JPS6180399A - Signal processing circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a signal processing circuit used, for example, in a Karman vortex flow meter that measures the flow rate of intake air taken into an automobile engine.

[Conventional technology]

As a device equipped with a signal processing circuit that processes signals that fluctuate over a wide range from low frequencies to high frequencies and that contain various noise components, this device utilizes Karman vortices as a means of measuring the intake air flow rate of engines. There is a Karman vortex flowmeter.

This Karman vortex flowmeter has a flow path 21 as shown in FIG.
A vortex generator 1 is installed approximately perpendicularly to the intake air flow along the inner path.
A Karman vortex 19 is generated downstream of this vortex generator 18 in response to the intake air flow rate, and this Karman vortex 19 is detected by a hot wire type vortex detector located downstream of the vortex generator 18. 2 is used to detect the generation frequency of the Karman vortex 19, and from this the intake air flow rate is detected.

A current is supplied to the hot wire 2 in advance so that it reaches a certain temperature, and the hot wire 2 is cooled every time the Karman vortex 19 passes through the hot wire 2. Therefore, at the same frequency as the generation frequency of the Karman vortex 19, The resistance value of the hot wire 2 fluctuates. In addition, the hot wire 2 constitutes a bridge circuit with other resistors,
The balance of the bridge circuit collapses according to the change in the resistance value of the hot wire 2, and this unbalanced voltage is input to the differential amplifier and amplified.
The output of this differential amplifier is input to a current amplifier, and current is supplied from this current amplifier so that the hot wire 2 has a constant temperature.

In addition, the output signal of the differential amplifier includes an AC change that occurs each time the Karman vortex passes, and a DC change that occurs because the intake air flow rate increases or decreases and the steady cooling state of the hot wire 2 changes. It changes as shown in Fig. 3 depending on the intake air flow rate.

The output signal of the differential amplifier is input to the signal processing circuit, and first the DC variation is cut by the bandpass filter circuit.
The desired rectangular wave is obtained by passing only the Karman vortex generation frequency band, amplifying this signal with an AC amplifier, and converting this amplified signal into a rectangular wave with a comparator. The intake air flow rate is determined by counting.

[Problem that the invention seeks to solve]

However, the change in the intake air flow rate taken into an automobile engine is extremely large, and it is also necessary to accurately measure the intake air flow rate in the minute flow range. Accurately detects the frequency of occurrence from low frequencies in low flow areas to high frequencies in high flow areas,
There is also a need for a signal processing circuit that can remove noise and create a desired rectangular wave that can be reliably counted. And, if a conventional signal processing circuit uses a bandpass filter circuit, it is necessary to switch filter characteristics depending on the flow rate, and this switching control is difficult.
There was a problem in that it was difficult to obtain a good signal over the entire flow range.

In a signal processing circuit disclosed in Japanese Patent Application Laid-Open No. 59-7215, a process is proposed in which a low-pass filter is operated only in a low flow rate range to prevent deterioration of the S/N ratio in the low flow rate range.

Therefore, an object of the present invention is to reliably remove noise from a signal that fluctuates over a wide range from low frequency to high frequency and contains various noise components, and to convert it into a desired rectangular wave signal. The object of the present invention is to provide a signal processing circuit with the following characteristics.

[Means for solving problems]

In order to solve the above problems, the present invention includes a plurality of filter circuits provided in parallel, each having different filter characteristics according to a frequency domain, and a plurality of filter circuits connected in correspondence with the filter circuits, each having a different filter characteristic according to a frequency domain. The signal processing circuit includes a plurality of comparators that convert the output signals of the comparators into pulse signals, and a synthesis circuit that synthesizes the output signals from the comparators.

Embodiment C] An embodiment of the present invention will be described below with reference to the drawings as an example in which it is applied to a Karman vortex flow meter.

As shown in FIG. 2, the Karman vortex 19 generated on the downstream side of the vortex generator 18 in the flow path 21 is detected by the hot wire type vortex detector 2. The configuration of the signal processing circuit of the Karman vortex flowmeter, which determines the flow rate from the Karman vortex generation frequency, is as shown in Figure 1, and includes a hot wire 2 forming a vortex detector, and a resistor 3.4.
．． Bridge circuit 1 composed of 5 and bridge circuit 1
a differential amplifier 6 that detects the unbalance of the differential amplifier 6; a current amplifier 7 that applies a current to the bridge circuit 1 based on the output signal of the differential amplifier 6; A flow rate range detection filter 81, a high flow rate range detection filter 82, a comparator 9 that compares the output waveform of each filter 81 and 82 with a predetermined threshold value to form a pulse signal, and the output of this comparator 9. An inversion circuit 10 that inverts a signal, an edge detection circuit 11 that detects the rising edge of the output waveform from the comparator 9 or the inversion circuit 10 and outputs a short pulse, and detects a Karman vortex 19 from the short pulse of the edge detection circuit 11. Flip-flop circuit 12 that creates a pulse signal synchronized with generation
It is composed of.

