JPH07294301A - Signal switching circuit and ultrasonic flowmeter - Google Patents

Abstract

PURPOSE:To increase the amplitude range of a signal switched by a switching semiconductor integrated circuit by biasing the voltage to the earth terminal as reference in a range of above or below the zero potential keeping a rated voltage value. CONSTITUTION:Earth terminals of power sources 13, 14 and 15 are connected to an earthing conductor of a circuit and in a level shift circuit 12, an output 157 of a switching signal 156 is connected to switching signal terminals Ka and Kb of integrated circuits 10a and 10b. As an output of a signal generation circuit 24 is transmitted by the integrated circuit 10a to a probe 1 (2) through a connector 11a (11b), the probe 1 (2) is excited and an ultrasonic pulse is transmitted into a liquid to be measured flowing through a pipe 3 from the probe 1 (2) to reach the probe 2 (1). Then, the pulse is converted to an electrical signal to be received by a connector 11b (11a) and transmitted to a receiving part by the integrated circuit 11b (11a). Thus, the relationship between the transmitting and the receiving of ultrasonic waves in a pair of probes is inverted periodically according to a switching signal 156.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a large amplitude signal switching circuit used in an ultrasonic flowmeter or the like.

[0002]

2. Description of the Related Art An ultrasonic flowmeter is a flowmeter that determines a flow rate from the difference between the ultrasonic wave propagation time in the flow direction of a fluid to be measured and the ultrasonic wave propagation time in the opposite direction to the flow of the fluid to be measured.

According to Japanese Patent Publication No. 46-14106,
“A pair of probes installed diagonally opposite to each other with respect to the flow direction of the fluid to be measured is connected to an ultrasonic electric pulse transceiver, and the ultrasonic pulse transmitted from one probe is transmitted to the other probe. When receiving, the electric pulse transmitter / receiver receives the ultrasonic electric pulse corresponding to the received pulse and subsequently transmits the ultrasonic electric pulse to the one probe, and each transmission of the pair of probes. Since the disclosure of the ultrasonic flowmeter in which the relationship between the received wave and the received wave is periodically reversed, many ultrasonic flowmeters have been manufactured by the above method.

FIG. 5 is a reprint of FIG. 1 of the above-mentioned patent application publication. 1 and 2 are a pair of ultrasonic probes, and 3 is a pipe through which a fluid to be measured flows. Reference numeral 4 is a switch, and 5 is a transceiver. Ultrasonic probe 1,
2. The switching device 4 and the transceiver 5 form a sing-around system that was the measurement principle of the initial ultrasonic flowmeter. In FIG. 5, 6 is a timer, 7 is an addition / subtraction counter, and 8
Is an integrated flow rate indicator, and 9 is an instantaneous flow rate indicator.

The switching device 4 in the figure is a circuit for "reversing the relationship between each transmitted wave and received wave of a pair of probes periodically" as disclosed in the above-mentioned patent application publication. In this circuit, since a high output pulse for exciting the ultrasonic probe on the transmission side is switched, a semiconductor element cannot be used, and a mechanical relay has been used since the early days of the ultrasonic flowmeter.

[0006]

However, in such a conventional switching device, the reliability of the mechanical relay is higher than that of other electronic components (semiconductor, resistor, condenser, etc.) of the ultrasonic flowmeter. Moreover, since the output of the transmitter of the ultrasonic electric pulse transmitter / receiver is a high-voltage pulse, the contact deteriorates more quickly than in the normal usage and there is a problem in reliability. Although the reliability can be improved by using a mercury relay, its reliability is still lower than that of other electronic components. Further, the mercury relay may cause an environmentally unfavorable problem in its manufacturing process and disposal after use. Further, since the mercury relay needs to be installed and used in a fixed direction, when it is used in a portable ultrasonic flowmeter, the direction in which the ultrasonic flowmeter is placed is limited and inconvenient.

