JPH0222525A - Electronic scale - Google Patents

Abstract

PURPOSE:To improve the accuracy of weight which can be weighed and to accurately weigh the weight of an object body by providing a weight- electrostatic capacity conversion part, an electrostatic capacity-frequency conversion part, a counter, and a microprocessor. CONSTITUTION:The weight-electrostatic capacity conversion part 1 converts the weight of the body to be weighed into corresponding electrostatic capacity and this electrostatic capacity is converted by the electrostatic capacity- frequency conversion part 2 into a pulse wave of corresponding frequency. Then, this frequency is multiplied, a next-stage counter 5 counts the increased frequency, and the microprocessor 6 performs weight conversion and outputs the result to a liquid crystal display part 8. Thus, the accuracy of the weight which is measured is improved and the weight of the object body is accurately measured.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Application The present invention relates to a capacitance type electronic balance υ, and includes a capacitance-frequency converter that outputs a change in capacitance as a change in oscillation frequency. It's about configuration.

←) Conventional technology An example of a capacitance type electronic scale is JP-A-53-51783.
As disclosed in the above publication, a dielectric plate is sandwiched between two plates, and the thickness of the upper E dielectric is changed by the load that compresses between the plates. 1 dielectric plate
a cell body configured with means for detecting the change in thickness as a change in capacitance of a capacitor with the dielectric plate as a dielectric between the electrodes; with an oscillator that converts the changes in.

A rate-of-change measuring circuit is provided for measuring the rate of change of the oscillation frequency and detecting the magnitude of the load.

However, in this example, the only part that converts changes in capacitance into changes in oscillation frequency is the so-called oscillator, and in order to improve detection accuracy, multiple dielectric plates are stacked, which causes the problem that the load cell part becomes larger. Kaauta.

The electronic scales described above generally operate at low voltage and current so that they can be used for long periods of time with a small number of batteries. Under such conditions, the operating speed of integrated circuits such as operational amplifiers that constitute the oscillation circuit becomes extremely slow. Therefore, the upper limit of the oscillation frequency is approximately several KI (z).Furthermore, the frequency of the oscillation circuit changes depending on the change in the capacitance of the weight-capacitance converter, but this change in capacitance is caused by the amount of N02. ~1# changes only about 20PF.

By the way, the accuracy of a weighing scale is improved if a slight change in capacitance is detected as a large change in frequency. For example 02
~1#, unless the frequency changes by 5oOHzL, the display can only be displayed every 2y, but if it is converted to 1000H2i, it can be displayed every 1y.

As mentioned above, the change in capacitance is determined by the structure of the load cell section, and the amount of change is extremely small. Therefore, in order to increase the amount of change in the frequency of the oscillation circuit, it is necessary to It is necessary to increase the frequency, but this frequency is limited to a low level by the operating speed of the operational amplifiers and other circuit components that make up the oscillation circuit, so as a result, the frequency does not change significantly. There was a drawback that it could not be used.

(c) Problems to be Solved by the Invention The problems to be solved by the present invention are to improve the accuracy of detected weight based on the slight capacitance change of the lid-capacitance converter. This is intended to increase the output frequency of the converter.

2) Means for Solving the Problem A weight-to-capacitance converter that detects the weight of an object to be weighed as a change in capacitance due to a change in the distance between electrode plates facing each other; a capacitance-frequency conversion section that converts the output of the capacitance conversion section into a pulse signal using an oscillation circuit included in the electrode plate; a counter that counts the number of output pulses of the capacitance-frequency conversion section; and a microprocessor for displaying a weight value on a display section according to a count value of a counter, and means for increasing the output frequency of the oscillation circuit is provided in the capacitance-frequency conversion section.

2) The working weight-to-capacitance converter converts the weight of the object to be measured into the corresponding capacitance, and the capacitance-to-frequency converter converts this capacitance into a pulse wave with the corresponding frequency. After that, this frequency is increased several times, the increased frequency is counted by a counter at the next stage, and this is converted into weight by a microprocessor and outputted to the display section.

(f) Examples The electronic scale of the present invention will be described in detail below with reference to the drawings.

FIG. 2 shows a basic block diagram (b) of an electronic scale.

In the same figure, (1) consists of a movable electrode plate that moves depending on the weight of the object to be measured, and a fixed electrode plate that is fixed.
ar, a weight-to-capacitance converter that detects the capacitance that changes due to changes in the distance between the electrode plates; (5) is a capacitance-to-frequency conversion section having an oscillation circuit (4) which forms a time constant circuit with the time constant circuit and oscillates at a frequency determined by the time constant circuit; A counter that counts the number of pulses of the oscillation output of section (2) at a predetermined sampling period; (6) is the counter (5);
A microprocessor calculates the counted value of , converts it into a weight value, outputs a weight signal, and outputs a cyclic coefficient from a built-in timer circuit. ), one input is connected to the output terminal of the capacitance-frequency converter (2), and the other input is connected to the clock terminal (CL) of the microprocessor (6). and an AND circuit that outputs an output to the counter (5); (8) a liquid crystal display unit that digitally displays a weight value corresponding to the weight signal from the microprocessor (6); It is a buzzer circuit that outputs a signal from the output terminal (BZ) of the microprocessor (6) when the weight value matches the setting value inputted by the switch circuit (IG) in the storage circuit in the microprocessor (6).

As shown in FIG. 1, the capacitance-frequency conversion unit (2) uses the oscillation circuit (4) and the output of this oscillation circuit (4) as one input, and branches the output of the oscillation circuit (4). and an exclusive OR circuit (131) which inputs the other input through a delay circuit consisting of a resistor (Ill) and a capacitor tiz.

In the electronic scale having the above configuration, the weight of the object to be weighed is determined by the capacitor (
3), and the oscillation output with a frequency determined by this capacitance value (position A in Figure 1 and waveform A in Figure 3)
) in the capacitance-frequency converter (2) oscillation circuit (
4) outputs. This output A is branched into two outputs and input to an exclusive OR circuit (13) either directly or via a resistor αD and a capacitor α21 (see position B in Figure 1 and waveform B in Figure 3). The output of the OR circuit (131 has a truth value (truth table)) Based on the table below, the output C generates an output pulse at the rising and falling edges of the large output, so as a result, the frequency of the large output is Therefore, the counter (5) is increased by two times.
The output C having twice the frequency is counted at a predetermined sampling period, and this counted value is input to the microprocessor (6) K. The microprocessor (6) displays the weight value on the display (8) K based on the counted value of the counter (5).

Note that the output waveform A of the oscillation circuit has a tutee ratio of 5096.
The closer it is, the more effective it is to double the frequency. Furthermore, an exclusive OR circuit (an integrated circuit with a 131tic-MO8 structure is common), and even a small current input of about 150/IA can sufficiently handle frequencies up to several tens of KHz.

(g) Effects of the Invention As described above, the present invention includes a weight-to-capacitance conversion unit that detects the weight of an object to be measured as a change in capacitance due to a change in the distance between electrode plates facing each other; a capacitance-frequency conversion section that converts the output of the weight-capacitance conversion section into a pulse signal using an oscillation circuit including the electrode plate; and a counter that counts the number of output pulses of the capacitance-frequency conversion section. and a microprocessor for displaying a weight value on a display section according to the count value of the counter, and the capacitance-to-frequency conversion section is provided with means for completely increasing the output frequency of the oscillation circuit. This has the effect of improving the accuracy of the weight that can be produced, and allowing the weight of the object to be weighed to be accurately measured.

[Brief explanation of the drawing]

FIG. 3 is a basic block circuit diagram of the child balance, and is a diagram showing output voltage waveforms of each part in FIG. 1. (1)...Weight-capacitance conversion section, (4)...Oscillation circuit, (2)...Capacitance-frequency conversion section, (5)...
... Counter, (6) ... Microprocessor, 0
31... Frequency increasing means.

Claims (1)

[Claims] (1) A weight-capacitance converter that detects the weight of the object to be weighed as a change in capacitance due to a change in the distance between electrode plates facing each other, and an output of the weight-capacitance converter that is A capacitance-frequency converter that converts into a pulse signal using an oscillation circuit including an electrode plate, a counter that counts the number of output pulses from the capacitor-frequency converter, and a weight displayed on the display based on the count value of the counter. 1. An electronic scale, comprising: a microprocessor for displaying a value, and wherein the capacitance-to-frequency conversion section is provided with means for increasing the output frequency of the oscillation circuit.