Wide range high accuracy weighing and counting scale

• US 4,375,243 A
• Filed: 03/30/1981
• Issued: 03/01/1983
• Est. Priority Date: 03/30/1981
• Status: Expired due to Fees

• Current Assignee: Doll W. Gary
• Original Assignee: Doll W. Gary
• Inventors: Doll, W. Gary
• Primary Examiner(s): MILLER JR, GEORGE
• Application Number:
  US06/249,081
• Time in Patent Office: 701 Days
• Field of Search: 177/25, 177/164, 177/200, 177/211
• US Class Current: 177/25.17
• CPC Class Codes: G01G 19/00 Weighing apparatus or methods adapted for special purposes not provided for in the preceding groups electric measuring arrangements involving comparison with a reference value G01R17/00
• CPC Class Codes: G01G 23/005 Means for preventing overload
• CPC Class Codes: G01G 3/142 Circuits specially adapted therefor

Abstract

An electronic scale is provided with two or more load cells in which the first load cell covers a low load range, and each successive cell covers a greater load range than the preceding cell. The cells are connected mechanically in tandem such that a load on the scales is applied to each cell simultaneously. Electrical signals from each load cell when performing a weighing operation are processed by a microcomputer to digitize the signals and to select the signal coming from the first load cell in the tandem connection which is not overloaded. The microprocessor scales the measurement signal and displays the weight on an alphanumeric readout. Memory circuits are included for storing tare weights and for storing unit weights during counting operations. When a number of units in a group is to be counted, the microprocessor divides a measured weight by the unit weight and outputs the count to the alphanumeric readout display. A low profile of the tandem load cell arrangement is obtained by the use of Z-brackets or L-brackets to provide the mechanical interconnections. All switching of ranges is done automatically by the microprocessor without attention of the user.

Claims

1. A wide range weighing and counting scale comprising:

(a) a first load cell having a first range of operation, and a second load cell having a range of operation higher than said first load cell, said second load cell mechanically coupled in tandem with said first low range cell;

(b) first conditioning amplifier means connected to said first load cell to receive electrical signals therefrom for producing a digital count proportional to the load applied to said first load cell, said amplifier having a preselected upper count limit;

(c) second conditioning amplifier means connected to said second load cell to receive electrical signals therefrom for producing a digital count proportional to the load on said second load cell; and

(d) computer means connected to said first and second conditioning amplifiers, said computer means for selecting the digital count for processing from said first conditioning amplifier when said count is less than a preselected upper limit, and for selecting the digital count from said second conditioning amplifier when said first count is greater than said selected upper limit, said computer means for calculating a number representative of the load on said scale from the selected digital count; and

(e) display means for displaying said calculated number.

2. The wide range weighing and counting scale recited in claim 1 in which said calculated number is the weight of the load on said coupled first and second load cells.

3. The wide range weighing and counting scale recited in claim 1 in which said calculated number is the number of units forming the load on said coupled first and second load cells.

4. The scale as defined in claim 1 in which said scale includes:

(a) a base plate;

(b) said mechanically coupled load cells include said second load cell bolted to said base along a bottom surface of said cell;

(c) a Z-bracket having an upper flange and a lower flange, said upper flange bolted to the top surface of said second load cell;

(d) said first load cell bolted to said lower flange of said Z-bracket along the bottom surface of said first cell; and

(e) a weighing platform bolted to the top surface of said first load cell;

whereby the force from a material to be weighed placed in said weighing platform is transmitted to said first load cell directly and to said second load cell via said Z-bracket.

5. The scale defined in claim 1 in which:

(a) said scale includes a base plate;

(b) said mechanically coupled load cells include said second load cell bolted to said base plate along a bottom surface of said cell;

(c) an L-bracket having a vertical flange and a lower horizontal flange, said vertical flange bolted to a vertical surface of said second load cell;

(d) said first load cell bolted to said horizontal lower flange of said L-bracket;

(e) a weighing platform pedestal bracket bolted to the vertical side surface of said first load cell adjacent to said vertical flange; and

(f) a weighing platform attached to the upper end of said pedestal bracket;

whereby a weight placed on said weighing platform is transferred to said first load cell via said pedestal bracket, and to said second load cell via said L-bracket.

6. The wide range weighing and counting scale recited in claim 1 in which said first and second conditioning amplifiers each includes:

(a) a preamplifier having low noise characteristics;

(b) a buffer amplifier;

(c) a low pass filter; and

(d) an analog-to-digital converter.

7. The wide range weighing and counting scale recited in claim 6 which said computer means includes:

(a) a microprocessor connected to said analog-to-digital converters;

(b) a memory connected to said microprocessor; and

(c) said display means includes display interface and alphanumeric displays.

8. The wide range weighing and counting scale recited in claim 6 in which said scale includes said analog-to-digital converters to convert analog signals from said load cells to binary counts, said counts limited to said selected upper limit.

9. An electronic counting scale for determining the number of units in a group of units, said scale having a high count accuracy over a wide range of weights of said units comprising:

(a) memory means for temporarily storing the unit weight of objects to be counted;

(b) a base;

(c) a platform for holding the group of units to be counted;

(d) a multiplicity of load cells mechanically and operatively connected in tandem between said platform and said base, wherein each successive load cell after a first load cell has a greater weight capacity than the preceding load cell;

(e) a multiplicity of electronic amplifier means for providing excitation to each of said load cells, for receiving analog electrical signals therefrom representative of the weight of a group of units on said platform, and for amplifying each of said signals;

(f) means for selecting the amplified signal from the load cell in tandem connection having the highest value and for which the weight capacity of such load cell is not exceeded;

(g) means for converting said selected signal to a weight measurement signal;

(h) means connected to said memory means for dividing said weight measurement signal by said temporarily stored unit weight to thereby produce an electrical count signal representative of the number of units in said group; and

(i) electronic display means for displaying the count of said group.

10. The scale as defined in claim 9 in which said mechanical connection between said multiplicity of load cells is by means of a Z-bracket arranged to minimize the overall height of said multiplicity of load cells.

11. The scale as defined in claim 9 in which each of said multiplicity of load cells includes a mechanical stop to prevent damage to a load cell when its weight capacity is exceeded.

12. The scale as defined in claim 9 in which said electronic amplifier means includes:

(a) a source of DC excitation voltage;

(b) a low noise amplifier;

(c) a low pass filter connected to said low noise amplifier; and

(d) analog-to-digitial converter connected to receive analog signals from said low pass filter and to produce a digital count representative of the amplitude of such analog signals.

13. The scale as defined in claim 12 in which said selection means includes:

(a) means for limiting the maximum value of the digital count from each of said analog-to-digital converters to a preselected value representative of the maximum load of each of said load cells; and

(b) microprocessor for comparing two successive digital counts resulting from the load on each successive load cell and selecting the first digital count which does not exceed said preselected maximum count value.

14. The scale as defined in claim 13 in which:

(a) said microprocessor multiplies said selected digital count by a predetermined constant for the selected load cell, and said weight measurement signal is an alphanumeric code; and

(b) said electronic display means is an alphanumeric readout responsive to said alphanumeric codes.