Note: Descriptions are shown in the official language in which they were submitted.
2170853
METHOD OF RECALIBRATING ELECTRONIC SCALES
Background of the Invention
The present invention relates generally to the field of electronic
weighing scales, and more particularly to a method for recalibrating such
scales to compensate for possible adverse effects on the accuracy of the
scales from variations in physical and/or environmental conditions under
which they operate, particularly the force of gravity.
This invention is an improvement on the inventions disclosed and
claimed in prior copending applications Serial Nos. 165,151 and 165,152,
filed December 10,1993, in the names of Gerald C. Freeman and Paul C.
Talmadge, and copending application Serial No. 364,168, filed December
12,1994, in the names of Gerald C. Freeman, Konstantin G. Kodonas and
Paul C. Talmadge, all assigned to the assignee of this application. This
application is also related to copending application Serial No. 364,169, filed
on December 12, 1994, in the name of Gerald C. Freeman, and assigned to
the assignee of this application, and which discloses and claims an
electronic scale of the type with which the recalibrating method disclosed
and claimed in this application may be practiced.
Since their introduction, electronic scales have become widely
accepted in many weighing applications for a number of reasons, primarily
the extreme degree of accuracy with which the scales can weigh articles, the
wide range of weights the scales are capable of handling and the ease and
convenience of digital display readout of the weight of an article. Electronic
scales are now used almost exclusively in such high volume utility situations
as mail, parcels, bulk food and dry goods sold by weight measure, air
terminal baggage, and other situations where highly accurate weight is
required on a repetitive basis with minimum recovery time between
individual weighings.
In recent years, electronic scales have become almost the universal
standard in connection with weighing mail and parcels, and it is in
connection with this utility that the present invention was developed,
although the utility of the present invention is not limited to this use. Perhaps
the primary contributing factor to the popularity of electronic scales in the
postal field is the high degree of accuracy inherent in such scales. When
one considers the billions of mail pieces weighed annually by the U. S.
Postal Service in the course of handling mail, and the millions of packages
2170853
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and parcels also handled not only by the Postal Service but also by all of the
courier services which compete with the Postal Service, one can begin to
appreciate the vast amount of money by which customers may be
overcharged or undercharged depending on whether scales are
overweighing or underweighing, in the course of dispatching all of this mail
and parcels if the scales which determine the mail and parcel postage
amount are not highly accurate.
For example, a generally accepted standard of accuracy among major
electronic scale manufacturers is that they be within .03% to .05% of full
scale. If we assume a 100 pound scale, the required accuracy becomes .03
to .05 pounds, or .48 to .80 ounces, over the range of the scale. Thus, it is
apparent that electronic scales are capable of weighing accurately to an
impressive less than one ounce in 100 pounds. Correspondingly, a one
pound letter scale can weigh letter mail accurately to within less than one
one hundredth of an ounce.
Aside from an inherent desire to provide highly accurate scales for
monetary purposes described above, a major factor contributing to this high
degree of accuracy is the requirement by the National Bureau of Weights
and Measures that a scale be capable of weighing within the above limits of
accuracy in order to be approved for commercial use in mail and parcel
applications. Although many customers in other applications may not
require this degree of accuracy, customers in the mail and parcel fields will
not purchase scales that do not have National Bureau of Weights and
Measures approval.
A major problem that occurs with electronic load cell scales is that the
accuracy of the scales can be adversely affected by variations in certain
physical and/or environmental conditions under which the scales are
required to operate, many of which are discussed in detail in the
aforementioned applications. In the first two of these applications, the
problems associated with maintaining the accuracy of the scale under
different operating conditions were addressed by providing an apparatus
and method for recalibrating an electronic scale in which an auxiliary weight,
which is constant although not necessarily precisely known, is mounted in
the scale so as to be movable between a first position in which the weight is
supported by a portion of the main frame of the scale, and a second position
in which the weight is supported by the platter of the scale on which the item
to be weighed is placed. A motor drives an eccentric mechanism which
raises and lowers the auxiliary weight, either on demand to place the weight
on the scale platter when the operator desires to recalibrate the scale, or
21 70853
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automatically in response to activation of various control elements caused by
various external influences, such as periodically, whenever the scale is
powered up, or when it senses a change in physical or atmospheric
conditions.
