JP2595406B2 - Weighing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic weighing system which amplifies an analog weight signal obtained by detecting the weight of an object to be measured, converts the signal into a digital value, and processes the digital value to display it on a display device. It concerns the device.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing a conventional electronic weighing device of this kind. In the figure, an analog weight signal output from a weight detector 1 including a load receiving table on which an object to be weighed is placed and a load cell for detecting the weight of the object to be weighed is amplified by a differential amplifier circuit 2, The filter 3 removes high-frequency components equal to or higher than the cutoff frequency, that is, vibration components mainly caused by mechanical vibration of the weight detector 1.

The signal from the analog filter 3 is AD
The signal is input to a converter and converted into a digital weight signal. The AD converter 4 is a double integral type (Japanese Patent Laid-Open No.
No. 2-69125, page 4, lower left column, lines 13-14) and a successive approximation type are used. 5 is CP
At U, the digital weight signal output from the AD converter 4 is input, the level of the digital weight signal is calculated, the span is adjusted so that the value falls within a predetermined width, and the display 6 Is programmed to display the weighing value.

The analog filter 3 is, for example, shown in FIG.
As shown in FIG. 1, a buffer amplifier OP and two input resistors R connected in series to its non-inverter terminal.
, R2 and RC integration circuit I having capacitor C1
And a capacitor C2 interposed between the middle point of the two input resistors R1 and R2 and the inverter terminal of the buffer amplifier OP, and the two resistors R1 and R2
And by selecting the constants of the capacitors C1 and C2,
The cutoff frequency is determined.

[0005]

In an electronic weighing device, the natural frequency of a load receiver or a load cell constituting a weight detector differs depending on the type of the weighing device. It is necessary to change the cutoff frequency for eliminating the noise.

However, the conventional measuring device has the following problems when the cutoff frequency is changed. That is, in order to change the cutoff frequency of the analog filter, it is necessary to replace elements such as a resistor and a capacitor, and to replace such elements, a special tool is required. Therefore, it takes time to change the cutoff frequency, and it is not possible to quickly respond to a sudden change request. In particular, when the behavior of the weighing device is examined by variously changing the cutoff frequency in order to determine the optimum cutoff frequency, a great deal of trouble is required. In addition, since analog filters having different element constants must be used for each model having a different natural frequency of the weight detector, there is a drawback that versatility is lacking.

Therefore, it is conceivable that a plurality of elements having different constants are mounted in an analog filter, and the cutoff frequency is made variable by switching them with a switch. However, in this case, not only the cost of the analog filter is significantly increased, but also an undesirable result such that the mounting area is increased.

The present invention has been made in view of the above circumstances, and provides a weighing device that can easily and quickly change a cutoff frequency, and that does not increase the cost and the mounting area. The purpose is to do.

[0009]

To achieve the above object, a weighing device according to the present invention comprises: a weight detector for detecting the weight of an object to be weighed and outputting an analog weight signal; A delta-sigma having a modulator for modulating a weight signal and a digital filter having a variable cutoff frequency for removing a high-frequency component of the digital weight signal according to the frequency of an input clock signal;
Type AD converter, and based on an external command signal the black
Tsu change the frequency of the click signal is made a filter characteristic control means Ru is changed the cutoff frequency of the digital filter. The above-mentioned AD converter is called a delta-sigma type, in which an analog signal is subjected to voltage / frequency modulation by a higher-order modulator, and then a high frequency component is removed by a digital filter. In addition, other components
The weighing device detects the weight of the object
A weight detector that outputs a signal.
Modulator for modulating a digital weight signal and the digital weight
Variable cutoff frequency to remove high frequency components
Digital filter and cutoff frequency control frequency
Delta-sigma type AD converter having number control means, and
And a numerical data signal based on the external command signal.
Output to the number control means and cut the digital filter.
Equipped with filter characteristic control means for changing off frequency
It becomes.

[0010]

According to the present invention, a delta-sigma type AD converter is used as an AD converter for converting an analog weight signal into a digital weight signal, instead of a conventionally used double integral type or successive approximation type. (Hereinafter, ΔΣ ADC
Therefore, by using a digital filter built in the ΔΣ ADC,
The cutoff frequency can be arbitrarily and easily changed based on an external command signal. This change of the cutoff frequency is possible even during the weighing operation.

In addition, it is not necessary to selectively use an analog filter having an element having a different constant for each model having a different natural frequency of the weight detector, and it is only necessary to prepare one kind of ΔΣ ADC. Thus, a high versatility that a cutoff frequency suitable for each of a plurality of models can be appropriately set can be obtained.

Further, by using a ΔΣ type ADC, it is possible to reduce the cost by omitting the analog filter,
The responsiveness superior to the multiple integration type ADC and the higher resolution (that is, higher accuracy) than the successive approximation type are obtained.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a first embodiment of the present invention. In FIG.
Are the same as those of the conventional example shown in FIG.

Reference numeral 7 in FIG. 1 denotes a ΔΣ ADC, which is a modulator 7A for modulating an analog weight signal from the differential amplifier circuit 2 into a digital weight signal, and a clock signal c input thereto.
a digital filter 7B having a variable cutoff frequency for removing a high-frequency component of the digital weight signal according to the frequency of k . Reference numeral 8 denotes a frequency dividing circuit which divides the oscillation frequency of the oscillator 8a to generate a clock signal c having a predetermined frequency.
k is created and the cutoff frequency of the digital signal is changed by changing the frequency of the clock signal ck to change the thinning cycle of the signal in the digital filter 7B. The frequency dividing ratio of the frequency dividing circuit 8 is selected by the select signal s output from the filter characteristic control means 5A provided in the CPU 5 based on the external command signal c .

Reference numeral 9 denotes a keyboard which outputs an external command signal c by an external operation. The keyboard 9 and the display 6 are connected to the CPU 5 via an interface 10. The frequency of the clock ck, that is, the cutoff frequency can be freely set and changed. Further, the CPU 5 includes memory means 5B for storing a cutoff frequency set based on a command signal c from the keyboard 9.

Next, the operation of the above configuration will be described. In the normal weighing mode, the analog weight signal from the weight detector 1 is input to the differential amplifier circuit 2, amplified, and then input to the ΔΣ ADC 7. This ΔΣ ADC
At 7, the input analog weight signal is first subjected to voltage / frequency modulation by a modulator 7A to be converted into a digital weight signal, and then passed through a digital filter 7B to set the digital weight signal in the digital weight signal. High frequency components higher than the cutoff frequency are filtered out. The digital weight signal obtained from the ΔΣ ADC 7 is input to the CPU 5, and the digital weight value is displayed on the display 6 via the interface 10.

Here, the cut-off frequency of the digital filter 7B in the ΔΣ ADC 7 is set and changed as follows. First, the shift key of the keyboard 9 is operated in the + direction or the-direction, and the CPU 5 is operated.
The value of the select signal s output from the filter characteristic control means 5A is changed. As a result, the frequency division ratio of the frequency dividing circuit 8 changes, the frequency of the clock ck generated by the frequency dividing circuit 8 changes, and accordingly, the thinning cycle of the signal in the digital filter 7B changes. The cutoff frequency is changed. The measurement is performed under the changed cutoff frequency, and the fluctuation (flicker) of the display output on the display 6 is observed. By weighing while changing the cutoff frequency by repeating the operation of the keyboard 9, the output fluctuation is observed, and the optimum cutoff frequency is obtained from the speed of convergence of the fluctuation. Thus,
The cutoff frequency in the digital filter 7B can be easily set to an optimum value.

