to the handle 10 when the
forward-directed force applied to the handle 10 or the rearward-directed
force applied to the front end 7 of the front sheath 6 is removed. By
virtue of the force of the front end of the rear sheath 17 against the
rear end of the front sheath 6, when the rear sheath 17 is in its
reference position relative to the handle 10 the front sheath 6 is held
against a threaded retainer 136 that screws onto the front end of the
handle 10. Removal of the threaded retainer 136 allows removal of the
probe 2 and the front sheath 6 from the handle 10.
The spring 21 is not an essential component of this invention. In some
embodiments, the spring 21 is omitted, and the rear sheath 17 is returned
to its reference position relative to the handle 10 manually or otherwise.
The wall of the rear end of the front sheath 6 is thickened to prevent the
front sheath from falling out of the handle 10 through the hole in the
retainer 136 through which the remainder of the front sheath 6 passes. The
internal diameter of the front end of the rear sheath 17 is enlarged with
respect to the internal diameter of the remainder of the rear sheath 17 to
accommodate the ferromagnetic disk 14 and the magnet 15. The external
diameters of the rear sheath and the rear part of the front sheath are the
same, so that a forward-directed force can be applied to the rear part of
the front sheath by the rear sheath, and an opposing force can be applied
by the rear part of the front sheath to the rear sheath.
It is to be noted that the construction of the probe instrument can be
simplified, if desired, by omision of the ferromagnetic disk 14 and the
magnet 15, with the result that the internal diameter of the front end of
the rear sheath 17 need not be enlarged and the external diameter of the
rear end of the probe 2 and the front end of the rod 16 can be reduced to
a value just enogh larger than th external diameter of the front part of
the probe 2 to prevent the probe from falling out through the opening in
the threaded retainer 136. Thus, the diameter of the probe instrument can
be reduced to an absolute minimum. The probe 2 is then held in position
with its rear end against the front end of the rod 16 by the small and
otherwise negligible friction of the front sheath 6 against the probe 2.
Also, if necessary, the probe 2 can be pushed back to its normal position
manually or otherwise.
In normal use, one edge of the front end 7 of the front sheath 6 is placed
against the edge of a pocket. If desired, a rest can be provided to widen
the edge of the front end of the front sheath. Such a rest may, for
example, consist of a tube 4 of short length that has a rest 5 in the form
of a sector of a circular disk extending at a right angle from it at one
end, the tube being of such internal diameter that it can be pressed over
the front part of the front sheath 6 and held in place there by friction
and being prevented from sliding too far along the front sheath by an
inner lip 1 that presses against the front end 7 of the front sheath 6.
Such a tube can be rotated manually so that the rest 5 is positioned at
any desired location along the periphery of the front end of the front
sheath. The handle 10 is then pushed in such a direction as to force the
front end 7 of the front sheath 6, or the rest 5 if used, against the edge
of the pocket and also forward to cause the handle 10 to slide forward on
the front sheath 6. The effect of such motion is to cause the front sheath
to push the rear sheath backward within the handle, compressing the spring
21; when the force applied to the handle by the user of the probe
instrument is removed, the spring 21 returns to its normal state, forcing
the front sheath to its normal rest position against the inner surface of
the retainer 136.
As the handle is pushed forward, the rod 16 is pushed forward also, by the
force transducer 20. The rod, in turn, pushes the probe 2 forward, via the
magnet 15 and the ferromagnetic disk 14, causing the probe to emerge from
the stationary front sheath and enter the pocket. No output signal is
generated by the force transducer, however, until the front end of the
probe contacts the bottom of the pocket, because the friction between the
rod and the rear sheath and the friction between the probe and the front
sheath are negligible.
When the front end of the probe encounters the bottom of the pocket, the
force of the pocket against the front end of the probe is coupled to the
force transducer 20 through the probe 2, the ferromagnetic disk 14, the
magnet 15, and the rod 16. This force against the front surface of the
force transducer is opposed by force that is applied to the handle 10 by
the user of the probe instrument and transmitted from the handle to the
force transducer through the cap 111 and the cup 11, on which the force
transducer is rigidly mounted.
The force transducer 20 is electrically connected to a voltage supply,
located in an interface circuit 138 on a printed-circuit board 139 that
connects to a microprocessor-based digital computer 140, with a pair of
conducting wires, in the customary manner. One of this pair of wires
serves as an electrical ground for the various electrical circuits in the
probe instrument. The electrical output signal from the force transducer
is available, with respect to ground, on a third conducting wire that
connects to the interface circuit 138 on the printed-circuit board 139.
The displacement transducer 24 is similarly electrically connected to the
voltage supply on the printed-circuit board 139, and the electrical output
of the displacement transducer, with respect to ground, is available on
another conducting wire that connects to the same interface circuit.
Although the interface circuit is shown external to the handle assembly,
in some embodiments the interface circuit 138 may be contaied within the
handle assembly (inside the cap 111, for example).
The conducting wires 43 and 41 that connect the output terminals of the
force transducer 20 and the displacement transducer 24, respectively, to
the interface circuit 138 on the printed-circuit board 139 pass through a
hole 137 centered in the rear surface of the cap 111. The function of the
interface circuit 138 is to convert the output signals from the force
transducer 20 and the displacement transducer 24 to digital form and
transfer them to the microprocessor-based digital computer 140. The
conversion is performed by two analog-to-digital converters, which are
well known to those skilled in the art; and the resulting digital signals
are transferred to the microprocessor in the digital computer by means of
two parallel input ports that are contained also within the interface
circuit 138, in a manner that is also well known.
A program stored in the digital computer 140 is in continuous operation,
repeatedly reading the digital signals provided by the force transducer 20
and the displacement transducer 24, via the analog-to-digital converters.
These digital signals are stored in reserved locations in the memory of
the digital computer. After each reading of the output signal derived from
the force transducer, the digital computer compares the value of that
signal with two reference values stored within the memory of the computer.
If the value obtained from the force transducer is less than the smaller
of the two reference values, the force exerted on the bottom of the pocket
by the probe is too small. If the value obtained from the force transducer
is larger than the larger of the two reference values, the force exerted
on the bottom of the pocket by the probe is too large. If, however, the
value obtained from the force transducer is larger than the smaller of the
two reference values and yet smaller than the larger of the two reference
values, then the force exerted on the bottom of the pocket by the probe is
within the acceptable range. In that event, the computer actuates an
indicator in the interface circuit 138 on the printed-circuit board 139,
through an output port in the iterface circuit, to inform the operator of
the probe instrument that a reading of the depth of the pocket may be
taken. The operator then actuates a foot-operated switch that is connected
through another input port in the interface circuit 138 on the
printed-circuit board 139 to the digital computer 140. In response to this
actuation of the foot-operated switch, the microprocessor stores the
current value of the digital signal obtained from the displacement
transducer in a new location, corresponding to the particular location
being probed at the time, in the memory of the digital computer and also
displays on the video display unit of the digital computer 140 the
location being probed and the depth that has just been measured. To
coordinate the location displayed on the video display unit of the
computer 140 and the location that is actually probed, a pointer within
the digital computer is initialized prior to the measurement of the depth
of the first in a sequence of pockets. The operator of the probe
instrument is informed of the exact sequence in which the pockets are to
be probed, and the pointer within the digital computer is incremented
after each reading has been stored in the memory of the digital computer.
Alternatively, the determination of whether the force exerted on the
bottom of the pocket by the probe is within the acceptable range can be
made by electronic means within the interface circuit 138 on the
printed-circuit board 139. In that event, the output signal of said
comparison means is transmitted to indicating means in the interface
circuit or in the digital computer or to actuating means in the digital
computer for reading the value of the depth of the pocket. When a hard
copy of the stored data concerning the depths of the various pockets that
have been probed is desired, such hard copy can be obtained by means of a
printer that is a part of the digital computer 140. The entire operation
of the digital computer described herein, including the printing of hard
copy of the stored data, will at times hereafter, for simplicity, be
referred to as processing of the first output signal and the second output
signal of the probe instrument.
In the foregoing discussion, it has been assumed that the nature of the
force transducer is such that no significant displacement of the rod 16
relative to the handle 10 is required to transmit the desired force to the
front tip of the probe 2. If that assumption is not valid, then the
computer must correct the digitized output of the displacement transducer
before storing it in the memory location within the digital computer
corresponding to the pocket being probed. For this purpose, a table of
digital values corresponding to displacement of the rod 16 relative to the
handle 10 is stored in the memory of the digital computer, as a function
of the digital value corresponding to the force sensed by the force
transducer 20. At the time a value of pocket depth is to be stored and
displayed, the digital value obtained from the force transducer 20 is then
subtracted from the digital value obtained from the displacement
transducer 24, and the difference thus obtained is stored as the corrected
value of the depth of the pocket and displayed as such.
From time to time, the probe instrument can be recalibrated by applying a
sequence of known forces to the front end of the probe 2 and storing in
the table contained in the memory of the digital computer the digital
value obtained from the force transducer 20 for each.
In the preferred embodiment, an acoustical tone generator or buzzer is
employed as the indicator in the interface circuit 138 on the
printed-circuit board 139 that is used to inform the operator of the probe
instrument that a reading of pocket depth may be taken. In an alternative
design, an indication is given on the output display unit of the digital
computer 140. Other kinds of indicator, such as a light-emitting diode,
may also be used.
A more detailed description of the interface circuit 138 is given with
reference to FIG. 2, in which the interface circuit 138 is shown enclosed
in a broken line. The operation of the components illustrated in FIG. 2 is
described in detail in various textbooks and reference books; in
particular, MICROPROCESSORS AND PROGRAMMED LOGIC, by Kenneth L. Short,
published by Prentice-Hall, Inc. in 1987 and MICROPROCESSOR-BASED PROCESS
CONTROL, by Curtis D. Johnson, published by Prentice-Hall, Inc. in 1984
provide background information on microprocessors, input ports, output
ports, decoders, flip-flops, and analog-to-digital converters. Background
information on displacement transducers and force transducers is available
in MEASUREMENT SYSTEMS, by Ernest O. Doebelin, published by McGraw-Hill
Publishing Company in 1990, for example.
The output signal provided by the displacement transducer 24 is connected
by a conducting wire 43 to the positive analog input terminal on a first
National Semiconductor ADC0804 analog-to-digital converter 250, and the
negative analog input terminal on that first analog-to-digital converter
250 is connected to the common ground, to which the analog ground terminal
and the digital ground terminal on that first analog-to-digital converter
250 are also connected. Similarly, the output signal provided by the force
transducer 20 is connected by a conducting wire 41 to the positive analog
input terminal on a second National Semiconductor ADC0804
analog-to-digital converter 252, and the negative analog input terminal on
that second analog-to-digital converter 252 is connected to the common
ground, to which the analog ground terminal and the digital ground
terminal on that second analog-to-digital converter 252 are also
connected. Each of the analog-to-digital converters has a clock circuit,
which is omitted in FIG. 2 for simplicity, the details of which are fully
explained in the manufacturer's data sheet for the ADC0804
analog-to-digital converter.
An eight-b | | |