The major disadvantage of this apparatus and method is the need for
providing the auxiliary weight device and the electric and electronic control
means for periodically placing the auxiliary weight on the scale platter in
order to recalibrate the scale. The advantage of having this internal auxiliary
weight mechanism is entirely lost in a small capacity scale, such as the one
described hereinafter, where the cost of providing the auxiliary weight
mechanism and control means therefore would be entirely prohibitive in a
small capacity scale. Thus, the third of the above mentioned applications
discloses and claims an improvement to the two previous applications in
which the motorized mechanism by which the auxiliary weight was added to
the scale platter at the appropriate times is eliminated. In the scale disclosedin that application, the scale platter is readily removable from the scale, and
is, therefore, used as the recalibrating weight, providing the actual weight of
the platter remains constant at both the site of origin and the site of
installation. Without the motorized recalibrating weight mechanism, it was
possible to produce a relatively small scale having a low weight range in the
order of 5 to 10 pounds, which was highly reliable and less prone to
mechanical breakdown, both factors tending make the new scale more
economically attractive and competitive than the prior scale. However,
notwithstanding these advantages, the disadvantage still remained, that the
recalibration process required a relatively complex series of steps to initiallycalibrate the scale at the site of origin and then recalibrate it at the site ofinstallation. Thus, there is a need for a method of recalibrating an electronic
scale which does not require that an auxiliary weight be added to the scale
at the site of installation, whether it be a built in weight that is added to the
scale platter as in the first two of the above mentioned applications, or a
removable scale platter, as in the last of those applications, and which
therefore requires fewer steps to carry out the entire process of calibrating
and recalibrating the scale.
Brief Summary of the Invention
The present invention satisfies the foregoing need and at least
obviates if not eliminates all of the problems discussed above relating to the
accuracy of electronic scales. And while the invention is disclosed herein as
21 708~i3
being practiced in conjunction with the same apparatus as that disclosed
above and disclosed and claimed in the third and fourth of the
aforementioned copending applications, it nevertheless can be practiced
apart from that particular apparatus, and therefore has separate and unique
utility in the art.
We have discovered that an electronic scale can be recalibrated in
the field to compensate for variations in the accuracy of the scale caused by
the force of gravity by utilizing the known principles of gravity that the relative
magnitude thereof can be determined at any point on the earth, and that it
remains constant at that point. Since the force of gravity varies from place to
place around the world, depending on the proximity of a given plate to the
equator, a scale properly calibrated at the factory in Connecticut may not be
accurate within the desired limits in Florida. Also, the effect of gravity varies
with height, so that a scale calibrated properly at sea level will not be
accurate within the desired limits in Denver, Colorado. Thus, by determining
the relative magnitude of the force of gravity at various locations in a
predetermined geographic area, and assigning electronic correction factors
in the microprocessor of the scale corresponding to those locations, it
becomes possible to electronically recalibrate the scale by applying
appropriate correction factors to the factory calibration of the scale
depending on where the scale is ultimately.
Thus, the present invention is a method of recalibrating an electronic
scale to indicate accurate weight measurements of articles placed on the
scale regardless of variations in the force of gravity under which the scale is
operating between a site of origin and a site of installation and which tend to
adversely affect accurate weight. The method is typically practiced in
conjunction with an electronic scale which has a load cell capable of
producing an analog voltage output signal indicative of the weight of an
article placed on the scale, an analog to digital converter for converting the
analog voltage output signal from the load cell into digital information
representing the analog output, a digital readout for displaying the weight of
the article, and a microprocessor for converting the digital representation of
the analog output of the load cell into information for driving the digital
readout to cause it to display desired information.
In its broader aspects the method comprises the steps of generating
first data relating to the effect on the accuracy of said scale due to variations
in the relative magnitude of the gravitational force between a site of origin
and a site of installation, at the site of origin placing the first data into the
memory of a microprocessor in the scale, determining an electronic count
21708~3
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differential between the scale with 0# weight on the platter and with a known
weight thereon and placing the first electronic count differential into a
memory to calibrate the scale for accurate weight measurement at the site of
origin. The method further includes the steps of removing the scale from the
site of origin to a site of installation at which the scale may operate under a
gravitationa! force different from that which prevailed at the site of origin, and
entering second data into the microprocessor relating to the relative
magnitude of the gravitational force at the site of installation which causes
the microprocessor to adjust the factory calibration to compensate for any
variation in the gravitational force between the site of origin and the site
installation, whereby the scale is recalibrated at the site of installation to
cause the scale to indicate accurate weight measurements regardless of any
variation in the gravitational force between the site of origin and the site of
installation.
In some of its more limited aspects, the step of generating the first data
includes the steps of assigning separate identifiers to the site of origin and
the site of installation which are indicative of the relative magnitudes of the
gravitational force at the site of origin and the site of installation respectively,
and ascertaining an arithmetic multiplier for each of the magnitudes of
gravitational force that will adjust the factory calibration of the scale to
compensate for a difference in the gravitational force between that at the site
of origin and that at the site of installation. Further, with the scale at a site of
origin, the step of placing the first data into the memory of a microprocessor
includes the step of placing the identifiers and the corresponding arithmetic
multipliers into the memory of the microprocessor. Subsequently, with the
scale at the site of installation, the step of entering the second data includesthe step of entering the identifier into the scale that corresponds to the site of
installation of the scale, whereby the identifier causes the corresponding
arithmetic multiplier to adjust the electronic count differential by the amount
of the arithmetic multiplier to readjust the electronic count differential to
compensate for the difference in the magnitude of gravitational force
between the site of origin and the site of installation.
In a presently preferred mode of carrying out the invention, the
geographic locations correspond to the locations identified by postal zone
codes applicable to the predetermined geographic area in which the
geographic locations are situated, which, at least in the case of the United
States and Canada, can be conveniently represented by the first three digits
of postal ZIP codes, although other forms of geographic location code
systems could be effectively utilized, such as the telephone number area
21708~3
code system. Further, in one embodiment of the invention, the step of
entering the identifier into the scale that corresponds to the geographic
location of the site of installation comprises the step of manually entering theidentifier through a data entry component of the scale. In other
embodiments, this step is carried out by inserting a PROM into the scale
which contains either the identifier or the appropriate representation of a ZIP
or other geographic location code.
Having briefly described the general nature of the present invention, it
is a principal object thereof to provide a method of recalibrating an electronicscale to indicate accurate weight measurements of articles placed on the
scale regardless of variations in the relative magnitude of gravitational force
under which the scale operates between a site of origin and a site of
installation and which tend to adversely affect accurate weight.
Another object of the present invention is to provide a method of
recalibrating an electronic scale according to the preceding object which
does not require that an auxiliary weight be added to the platter of the scale
in order to achieve a recalibration, thereby avoiding the expense of
providing either a built in auxiliary weight that must be periodically added to
the weight of the platter, or going through a complex series of steps as
required with using a removable platter in lieu of an auxiliary weight.
These and other objects, advantages and features of the method of
the present invention will become more apparent from an understanding of
the following detailed description of a preferred embodiment of the invention
when considered in conjunction with the accompanying drawings.
Description of the Drawings
FIG. 1 is an exploded, perspective view of the major components of a
representative electronic scale with which the method of the present
invention is practiced.
FIG. 2 is a chart representing the relationship between all United
States ZIP codes and corresponding identifiers which are indicative of the
relative magnitude of gravitational force of the locations identified by the ZIPcodes.
FIG. 3 is a chart representing the relationship between the identifiers
shown in Fig. 2 and arithmetic multipliers by which an electronic count
differential in memory in the scale is adjusted to compensate for variations in
the relative magnitude of gravitational force between the site of origin and
the site of installation.
2170853
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FIG. 4 is a relatively simple schematic of the principal control
components of an electronic scale required for the practice of the present
invention.
FIG. 5 is a view similar to Fig. 4 illustrating another embodiment of the
practice of the present invention.