Of course, without observing such output fluctuations, the cutoff frequency which is considered optimal may be set in anticipation. Further, the cutoff frequency can be changed according to the weight of the object to be weighed. For example, when an object to be weighed is in a certain weight range, a cutoff frequency corresponding to the object is predicted and stored in preset means, and this is performed for various weight ranges, and the weight of the object to be weighed is measured at the time of weighing. Call the cutoff frequency corresponding to the range. This makes it possible to easily change the cutoff frequency according to the weight of the object to be weighed.

Although the setting and change of the cutoff frequency are performed prior to the weighing, the cutoff frequency may be set during the weighing operation. For example, when the display output of the display 6 becomes unstable because the response is too fast in a state where the object to be weighed is placed thereon, the cutoff frequency is lowered to speed up the stability. Thereby, the weighing operation is performed smoothly.

FIG. 2 is a block diagram showing a second embodiment of the present invention. In FIG. 2, the difference from the first embodiment is that the digital filter 7 in the .DELTA..SIGMA.
Only the means for changing the setting of the cut-off frequency B is the same as that of the first embodiment, and the same components are denoted by the same reference numerals and detailed description thereof will be omitted.

In this embodiment, the frequency divider is not used, and the filter characteristic control means 5A of the CPU 5 supplies the above Δ
The numerical data signal d indicating the cutoff frequency is directly input to the frequency control means 7C inside the Σ-type ADC 7, and also in this case, similarly to the first embodiment, the cutoff frequency of the digital filter 7B is changed. Can be easily set and changed by the external command signal c from the keyboard 9.

[0022]

As described above, according to the present invention, a ΔΣ ADC having a built-in modulator and digital filter is provided.
Not only as an A / D converter, but also using its digital filter to change the filter characteristics, that is, the cutoff frequency, based on the command signal. Accordingly, the cutoff frequency suitable for each model can be easily and quickly set by performing a simple input operation.
In addition, versatility that it can be applied to a plurality of models by simply preparing one kind of ΔΣ ADC is obtained.

Further, since the cutoff frequency can be easily changed even during the weighing operation, the weighing operation can be smoothly performed. Further, the use of the ΔＤＣ type ADC makes it possible to reduce the cost as compared with the case where a conventional analog filter is used in combination with a double integration type or successive approximation type AD converter, and the double integration type ADC is used. There is also an advantage that the responsiveness is higher than that of the successive approximation type and a higher resolution (higher measurement accuracy) is obtained than that of the successive approximation type.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a weighing device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a weighing device according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a conventional weighing device.

FIG. 4 is a circuit diagram illustrating a schematic configuration of an analog filter in FIG. 3;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Load cell (weight detector), 5 ... CPU, 5A ... Filter characteristic control means, 7 ... DELTA. Type ADC, 7A ... Modulator, 7B ... Digital filter.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-238423 (JP, A) JP-A-63-39216 (JP, A) JP-A-1-101027 (JP, A) JP-A-3-3 102400 (JP, A) JP 2-12060 (JP, B2) WO 91/11687 (WO, A)

Claims (2)

(57) [Claims] 1. A weight detector for detecting the weight of an object to be weighed and outputting an analog weight signal, a modulator for modulating the analog weight signal into a digital weight signal, and a modulator responsive to a frequency of an input clock signal. delta and a digital filter having a cut-off frequency of the variable to eliminate high frequency components of <br/> SL digital weight signal,
The frequency of the clock signal is changed based on a sigma-type AD converter and an external command signal.
Change the cutoff frequency of the digital filter owl
Weighing apparatus comprising a filter characteristic control means Ru is. 2. The analog weight is detected by detecting the weight of the object to be weighed.
Weight detector that outputs a signal, Modulates the analog weight signal into a digital weight signal
Removes high frequency components of modulator and digital weight signal
Digital filter with variable cutoff frequency and cut
Having frequency control means for controlling the off-frequency
A sigma-type AD converter, and The numerical data signal is controlled based on the external command
Output to the control means to cut off the digital filter.
It has a filter characteristic control means for changing the frequency.
Weighing device.