JPH03181823A - Electronic weighing device - Google Patents

Abstract

PURPOSE:To accurately perform weighing by measuring the time interval of a predetermined number of pulses of the pulse signal from a V/F converter to calculate the frequency of the pulse signal. CONSTITUTION:A V/F converter 5 is constituted so as to output pulses of frequencies of 5kHz in the case of load 0g, 6.5kHz in the case of load 1,500g and linearly changing between both loads. When a power supply switch 8 is turned ON, a transistor Q is turned ON and a load detection means 2, the converter 5 and a microcomputer 6 are operated and the control of a zero point is carried out. Next, when an object to be weighed is placed on a weighing tray, the equilibrium of the bridge circuit of the means is collapsed and the micro-voltage corresponding to the wt. of the object to be weighed is generated. This micro-voltage is amplified by the amplifier circuit 3 of the converter 5 and converted to a pulse signal of frequency between 5 - 6.5kHz by a V/F converter circuit 4. Subsequently, the time intervals of 1,000 pulses from the converter 5 are counted by the microcomputer 6 and frequency and load are calculated and a load value is displayed on a display apparatus 9.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an electronic scale.

(Prior art) Electronic scales use a V/F converter to convert the output voltage from a strain gauge type or capacitance type load detection means into a pulse signal with a frequency corresponding to the voltage. A calculation processing device such as a computer measures the frequency of this pulse signal to determine the load, and this load value is displayed on a display device.

Conventionally, the frequency of the pulse signal output from the V/F converter can be measured using two methods: directly counting the number of pulses over a certain period of time, and measuring the wavelength of the pulse and determining the frequency from this wavelength. Normally, the display device of a weighing machine takes 0.5 seconds at most! This measurement must be completed within 0.2 seconds because the display must be changed each time.

(Problem to be Solved by the Invention) When the former method is adopted for a small household weighing device that can weigh up to 150 og with a required accuracy of 0.1 g, the required accuracy is 0.1 g.
Since 150010.1=15000 pulses must be measured in 2 seconds, the output frequency of the V/F converter must be at least 61500010.2=75 KHz. Actually, even if the weight is Og, the output of the V/F converter is not OHz, so if this is set to 25KHz,
It must be able to output a pulse signal with a maximum frequency of 25KHz+75KHz=100KHz. in this way,
The higher the frequency of the output pulse signal of the V/F converter, the greater the degree of amplification in the amplifier circuit in front of the V/F converter must be. It is necessary to provide a very small amplification circuit, which poses a problem in that it is expensive. Further, the oscillation circuit of the V/F converter also has a problem in that the higher the frequency, the more difficult it becomes to obtain linearity between the input signal voltage and the output frequency.

On the other hand, when adopting the latter method of determining the frequency of a pulse signal from its wavelength, the minimum unit measurement time is 1 when measuring with an IMHz signal obtained by dividing the normal 4MHz clock by 4.
Therefore, to ensure the above accuracy, the wavelength τ is at least 150010.1×1μ5−15m5, which is 67H.
It must have a low frequency output of z. In this case,
A capacitor with a large capacity and low leakage current must be used, resulting in an expensive problem.

The present invention has been made in view of such problems, and an object of the present invention is to provide an electronic weighing device that can perform accurate weighing using an inexpensive V/F converter of several KHz.

(Means for Solving the Problem) In order to achieve the above object, the present invention includes a load detection means that outputs a DC voltage according to the load of an object to be weighed, and an output voltage from the load detection means that outputs a DC voltage according to the load of the object to be weighed. A V/F' converter converts the pulse signal into a pulse signal with a frequency of The device is equipped with an arithmetic processing device that calculates the calculated load and displays it.

(Example) Next, one embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a circuit diagram of an electronic weighing device according to the present invention,
In the figure, 1 is a battery serving as a power source, 2 is a load detecting means which constitutes a Blitzno circuit with four strain gauges attached to an elastic flexural body of the scale body (not shown), and 3 is a load detecting means of the load detecting means 2. An amplifier circuit 4 that amplifies the output voltage is a V/P conversion circuit that converts the DC voltage amplified by the amplifier circuit 3 into a frequency, and together with the amplifier circuit 3 constitutes a V/F converter 5. Reference numeral 6 designates a microcombisuiter (hereinafter referred to as a microcomputer) constituting an arithmetic processing unit, 7 a 2 KHz original oscillator, 8 a power switch, and 9 a display device for displaying load values.

The battery 1 supplies current to the load detection means 2, the amplifier circuit 3, the V/F conversion circuit 4, and the microcomputer 6 via the transistor Q.