Detailed Description of the Invention
Referring now to the drawings, and more particularly to Fig. 1 thereof,
the major components of a representative scale with which the present
invention is practiced are shown in an exploded manner, and are seen to
comprise a housing, indicated generally by the reference numeral 10, a load
cell, indicated generally by the reference numeral 12, a weight distribution
plate, indicated generally by the reference numeral 14, a top cover, indicated
generally by the reference numeral 16, and finally a platter, indicated
generally by the reference numeral 18, on which the mail piece to be
weighed is placed.
The housing 10 is generally rectangular and has oppositely disposed
upstanding side walls 20, an upstanding rear wall 22, a very short,
upstanding front wall 24, and a bottom wall 26 to which the side, rear and
front walls are connected. A plurality of feet 28 are suitably connected to the
underside of the bottom wall 26 in recesses defined by bosses 30 for
supporting the scale. The housing 10, as well as the top cover 16 and the
platter 18, are formed of injection molded polycarbonate blend plastic. An
upstanding wall 32 extends across the housing 10 between the side walls
20 to divide the space within the base and housing 10 into forward and
rearward compartments 34 and 36, the former for the electronic components
which are actuated by a plurality of push buttons that extend through suitable
openings 38 formed in the top cover 16, the latter for the load cell 12 and
other electronic components that will not fit in the forward compartment 34.
A metal support plate 40 is suitably secured to the bottom wall 26 for
supporting the fixed end 42 of the load cell 12, which is positioned on the
support plate 40 and is connected to the housing 10 by suitable screws 44
which pass through openings in the bottom wall 26 and the support plate 40
and threadedly engage the fixed end 42 of the load cell 12. The opposite or
free end 46 of the load cell 12 is connected to the weight distribution plate 14by means of similar screws 48 which pass through openings in the plate 14
and are threadedly engaged with the free end 46 of the load cell 12.
2I 7~ 853
- 8 -
The top cover 16 is dimensioned to overlie the housing 10, and
includes a push button access portion 50 which includes the aforementioned
button access openings 38 and overlies the forward compartment 34 in the
housing 10. The remainder of the top cover 16 is a generally rectangular
portion 52 which overlies the rearward compartment 36 in the housing 10. A
pair of screws 54 suitably connect the rectangular portion 52 of the top cover
16 to the upper ends 56 of a pair of posts 58 to secure the top plate 16 to the
housing 10.
The scale platter 18 is basically a generally rectangular body member
60 which has approximately the same dimensions as the rectangular portion
52 of the top cover, and is provided with four identical legs 62, only two of
which are shown in Fig.1. Each leg 62 extends through one of the openings
64 in the weight distribution plate 16 and seats firstly in the apertures 66 of
one of a plurality of grommets 68 which in turn fit into suitable recesses 70
formed adjacent the four corners of the weight distribution plate 14. The legs
62 are gripped by the inner edges of the apertures 66 with sufficient strength
to firmly retain the platter 18 on the weight distribution plate 14, but not so
tightly that it cannot be readily removed by a user simply by lifting the platter
upwardly. It should be noted that the openings 64 in the top cover 16 are
sufficiently large to enable the legs 62 to pass freely therethrough without
touching the inner edges of the apertures 66 so that the platter 18 is
supported solely by the weight distribution plate 14, which, as described
above, is in turn supported solely by the load cell 12.
It should be understood that the foregoing scale has been shown and
described simply for the purpose of illustrating a type of electronic scale withwhich the present invention can be practiced, and that other scales having
different forms of construction could be utilized.
Coming now to a detailed description of the method of the present
invention, it will be seen that the invention, in its broader aspects, comprisesa series of steps directed toward generating certain data relating to the effecton the accuracy of the scale due to variations in the relative magnitude of the
gravitational force between a site of origin and a site of installation, which
data is later used when additional data is entered into the scale at a site of
installation. It is possible that some of this data pre-exists, in which case itcan be utilized in the practice of the invention; if not, it must be ascertained.
In its more limited aspects, the invention also includes a series of steps that
are carried out to generate the aforementioined data, and other steps are
carried out in connection with how the additional data is entered into the
scale. In order to facilitate a clear understanding of the invention, the
21 7l~853
g
complete series of steps will be described in the sequence in which they are
carried out in the most limited aspect of the invention, with the understanding
that the breadth of the invention is not intended to be limited by this form of
description, but rather only by reference to the claims appended hereto.