Recently, integrated circuits capable of switching analog electrical signals of relatively large amplitude have become commercially available. An example of such an integrated circuit is shown in FIG. In the figure, reference numeral 10 denotes an integrated circuit (hereinafter, referred to as "integrated circuit") that switches an analog electric signal. In FIG. 6 and FIGS. 1 and 3 which will be described later, in order to make the drawings easy to understand, only the analog switch circuit portion in the integrated circuit is denoted by a symbol. The terminal C of the integrated circuit 10,
The terminals A and B are terminals connected to the analog switch circuit inside the integrated circuit 10. The terminal K is a terminal to which the switching signal 156 for controlling switching of the analog electric signal is input. The switching signal 156 is at a high level (for example, +15
In the case of V), the terminal C and the terminal A are connected inside the integrated circuit, and the terminal C and the terminal B are disconnected inside the integrated circuit. Switching signal 156 is at low level (normally 0V)
At this time, the terminal C and the terminal A are separated inside the integrated circuit, and the terminal C and the terminal B are connected inside the integrated circuit. In the integrated circuit 10, the analog electric signal can be transmitted from the terminal C to the terminal A or the terminal B and from the terminal A or the terminal B to the terminal C.

In the above switch circuit, the other end of the wiring 220 connected to the terminal C is connected to an analog electric signal source (not shown), and the output of the analog electric signal source is connected to the terminal A.
The wiring is switched to either the wiring 221a connected to the terminal 221a or the wiring 221b connected to the terminal B. Wiring 221
The other ends of a and 221b are connected to other circuits (not shown) or connectors.

The terminal D of the integrated circuit 10 is a power supply terminal of a logic circuit inside the integrated circuit 10, and the other end of the wiring 124 connected to the terminal is connected to the circuit power supply 16. The rated voltage of the logic circuit power supply terminal D is usually specified by the manufacturer of the integrated circuit within the range of + 5V to + 15V. The output voltage of the circuit power supply 16 needs to be equal to the rated voltage. In this specification, the “rated voltage” of each power supply terminal of an integrated circuit is a voltage value with reference to the ground terminal of the integrated circuit, and the manufacturer of the integrated circuit applies the power supply terminal to the corresponding power supply terminal. Refers to the voltage value specified or recommended to The terminal P of the integrated circuit 10 is a positive power supply terminal for analog circuit (hereinafter, referred to as “positive high voltage power supply terminal”), and the other end of the wiring 201 connected to the terminal is connected to the positive power supply 51. The output voltage of the positive power supply 51 needs to be equal to the rated voltage of the positive high-voltage power supply terminal P.

The terminal N of the integrated circuit 10 is a negative power supply terminal for analog circuits (hereinafter referred to as "negative high voltage power supply terminal"), and the other end of the wiring 202 connected to the terminal is a negative power supply 52.
Connected to. The output voltage of the negative power supply 52 needs to be equal to the rated voltage of the negative high-voltage power supply terminal N. Although not shown, the ground terminals of the three power sources 51, 52 and 16 are connected to the ground line of the circuit. Terminal G of integrated circuit 10
Is a ground terminal and is connected to the ground wire of the circuit. Normally, the rated voltage of the positive high voltage power supply terminal P and the negative high voltage power supply terminal N
Is equal to the absolute value of the rated voltage of. The larger the absolute value of the rated voltage, the larger the voltage amplitude of the analog electric signal that can be switched by the integrated circuit 10. Currently, the rated value of the positive and negative high voltage power supplies of commercially available integrated circuits capable of switching analog electric signals having a frequency of 10 MHz is about 80V.

FIG. 7 illustrates the power supply voltage distribution of the integrated circuit 10 in FIG. The line 125 is at 0V level, that is, the voltage at the terminal G. Line 211 shows the rated voltage (positive voltage) level of the terminal P, and line 212 shows the rated voltage (negative voltage) level of the terminal N. Line 213
Is the upper voltage level of the analog input signal,
4 is the lower limit voltage level of the analog input signal. Integrated circuit 10 is capable of switching analog electrical signals having voltage swings in the range of lines 214 to 213. The voltage difference between the line 211 and the line 213 and the voltage difference between the line 212 and the line 214 varies depending on the type of integrated circuit, but is usually 10 to 20V. In the present specification, the upper limit and the lower limit of the analog input signal are the upper limit and the lower limit of the analog input signal voltage value that can maintain a linear relationship between the input and the output of the analog electric signal of the integrated circuit. Say.

