Electronic weighing apparatus

• US 4,696,359 A
• Filed: 08/22/1986
• Issued: 09/29/1987
• Est. Priority Date: 08/22/1986
• Status: Expired due to Fees

• Current Assignee: National Transducer Corporation
• Original Assignee: National Transducer Corporation
• Inventors: Glibbery, Albert W.
• Primary Examiner(s): Miller, Jr., George H.
• Application Number:
  US06/899,487
• Time in Patent Office: 403 Days
• Field of Search: 177/211, 73/862.67
• US Class Current: 177/211
• CPC Class Codes: G01G 19/18 having electrical weight-sensitive devices
• CPC Class Codes: G01G 23/007 Integrated arrangements for generating electrical power, e.g. solar cells
• CPC Class Codes: G01G 23/163 involving digital counting
• CPC Class Codes: G01G 23/37 involving digital counting
• CPC Class Codes: G01G 3/147 involving digital counting

Abstract

An electronic weighing apparatus providing accurate weight using a low level power supply. A force responsive strain gauge having a high impedance, provides an electrical output to a sample and hold circuit. The signal from the strain gauge is conditioned by a sequencing circuit which turns the strain gauge and sample and hold circuit on and off at a rate providing a very low duty cycle to keep power consumption to a low level. Power is supplied by a photo-voltaic panel built into the electronic weighing apparatus responsive in light levels as low as 50 lux.

Claims

1. A weighing apparatus comprising:

force responsive strain gauge means providing an electrical output;

said force responsive strain gauge means having a high impedance;

sample and hold circuit means receiving the output from said force responsive transducer means for sampling and holding said output;

sequencing means for sequentially turning said force responsive strain guage means and said sample and hold means on and off;

digital processing means for processing the output of said sample and hold means;

display means for displaying the output of said digital processing means; and

low voltage power supply means supplying power to said force responsive transducer and to said sample and hold circuit means.

2. Apparatus according to claim 1 wherein said high impedance force responsive transducer means is a high impedance bridge.

3. The apparatus according to claim 2 wherein said high impedance bridge has an impedance in the range of 4000 to 6000 ohms.

4. The apparatus according to claim 2 in which the duty cycle in said sequencing means is in the range of 1% to 5%.

5. The apparatus according to claim 2 in which the duty cycle of said sequencing means is approximately 1%.

6. The apparatus according to claim 1 in which said low level power supply means is a light responsive power supply means producing a low level power output.

7. The apparatus according to claim 6 with said light responsive power supply means is a photo-voltaic panel means.

8. The apparatus according to claim 1 in which said sequencing means sequences said sample and hold means on and off at a duty cycle in the range of 1% to 10%.

9. The apparatus according to claim 1 in which said digital processing means includes;

a summing circuit receiving output of said sample and hold means;

analog to digital converting means receiving the output of said summing circuit; and

display logic means receiving the output of said analog to digital converting means to drive said display means.

10. The apparatus according to claim 9 including zero-tracking means;

said zero-tracking means continuously sampling small amounts of contamination weight on a weight container on said scale;

the output of said zero-tracking circuit being connected to said summing circuit to re-adjust the display to zero periodically.

11. The apparatus according to claim 9 including;

a dual range switch cavity;

said dual range switching circuit receiving the output of said sample and hold circuit and providing an output to said summing circuit to switch said summing circuit to or from a high resolution to a low resolution when the weight on the scale exceeds a predetermined amount.

12. The apparatus according to claim 11 in which said dual range switching circuit switches the output of said display to or from a two decimal point resolution to a single decimal point resolution.

13. The apparatus according to claim 9 including a tare circuit for adding the tare weight of a container.

14. The apparatus according to claim 13 in which said tare circuit comprises;

switch means for inserting up or down counts to the display.

15. The apparatus according to claim 14 in which said switch means comprises a pair of pushbutton switches;

an up/down counter activated by said pushbutton switches;

said pushbutton switches being connected to reset said tare circuit to zero when activated simultaneously.