Assuming for the sake of this description that none of the necessary
information already exists, and with reference to Fig. 2, the first step in the
practice of the invention is to identify a predetermined number of geographic
locations within a predetermined geographic area. This involves first making
a determination of the geographic area, which may be the entire world or
any portion thereof. For convenience of illustration, the predetermined
geographic area is the United States, and the selected geographic locations
are the areas within the United States identified by the first three digits of
postal ZIP codes. As is well known, the U. S. Postal Service has established
a zone system for the country in which postage rates between any two given
zones are established for a given base weight. Also, all ZIP codes in the
country are identified as being distributed among these zones. Thus, if one
knows the ZIP code of the destination of a parcel, he can determine the
postal zone for that destination, from which he can determine the rate per
base weight, and by applying this to the weight of the parcel he determines
the amount of postage required. It should also be understood that additional
locations could be included, such as Europe, and additional geographic
locations could be identified, again using postal zone codes for
convenience, but other location codes, such as the aforementioned
telephone area codes, could be utilized. The two letter state abbreviation
system adopted by the U. S. Postal Service could also be utilized, and any of
these systems could be utilized alone or in combination with other systems.
Thus, in the case illustrated in Fig. 2, it will be seen that all of the ZIP
codes in the United States have been listed in the first three digit format, buthave been grouped in a predetermined manner by closely adjacent ZIP
codes simply to reduce the number of geographic locations which must be
identified. Column A shows a representative listing of ZIP codes in such
groups, commencing with the lowest number existing ZIP code and ending
with the highest number existing ZIP code.
The next step is to ascertain the relative magnitude of gravitational
force for each of the geographic locations within the predetermined
geographic area. This information generally exists and is available in some
form for various parts of the world, but if a specific geographic location to becovered in the practice of the invention is one for which this information is not
available, it must then be ascertained.
2~ 70853
- 10-
Once the relative magnitude of gravitational force for all of the
geographic locations has been ascertained, an arbitrary identifier is
assigned to each of the geographic locations that is indicative of the relative
magnitude of the gravitational force at each of these locations. As seen in
Column B of Fig. 2, the identifiers, listed in Column B, are two digit numbers,
although other forms of alpha or numeric designations could be used. Two
digit numbers, assigned in random order, are preferred for security reasons
so that owners of the scales cannot ascertain the identifiers for geographic
locations other than the location at which the scale is installed. This
prevents them from improperly recalibrating the scale to indicate a lower
weight than the actual weight of a mail piece at the site of installation of thescale and consequently paying insufficient postage for that mail piece.
It will be seen from Fig. 2 that the same identifier is assigned to more
than one geographic location for the reason that there are a large number of
ZIP code areas in the United States where the gravitational force is the
same. It should be understood, as previously mentioned, that the magnitude
of gravitational force for any location is a function of the elevation of that
location relative to sea level and the proximity of it to the equator. More
particularly, the higher a point is above sea level, the lower is the
gravitational force since it is further from the center of the earth. Similarly,the closer a point is to the equator, the less is the gravitational force due tocentrifugal force caused by the rotation of the earth which negatively affects
gravitational force. Thus, a ZIP code in Boulder, Colorado, at an elevation of
5,000 feet, may have the same gravitational force as a ZIP code in San
Diego, California at sea lev~' because the closer proximity of sea level
Miami to the equator offsets the 5,000 foot elevation of Boulder, even though
Denver i_ considerably farther from the equator than San Diego.
The next step is that of ascertaining an arithmetic multiplier for each of
the different magnitudes of gravitational force that will adjust the factory
calibration of the scale to compensate for a difference in the gravitational
force between that at the site of origin of the scale, typically the factory, and
that at the site of installation. Thus, with reference to Fig. 3, it will be seen
that each of the gravitational identifiers listed in Column A has a
corresponding arithmetic multiplier listed in Column B. How these
multipliers work to recalibrate the scale at the site of installation will be fully
explained below. However, it should be noted here that if a scale is installed
at a location that has the same relative magnitude of gravitational force as
that which exists at the site of origin of the scale, it is not necessary to
recalibrate the scale since the factory calibration will suffice to cause the
2170853
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scale to provide accurate weight measurements at the site of installation.
