JPS62150167A - Semiconductor flow velocity detector - Google Patents

Abstract

PURPOSE:To fetch a flow velocity detection signal without pulsating components, by providing a circuit for subtracting pulsating components extracted from an output signal of a flow velocity element from the output signal. CONSTITUTION:A waveform processing circuit 3 made up of a pulsating component extraction circuit 31 which extracts pulsating components alone from an output signal Vc of a flow velocity detection element 1 and a differential circuit 32 which subtracts the pulsating components extracted with the circuit 31 from the signal Vc. An output adjusting circuit 4 comprises a differential amplifier using an operational amplifier 84 and a buffer circuit for zero-adjustment and gain adjustment using an operational amplifier 85. Here, the pulsating components extraction circuit 31 extracts pulsating components from the signal Vc of an element 1 and the differential circuit 32 subtracts the pulsating components from the signal Vc. Thus, a flow velocity detection signal without pulsation is fetched from the output adjusting circuit 4.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor flow velocity detector for detecting the flow velocity of a fluid, and particularly to improvements in its signal processing circuit section.

[Technical background of the invention and its problems]

An example of the configuration of a conventional semiconductor flow rate detector is shown in FIG. The semiconductor flow rate detection element 1 is formed by integrating a substrate temperature measuring transistor 5 and a heat generating transistor 6 on a single semiconductor substrate. Reference numeral 7 designates a transistor for measuring fluid temperature, which is provided separately from the flow rate detection element 1 and the like. The fluid temperature measuring transistor 7, the performance amplifier 81, and the constant current sources 91 and 92 constitute the drive circuit 2. This drive circuit 2 operates to drive the heat generating transistor 6 to 1ill so that the element temperature measured by the substrate temperature measuring transistor 5 of the detection element 1 is always a certain temperature higher than the fluid temperature measured by the fluid temperature measuring transistor 7. It is something to do. This flow rate detector utilizes heat dissipation by the fluid in the detection element 1, and uses, for example, the collector potential Vc of the heat generating transistor 5, which changes depending on the flow rate of the fluid, as a flow rate detection signal.

This detection signal is taken out via an output adjustment circuit 4 that performs zero adjustment and gain adjustment.

FIG. 6 is a response signal waveform of the flow velocity output vout of the flow velocity detector shown in FIG. The drive circuit 2 controls the current of the heat generating transistor 6 using the operational amplifier 81, but since this control is an on-2-off type control, the detection signal has a pulsating waveform. Therefore, for example, if a digital voltmeter is used to read the flow rate output, the displayed value will change with each sampling even if the flow rate does not change.
The problem was that it was difficult to accurately measure the flow velocity.

In order to obtain a direct current output instead of the pulsating waveform as described above, one method is to add a capacitor CI to the operational amplifier 81 in the drive circuit 2, as shown in FIG. It is conceivable to blunt the pairing drive signal waveforms. However, this method sacrifices response characteristics to changes in flow velocity in exchange for making the flow velocity output signal DC. That is, according to this method, a response characteristic as shown in FIG. 7 can be obtained in contrast to the response characteristic shown in FIG.

Another method for obtaining a DC output is to use a resistor Rf and a capacitor Re as shown in FIG.
It is also possible to add a filter consisting of: However, this method also sacrifices response characteristics.

As described above, the conventional semiconductor flow velocity detector has a problem in that it is not possible to obtain a stable DC output and an output with good response characteristics.

[Purpose of the invention]

The present invention has been made in view of the above points, and an object of the present invention is to provide a semiconductor flow velocity detector that has good response characteristics and is capable of obtaining stable DC output.

[Summary of the invention]

The semiconductor flow rate detector according to the present invention is provided with a circuit that extracts only the pulsating component from the output signal of the semiconductor flow rate detection element,
The present invention is characterized in that a circuit for subtracting the pulsation component extracted by this circuit from the output signal of the semiconductor fluid detection element is provided to obtain a flow velocity detection signal free of pulsation.

〔Effect of the invention〕

According to the present invention, a stable direct current flow velocity output signal can be obtained without impairing the response characteristics of the flow velocity detection element. Therefore, the accuracy of flow velocity measurement can be improved. Furthermore, since the response characteristics are not impaired, it can be applied to applications that require fast response characteristics, and the range of application of the semiconductor flow velocity detector is widened.

[Embodiments of the invention]

The present invention will be explained in detail below.

FIG. 1 shows a schematic configuration of an embodiment. Semiconductor flow velocity detection element 1, drive circuit 2 for driving it, and output adjustment circuit 4
The portion shown in FIG. 5 is the same as the conventional structure shown in FIG. In this embodiment, a waveform processing circuit 3 is provided between the flow velocity detection element 1 and the output adjustment circuit 4.

FIG. 2 shows a specific example of the configuration of the waveform processing circuit 3 and output adjustment circuit 4. In FIG. The waveform processing circuit 3 includes a pulsating component extraction circuit 31 that extracts only the pulsating component from the output signal Vc of the flow velocity detection element 1 (for example, a change in the collector potential of the heat generating transistor as described above), and The differential circuit 32 subtracts the pulsating component from the detection element output signal Vc. Pulsating component extraction circuit 31
is a type of band-pass filter configured using an operational amplifier 82, and the differential circuit 32 is a differential amplifier configured using an operational amplifier 83.

The output adjustment circuit 4 includes a differential amplifier using an operational amplifier 84 and a buffer circuit for zero adjustment and gain m adjustment using an operational amplifier 85.

FIG. 3 shows the response characteristics of the flow velocity detection signal according to this embodiment. As is clear from a comparison with FIGS. 6 and 7, according to this embodiment, a stable DC output from which only the pulsation component is removed is obtained as a flow velocity detection signal, and the responsiveness is not impaired.

FIG. 4 shows the main structure of another embodiment. In this embodiment, a buffer 10 using an operational amplifier 86 is inserted before the waveform processing circuit, and the output adjustment circuit 4 and the differential circuit 32 in front of it shown in FIG. 2 are used as the output adjustment circuit 4'. The operational amplifier 84 is shared and integrated. Other parts are the same as in the previous embodiment.

This embodiment also provides the same effects as the previous embodiment.

The present invention is not limited to the embodiments described above. For example, in all of the above examples, the collector potential of the heat generating transistor was used as the output signal of the semiconductor flow velocity detection element, but it is also possible to use the potential, voltage, current, etc. of other parts of the heat generating transistor that contribute to heat generation as the output signal. I can do it. Further, it is possible to use, for example, a diode as the temperature measuring element, and a resistor, etc. as the heating element.

The pond water invention can be implemented with various modifications without departing from the spirit thereof.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a schematic configuration of a flow velocity detector according to an embodiment of the present invention, FIG. 2 is a diagram showing a specific configuration example of the main part, and FIG.
The figure shows the response characteristics of the fluid detector according to this embodiment.
FIG. 4 is a diagram showing the main part configuration of a flow velocity detector of another embodiment,
FIG. 5 is a diagram showing an example of the configuration of a conventional semiconductor flow velocity detector, FIG. 6 is a diagram not showing its response characteristics, FIG. 7 is a diagram showing how the response characteristics are impaired by the conventional pulsation removal method, and FIG. FIG. 8 is a diagram showing an example of a conventional pulsation removal method. DESCRIPTION OF SYMBOLS 1... Semiconductor flow velocity detection element, 2... Drive circuit, 3...
...Waveform processing circuit, 4...Output adjustment circuit, 31...
Pulsating component extraction circuit, 32... Differential circuit, 5... Transistor for substrate temperature measurement, 6... Transistor for heat generation, 7... Transistor for fluid temperature measurement. Applicant's Representative Patent Attorney Takehiko Suzue J1rXJ M2 Figure 4 Time Figure 7

Claims (3)

[Claims] (1) Includes a semiconductor flow rate detection element in which a heating element and a substrate temperature measurement element are integrated on a semiconductor substrate, and a fluid temperature measurement element that measures the temperature of the fluid to be measured; a drive circuit that controls the heat generating element so that the temperature of the detection element is a certain temperature higher than the temperature of the fluid to be measured using the output and the output of the substrate temperature measuring element; In a semiconductor flow velocity detector that measures flow velocity by detecting a current that contributes to heat generation or a potential or voltage that changes in response to this current, a circuit that extracts only a pulsating component from an output signal of the semiconductor flow velocity detection element. , and a circuit for obtaining a flow velocity detection signal by subtracting the pulsation component extracted by this circuit from the output signal of the semiconductor flow velocity detection element. (2) The semiconductor flow rate detector according to claim 1, wherein the heat generating element in the semiconductor flow rate detection element is a transistor. (3) The semiconductor flow rate detector according to claim 1, wherein the substrate temperature measuring element in the semiconductor flow rate detection element is a transistor or a diode.