JPH0631373Y2 - Excitation circuit of electromagnetic flowmeter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to an exciting circuit capable of reversing the polarity of an exciting current used in an electromagnetic flow meter, and particularly to a switch for reversing the polarity of the exciting current. It is connected to an exciting circuit of an electromagnetic flow meter in which the number of independent power sources is reduced by obtaining the operating power source from the exciting power source.

<Prior Art> FIG. 4 is a configuration diagram of a basic circuit of a conventional excitation circuit capable of reversing the polarity of an excitation current.

E Is the excitation power supply, SW₁~ SW_FourIs a switch and L is an excitation
It is a coil.

The switches SW _{1 to} SW ₄ form a bridge with them, and the switch SW ₁ is connected in parallel to the power supply terminals T ₁ and T _2.
And SW ₃ are connected in series, and the power supply terminals T ₁ and T _{2 are} further connected.
The switches SW ₂ and SW ₄ are connected in series in parallel with. The output terminals T ₃ and T ₄ are switch SW respectively.
It is connected to the connection point of ₁ and SW ₃ and the connection point of switches SW ₂ and SW ₄ , respectively, and is also connected to the exciting coil L.

The timing signal _S T1 _{to S T4} from the timing control circuit switches _SW 1 to SW ₄ are not shown, respectively, switch SW ₁ and the set and switch SW ₂ of the SW ₄
And SW ₃ are opened and closed with opposite polarities, and the polarity of the exciting current flowing through the exciting coil L is reversed.

By the way, when such a switch is composed of a semiconductor element, a switch drive circuit as shown in FIG. 5 or 6 is usually used.

FIG. 2 shows a circuit when npn transistors are used for all the switches. Control circuit _BT 1 to BT ₄ which corresponds to the switch _SW 1 to SW ₄ controls the base current of this like is provided transistor _Q 1 to Q ₄ are respectively provided in the transistor of this like.

This also of the control circuit _BT 1 to BT driven independently for driving the like to ₄ Power _E D1 _{to E D3} is applied (control circuit BT ₄ is supplied in common with BT ₃ from _{E D3)} Timing signals S _{T1 to} S _T4 are input to these control circuits BT _{1 to} BT _4, and the transistors Q _{1 to} Q ₄ are opened / closed by these timing signals. The driving power supply E _D1 has an output terminal T ₃ and the driving power supply E _D2 has an output terminal T 3.
_4, the driving power source _{E D3} is applied to the control circuit _BT 1 to BT ₄ power terminal _{T 2} as a reference.

However, according to the circuit shown in FIG. 5, three independent driving power sources, E _{D1 to} E _D3 , are required.
It is extremely inconvenient in circuit design.

Therefore, in order to reduce the number of independent driving power supplies, as shown in FIG. 6, a circuit is shown in which two types of transistors, npn and pnp, are combined and used as a switch.

FIG. 6 shows the npn transistors Q ₁ and Q ₂ shown in FIG.
Is replaced by pnp transistors Q ₁ ⁻ and Q ₂ ⁻ , and accordingly, the drive power supply _ED1 applies a drive voltage to the control circuits BT ₁ and BT ₂ with the power supply terminal T ₁ as a reference, The drive power supply E _D3 is configured to apply a drive voltage to the control circuits BT ₃ and BT ₄ with the power supply terminal T ₂ as a reference. In this case, the number of independent drive power sources can be reduced to two, E _D1 and E _D3 .

Therefore, this independent drive power source E_D1And E_D3Excitation power
E In the case of making from, the configuration shown in FIG. 7 can be considered.

Capacitor C₁And Zener diode D_Z1Connected in parallel
Resistor R in series with the circuit₁The series circuit connected to
Magnetic power E Connected in parallel to C₁From both ends of
Drive voltage V_D1Is the drive circuit BT_ThreeAnd BT_FourBeing supplied to
There is. Furthermore, the capacitor C_TwoAnd Zener diode D
_Z2Resistor R in series with the circuit connected in parallel_TwoIs connected
Excited power supply E Connected in parallel to the conden
SA C_TwoDrive voltage V from both ends of_D2Is the drive circuit BT₁And B
T_TwoIs being supplied to.

According to the above configuration, there is an advantage that a driving power supply for driving each transistor can be made by using the excitation power supply.

<Problems to be Solved by the Invention> However, in the case of the circuit shown in FIG.
_The polarity of the semiconductor transistors used as _{1 to} SW ₄ is limited. Specifically, the switches SW ₁ and SW ₂ are pnp-type transistors (or P
-Channel type FET), npn type transistors (N in case of using FET) for switches SW ₃ and SW _4.
-Channel type FET) must be used.

However, in the case of the exciting circuit of the electromagnetic flow meter, since it is necessary to apply a high voltage to switch because the rising of the exciting current after the polarity reversal is fast, it is necessary to use a pnp-type transistor (or P-channel FET). It is difficult to obtain an element having a large voltage and a small driving power source in terms of product type and price.