Therefore, assuming that the identifier at the site of origin is #41, the
corresponding multiplier for all ZIP codes having that gravitational force will
be 1.000. Again for the sake of illustration, it has been assumed that the
difference in the relative magnitude of gravitational force between the
geographic locations identified by the gravitational identifiers 0.0005.
It should be noted at this point that the two previous steps, i.e.,
assigning an identifier to each geographic location and ascertaining an
arithmetic multiplier, have been collectively designated, in a broader aspect
of the invention, as generating first data relating to the effect on the accuracy
of the scale due to variations in the relative magnitude of gravitational force
between the site of origin and the site of installation, and in a slightly more
limited aspect of the invention, as generating first data relating to the effecton the accuracy of the scale due to variations in the relative magnitude of
gravitational force between all of the geographic locations.
The next step is to place the identifiers and the corresponding
arithmetic multipliers, or the first data as the case may be, depending on
whether one is considering the most limited aspect of the invention or one of
the broader aspects as described above, into the memory of a
microprocessor in the scale. Thus, with reference to the schematic diagram
of Fig. 4, it will be seen that the scale includes a microprocessor 80 which
includes several memory registers, one of which 82 is for permanent storage
of the identifiers listed in Column A of Fig. 3. Another memory register 84 is
for permanent storage of the multipliers listed in Column B of Fig. 3. This
step is performed at the site of origin and is part of the general software
installation for the scale.
The next step is to determine an electronic count differential between
the scale with 0# weight on the platter and with a known weight on the
platter, and placing the electronic count differential into a memory in the
microprocessor to calibrate the scale for accurate weight measurement at
the site of origin. The determination of the electronic count differential itself
involves three successive steps, which commences with determining a raw
electronic count of the scale with 0# weight on the platter which, by way of an
example, might be 21,200. This is accomplished by the load cell 12
generating an analog voltage indicative of the weight of the empty platter 18.
Basically, a load cell, as seen in Fig. 1, using strain gage technology can be
a generally rectangular metallic body member which is adapted to have one
end 42 thereof rigidly mounted on a frame so that the load cell 12 is
supported only at that end, with the rest of the body member being
21 708a3
- 12-
cantilevered from the mounting end. The other end 46 of the body member
is provided with some means for supporting a weight, such as the weight
distribution plate 14 and the platter 18. Strain gages are mounted on the
body member in appropriate locations that stretch very slightly when the
body member is deflected by the application of the weight. An electric
voltage is applied across the strain gage, the output of which varies in
accordance with the extent to which the strip is strained by weight imposed
on the free end of the body member. Referring to Fig. 4, the output load cell
voltage is amplified by the amplifier 86 and applied to an analog to digital
converter 88 which converts the analog voltage into a digital signal which
can be recognized by a microprocessor 80 for further processing. In a
manner known in microprocessor technology, the details of which are not
necessary to an understanding of the invention, the microprocessor 80
converts the digital signal into a predetermined electronic count, which is
transferred to and temporarily stored in a working memory register 90.
A known weight is then placed on the platter 18, which typically
weighs approximately the same as the weight capacity of the scale, which in
the scale disclosed herein is 5 pounds. A raw electronic count of the scale
with the known weight on the platter 18 is then determined in the same
manner as just described for determining and storing the raw electronic
count of the scale with 0# weight on the platter 18, which, again by way of
example, might be 1 10,100, and this count is also placed in the working
memory register 90.
Again in known manner in microprocessor technology, the
microprocessor accesses the two raw electronic counts in the working
memory register 90 and subtracts the first count from the second count to
determine a first electronic count differential, which in the example being
given, is 88,900, and which represents the counts per known weight at the
site of origin. This electronic count differential is then placed in a permanentmemory register 92.
The scale is then removed from the site of origin to the site of
installation at one of the geographic locations at which the scale may
operate under a gravitational force different from that which prevailed at the
site of origin. At the site of installation, when the scale is first powered up, it
prompts the operator to enter the identifier into the scale that corresponds to
the geographic location of the site of installation, which he obtains from a
chart supplied with the scale which, in the manner shown in abbreviated
version in Fig. 2, lists the identifiers for all of the ZIP groups for the country.
This is accomplished most conveniently by utilizing the data entry keypad 94
- 13 - 2 1 7 0 8 5 3
of the scale which is also used to enter other information pertinent to
determining the amount of postage required for the mail piece being
weighed, such as the class of mail or a ZIP to Zone and special fees
conversion factor in the case of a parcel, although some other form of data
entry device could be utilized. The keypad 94 transmits this information to
the identifier memory register 82 of the microprocessor, where, in a manner
known in microprocessor technology, the corresponding identifier stored in
the memory register 82 is accessed and transferred to the multiplier memory
register 84. This in turn accesses the appropriate multiplier for the identifierjust accessed from the identifier memory register 82, and this multiplier is
transferred to the storage memory 92 which contains the electronic count
differential determined at the site of origin. The electronic count differential is
then adjusted by the product of the multiplier and the electronic count
differential to establish a new electronic count differential for the scale to
compensate for the difference in the relative magnitude of gravitational force
between the site of origin and the site of installation. In the example stated
above, if it is assumed that the site of origin is Connecticut, and the site of
installation is Boulder, Colorado, and that the identifier for Boulder is 76,
then from Fig. 3, the new arithmetic multiplier is .9995, and the new
electronic count differential for the scale in Boulder is 88,900 times .9995, or88.885.5. Thus, when an article is now placed on the scale, the accurate
weight thereof will appear on the digital display 96.
Fig. 5 illustrates another embodiment of the invention in which the
appropriate multiplier for the electronic count differential is selected by an
identifier which in turn is selected by a ZIP code entered into the scale via a
PROM. Although the above described ZIP code information is readily
available on charts supplied with less sophisticated scales, most electronic
scales are provided with software which includes the ZIP to ZONE
conversion information in the form of a ZIP to ZONE PROM, which is supplied
with the scale. Thus, it will be apparent that if the ZIP code information
shown in Fig. 2 is placed in memory in the microprocessor, as in the memory
register 98 shown in Fig. 5, at the site of origin, and an appropriate PROM, as
indicated by the box labeled 100 in Fig. 5, is inserted into the scale, either at
the site of origin if the site of installation is then known, or at the site of
installation itself, the site of installation ZIP code on the PROM will, again in a
manner well known in microprocessor technology, access the appropriate
ZIP code stored in the memory register 98 which, in turn, accesses the
corresponding identifier from the memory register 82. The identifier then
2170853
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accesses the corresponding multiplier from the memory register 84, and the
recalibration process described above can then take place.
One disadvantage of the embodiment just described is that it requires
a substantially large capacity memory in the scale in order to store all of the
ZIP code groups listed on the actual ZIP to identifier chart, and this tends to
increase the cost of the scale. This disadvantage is overcome in another
embodiment of the invention, which is a modification of that shown in Fig. 4,
in which the appropriate identifier contained in the memory register 82 is
accessed by entering the identifier for the site of installation through a PROM
which includes the identifier for the site of installation of the scale, rather than
through the data entry keypad 94. This requires a further step in the overall
process, that of placing the identifier in a PROM at the time that the ZIP code
information for a particuiar scale is programmed into the PROM. Thus, if the
PROM is already in the scale when it is first powered up at the site of
installation, a recalibration will take place instantly.
In a still further embodiment of the invention, it is possible to enter the
ZIP code of the site of installation through a data entry keypad in the same
manner as the identifier was entered in the previously described
embodiment illustrated in Fig. 4. The advantage of this is that the scale can
be recalibrated at the site of installation in the event that the PROM is
missing or defective when the scale is first powered up at the site of
installation.
It is to be understood that the method of the present invention are not
to be considered as limited to the practice of the specific steps described
above, which are merely illustrative of the best mode presently contemplated
for carrying out the method of the invention and which are susceptible to
such changes as may be obvious to one skilled in the art, but rather they are
intended to cover all such variations, modifications and equivalents thereof
as may be deemed to be within the scope of the claims appended hereto.
