Electronic weighing apparatus utilizing surface acoustic waves using sensors operating at different frequencies, having temperature compensation, and a push oscillator

• US 7,053,319 B2
• Filed: 02/01/2002
• Issued: 05/30/2006
• Est. Priority Date: 02/02/2001
• Status: Expired due to Term

• Current Assignee: Circuits & Systems, Inc.
• Original Assignee: Circuits & Systems, Inc.
• Inventors: Kats, Vyacheslav D., Gordon, Arnold S.
• Primary Examiner(s): Gibson, Randy W.
• Application Number:
  US10/470,935
• Publication Number:
  US 20040065485A1
• Time in Patent Office: 1,579 Days
• Field of Search: 177/210.FP, 177/210.R, 735/80, 738/625.9, 73D/IG.4
• US Class Current: 177/210.0FP
• CPC Class Codes: G01G 3/13 having piezoelectric or piezoresistive properties
• CPC Class Codes: Y10S 73/04 Piezoelectric

Abstract

A weighing apparatus includes a SAW oscillator and a “push oscillator” to force the SAW oscillator into a desired mode of operation. A SAW temperature oscillator and a thermistor are also provided. The frequency of the “push oscillator” is made immune to temperature changes by generating it via a mixer mixing the SAW temperature oscillator with an adjustable fixed frequency oscillator. Long term stability of the SAW temperature oscillator is achieved by periodic calibration with the thermistor.

Claims

1. A weighing apparatus, comprising:

a) a first SAW sensor including a first SAW transmitter and a first SAW receiver;

b) a second SAW sensor including a second SAW transmitter and a second SAW receiver;

c) a displaceable member, at least one of said first and second SAW sensors being coupled to said displaceable member such that displacement of said displaceable member results in displacement of one of said transmitter and receiver relative to the other;

d) a amplifier having an input and an output, both of said SAW sensors being coupled in parallel to said amplifier, wherein

said first SAW sensor is arranged to oscillate at a first frequency and said second SAW sensor is arranged to oscillate at a second frequency different from said first frequency.

2. A weighing apparatus according to claim 1, further comprising:

e) a controllable oscillator coupled to the output of said amplifier.

3. A push oscillator for use with a first SAW oscillator to force the first SAW oscillator into a desired mode of operation:

a) a temperature sensing oscillator having a first output;

b) a fixed frequency oscillator having a second output; and

c) a mixer having two inputs and a third output, wherein

said first and second outputs are coupled to respective of said two inputs and said third output forms the output if said push oscillator.

4. A push oscillator according to claim 3, wherein:

said fixed frequency oscillator is a crystal oscillator.

5. A push oscillator according to claim 3, wherein:

said temperature sensing oscillator is a second SAW oscillator.

6. A weighing apparatus, comprising:

a) a displaceable member;

b) a first SAW oscillator coupled to said displaceable member such that displacement of said displaceable member causes a change in the frequency of said first SAW oscillator;

c) a second SAW oscillator coupled to said displaceable member such that displacement of said displaceable member causes a change in the frequency of said second SAW oscillator; and

d) a weight indicator coupled to said first and second SAW oscillators, wherein

the frequency of said first SAW oscillator and the frequency of said second SAW oscillator are different; and

said first SAW oscillator and said second SAW oscillator are arranged such that what said first SAW oscillator frequency increases due to displacement of said displaceable member, said second SAW oscillator frequency decreases.