The filters 81 and 82 have frequency characteristics 8La and 82a as shown in FIG. 4, respectively. Further, the flip-flop circuit 12 is N.

It is composed of an R circuit, and the initial level at startup is set to L.
A circuit 13 for setting the level is added.

Further, the inverting circuit 10, the edge detection circuit 1, and the flip-flop circuit 12 constitute a synthesis circuit that synthesizes a signal in a low flow rate region and a signal in a high flow rate region.

In FIG. 1, the output signal outputted from the comparator 9 via the low flow rate detection filter 81 is represented by ■, the output signal ■ of the edge detection circuit 11 to which this output signal is directly input, and the output signal ■ The output signal of the edge detection circuit 11 inputted via the inversion circuit 10 is ◎, the signal outputted from the comparator 9 via the high flow rate detection filter 82 is ◎, and the output signal ◎ is directly inputted. The output signal of the circuit 11 is ■, and the output signal of the edge detection circuit 11 to which the output signal ◎ is input via the inverting circuit 10 is [F].
, the output signal of the flip-flop circuit 12 to which the above output signals ■, ◎, ■, and [F] are input is indicated by ◎.

The operation of the above configuration will be described below.

The hot wire 2 installed downstream of the vortex generator 18 placed in the flow path 2.1 is supplied with a current from a current amplifier 7 so as to reach a certain temperature in advance. At this time, each time the Karman vortex 19 passes through the hot wire 2, the hot wire 2 is cooled, so the resistance value of the hot wire 2 changes at the same frequency as the generation frequency of the Karman vortex 19, and accordingly the bridge circuit 1 is balanced. My body collapses. However, the unbalanced voltage of the bridge circuit 1 is immediately amplified by the differential amplifier 6, and the current amplifier 7 adjusts the current supplied to the bridge circuit 1 based on the output signal, so the temperature of the hot wire 2 remains constant. It is maintained.

The output signal of the differential amplifier 6 includes an AC change that occurs each time the Karman vortex 19 passes, and a DC change that occurs because the steady state of cooling of the hot wire 2 changes due to an increase or decrease in the flow rate. The flow rate changes as shown in Figure 3 depending on the flow rate.

As can be seen from FIG. 3, the output signal of the differential amplifier 6 has a different waveform depending on the flow rate change, and
The frequency also changes from low to high as the height changes, and in addition to the frequency components synchronized with the generation of the Karman vortex 19,
It has many frequency components as noise components. Although this noise component also differs depending on the flow rate, in this embodiment, a filter 81 for detecting a low flow rate region for low frequencies and a filter 81 for detecting a low flow rate region for high frequencies having frequency characteristics 81a and 82a shown in FIG. A detection filter 82 is provided, and each of the filters 81 and 82 functions to remove noise components according to the flow rate, and inputs the noise components to the comparator 9 at the next stage.

As shown in FIG. 5, the low flow rate detection filter 81 outputs a signal from which the noise component of the output signal of the differential amplifier 6 in the low flow rate area is removed according to the frequency characteristic 81a shown in FIG. A comparator 9 in the stage compares it with a predetermined threshold value, converts it into a pulse signal, and outputs an output signal (2). Furthermore, the frequency characteristic 81a of the low flow rate region detection filter 81 is the fourth one.
As shown in the figure, the output of the low flow rate detection filter 81 in the high flow rate range becomes small, and the comparator 9 at the next stage does not output a pulse signal in the high flow rate range.

Similarly, as shown in FIG. 6, the high flow rate detection filter 82 outputs a signal from which the noise component of the output signal of the differential amplifier 6 in the high flow rate area is removed according to the frequency characteristic 82a shown in FIG. A comparator 9 in the next stage compares it with a predetermined threshold value, converts it into a pulse signal, and outputs an output signal ◎. In addition, the frequency characteristic 82a of the filter 82 for detecting a high flow rate region
is as shown in FIG. 4, the output of the high flow rate detection filter 82 in the low flow rate range becomes small, and the comparator 9 at the next stage does not output a pulse signal in the low flow rate range.

Of the output signals obtained by each comparator 9 as described above, or ◎ is inputted directly to the edge detection circuit 11 and also inputted to the edge detection circuit 11 via the inversion circuit 10. Then, each error detection circuit 11 detects the rising edge of the direct output signal ■ from the comparator 9, or the rising edge of ◎, or the rising edge of the output signal of the comparator or the signal inverted by the inverting circuit 10 of ◎. Then, short pulse output signals ■, and ◎, or ■, and ■ are output.

If the output signals ■ and ◎ or ■ and 0 from the edge detection circuit 11 are input to the set terminal S and reset terminal R of the flip-flop circuit 12, When at least one of the output signals ■ and ■ from 11 is input, the flip-flop circuit 12 is turned on,
When at least either the output signal ◎ or [F] is input to the reset terminal R of the flip-flop circuit 12, the flip-flop circuit I2 is reset. In this way, the flip-flop circuit 12 is set and reset, and the output signals from the comparator 9 and ◎ are combined from the flip-flop circuit 12.
An output signal ◎ is output in which pulses are generated at a period synchronized with the generation of the Karman vortex 19 in the entire flow range.

FIG. 7 shows the process in which the output signal ■ obtained from the comparator 1 described above is outputted as the output signal ◎ from the flip-flop circuit 12 via the inverting circuit 10 and the edge detection circuit 11. Since there is no output from the high flow rate detection filter 82 in the low flow rate range, only the output signal from the comparator 9 on the low flow rate detection filter 81 side is output, and this output signal is directly , it is inverted again and input to the edge detection circuit 11, and when the rising edge of the signal is detected, short pulse output signals ■ and ◎ are output, and these output signals ■ and ◎ are used as flip-flop circuits. The signal is input to the terminal S and the reset terminal R, and the output signal ◎ is outputted as described above. Moreover, in the high flow range, conversely, there is no output from the low flow range detection filter 81, so only the output signal ◎ from the comparator 9 on the high flow range detection filter 82 side is output, and this output signal ◎ is directly Then, the signal is inverted and inputted to the edge detection circuit 11 to output short pulse output signals 0 and ■, and the flip-flop circuit 12 outputs an output signal ◎.

Furthermore, in the intermediate flow rate range, output is generated from both the low flow rate detection filter 81 and the high flow rate detection filter 82.
Output signals ■ and ◎ are both outputted from both comparators 9, and as mentioned above, they are input directly and inverted to the edge detection circuit 11, and the output signals ■ and ◎ and ■
and ■ are output, and the flip-flop circuit 12
is input. Note that these output signals ■ and ◎, ■ and 0 are signals obtained from the same Karman vortex 19, so the short pulses of output signals ■ and ■ are generated almost simultaneously,
Similarly, short pulses of the output signals ◎ and 0 are generated almost simultaneously. Therefore, the cent terminal S of the flip-flop circuit 12
The output signals 0 and ■ are input almost simultaneously to the reset terminal R, and the output signals ◎ and [F] are input almost simultaneously to the reset terminal R.

Then, as described in -, the flip-flop circuit 12 outputs the output signal ◎.

In this way, the flip-flop circuit 12 outputs 13) When at least one of the short pulses of the signal ■ or ■ is input to the set terminal S, it is set, and the output signal ◎ or [F] is set.
Since it is reset when at least one of the short pulses is input to the reset terminal R, the output signals of the pulses in the low flow rate region and the high flow rate region obtained from each comparator 9 and ◎ are combined, and the flip The output signal of the flop circuit becomes ◎. Therefore, from the flip-flop circuit 12, a pulse-like output signal ◎ having a frequency corresponding to the generation frequency of the Karman vortex 19 over the entire flow range is obtained.

Therefore, in the present embodiment, the low flow rate detection filter 81 and the high flow rate detection filter 82, which have frequency characteristics according to each flow rate range, convert the signal from the differential amplifier 6 into appropriate signals according to each flow rate range. The noise component is removed, and the output signal or ◎ of the pulse corresponding to the generation frequency of the Karman vortex 19 in each flow rate region is reliably detected via the comparator 9, and the ◎ of this output signal is detected by the inversion circuit 10 The edge detection circuit 11 and the flip-flop circuit 12 combine the processes described above to obtain an output signal ◎ over the entire flow rate range, and this output signal ◎ corresponds to the frequency at which the Karman vortex 19 occurs in each flow rate range. Since it is a composite of the signals ◎, a stable pulse signal can be obtained over the entire flow range, and therefore the accurate intake air flow rate can be calculated by counting this pulse signal (output signal ◎). It is measured by

Note that if the signal from the differential amplifier 6 is a low frequency signal in a low flow rate range and this signal contains high frequency noise, the signal from the low flow rate range detection filter 81 is synchronized with the Karman vortex 19. The resulting signal is input to the next-stage comparator 9, and the high-frequency noise contained above the signal is outputted from the high-flow range detection filter 82, and is input to the next-stage comparator 9. However, since the amplitude of this high-frequency noise is extremely small, the predetermined threshold value of the comparator 9 in the next stage is set higher than the high-frequency noise, and the Karman vortex 1 output from the high-flow rate detection filter 82 in the high-flow rate area is
If the signal is set lower than the signal synchronized with the occurrence of 9, high frequency noise in the low flow rate region can be reliably removed.

In the above-described embodiment, the filter 81 for detecting a low flow rate region and the filter 82 for detecting a high flow rate region 2 are in charge of each flow rate region.
Although three or more filters may be provided, filter circuits 81 to 8n each having different frequency characteristics are connected in parallel as shown in FIG. Inversion circuit 10, edge detection circuit 1
1, and a flip-flop circuit 12 inputting the entire output of this edge detection circuit 11 may be provided so that each filter circuit 81 to 8n is in charge of each flow rate range. By removing the noise component of the Karman vortex signal in each flow rate region and obtaining a desired pulse signal, it is possible to measure the intake air amount more accurately.

Further, although the flip-flop circuit 12 in the above embodiment is constructed of a NOR circuit, it may be constructed of other logic circuits such as an AND circuit.

〔Effect of the invention〕

As described above, in the present invention, a plurality of filter circuits are provided in parallel, each having different filter characteristics according to a frequency domain, and a plurality of filter circuits are connected correspondingly to the filter circuits, and the output signal from the filter circuit is Since the signal processing circuit is characterized in that it is equipped with a plurality of comparators that convert the signals into pulse signals and a synthesis circuit that synthesizes the output signals from the comparators, each of the filter circuits can be configured according to its filter characteristics. Since a plurality of the filter circuits are provided so as to cover the entire frequency domain, noise components in the frequency domain are reliably removed. An output signal from which noise components have been removed is obtained, this signal is converted into a pulse signal by a comparator, and the resulting output signal is synthesized by a synthesis circuit and is obtained as a stable pulse signal over the entire frequency range. Therefore, signals that fluctuate over a wide range from low frequency to high frequency and contain various noise components are reliably noise-removed, and are converted into the desired pulse signal and output. effective.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing the main part configuration when an embodiment of the present invention is applied to a Karman vortex flowmeter, and Fig. 2 shows the state of the Karman vortex generated by the vortex generator provided in the flow path. Figure 3 is a waveform diagram showing the output signal from the differential amplifier,
Fig. 4 is a characteristic diagram showing the frequency characteristics of the filter for detecting a low flow rate region and the filter for detecting a high flow rate region;
l is a waveform diagram showing the output signal of the filter for low flow rate detection and the output signal processed by the comparator, Figure 6 (a+, (bl) is the output signal of the filter for high flow rate detection and the signal processed by the comparator. 7 is a signal time chart showing how the output signal ◎ of the output signal from the comparator is synthesized to obtain the output signal ◎ of the flip-flop circuit. 81.82.8n... Filter circuit, 9... Comparator, 10... Inversion circuit, 11... Edge detection circuit. 12...・Flip-flop circuit.

Claims (2)

[Claims] (1) A plurality of filter circuits provided in parallel, each having different filter characteristics according to a frequency domain, and a plurality of filter circuits connected in correspondence with the filter circuit and converting the output signal from the filter circuit into a pulse signal. A signal processing circuit comprising: a comparator; and a synthesis circuit that synthesizes output signals from the comparator. (2) The synthesis circuit includes an edge detection circuit that detects rising and falling signal changes of the pulse signals output from the plurality of comparators, and outputs a short pulse signal in response to this; 2. The signal processing circuit according to claim 1, further comprising a flip-flop circuit that is set and reset by inputting a short pulse signal output from the circuit.