JPS604428B2 - Hot wire flow rate measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flow velocity measuring device, particularly a hot wire flow velocity detector that generates an electrical signal according to the flow velocity of a fluid, and an analog/digital (A/D) sensor that converts this electrical signal into a corresponding digital signal. D) A flow rate measuring device including a converter.

Conventionally, such flow rate measurement devices have been widely used in centralized control systems for internal combustion engines, particularly automobiles, which control the air-fuel ratio of internal combustion engines by processing digital signals representing the flow rate of the inhaler using a digital computer. .

Hot wire flow rate detectors generally have output characteristics such that they generate a constant initial voltage level at zero flow rate and generate a voltage level higher than this initial voltage when a finite value of flow rate is detected. On the other hand, in an integral type A/D converter, as long as a constant clock is supplied, the time required for the A/D converter, in other words, the reciprocal of the A/D conversion speed is proportional to the magnitude of its input voltage. . In conventional flow velocity measurement devices, such output voltage from the flow velocity detector is inputted as is to the A/D converter, and the A/D converter always converts the input containing the initial voltage level into A/D. Must. Therefore, the faster the flow rate, the slower the A/D conversion speed. So A/
The D converter must be designed with a fairly high performance that can achieve the required conversion time at a conceivable high flow rate. This complicates the configuration of the A/D converter, resulting in poor reliability and cost.
Furthermore, A/D conversion with a suppressed upper limit converts an initial voltage that does not normally change, resulting in a narrow dynamic range of the signal and a disadvantage that highly accurate measurement cannot be performed. It is an object of the present invention to eliminate these conventional drawbacks and to economically provide a flow velocity measuring device with good response characteristics and a short time required for A/D conversion when the flow velocity is far.

Another object of the present invention is to provide a flow velocity measurement device that can accurately measure flow velocity in a high-speed region, which conventional flow velocity measurement devices could not accurately measure due to performance limitations of A/D converters. .

These objects are achieved by the flow rate measuring device according to the present invention as follows.

That is, this flow velocity measuring device includes means for setting a voltage equal to or higher than the level corresponding to the maximum output voltage electrical signal of the hot wire flow velocity detector as a reference voltage;
and a subtraction means disposed between the flow velocity detector and the A/D converter to provide the A/○ converter with a subtraction output obtained by subtracting the output electrical signal of the flow velocity detector from the reference voltage set in this way, As a result, the value of the digital signal output from the A/D converter decreases as the flow velocity increases. Embodiments of the flow rate measuring device according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram showing the system configuration of a hot wire flow rate measuring device according to the present invention.

In the figure, an electrical signal representing the flow velocity detected by a hot wire flow velocity detector 10 is applied to a differential amplifier 141 via a lead 12. The differential amplifier 14 has a voltage divider 16 for setting a reference voltage, and the output 18 of the amplifier 14 is connected to an analog-to-digital (A/D) converter 201. This A/D converter may also be a voltage/frequency (Vf) converter. The digital signal (
This represents a flow rate measurement) that is transferred via input/output interface 22 to a processing device, such as a digital computer 24 . By the way, it is known that the output voltage characteristic of a hot wire type flow velocity detector draws a curve 30 shown in FIG.

Therefore, when designing a desired flow velocity measurement range, a voltage Vs equal to or higher than the output voltage of the detector 10 corresponding to the maximum flow velocity value assumed is set as the reference voltage of the differential amplifier 14 by the voltage divider 16. . Amplifier 14
slices and inverts the input electrical signal at this voltage level Vs. That is, a voltage having a magnitude obtained by subtracting the input electrical signal of the lead 12 from the voltage level VS is output to the output lead 18. This world power signal is plotted on the graph of Figure 3. According to this, when the flow rate is ○, the A/D converter 201 receives a finite value input Vs-Uo (Uo is the output level of the detector 10 when the flow rate is ○), and as the flow rate increases, the converter 20 The input level is gradually reduced. For example, if the output level of the detector 10 at a certain flow rate Qa is Us, the input level of the converter 20 at that flow rate Qa is Vs-Us.
, which is much smaller than when the flow rate is ○. The smaller the input voltage to the integral type A/D converter 201, the shorter the time required for A/D conversion, that is, the response speed, so the faster the flow rate, the shorter the conversion time. With this configuration, the flow velocity measuring device according to the present invention is suitable for high-speed flow velocity measurements that require far-reaching responsiveness, and the response characteristics in the high-speed flow velocity region are particularly imitable. Therefore, an A/D converter with a low response characteristic is sufficient for high-speed measurements, and even with the addition of a differential amplifier, the overall equipment configuration is simplified, and improvements in reliability and cost efficiency are expected. can. In addition, the integral type A/
It also becomes possible to perform high-speed measurements in high flow velocity regions that cannot be followed by D converters or Vf converters.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the system configuration of an embodiment of the flow rate measuring device according to the present invention, and FIGS. 2 and 3 are graphs plotting the response characteristics of the blocks shown in FIG. 1. Explanation of symbols of main parts, 10...Hot wire flow velocity detector, 14...Differential amplifier, 16...Voltage divider, 20...Analog-digital conversion vessel. Shige no zu Figure 2 Figure 3

Claims (1)

[Scope of Claims] 1. A flow velocity measuring device including a hot wire flow velocity detection means that generates an electrical signal corresponding to the flow velocity of a fluid, and an analog-to-digital converter that converts the electrical signal into a corresponding digital signal. , means for setting a voltage equal to or higher than the level corresponding to the maximum output voltage electrical signal in the measurement range of the flow rate detector as a reference voltage;
subtracting means disposed between the flow rate detection means and the analog-to-digital converter, and providing a subtracted output obtained by subtracting the electric signal from the set reference voltage to the analog-to-digital converter; A flow velocity measurement device characterized in that the value of the digital signal decreases in a higher flow velocity region. 2. The flow velocity measuring device according to claim 1, wherein the subtraction means includes a differential amplifier connected to the setting means and generating a subtracted output in response to an electrical signal from the flow velocity detection means. A flow velocity measuring device characterized by: