FORCE MEASURING APPARATUS INCLUDING SENSITIVITY SELECTION MEANS

• US 3,788,410 A
• Filed: 08/02/1972
• Issued: 01/29/1974
• Est. Priority Date: 08/19/1971
• Status: Expired due to Term

• Current Assignee: Mettler-Toledo AG IM Langacher Greifensee Switzerland
• Original Assignee: Eugen Meier, Heinz Allenspach
• Inventors: Meier, Eugen, Allenspach, Heinz
• Primary Examiner(s): Wilkinson, Richard B.
• Assistant Examiner(s): Miska, Vit W.
• Application Number:
  US05/277,162
• Time in Patent Office: 545 Days
• Field of Search: 324/78D,79D 73/133,67.2,137,138 235/151.33 177/210,211,25
• US Class Current: 177/25.14
• CPC Class Codes: G01G 3/16 measuring variations of frequency of oscillations of the body
• CPC Class Codes: G01L 1/10 by measuring variations of frequency of stressed vibrating elements, e.g. of stressed strings using resistance strain gauges G01L1/22

Abstract

Force measuring apparatus of the type including a mechanical oscillator, such as a string, that vibrates under load to produce a signal voltage the frequency of which is a function of the force to be measured. The invention is characterized in that following multiplication of the signal frequency, the signal is fed to multi-stage counter means for selected long or short periods of time corresponding with the desired sensitivity of measurement. The duration of the period of connection is controlled by a gate timing switch which is operable simultaneously with a stage selection switch associated with the counter, whereby when the connection periods are alternately long and short, the signal to be counted is fed to lower and upper counter stages, respectively. The gate tuning switch is operable alternately by a reference signal supplied from a mechanical oscillator, such as a crystal, or a reference string contained in the same housing as the measuring string.

Claims

1. Weighing apparatus, comprising a. means including at least one mechanical oscillator for producing a signal voltage the frequency of which is a function of the force to be measured;

b. frequency multiplier means for multiplying the frequency of said signal voltage, thereby to provide a high frequency counting pulse signal;

c. pulse counter means having first and second stages;

d. stage selection switch means including a pair of output terminals connected with the first and second stages of said counter means, respectively, said stage selection switch means including also an input terminal;

e. gate means having an output terminal connected with the input terminal of said stage selection switch means, said gate means including an input terminal connected with said frequency multiplier means;

f. means including a reference oscillator and frequency divider means for operating said gate means between conductive and nonconductive conditions in which counting pulses from said frequency multiplier means are conducted to and isolated from said stage selection switch means, respectively, said frequency divider means including high and low frequency output terminals;

g. means including a gate timing switch for varying between two given lengths the duration of the conductive periods of said gate means, said gate timing switch being operable between first and second positions to alternately supply said high and low frequency outputs to said gate means and to simultaneously switch said stage selection switch means between its first and second positions, respectively, whereby when said gate timing and stage selection switches are in their first positions, counting pulses for a measurement of one order of sensitivity are supplied to one stage of said counter means, and when said switches are in their second positions, counting pulses for a measurement of another order of sensitivity are supplied to the other stage of said counter means; and

h. indicator means connected with said counter means for digitally representing the magnitude of the loda being measured as a function of the instantaneous count of said counter means.

2. forward-reverse logic means controlling the direction of operation of said counter means;

3. Apparatus as defined in claim 2, wherein said frequencies and counting periods have such a relationship that the counter result is represented by said indicator means in units of weight.

4. zero detector means connected with said logic means for reversing the direction of said counter means when the count thereof equals zero, whereby when a gross weighing operation follows a determination of tare, the weighing result is the net weight.

5. Weighing apparatus, comprising a. at least one mechanical oscillator means for producing a signal voltage the frequency of which is a function of the force to be measured;

b. FREQUENCY multiplier means for multiplying the frequency of said signal voltage;

c. counter means for counting the number of pulses of said multiplied signal during a given period of time, said counter means including a forward-reverse counter;

d. indicator means connected with said counter means for digitally representing the force to be measured as a function of the instantaneous count of said counter means;

e. means for varying the duration of said counting period, including normally non-conductive gate means connected between said frequency multiplier means and said counter means, and means including a gate timing switch for rendering conductive said gate means for relatively long and relatively short conductive periods, respectively; and

f. taring means comprising