JPH06241879A - Weighing apparatus having digital indicator - Google Patents

Abstract

PURPOSE:To markedly reduce current consumption of an A/D convertor of the title apparatus. CONSTITUTION:The title apparatus comprises an exchanging function of two or more resolutions whereby a first A/D convertor 1 having a resolution required for attaining the prescribed accuracy and a second A/D convertor 2 having a resolution lower than that of the first A/D convertor are exchanged. The second A/D convertor 2 having the rough resolution is normally activated to detect fluctuation of a weight. On the basis of the fluctuation of the weight, the A/D convertors are exchanged. Only when it is needed to attain the accuracy, the first A/D convertor 1 is activated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to reducing power consumption of an electronic digital display weighing scale.

[0002]

2. Description of the Related Art Conventionally, a battery-operated digital display weighing scale operates an A / D converter for a time shorter than a display cycle in order to reduce current consumption, and a part of the display cycle operates the A / D converter. By stopping, the average current consumption due to A / D conversion is kept low. FIG. 1 shows a basic configuration example thereof, FIG. 2 shows a timing chart of A / D conversion, and FIG. 3 shows a flowchart thereof.

The A / D converter is controlled by a control terminal Va, and when Va = 0V, the A / D conversion is stopped and A / D conversion is stopped.
The current consumed by D conversion is close to zero. When Va = Vdd, A / D conversion is performed, and the result is processed by the arithmetic unit and displayed. As shown in FIG. 2, Va is switched between 0V and Vdd so that a short sampling time t is obtained with respect to the sampling interval T, and the average current of the A / D converter is reduced.

As shown in the flowchart of FIG. 3, A / D conversion is performed at time t to obtain a display reference value at the time of start-up or tare setting, and the A / D conversion result (sampling value) at that time is stored. Stored in device, A / for T-t time
The D conversion is stopped, the current consumption during that period is reduced, and then A / D conversion is performed at time t, and the difference from the display reference value is converted into weight and displayed. By repeating this, the measured values of the scale are continuously displayed at the display interval T.

[0005]

However, the A / D conversion time cannot be shortened too much in order to obtain the resolution necessary to ensure the accuracy, while if the sampling time is too short, the load will be reduced. There is also a problem that it is easy to obtain an incorrect measurement value when the
It was difficult.

Generally, in order to obtain high resolution, the drive current of the sensor and the A / D converter is required to some extent, and if the current consumption is reduced, it is inevitable that the accuracy and resolution will be reduced. It is extremely difficult to reduce the drive current while maintaining high resolution.

However, for the weighing scale, it is necessary to ensure the accuracy only when obtaining the no-load value or the tare amount (when obtaining the reference value for measurement) and when obtaining the weight value of the load.
Most of the others are sensors and A / D that can ensure accuracy.
It is sufficient to be able to determine when it is necessary to operate the converter.

[0008]

A first A / D conversion function having a resolution sufficient to ensure accuracy for obtaining a reference value for measurement and a weight value for load, and detecting a change in load, An A / D conversion function having two or more resolutions with a second A / D conversion function having a coarser resolution than the resolution of the first A / D conversion function for deciding when it is necessary to ensure accuracy. When it is necessary to secure the accuracy by operating the second A / D conversion function, which is usually a coarse resolution, to detect the change in the load and switch the A / D conversion function based on the change in the load. Only the first A / D conversion function is operated.

[0009]

[Function] Two A / D conversions of the high resolution / high accuracy A / D converter shown in the circuit configuration of FIG. 4A and the low resolution / low accuracy A / D converter with low current consumption When switching the A / D converter (2), the control device normally connects the sensor to the A / D converter (2) of the A / D converter that consumes low current at the control terminal b instead of the coarse resolution. The control terminal a is a sensor and an A / D that is a high-resolution A / D converter.
The A / D (1) is stopped by disconnecting it from (1). As a result, the current consumption of the A / D (1) is normally zero.

When precision is required, the control terminal a connects the sensor to the A / D (1) to drive the A / D (1), and the control terminal b connects the sensor and the A / D (2). Separate A / D
(2) is stopped.