As when switching the output of the transmitting section of the ultrasonic flowmeter, one of the analog input (input of the terminal C) of the integrated circuit 10 of FIG. 6 which is a positive value or a negative value is selected by the circuit design. If the signal takes only a value, the amplitude range of the signal that can be switched by the circuit in FIG. 6 is the range from line 125 to line 213 or the range from line 125 to line 214 in FIG. The above range is unsatisfactory in comparison with the amplitude of the transmission output required for the ultrasonic flowmeter. This problem is not limited to ultrasonic flowmeters, but is a problem common to circuits that switch large amplitude signals.

[0013]

SUMMARY OF THE INVENTION The present invention has been made by paying attention to such a conventional problem, and has a power supply terminal, a ground terminal and a switching signal terminal and is connected to the switching signal terminal. An integrated circuit that switches an analog electric signal by a switching signal that is applied, wherein the voltage applied to the power supply terminal and the voltage applied to the ground terminal are biased in a positive direction or a negative direction. It is an object of the present invention to solve the above problems by using a signal switching circuit that

Alternatively, it has two integrated circuits each having a power supply terminal, a ground terminal, and a switching signal terminal and switching the direction in which an analog electric signal is transmitted by a switching signal connected to the switching signal terminal. For two integrated circuits,
The voltage applied to the power supply terminal and the voltage applied to the ground terminal are biased in a positive direction or a negative direction, and the analog electric signal terminals of the two integrated circuits are connected to each other by the analog electric signals. It is an object of the present invention to solve the above problems by using a signal switching circuit characterized in that signals are connected so that the directions of transmitting the signals are opposite to each other.

[0015]

As described above with reference to FIG. 7, the voltage range of the analog electric signal that can be switched by the integrated circuit has the upper limit of the voltage of the positive high voltage power supply terminal and the lower limit of the voltage of the negative high voltage power supply terminal. It is inside the range. Therefore, by biasing the voltage distribution of each power supply terminal and the ground terminal of the integrated circuit to the range of zero V or more or the range of zero V or less while keeping the voltage with respect to the ground terminal as the rated voltage,
The range of voltage amplitude that can be switched by the integrated circuit can be greatly improved for signals that take only positive values or signals that take only negative values.

FIG. 2 illustrates the power supply voltage distribution when the voltage distribution of each power supply terminal and ground terminal of the integrated circuit shown in FIG. 6 is biased to a range of 0 V or higher. Line 1
Reference numeral 25 indicates a 0V level, that is, the voltage level of the ground line, which is the voltage of the negative high voltage power supply terminal of the integrated circuit. Line 1
Reference numeral 11 denotes a positive voltage level equal to the sum of the rated voltage of the positive high voltage power supply terminal of the integrated circuit and the absolute value of the rated voltage of the negative high voltage power supply terminal, which is set to the voltage of the positive high voltage power supply terminal.
Line 112 represents a positive voltage level equal to the absolute value of the rated voltage of the negative high voltage power supply terminal and is at the voltage of the ground terminal of the integrated circuit. Line 113 is the upper limit voltage level of the analog input signal and line 114 is the lower limit voltage level of the analog input signal. In the above power supply voltage distribution, the integrated circuit can switch an analog electrical signal having a voltage swing in the range from line 114 to line 113. Normally, the absolute value of the rated voltage of the positive high voltage power supply terminal is equal to the absolute value of the rated voltage of the negative high voltage power supply terminal. Therefore, line 114 and line 11 in FIG.
3 is twice the voltage difference between lines 125 and 213 in FIG. Therefore, for signals that take only positive values, the amplitude of the switchable signal can be doubled compared to the prior art.

