JPH0224451B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a measuring device that removes noise components contained in a measuring signal, and more particularly to a measuring device that continuously variably controls a cutoff frequency using a pulse signal according to signal changes.

BACKGROUND OF THE INVENTION Various measuring devices have been considered in the past depending on objects to be measured, and one of them is a weighing device that measures the weight of an article.

In this type of weighing device, a measurement cell, which is a scale, is used to obtain an analog measurement signal corresponding to the weight of the object to be measured. It contains various noise components such as noise generated from each electrical circuit that makes up the cell and excessively damped vibration of the measurement cell.

Conventionally, in the above-mentioned measuring devices, a fixed frequency low-pass filter or a variable frequency low-pass filter has been used on the output side of the measurement cell as a means to remove noise components contained in analog measurement signals. What I used (Utility Model 55-154440
There are also microfilms using a variable time constant filter circuit (microfilms related to Japanese Utility Model Application Laid-open No. 134640/1983).

However, in the former case, which uses a fixed frequency low-pass filter, the cut-off frequency of the low-pass filter is set low in order to obtain a large noise rejection ratio, but this increases the delay time and There is a problem in that it takes a long time to obtain an analog measurement signal from the low-pass filter after the weight of the object has been measured and the measurement cell has reached a stable state.

On the other hand, those using a variable frequency low-pass filter include a variable frequency low-pass filter and an A-D conversion circuit on the output side of the measurement cell.
In addition, a balance detection circuit is provided between the output of this A-D conversion circuit or the output side of the measurement cell and the filter, and this balance detection circuit compares the previous weight value and the current weight value, and calculates both weight values. The low-pass filter is configured to be switched to a lower frequency when the balance is lost during this period.

However, in this weighing device, the cut-off frequency of the filter is switched in only two steps, high and low, so the response is poor like the fixed frequency type.
There is a problem that it lacks versatility because it is difficult to change the frequency to a frequency other than the frequency range.

Furthermore, the latter type that uses a variable time constant filter circuit has a switch on the output side of the measurement cell.
A variable time constant filter circuit using a CR circuit element that switches the CR time constant is provided, and when the voltage difference between the input and output terminals of this filter circuit is small, the time constant of the filter circuit is set large; When the time constant of the filter circuit is large, the time constant of the filter circuit is set small.

However, since the circuit elements of this filter circuit are composed of passive filters (RC filters), the attenuation factor Q in the transmission characteristics becomes small, the out-of-band cutoff characteristics become very poor, and the cut-off frequency of the filter is high. Since it is a two-stage low switching,
As mentioned above, responsiveness is poor. Furthermore, since the configuration uses a switch to switch the CR element, the entire device becomes complicated and complicated when switching in multiple stages.
There is a problem that it is expensive and generates switching noise during switching. In addition, some of these conventional examples use circuit elements with voltage-dependent characteristics such as diodes and varistors, but since the characteristics of these circuit elements are uniquely fixed by the voltage applied to both ends, control There is a problem that the characteristics cannot be varied continuously.

The present invention has been made to eliminate the above-mentioned problems, and the cutoff frequency of the filter can be continuously varied according to the magnitude of change in the analog measurement signal containing noise components, thereby increasing the noise rejection ratio. It is an object of the present invention to provide a measuring device that is large and capable of measuring with a fast response speed.

Below, the basic configuration when the measuring device according to the present invention is applied to, for example, a weight measuring device will be explained in the first part.
This will be explained with reference to FIGS. FIG. 1 is a diagram showing the basic configuration applied to a weight measuring device, FIG. 2 is a diagram embodying a part of the device in FIG. 1, and FIG. 3 is an operational waveform diagram of the device in FIG. 1.

In FIG. 1, reference numeral 1 denotes a measuring cell such as a weighing device, and an object to be measured 3 is placed on a mounting table 2 of this measuring cell 1. As shown in FIG. This measurement cell 1 outputs an electrical analog measurement signal according to the amount of downward displacement of the support arm 4 that supports the mounting table 2, and uses, for example, a differential transformer.

Since the analog measurement signal representing the weight measured by this measurement cell 1 has a small signal level, the signal is amplified by an amplifier 5 and then passed through an externally controlled filter 6.
sent to. This externally controlled filter 6 is a filter that can continuously vary the cutoff frequency by receiving a control signal from the outside, and by continuously varying the cutoff frequency, mechanical vibrations and disturbance noise contained in the analog measurement signal are reduced. Remove noise components such as

Furthermore, an A/D conversion circuit 7 is connected to the output side of the externally controlled filter 6 to digitize the analog measurement signal from which noise components have been removed. The weight value is displayed here.

By the way, the basic idea of this device is to connect a comparator circuit 9 between the input terminal and output terminal of the externally controlled filter 6, and to use the comparator circuit 9 to detect both the input terminal and the output terminal of the filter 6. The cut-off frequency of the externally controlled filter 6 is continuously varied by detecting a signal difference, converting it into a control signal proportional to the difference signal, and applying this control signal to the filter 6. At this time, for example, a voltage-controlled filter is used as the externally-controlled filter 6. Further, the comparison circuit 9 uses, for example, a differential amplifier 91 as shown in FIG. 2, the gain of which can be adjusted by varying the resistance R.

Therefore, for example, by measuring the weight of the object to be measured 3, the measurement cell 1 outputs an analog measurement signal that exhibits a steep rise characteristic as shown in FIG. 3A, and then converges due to damped vibration. and,
When a conventional fixed-frequency low-pass filter is used, an output waveform as shown in FIG. 3B is obtained. As is clear from these waveforms, although the waveform in figure A has a steep rising characteristic, the waveform in figure B has a slow rising characteristic, as shown in figure A. Although the noise component contained in the analog measurement signal has been completely removed, it can be seen that it takes a long time to reach the level St corresponding to the true weight value. Incidentally, since the variable time constant filter or variable frequency filter described in the conventional example also uses a two-stage switching system, the response characteristic at the rise does not change much.

On the other hand, the basic configuration of the device of the present invention is such that when a signal as shown in FIG. Since the signal voltage difference between the
When a control signal Sco as shown in FIG. C is outputted and supplied to the externally controlled filter 6, the filter 6 controls the cutoff frequency to a large value in accordance with the voltage value of the control signal Sco, since the voltage value of the control signal Sco is large.

Due to this control, the output of the externally controlled filter 6 follows the analog measurement signal of FIG. 3A with a small feed time, so that it has a waveform as shown in FIG. 3D. Then, when the voltage rises relatively quickly as shown in FIG. As the weight decreases, it quickly reaches the level St corresponding to the true weight value and becomes stable. Figure 3C
BV indicates the bias voltage, which is the filter 6
A control signal Sco having a predetermined voltage is output from the comparator circuit 9 even if the voltage difference between the input and output terminals of
This is an attempt to define the lower cutoff frequency.

However, the device that adopts the basic configuration described above is explained in the case where a voltage control type is used for the externally controlled filter 6, but in this case, it is faster than the conventional device in terms of measurement time and response. Although it is excellent, it still leaves a lot to be desired in terms of detecting changes in the measurement signal and setting the desired cutoff frequency.

Therefore, the apparatus of the present invention is realized based on the basic configuration shown in FIG. 1, using a pulse-controlled filter whose cut frequency is continuously variable as the externally-controlled filter 6. As this pulse control type filter, for example, a switch capacitance filter or the like is used. Further, as the comparison circuit 9, in addition to the circuit shown in FIG. 2, for example, a pulse conversion circuit for converting into a pulse signal of a frequency proportional to the difference signal between the input and output of the filter 6 is provided. Therefore, the comparison circuit and pulse conversion circuit shown in FIG. 2 constitute a pulse signal conversion means. Moreover, a conventionally known pulse signal conversion circuit may be used as this pulse signal conversion means.

Therefore, according to the above configuration, after obtaining a pulse signal with a frequency proportional to the difference signal between the input end side signal and the output end side signal of the externally controlled filter 6 as the control signal Sco, this control is performed. When the signal Sco is supplied to the externally controlled filter 6, the externally controlled filter 6 continuously varies the cutoff frequency according to the pulse frequency and sets it to a desired value, thereby eliminating vibration caused by changes in the measurement signal. It is possible to quickly shift to a stable state according to the weight value by removing not only noise but also various noise components, and it is possible to further improve responsiveness compared to the voltage control type.

Note that the present invention is not limited to the above embodiments. Although a specific circuit is shown in FIG. 2 as the comparison circuit 9, it may have a configuration as shown in FIG. 4, for example. That is, this comparator circuit 9 includes a differential amplifier 91 (no bias) having a gain adjustable means, and a differential amplifier 91 (no bias) that has a means for adjusting the gain.
an absolute value circuit 92 that outputs a positive voltage when a negative direction signal is output from 1; and a bias adjustment section 9 for defining a lower limit cutoff frequency.
3, a clip circuit 94 for defining the upper limit cutoff frequency, and a log amplifier 95 that compresses or expands the control signal output from the clip circuit 94 to vary the rise characteristics. Alternatively, one or more of the above elements 91 to 95 may be combined. Also,
Although the measurement cell 1 has been described using a differential transformer, it can be any cell as long as it converts a physical quantity into an analog electrical signal, such as a piezoelectric element or a photoelectric element. Of course, the physical quantity of the object to be measured may be other than weight, and the present invention can be applied to anything that handles analog signals containing noise components.

In addition, the present invention can be implemented with various modifications without departing from the gist thereof.

As explained above, according to the present invention, when filtering out noise components included in analog measurement signals of objects to be measured, such as weight, pressure, flow rate, etc., a pulse control type filter is used, and the input/output of this filter is A pulse signal corresponding to the signal difference between the two is supplied as a control signal to a pulse control type filter,
When the input signal to the filter changes rapidly, a high-frequency pulse signal is applied to the filter to increase the cutoff frequency, and conversely, when the signal changes are small and stable, the cutoff frequency is controlled low. It is possible to remove noise components by continuously and rapidly varying the cutoff frequency according to the magnitude of the noise component. Moreover, when the input signal changes drastically due to noise components, the cutoff frequency is set high, so the filter output quickly follows the changes and becomes stable. Moreover, since it is a pulse control type, it can be cut off in a relatively short time. A desired cutoff frequency can be set. For example, when measuring the weight of a large number of products, this can significantly shorten the measuring work time and greatly contribute to improving the efficiency of the measuring work. Further, since the cutoff frequency is automatically controlled to be low when a stable state is reached, it is possible to provide a measuring device that can increase the noise component removal ratio and measure physical quantities with high precision.

[Brief explanation of drawings]

1 to 3 are shown to explain the basic principle applied to the device of the present invention. FIG. 1 is a diagram explaining the basic principle, and FIG. FIG. 3 is an operational waveform diagram illustrating FIG. 1, and FIG. 4 is a configuration diagram showing another example of the comparator circuit. 1...Measurement cell, 2...Placement table, 3...
Object to be measured, 6... Externally controlled filter, 7...
A/D conversion circuit, 8...display section, 9...comparison circuit.

Claims (1)

[Claims] 1. A measuring device that measures a physical quantity of an object to be measured and extracts the measured value as an analog measurement signal, an externally controlled filter having a variable cutoff frequency in order to remove noise components contained in the analog measurement signal; The input signal and output signal of this externally controlled filter are compared, the difference signal is converted into a pulse signal proportional to the signal, and this pulse signal is used as a control signal to continuously vary the cutoff frequency of the externally controlled filter. A measuring device comprising: pulse signal converting means, and varying the output response speed of the externally controlled filter.