For most of the measurement cycle, only the low current consumption A / D converter operates, and the high precision high current consumption A / D converter operates only when it is necessary to secure a part of the accuracy. , The average current consumption is greatly reduced.

By switching the input voltage of the sensor shown in the circuit configuration of FIG. 4B, the A of one A / D converter is changed.
When the D / D conversion function is switched and used, an electric resistance wire type load cell is often used as a sensor of the weighing scale. Generally, the electric current consumption of the electric resistance wire type load cell is A / D.
The current consumption is larger than that of the converter, and it is effective to reduce the current consumption of this sensor in order to reduce the current consumption of the weighing scale.

Under the same load, the consumption current Ia of the electric resistance wire type load cell is proportional to the input voltage Va of the sensor, and the output voltage Vm of the sensor is also proportional to the input voltage Va. Normally, the control device controls the input voltage Va of the sensor to Va / n. Then the current consumption is Ia / n and the output voltage is V
Since m / n is obtained and the input voltage of the sensor is set to 1 / n, an A / D conversion result with a consumption current of 1 / n and an accuracy of 1 / n can be obtained. When precision is required, the input voltage is kept at Va at the control terminal.

A high-resolution, high-precision A / D converter and a low-resolution, low-precision A / D that consumes less current
As in the case of switching between two A / D converters with the converter, most of the measurement cycle is low current consumption and low resolution A / D converter.
A / D conversion is performed and only a part of the high-precision A / D conversion function is operated, and current consumption is significantly reduced.

When the A / D converter is a CR oscillator, a VF converter, or the like, and the output is frequency, by switching the sampling time of the A / D conversion shown in the circuit configuration of FIG. The A / D conversion function of one A / D converter is switched. When the output of the A / D converter is a frequency, the frequency pulse number f is counted for a constant time t. Therefore, when the load is constant, the result value Cp of the A / D conversion is
Is proportional to the time t required for A / D conversion. V in the control device
a is time-controlled, and is usually A / with sampling time t / n
D conversion is performed to obtain a sampling value of Cp / n, and when accuracy is required, the sampling time is switched to t and A /
D conversion is performed to obtain a sampling value Cp.

Also in the case of the double integration type A / D converter which is widely used in weight scales, if the voltage output from the sensor is represented by Vg, the count number Cp is Cp = Vg / Vr * It is represented by N (N and Vr are constants). The A / D conversion time t at this time is represented by t = NTcl + Cp Tcl = NTcl (1 + Vg / Vr), where Tcl is one cycle of the reference clock. If N is N '= N / n, then C'p = C
p / n, t '= t / n, and the A / D conversion time is 1 / n
Then, the count number becomes 1 / n. Therefore, FIG. 4 (C)
The A / D conversion function of one A / D converter can be switched by switching the sampling time of the A / D conversion shown in the circuit configuration.

Va is time-controlled by the control device, and A / D conversion is usually performed at a sampling time t / n to obtain a sampling value of Cp / n. When accuracy is required, the sampling time is switched to t. A / D conversion is performed to obtain a sampling value Cp. Sampling time = A / D conversion time required to obtain resolution "1" x resolution. To obtain a resolution of 1 / n, the sampling time is 1 / n for the same load.
n is sufficient, and most of them operate the A / D conversion function of coarse resolution, so that the sampling time is shortened and the average current of A / D conversion is significantly reduced.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to a solar cell driven scale that is one embodiment of the present invention in which the effect is more effective as the current consumption decreases. FIG. 5 shows a flowchart and FIG. 6 shows a timing chart of A / D conversion.

In order to obtain the measurement reference at the time of starting (no load), the normal A / D conversion of the sampling time t is performed, the sampling result f0 is stored as the no load value, "0" is displayed, and the sampling time t A standby mode is performed in which the A / D conversion is performed with a coarse resolution of / n and the A / D conversion is repeated at the sampling interval T. When the Fx of the sampling result obtained successively in the standby mode does not change for a predetermined time, it is switched to the normal A / D conversion, the measurement standard is confirmed, the value is updated to a new value, and the mode is returned to the standby mode.

When the Fx of the sampling results obtained successively are compared and the value Fx (n) of this time greatly fluctuates with respect to the value Fx (n-1) of the previous time, and it is determined that the load fluctuates, the sampling time The normal A / D conversion of t is switched to, the A / D conversion is performed at a sampling interval T ′ shorter than T, and fw of the results obtained successively are compared.

When it is judged that there is no difference between the current fw (n) and the previous time fw (n-1) and it is judged to be stable, the difference from the measurement reference value f0, fw-f0, is converted into a load value. Then, the display is switched to the coarse resolution A / D conversion of the sampling time t / n, and the standby mode in which the A / D conversion is repeated at the sampling cycle T is returned.

After that, when the same operation as in the previous section, that is, when there is a change in load is detected, the sampling interval is changed, A / D conversion is switched, an accurate load value is measured and displayed, and the standby mode is set. Repeat the returning operation. When no difference is found between the accurately measured value and f0 and it is determined that there is no load, the process returns to paragraph number 0020.

In this embodiment, when the change of the load is detected, the resolution of the A / D converter is changed to the measurement mode. However, when the change of the load is detected in the standby mode, the sampling interval is short. Is displayed, indicating that the measurement is in progress, and A / D conversion with coarse resolution, that is, A / D conversion is performed with the sampling time t / n kept unchanged, the sampling value does not fluctuate, and the load becomes stable. When it is judged that the average consumption is the method that switches to the accurate measurement mode that performs A / D conversion at the normal sampling time t, measures and displays the accurate load value, and returns to the standby mode for coarse resolution A / D conversion. It is a more effective means for reducing the current.

The weight scale measures the load value when the load is unloaded and when the load is weighted (the person to be measured is placed on the weight scale) and is stable, and the load is about 100 to 1000 times the measurement accuracy. Since it is an object that is loaded in a short time, the resolution of the A / D converter for detecting load fluctuations is about 1/10 of the resolution of the A / D converter for determining the load value. Yes, the sampling time required for that is 1/10 of the sampling time for determining the load value and A / D
The average current of conversion is greatly reduced.

In the above, the case of applying to a weight scale driven by a solar cell has been described by taking a method of switching the A / D conversion function of one A / D converter by switching the sampling time of the A / D conversion. Depending on the purpose of use of the weighing scale, select the determination method when accurate measurement suitable for each purpose is required, and switch the A / D conversion function to make the consumption current of the desired weighing scale suitable for various purposes. Can be significantly reduced.

[0026]

As described above, the current consumption can be greatly reduced with a simple structure, and it becomes possible to obtain a product that obtains power from a solar cell or a microcomputer port that cannot expect a large current.
In addition, even in the case of portable use of dry batteries, it has a great effect that it becomes smaller and lighter, and if it has the same shape, it becomes a product that can be used for a long time.

[Brief description of drawings]

FIG. 1 is a block chart of a basic configuration of a conventional technique.

FIG. 2 is a conventional A / D conversion timing chart.

FIG. 3 is a flowchart of a conventional technique.

FIG. 4 is a circuit configuration diagram of the present invention.

FIG. 5 is a flowchart of an embodiment of the present invention.

FIG. 6 is an A / D conversion timing chart of the embodiment of the present invention.

FIG. 7 is a flowchart of another embodiment of the present invention.

FIG. 8 is an A / D conversion timing chart of another embodiment of the present invention.

[Explanation of symbols]

T sampling interval (standby) T'sampling interval (measurement) t sampling time n resolution ratio of the first A / D converter and the second A / D converter

Claims (3)

[Claims] 1. In a digital display weighing scale, a first A / D conversion function having a resolution necessary for ensuring accuracy and a second resolution having a coarser resolution than the resolution of the first A / D conversion function. The second, which has an A / D conversion function and an A / D conversion function with two or more resolutions, and is usually a coarse resolution
The A / D conversion function of is operated to detect the change in load,
A digital display weighing scale characterized in that the first A / D conversion function is operated only when it is necessary to switch the A / D conversion function based on a change in load and ensure accuracy. 2. By changing the input voltage of the sensor, A
The weighing scale according to claim 1, wherein the resolution of the / D converter is switched. 3. The weighing scale according to claim 1, wherein the resolution of the A / D converter is switched by changing the sampling time of the A / D conversion.