FIG. 4 shows the power supply voltage distribution when the voltage distribution of each power supply terminal and ground terminal of the integrated circuit shown in FIG. 6 is biased to a range of zero V or less. Line 1
Reference numeral 25 indicates a 0V level, that is, a voltage level of the ground line, which is the voltage of the positive high voltage power supply terminal of the integrated circuit. Line 1
Reference numeral 15 indicates a negative voltage level having an absolute value equal to the sum of the rated voltage of the positive high voltage power supply terminal and the absolute value of the rated voltage of the negative high voltage power supply terminal of the integrated circuit, which is the voltage of the negative high voltage power supply terminal. . Line 116 represents a negative voltage level having an absolute value equal to the rated voltage of the positive high voltage power supply terminal and is at the voltage of the ground terminal of the integrated circuit. Line 117 is the upper limit voltage level of the analog input signal and line 118 is the lower limit voltage level of the analog input signal. With the above power supply voltage distribution, integrated circuit 10 can switch an analog electrical signal having a voltage swing in the range of lines 117 to 118. Therefore, for a signal that takes only a negative value, the amplitude of the switchable signal can be doubled as compared with the conventional technique.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing one embodiment of the invention of claim 2. In FIG. In the figure, 10a and 10b are integrated circuits respectively, and the operation of each terminal of both integrated circuits is the same as the operation of each terminal of the integrated circuit 10 of FIG. 6, and the distribution of the power supply voltage of each terminal is shown in FIG. This is the same as the voltage distribution shown in 2. First
The positive power supply 13 has positive and high voltage power supply terminals Pa and Pb of the integrated circuits 10a and 10b (the terminal symbol of the integrated circuit 10a is attached with "a", and the terminal symbol of the integrated circuit 10b is attached with "b"). Is a power supply that outputs a positive DC voltage equal to the sum of the rated voltage of the integrated circuit 10a and the absolute value of the rated voltage of the negative high-voltage power supply terminals Na and Nb of the integrated circuits 10a and 10b. It is connected to the positive and high voltage power supply terminals Pa and Pb of the same 10b.

The second positive power supply 14 is a power supply for outputting a positive DC voltage equal to the absolute value of the rated voltage of the negative high voltage power supply terminals Na and Nb of the integrated circuits 10a and 10b, and its output 122 is an integrated circuit. Ground terminal G of 10a and 10b
a and Gb. The third positive power supply 15 is a power supply that outputs a positive DC voltage equal to the sum of the output voltage of the second positive power supply 14 and the rated voltage of the logic circuit power supply terminals Da and Db of the integrated circuits 10a and 10b. , Its output 123
Is a power supply terminal D for the logic circuits of the integrated circuits 10a and 10b
It is connected to a and Db. Integrated circuits 10a and 10b
The negative high voltage power supply terminals Na and Nb are connected to the ground line. Although not shown, the three power sources 13 and 1
Each of the ground terminals 4 and 15 is connected to the ground wire of the circuit.

For example, the rated voltage of the positive high voltage power supply terminals Pa and Pb of the integrated circuits 10a and 10b is + 80V, the rated voltage of the negative high voltage power supply terminals Na and Nb is -80V, and the rated voltage of the logic circuit power supply terminals Da and Db. Is + 15V, the output voltage of the first positive power supply 13 needs to be + 160V, the output voltage of the second positive power supply 14 needs to be + 80V, and the output voltage of the third positive power supply 15 needs to be + 95V.

The level shift circuit 12 level-shifts the voltage when the switching signal 156 transmitted from another circuit (not shown) is at a low level from a normal 0 V to a voltage equal to the output voltage of the second positive power source 14. The output 157 is connected to the switching signal terminals Ka and Kb of the integrated circuits 10a and 10b. Such a circuit can be easily realized by using, for example, a photocoupler. Switching signal 156 is 0V and + 15V 2
When the pulse signal takes a value, in the specific example of the voltage value, the output pulse of the level shift circuit is + 80V.
And + 95V binary. The signal generation circuit 24 is a circuit that outputs a signal having only a positive voltage value in synchronization with a synchronization signal 151 transmitted from another circuit (not shown).
The output 152 is connected to the analog electric signal terminal Ca of the integrated circuit 10a.