The V/F converter 5 has a frequency of 5 kHz at a load of Og, and a load of 15
It is designed to output a pulse signal with a frequency of 6.5 KHz at 00g and a frequency that changes linearly during that time.

The microcomputer 6 detects the rising edge of the pulse signal from the V/F converter 5 and an internal counter ti that counts a basic signal obtained by dividing the 2 MHz clock signal from the original oscillator 7 by four using the frequency divider circuit 10. V/F converter 5 according to the built-in program.
The frequency of the pulse signal from is determined, the load is calculated, and the load value is output to the display device 9.

That is, as shown in FIG.
After adjusting the zero point with OI, the event counter 12 is set in step 5t02, and if the sixth pulse, which is the measurement start time, is detected in step 5103, step 5
At step 104, the internal counter 11 is set. Then, if the 1000th pulse, which is the measurement end time, is detected in step 5105, the internal counter l! is detected in step 5106.
After taking in the count value n and converting it into a frequency n in step 5107, the load W is calculated in step 5108, the load value is output in step 5109, and the process returns to step 5102 to repeat the above steps. It has become.

As mentioned above, the pulse signal output from the V/F converter 5 is 5 KHz at a load of Og and 6.5 KHz at a load of 1500 g.
KHz, so the period is 200μsS each.
The time interval for 1000 pulses is 200+++s at a load of 0g, and approximately 154s at a load of 150 og.
It is m5. During this time interval of 1000 pulses, the internal counter 11 counts a basic signal of 500 KH2 (period 2 μS) obtained by dividing the 2 MHz clock from the original oscillator 7 by 4. This count value n is 00000 when the load is Og, and 769 when the load is 1500g.
It will be 23. When this count value n is converted into a frequency using the following formula (■), it becomes 80,000 with a load of Og. It is 104,000 at a load of 150 og.

a+=8X10''/n ·-■ Therefore, the load of the unknown object to be weighed can be calculated using the following formula 0.

v-(m-80000)x1500/24000...■ Therefore, the accuracy of this scale ffl is 0.062 per unit.
5, which satisfies the required accuracy of 0.1 g.

Further, if an error of the basic signal l occurs in the count value n, for example, when the load Og becomes n-100001 or 99999, m=79999 or 80000. Similarly, with a load of 1500g, n=76922 or 769
24 mag, m=104001 or 103
It becomes 998. Therefore, the converted frequency m has a maximum error of 1 when the load is around 0g and a maximum error of 2 when the load is around 1500g, but this corresponds to 0.0625g and 0.125g, respectively, and has sufficient accuracy for practical use, equivalent to the measurement unit. It is.

In the electronic scale having the above configuration, the power switch 8
When turned on, the transistor Q is turned on and the load detection means 2. The V/F converter 5 and the microcomputer 6 begin to operate, and the microcomputer 6 holds the transistor Q in the on state, and the absolute value of the detected weight when the power is turned on is set to "Og", and zero point adjustment is performed. .

Next, when an object to be weighed is placed in a weighing recess attached to a strain body (not shown), the strain body is displaced and the strain gauge is distorted.
As a result of the bridge circuit being unbalanced, a minute voltage is generated depending on the weight of the object to be weighed. This minute voltage is amplified by the amplifier circuit 3 of the V/F converter 5, and then 5KH by the V/F converter circuit 4.
z to 6.5 KHz. Then, the microcomputer 6 outputs 1 from the V/F converter 5.
The time intervals of 000 pulses are counted, the frequency side load W is determined based on this, and this load value is output to the display device 9. Thereby, the load value of the object to be weighed is displayed on the display device 9.

(Effect of the invention) As is clear from the above explanation, according to the present invention, V/
Since the frequency of the pulse signal is determined by measuring the time interval of a predetermined number of pulse signals from the F converter, a V/F converter with an output of several KHz can be used. In addition to being inexpensive, it has the effect of providing the same accuracy as the Habo measurement unit.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an electronic weighing device according to the present invention, and FIG. 2 is a flow chart of a microcomputer. 2...Load detection means, 5...V/F converter, 6...
- Arithmetic processing unit, 9... display device.

Claims (1)

[Claims] (1) A load detection means that outputs a DC voltage according to the load of the object to be weighed, a V/F converter that converts the output voltage from the load detection means into a pulse signal of a frequency corresponding to the output voltage, and A calculation processing device that measures the time interval of a predetermined number of pulses of the pulse signal from the /F converter, calculates the frequency of the pulse signal from the reciprocal of the measured time, calculates the load, and displays this. An electronic weighing device characterized by: