Electronic scale and method for weight measurement including correction means for correcting a weight dependent signal
A scale having an electronic weighing system to generate a weight-dependent signal and a digital signal processing unit ( 18 ). The digital signal processing unit ( 18 ) has a circuit or program parts which measure the time elapsed since connection of the voltage to the scale. To dramatically reduce the time required for the scale to reach its full accuracy after connection of the voltage supply, the digital signal processing unit ( 18 ) has computation modules ( 34, 35 ) that correct the weight-dependent signal generated by the weighing system by a correction value that depends on the time elapsed. The magnitude of this correction value, starting from an initial correction value, converges with increasing time elapsed to a constant end value that differs from the initial correction value.
1. A scale comprising:
an electronic weighing system operative to generate a weight-dependent signal; and
a digital signal processing unit,
wherein the digital signal processing unit comprises at least one of a circuit and program parts operative to measure a time elapsed from connection of a voltage supply to the scale, and
said digital signal processing unit further comprising:
computation means for correcting the weight-dependent signal by a correction value, the correction value depending on the time elapsed from connection of the voltage supply to the scale,
wherein a magnitude of the correction value starts at an initial correction value upon connection of the voltage supply to the scale, and converges to a constant end value as time elapses.
2. The scale as claimed in claim 1 , wherein the constant end value is zero.
3. The scale as claimed in claim 2 , wherein the correction value decreases to zero in accordance with an exponential function.
4. The scale as claimed in claim 1 , wherein a correction value at any point in time is determined by:
K
(
t
)
=
∑
n
=
1
N
K
n
·
ⅇ
t
/
tn
where K 1 , K 2 , . . . , K N are the initial correction values and t 1 , t 2 , . . . , t N are decreasing time constants.
5. The scale as claimed in claim 1 , wherein the scale further comprises a clock, wherein the clock provides information used to determine an OFF duration, and wherein the initial correction value is selected as a function of the OFF duration.
6. The scale as claimed in claim 5 , wherein the OFF duration is determined by a difference between a current time and a power-off time, wherein the power-off time is obtained from a memory of the scale.
7. The scale as claimed in claim 5 , wherein the clock is a radio clock.
8. The scale as claimed in claim 5 , wherein the clock includes a voltage supply independent of the voltage supply used to supply a voltage to the scale.
9. The scale as claimed in claim 5 , wherein the clock comprises a capacitor set to discharge via a resistor.
10. The scale as claimed in claim 1 , further comprising at least one of a wire-bound and wireless connection operable to connect to an external clock.
11. The scale as claimed in claim 1 , wherein the scale includes at least one temperature sensor, and the initial correction value is selected as a function of a rate of change of an output signal of the at least one temperature sensor following the connection of the voltage supply to the scale.
12. The scale as claimed in claim 11 , wherein the rate of change of the output signal of the at least one temperature sensor is determined from at least two measurements taken at a predefined time interval, wherein a first measurement of the at least two measurements is taken following the connection of the voltage supply to the scale.
13. The scale as claimed in claim 1 , wherein the scale has at least two temperature sensors, the at least two sensors disposed at differing locations, and wherein the initial correction value is selected as a function of a difference of output signals of the at least two temperature sensors following the connection of the voltage supply to the scale.
14. The scale as claimed in claim 1 , wherein the correction value comprises both a component for a zero point and a component for sensitivity.
15. The scale as claimed in claim 5 , wherein the weighing system operates according to a principle of electromagnetic force compensation, and the initial correction value is selected as a function of the magnitude of the weight-dependent signal following the connection of the voltage supply to the scale.
16. The scale as claimed in claim 10 , wherein the weighing system operates according to a principle of electromagnetic force compensation, and the initial correction value is selected as a function of the magnitude of the weight-dependent signal following the connection of the voltage supply to the scale.
17. The scale as claimed in claim 11 , wherein the weighing system operates according to a principle of electromagnetic force compensation, and the initial correction value is selected as a function of the magnitude of the weight-dependent signal following the connection of the voltage supply to the scale.
18. The scale as claimed in claim 13 , wherein the weighing system operates according to a principle of electromagnetic force compensation, and the initial correction value is selected as a function of the magnitude of the weight-dependent signal following the connection of the voltage supply to the scale.
19. The scale as claimed in claim 1 , wherein the constant end value differs from the initial correction value.
20. The scale as claimed in claim 1 , wherein the computation means comprises a microprocessor.
21. A method for weight measurement of an object using a scale, comprising:
generating a weight-dependent signal of an object to be weighed;
determining an OFF duration of the scale; and
correcting the weight-dependent signal by a correction value,
wherein a magnitude of the correction value starts at an initial correction value determined from the OFF duration, and
wherein the magnitude of the correction value converges to a constant end value as time elapses from supply of a voltage to the scale.
22. The method for weight measurement as claimed in claim 21 , wherein the OFF duration is determined by a difference between a current time and a power-off time.
23. The method for weight measurement as claimed in claim 21 , wherein the initial correction value is selected as a function of a rate of change of a temperature signal following the supply of the voltage to the scale.
24. The method for weight measurement as claimed in claim 21 , wherein the initial correction value is selected as a function of a temperature differential within the scale, following the supply of the voltage to the scale.
25. A method for weight measurement of an object using an electronic scale, comprising:
generating a weight-dependent signal of an object to be weighed; and
correcting the weight-dependent signal by a correction value,
wherein the correction value depends on a time elapsed from switching on the scale, and
wherein a magnitude of the correction value starts at an initial correction value at the time of switching on the scale and converges to a constant end value in accordance with the time elapsed.