Reference numerals 11a and 11b in FIG. 1 are connectors. Reference numerals 1 and 2 in the same figure are probes used when the circuit of FIG. 1 is applied to an ultrasonic flowmeter. The probe 1 is connected to the connector 11a and the probe 2 is connected to the connector 11b. Reference numeral 3 in the figure denotes a pipe through which the fluid to be measured flows. The connector 11a is an integrated circuit 10a
Connected to the analog electric signal terminal Aa of the connector 11
b is connected to the analog electric signal terminal Ba of the integrated circuit 10a. Therefore, the integrated circuit 10a outputs the output 152 of the signal generating circuit 24 to the connector 11 in response to the output 157 of the level shift circuit, that is, in response to the switching signal 156.
A switching action is performed to output to an external device or the like (probe in the example of FIG. 1) via either a or the connector 11b.

Further, the connector 11a is the capacitor 1
The analog electric signal terminal Bb of the integrated circuit 10b is AC-connected via 7a, and the connector 11b is AC connected to the analog electric signal terminal Ab of the integrated circuit 11b via a capacitor 17b. The analog electric signal terminal Cb of the integrated circuit 10b is AC-connected to the receiving unit 25 via the capacitor 21. As described above, both the switching signal terminals Ka and Kb of the integrated circuits 10a and 10b have the output 15 of the level shift circuit.
7 is connected. Therefore, when the output 152 of the signal generating circuit 24 is connected to the connector 11a by the integrated circuit 10a, the integrated circuit 10b connects the connector 11b and the receiving unit 25. When the output 152 of the signal generating circuit 24 is connected to the connector 11b by the integrated circuit 10a, the integrated circuit 10b connects the connector 11a and the input of the receiving unit 25.

In FIG. 1, the lower limit of the voltage range of the input signal that can be switched by the integrated circuit 10b is a positive voltage value, and a signal that oscillates around the level of zero V with respect to the ground cannot be switched. . The capacitors 17a and 17b, the resistors 18a, 18b and 19, and the capacitor 20 shown in FIG. 1 serve to shift the central voltage of the signal switched by the integrated circuit 10b to a voltage range in which the integrated circuit can switch. Capacitor 17a and resistor 18a
And cut off the input signal in a direct current. The time constant given by the product of the capacitance value of the capacitor 17a and the resistance value of the resistor 18a needs to be sufficiently larger than the oscillation period of the signal to be switched. The functions of the capacitor 17b and the resistor 18b are the same as those of the capacitor 17a and the resistor 18a.

In the resistor 19 and the capacitor 20, the output signal 151 of the signal generating circuit 24 output to the terminal Aa or Ba of the integrated circuit 10a is the capacitor 17a and the resistor 18.
via a, or a capacitor 17b and a resistor 18b
It has the function of preventing the terminal Ga of the integrated circuit 10a and the terminal Gb of the integrated circuit 10b from wrapping around. The absolute value of the impedance of the capacitor 20 with respect to the output signal 151 of the signal generating circuit 24 needs to be sufficiently smaller than the resistance value of the resistor 19. The capacitor 21 and the resistor 22 serve to return the center voltage of the signal switched by the integrated circuit 10b to zero V with respect to the ground. The time constant given by the product of the capacitance value of the capacitor 21 and the resistance value of the resistor 22 needs to be sufficiently larger than the oscillation period of the switched signal.

From the elements shown in FIG. 1, ultrasonic probe 1, ultrasonic probe 2, pipe 3, integrated circuit 10b, condenser 17 are provided.
a, same 17b, same 20, same 21, resistance 18a, same 18
A circuit excluding the wirings b, 19 and 22, the receiver 25, and the wirings connected to the respective elements is one embodiment of claim 1.

Hereinafter, in this paragraph and the next paragraph,
The operation when the embodiment of FIG. 1 is applied to an ultrasonic flow meter will be described. In the ultrasonic flowmeter, the signal generation circuit 24 is a transmitter. When the output of the transmitter is transmitted from the integrated circuit 10a to the probe 1 via the connector 11a, the probe 1 is excited and an ultrasonic pulse from the probe 1 flows in the pipe 3 to be measured. It is radiated inside. When the ultrasonic pulse reaches the probe 2, it is converted into an electric signal. The electrical signal is the connector 1
The signal is received at 1b and transmitted to the receiving unit 25 by the integrated circuit 10b.

When the output of the transmitter is transmitted to the probe 2 by the integrated circuit 10a via the connector 11b, the probe 2 is excited and an ultrasonic pulse is radiated from the probe 2 into the liquid to be measured. It When the ultrasonic pulse reaches the probe 1, it is converted into an electric signal.
The electric signal is received by the connector 11a, and the integrated circuit 1
It is transmitted to the reception unit 25 by 0b. Thus, FIG.
This embodiment functions as a switch, a transmitter, and a receiver of the ultrasonic flowmeter, which periodically inverts the relationship between the transmitted wave and the received wave of the pair of probes according to the switching signal.

According to the embodiment shown in FIG. 1, the switching device of the ultrasonic flowmeter and other circuits for switching a signal with a large amplitude can be a circuit using a semiconductor, and the reliability of the entire apparatus using the switching device can be improved. It is possible to significantly improve the sex. Further, it can greatly contribute to downsizing and low power consumption of the device. Further, even when the device is portable, it is not necessary to limit the direction in which the device is placed.

FIG. 3 is a diagram showing another embodiment of the invention of claim 2, and the voltage distribution of each power supply terminal and ground terminal of the integrated circuits 10a and 10b is the same as the voltage distribution shown in FIG. The operation and effect of the circuit of FIG. 3 are basically the same as the operation and effect of the circuit of FIG.
Differences from FIG. 1 will be described. The first negative power supply 32 is the sum of the rated voltage of the positive high voltage power supply terminals Pa and Pb of the integrated circuits 10a and 10b and the absolute value of the rated voltage of the negative high voltage power supply terminals Na and Nb of the integrated circuits 10a and 10b. A power supply that outputs a negative DC voltage having an equal absolute value, and its output 131 is connected to the negative high voltage power supply terminals Na and Nb of the integrated circuits 10a and 10b.

The second negative power supply 33 is a power supply for outputting a negative DC voltage having an absolute value equal to the rated voltage of the positive high voltage power supply terminals Pa and Pb of the integrated circuits 10a and 10b, and its output 132 is integrated. It is connected to the ground terminals Ga and Gb of the circuits 10a and 10b. The third negative power source 34 is
The output voltage of the second negative power supply 33 and the integrated circuits 10a and 10
b is a circuit for outputting a negative DC voltage equal to the algebraic sum of the rated voltage of the logic circuit power supply terminals Da and Db, the output 133 of which is the logic circuit power supply terminals Da and Db of the integrated circuits 10a and 10b. Connected to. Integrated circuit 10a
Further, the positive and high voltage power supply terminals Pa and Pb of the same 10b are connected to the ground line. Although not shown, the ground terminals of the three power sources 32, 33 and 34 are connected to the ground line of the circuit.

For example, the rated voltage of the positive high voltage power supply terminals Pa and Pb of the integrated circuits 10a and 10b is + 80V, the rated voltage of the negative high voltage power supply terminals Na and Nb is -80V, and the rated voltage of the logic circuit power supply terminals Da and Db. Is + 15V, the output voltage of the first negative power supply 32 needs to be −160V, the output voltage of the second positive power supply 14 needs to be −80V, and the output voltage of the third positive power supply 15 needs to be −65V.

The level shift circuit 31 level-shifts the voltage when the switching signal 156 transmitted from another circuit (not shown) is at a low level from a normal 0 V to a voltage equal to the output voltage of the second negative power supply 33. The output 176 is connected to the switching signal terminals Ka and Kb of the integrated circuits 10a and 10b. The signal generation circuit 35 is
The output 171 is a circuit that outputs a signal having only a negative voltage value in synchronization with a synchronization signal 151 transmitted from another circuit (not shown), and its output 171 is connected to the analog electric signal terminal Ca of the integrated circuit 10a.

From the elements shown in FIG. 3, ultrasonic probe 1, ultrasonic probe 2, pipe 3, integrated circuit 10b, condenser 17 are provided.
a, same 17b, same 20, same 21, resistance 18a, same 18
A circuit excluding the wirings b, 19 and 22, the receiver 25 and the wirings connected to the respective elements is another embodiment of the first aspect.

1 and 3 show an embodiment using an integrated circuit having a positive power supply terminal for an analog circuit, a negative power supply terminal for an analog circuit, and a power supply terminal for a logic circuit, the present invention is not limited to this. Not limited. The present invention can be implemented regardless of the number of power supply terminals included in the integrated circuit used.

Although the first positive power source, the second positive power source, and the third positive power source are described as independent power sources in FIG. 1, they are not always necessary in the practice of the present invention. The output voltage of the second positive power supply and the output voltage of the third output power supply can be generated from the output of the first positive power supply having the largest output voltage by a constant voltage circuit or a resistance division circuit. First of FIG.
The same applies to the negative power source, the second negative power source, and the third negative power source. Further, the signal generation circuit 24 of FIG. 1 and the signal generation circuit 35 of FIG. 3 have been described as outputting signals synchronized with the synchronization signal, but both the signal generation circuits described above do not synchronize with signals from other circuits, A free-run circuit that generates a signal may be used.

[0037]

According to the present invention, the reliability of the entire apparatus can be greatly improved by making the switch of the ultrasonic flowmeter and other circuits for switching signals of large amplitude into semiconductors. Further, it can greatly contribute to downsizing and low power consumption of the device. Further, even when the device is portable, it is not necessary to limit the direction in which the device is placed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing voltage distribution of power supply terminals of the integrated circuit used in the embodiment of FIG.

FIG. 3 is a block diagram showing another embodiment of the present invention.

FIG. 4 is a diagram showing voltage distribution of power supply terminals of the integrated circuit used in the embodiment of FIG.

FIG. 5 is a diagram showing one configuration example of a conventional ultrasonic flowmeter.

FIG. 6 is a diagram showing a usage example of an analog electric signal switch integrated circuit according to a conventional technique.

7 is a diagram showing voltage distribution of power supply terminals of the integrated circuit in the usage example of FIG. 6;

[Explanation of symbols]

1 and 2 are a pair of ultrasonic probes of an ultrasonic flow meter, 3 is a pipe through which the fluid under measurement of the ultrasonic flow meter flows, 4 is a switch, 5 is a transceiver, 6 is a timer, 7 is an addition / subtraction counter, Reference numeral 8 is an integrated flow rate indicator, and 9 is an instantaneous flow rate indicator. In FIG. 1, 10a and 10b are integrated circuits for switching analog electric signals, 12 is a level shift circuit,
Reference numeral 13 is a first positive power source, 14 is a second positive power source, 15 is a third positive power source, 24 is a signal generating circuit, and 25 is a receiving unit. In FIG. 3, 31 is a level shift circuit, 32 is a first negative power supply,
33 is a second negative power supply, 34 is a third negative power supply, and 24 is a signal generating circuit.

Claims (3)

[Claims] 1. A voltage applied to the power supply terminal, the integrated circuit having a power supply terminal, a ground terminal, and a switching signal terminal and switching an analog electric signal according to a switching signal connected to the switching signal terminal. And a voltage applied to the ground terminal are biased in a positive direction or a negative direction. 2. An integrated circuit which has a power supply terminal, a ground terminal, and a switching signal terminal, and which switches two directions of transmitting an analog electric signal according to a switching signal connected to the switching signal terminal, With respect to the two integrated circuits, the voltage applied to the power supply terminal and the voltage applied to the ground terminal are biased in the positive direction or the negative direction, and the analog electric signal terminals of the two integrated circuits are set to the two A signal switching circuit characterized in that the integrated circuits are connected so that the directions of transmitting analog electric signals are opposite to each other. 3. A pair of ultrasonic probes for transmitting and receiving ultrasonic waves, which are installed on a pipe wall of a fluid channel at a predetermined distance in the direction of fluid flow, and a pair of ultrasonic probes for transmitting and receiving the ultrasonic probes. An ultrasonic flowmeter having a transmission / reception switching circuit that switches for each sonic probe, wherein the transmission / reception switching circuit is the signal switching circuit according to claim 2.