Weighing scales – Self-positioning – Repositioning in response to deflection under load
Patent
1981-07-13
1983-11-29
Miller, Jr., George H.
Weighing scales
Self-positioning
Repositioning in response to deflection under load
177248, G01G 700, G01G 126
Patent
active
044176325
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THIS INVENTION
1. Field of this Invention
This invention relates to a process for automatic weighing, whereby the deflection of the balance beam is compensated within the scope of a regulating process electromagnetically and/or by other methods, for example, by substitution weights, and the compensation force needed for this is used as a measure for the mass to be determined. The apparatus of this invention for executing this process is built up according to the principle of the electromagnetic force compensation, possibly in connection with other compensating systems (for example, substitution control weights) and with the use of a microprocessor as well as of an arrangement for signaling the deflection of the balance beam from the rest position, and it has a digital recording.
2. Prior Art
Electronic balances have been known, for example a sensor, attached to the balance beam in the manner of a closed control loop, which signal the non-existence of the rest position to an electromagnetic force compensation system. A current of sufficient strength is produced in dependence on this deflection in order to compensate for the distortion of the balance beam. At the same time, the sensor is returned automatically into the zero position. The current needed in order to bring about the zero position is measured and is used as a measure for the weight to be determined (for example, Gast, Feinwerktechnik 53, 167-172, 1949). More recent developments provide microprocessors which are able to store and process the measuring values obtained from the control loop. At the same time, the microprocessor merely serves for the evaluation of the measurement results and has no function within the control loop.
Furthermore, substitution balances are known where a weight compensation is accomplished by lifting off of control weights.
The force compensation systems of conventional balances must operate with a precision which corresponds to the entire weighing range to be resolved. In the case of analytical balances, for example, the error must not amount to more than fractions of one per mil. Temperature differences and other possible disturbing values must be compensated over the same range by physical measures. Thus, for example, control weights of 100 g must be made precisely to 10.sup.-5, as a result of which the production process becomes more expensive. In the case of such systems, furthermore, the zero indicator must be capable of indicating the exact rest position of the balance beam since any deviation will cause a more or less severe measuring error.
BROAD DESCRIPTION OF THIS INVENTION
This invention is based on the object of providing a process and a device with which (while avoiding the disadvantages of the above mentioned methods and devices) disturbing factors--for example, temperature influences--may be precisely compensated in a simple manner. Furthermore, merely the deflection of the balance beam is to be signaled and not its precise rest position.
It has turned out that this object may be solved with a process of the initially described kind whenever compensating forces are used which are graded according to decreasing powers of a numerical system of an appropriate basis, whereby the weight value of each power is always compensated by (n-1) quantization steps, whereby n signifies the number of quantization steps within the numerical system used which causes an overcompensation, and in that the weight is determined from the sum of the compensation forces of all powers. The weighing result is determined by adding the sum of the compensation forces of all powers and from the sum of the electronically stored correction values according to numbers, whereby the correction values correspond to the compensation errors which were determined for each compensation step once within the scope of a calibrating process. Advantageously the compensation forces are scaled decadically. Also advantageously the correction values are taken into account both in case of electromagnetic force compensation as well as in
REFERENCES:
patent: 4004458 (1977-01-01), Knothe et al.
patent: 4149605 (1979-04-01), Mettler et al.
patent: 4153124 (1979-05-01), Knothe et al.
Battelle - Institut e.V.
Miller Jr. George H.
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