JPS6032567Y2 - Flow rate/flow rate detection device - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to a device for detecting flow velocity and flow rate.

2. Description of the Related Art A flow velocity/flow rate detection device is known in which a thermistor, which is a temperature-sensitive element, is used as a detector, a vortex generator is disposed in the flow velocity, and the Karman vortex generated by the vortex generator is detected by the thermistor.

In such devices, the electrical signal from the detector is typically pulsed by a zero-crossing detector and then supplied to a counting circuit or the like for use.

However, when the flow rate becomes high and the frequency of the electrical signal from the detector increases, low-frequency components are superimposed on the electrical signal from the detector, and as a result, the zero-crossing detector detects the detected electrical signal. It becomes impossible to pulse accurately.

Furthermore, due to the thermal time constant of the temperature sensing element, etc., when the flow velocity becomes high and the frequency of the vortex increases, the signal voltage tends to decrease.

As a countermeasure to this, the electrical signal from the detector is differentiated,
A technique has also been proposed in which this differentiated electrical signal is supplied to a zero-crossing detector and made into a pulse, but according to this technique,
The signal-to-noise ratio obtained in the low flow velocity and flow rate range deteriorates, which is not so desirable.

The present invention was developed in view of the above points, and its purpose is to be able to obtain accurate flow velocity signals from low flow velocities and flow areas to high flow velocities and flow areas, and to effectively eliminate superimposed low frequency components. The object of the present invention is to provide a flow velocity/flow rate detection device that can accurately measure flow velocity and flow rate.

Next, a preferred embodiment of the present invention will be explained based on the drawings.

In the figure, a detector 1 consisting of a temperature-sensitive element such as a thermistor is attached to a pipe through which a fluid to be measured flows, and detects the Karman vortex generated and outputs a flow velocity signal having a frequency proportional to the flow velocity. Outputs electrical signal 2.

The differentiating circuit 3 to which the signal 2 is supplied includes a capacitor 4, an operational amplifier 5, a resistor 6, a capacitor 7, and a field effect transistor 8.
The drain-source connection is used as a variable resistance.
Capacitor 7 is for stabilizing high frequency characteristics.

When the resistance between the drain and the source of the transistor 8 is set to the highest value, the frequency f-gain characteristic curve 9 of the differentiator circuit 3 is set, while the resistance between the drain and the source of the transistor 8 is set to the lowest value. When set to , the f-G characteristic of the differentiating circuit 3 becomes as shown by the curve 10.

In curves 9 and 10, the region exhibiting differential characteristics is the slope portion.

The output of the operational amplifier 5 is connected to the operational amplifier 11, the shelf piles 12, 1
The trigger circuit 14 pulses a signal 15 obtained by differentiating the signal 2 and outputs a pulse signal 16.

A frequency-to-voltage converter 17, to which the signal 16 from the Schmitt trigger circuit 14 is supplied, converts the frequency of the signal 16 into a voltage, producing a high voltage when the frequency of the signal 16 is high, and a low voltage when the frequency of the signal 16 is low. Output.

The voltage from the converter 17 is amplified and inverted by an inverting amplifier 21 consisting of resistors 18 and 19 and an operational amplifier 20, and is supplied to the gate of the transistor 8.

The transistor 8 operates to lower the resistance between the drain and source when the voltage applied to the gate is high, and to increase the resistance between the drain and source when the voltage is low.

The operation of the flow rate and flow rate detection device configured as described above will be explained.

First, when detecting a high flow rate and flow rate, the detector 1 supplies a signal 2 having a relatively high frequency f1 on which a low frequency component is superimposed to the differentiating circuit 3; The differential signal is output as a signal 15 with low frequency components removed, and is supplied to the Schmitt trigger circuit 14.

The Schmitt trigger circuit 14 compares the signal 15 with a reference level, pulses it, and outputs the signal 16.

Converter 17 detects frequency f1 of signal 16 and outputs a voltage proportional to this frequency.

In this case, the frequency f1 based on the high flow rate and the flow rate is set to the signal 16.
Therefore, a relatively high voltage is output from the converter 17, and this voltage is inverted and amplified by the amplifier 21 and supplied to the gate of the transistor 8.

When a relatively large negative voltage is applied to the gate, the trace-to-source resistance of transistor 8 becomes substantially large, and the current based on signal 2 flows mostly through capacitor 4, and signal 2 is transferred to differentiating circuit 3. Almost completely differentiated and output.

Therefore, the low frequency component superimposed on signal 2 is
The signal 15 is substantially removed by the differential circuit 3 as a signal 15, and then the signal 15 is pulsed without missing by the Schmitt trigger circuit 14 and output.

By supplying the signal 16 output from the Schmitt trigger circuit 14 to a flow rate, flow rate indicator, etc., the flow rate and flow rate can be accurately obtained.

On the other hand, when detecting a low flow rate or flow rate, the detector 1 supplies a signal 2 having a relatively low frequency f2 to the differentiating circuit 3, and the signal 2 is sent to the Schmitt trigger circuit 14 via the differentiating circuit 3. Supplied and pulsed.

The pulsed signal is input to the converter 17, and this frequency f2 is detected by the converter 17.

When supplied with a low flow rate signal having a frequency f2 based on the flow rate, the converter 17 outputs a relatively low voltage, which is inverted and amplified by the amplifier 21 and supplied to the gate of the transistor 8.

When a relatively small negative voltage is applied to the gate, the drain-source resistance of the transistor 8 becomes small, and the current based on the signal 2 flows through the drain-source resistance of the transistor 8 in addition to the capacitor 4. As a result, the signal 2 is not differentiated so much, but is instead amplified with an amplification degree based on the drain-source resistance of the transistor 8 and the resistor 6, and is output from the differentiating circuit 3.

Therefore, the signal 2 at low frequency is substantially amplified and supplied to the Schmitt trigger circuit 14, which pulses it and outputs it, and this pulsed signal 16 indicates the flow rate, flow rate, It is supplied to the display instrument for measurement.

That is, when the frequency of the signal from the detector 1 is low, the differential characteristic of the differentiating circuit 3 is substantially reduced.

In the above specific example, the frequency of the signal supplied was continuously converted into voltage using a frequency-voltage converter, but instead of this, a reference signal oscillator and a reference frequency of the signal from this oscillator were used. , and a frequency comparator that compares the frequency of the signal from the differentiating circuit, and the resistance between the tray source of the transistor 8 is controlled by the comparison result signal from this comparator, and the resistance of the differentiating circuit 3 in the low frequency region is controlled. The differential characteristics may be reduced.

As described above, according to the present invention, since the characteristics of the differentiating circuit are changed in accordance with the frequency of the input signal, it is possible to reliably remove low frequency components from a high frequency input signal on which low frequency components are superimposed, for example. Moreover, it is possible to amplify and output a low frequency input signal without differentiating it, and as a result, it is possible to improve the S/N in the low frequency region and prevent signal loss, and it is possible to accurately determine the flow rate and flow rate. In addition, the measurement area can be expanded by seven times.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a block diagram of a preferred embodiment of the present invention;
2 is a waveform diagram of each part in the specific example shown in FIG. 1, and FIG. 3 is a characteristic curve diagram of the differential circuit shown in FIG. 1. 1...Detector, 3...Differential circuit, 17
...Frequency-voltage converter.

Claims (1)

[Scope of utility model registration request] The frequency detection circuit consists of a detector that detects the flow velocity and outputs a flow velocity signal having a frequency based on the flow velocity, a differentiation circuit that differentiates the flow velocity signal from the detector, and a frequency detection circuit that detects the frequency of the flow velocity signal. A flow rate/flow rate detection device that uses a detection signal from the differential circuit to reduce the differential characteristics in the low frequency range.