<Means for Solving the Problems> In order to solve the above problems, according to the first aspect of the present invention, opening and closing is controlled through a control circuit which is supplied with a timing signal and controlled by the timing signal. Each side of the bridge is formed by four switches, an exciting voltage is applied to its power supply terminal, an exciting coil is connected to its output terminal, and switches on opposite sides of the bridge are simultaneously opened and closed to form an exciting coil. In an exciting circuit of an electromagnetic flowmeter that reverses the polarity of an exciting current that flows, a first series circuit of a Zener diode and a resistor in which a first capacitor is connected in parallel is connected in parallel to a power supply terminal, and a second capacitor is connected in parallel. A zener diode in which a second series circuit of a zener diode and a resistor has a third capacitor connected in parallel between one of the power supply terminal and one of the output terminals. A third series circuit of a battery and a resistor is respectively connected between one of the power supply terminals and the other of the output terminals, and the voltage of the charge accumulated in these capacitors is used as the power supply of the control circuit. According to the second aspect, each side of the bridge is formed by four switches which are supplied with a timing signal and whose opening and closing are controlled via a control circuit controlled by the timing signal, and an exciting voltage is applied to a power supply terminal thereof. In the exciting circuit of the electromagnetic flow meter, the first capacitor is connected in parallel in which the exciting coil is connected to its output terminal and the switches of the opposite sides of the bridge are simultaneously opened and closed to invert the polarity of the exciting current flowing in the exciting coil. A first series circuit of a Zener diode and a resistor connected to is connected in parallel to a power supply terminal, and a second series circuit of a Zener diode and a resistor to which a second capacitor is connected in parallel.
A series circuit is connected between one of the power supply terminals and one of the output terminals, respectively, and one of the control circuits is supplied with an independent power supply and further supplied with a timing signal so that one of the switches is connected.
Drive the other control circuit to control the rest of the control circuit with a timing signal that is a direct current insulated timing signal formed by this control circuit, and to control the rest by using the voltage due to the charges accumulated in the first and second capacitors. It is designed to be used as the power source of the circuit.

<Operation> According to the first claim, the third and fourth switches are controlled by the control circuit to which the driving power is supplied by the electric charge stored in the first capacitor of the first series circuit, and the third switch of the second series circuit is controlled. (2) Controlled by a control circuit that is supplied with drive power from the electric charge accumulated in the capacitor and controlled by a control circuit that is supplied with drive power from the electric charge accumulated in the third capacitor of the third series circuit The third switch charges its own capacitor with the excitation voltage when its own switch is not conducting, and maintains its continuity with the voltage stored in its own capacitor when its own switch is conducting.

According to the second claim, the third and fourth switches are the first
Controlled by the third and fourth control circuits to which drive power is supplied by the charge accumulated in the first capacitor of the series circuit,
The first switch controlled by the first control circuit, which is supplied with the drive voltage by the charge accumulated in the second capacitor of the second series circuit, charges its own capacitor with the excitation voltage when its own switch is not conducting, When its own switch conducts, it maintains conduction by the voltage accumulated in its own capacitor, and the second switch is controlled by a second control circuit to which an independent power source is supplied, and a timing signal output from this second control circuit. The first, third, and fourth control circuits are controlled by the insulated timing signal.

<Embodiment> An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention. The parts having the same functions as those of the conventional circuit elements shown in FIGS. 4 to 7 are designated by the same reference numerals, and the description thereof will be appropriately omitted.

Between the power supply terminal T ₁ and the output terminal T _3, a series circuit of the capacitor C ₃ is connected Zener diodes and D _Z3 and the resistance R ₃ is connected through a diode D ₃ in parallel,
The drive voltage V _D3 across the capacitor C ₃ is applied to the control circuit BT ₁ .

Further, a zener diode D _Z4 in which a capacitor C ₄ is connected in parallel is provided between the power supply terminal T ₁ and the output terminal T _4.
And a resistor R ₄ are connected in series via a diode D _4, and the drive voltage V _D4 across the capacitor C ₄ is applied to the control circuit BT ₂ .

Further, all the transistors Q ₁ to Q ₄ functioning as switches arranged on each side of the bridge are npn type transistors.

Next, the operation of the circuit will be described. Timing now
Signal S_T1And S_T4Transistor Q₁And Q_FourIs o
And the timing signal S_T2And S_T3By
Langista Q_TwoAnd Q_ThreeIs turned on, the
Mode D_ThreeThrough the capacitor C_ThreeAnd Zener diode
D_Z3Parallel circuit with resistor R_ThreeExcitation voltage in series circuit with
E Is applied. Therefore, the capacitor C_ThreeHas a charge
Drive voltage V accumulated_D3Occurs, and this is the control circuit B
T₁It becomes the driving power source.

Next, the transistors Q ₁ and Q ₄ are turned on by the timing signals S _T1 and S _T4 , and the timing signals S _T2 and S ₄ are turned on.
_In a state where the transistors Q ₂ and Q ₃ are switched off by _T3 , conversely, charges are accumulated in the capacitor C ₄ to generate the drive voltage V _D4 , which is the same as the previous transistor Q ₂
Serves as a driving power source for the control circuit BT ₂ in a state where is turned on.

Also, when the transistors Q ₁ and Q ₄ are turned on, the transistor Q
_{When 2} and Q ₃ are off, the charge accumulated in the capacitor C ₃ is blocked by the diode D ₃ and is discharged only through the control circuit BT ₁ , but this discharge time is the control circuit BT ₁ Can be selected so as to keep the transistor Q ₁ on continuously by properly designing.

Furthermore, the transistor Q_FourIs the excitation power source E Continuously
Control circuit BT_FourDrive voltage V_D1Is being applied
Then, the timing signal S_TCan be turned on / off by
You can

In the circuit shown in FIG. ₁ , transistors Q ₁ and Q ₂ are each provided with a control circuit corresponding to one to one, and a drive power supply subordinate to the excitation power supply is provided to each of them, but the circuit shown in FIG. An example is shown that can be configured when the generator circuit and its power supply are present.

A bridge is constituted by field effect transistors Q _{1e to} Q _4e corresponding to the transistors Q _{1 to} Q ₂ . This circuit of a transistor _{Q 1e, Q} 3, e, and control of the respective identical construction to the _{Q 4e} circuit _BT 5, BT _7, and BT ₈ is provided, by supplying a base current to control the opening and closing each of the base ing. The control circuit BT ₆ controls the base current of the transistor Q _2e .

This is the control circuit BT ₆ is provided independently of the power source E _B, are controlled by the timing signal S _T2 supplied from the outside, the photocoupler PC ₇ of the control circuit BT ₇ via a terminal timing signal S _T3 from its output Is applied to one end of a phototransistor which constitutes the control circuit B, and the inversion timing signals S _T1 and S _T4 are respectively applied via terminals to the control circuit B.
It is applied to one ends of the phototransistors constituting the photocouplers PC ₅ and PC ₈ of T ₅ and BT ₈ , respectively.

Also, independent of the power supply E _B is applied to the other end of each phototransistor constituting the photocoupler PC _5, PC _7, PC ₈ of the control circuit via the terminal.

Incidentally, the control circuit BT ₅ is voltage charged in the capacitor _{C 3,} the control circuit BT ₆ by the power supply _{E B,} the control circuit BT ₇ and BT ₈ are each driven by a voltage charged in the capacitor _{C 1.}

The circuit shown in FIG. 3 shows an embodiment in which a voltage adjusting circuit is added after the exciting power source.

Excitation power supply E And bridge power supply terminal T₁And T_TwoIn between
The excitation voltage is controlled to be constant via the pressure adjustment circuit REG.
It shows the case of supply. Switch SW₅From the outside
It is opened and closed by the control signal and its output is the inductance L._i
And capacitor C_iSmooth with the power supply terminal T of the bridge₁,
T_TwoIs applied as a constant voltage. like this
The present invention can be applied to excitation circuits having various configurations.

As described above, according to this embodiment, when the switch timing generation circuit and its power source are present, there is an advantage that the circuit configuration is simplified.

In the embodiment shown in FIG. 1, the diode ▲ D ^- ₃
▼ and D ₄ can be omitted by appropriately selecting the control circuit of the switch and the constants of the resistors R ₃ , R ₄ and the capacitors C ₃ , C ₄ .

For example, transistor Q₁Capacitor C when is off
_ThreeCharging current i_cIs i_c~ (E -V_D3) / R_Three And the transistor Q₁Capacitor C when is on
_ThreeDischarge current i_cnIs i_cn~ V_D3/ R_Three+ (BT₁Current consumption)_c≫ i_cnIf you design the circuit so that
Capacitor C for required time_ThreeCan hold a charge on
Because it is Noh.

<Effects of the Invention> As described above in detail with the embodiments, according to the first claim, it is possible to minimize the number of driving power supplies for the switch for controlling the exciting current, and to control the semiconductor. The same type of switch can be used, an inexpensive excitation circuit can be used, and the second claim requires one independent power source as compared with the first claim. However, the circuit configuration can be simplified.

[Brief description of drawings]

 FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, and FIG.
Is a circuit diagram showing a modification of the embodiment shown in FIG.
The drawing shows a further modified embodiment of the embodiment shown in FIG.
Fig. 4 shows the basic structure of the conventional first excitation circuit.
FIG. 5 is a block diagram showing the configuration of the conventional second excitation circuit.
FIG. 6 is a circuit diagram showing the configuration of a conventional third excitation circuit.
FIG. 7 and FIG. 7 are circuit diagrams showing the configuration of a conventional fourth excitation circuit.
Indicates. E …… Excitation power supply, L …… Excitation coil, SW₁~ SW_Four
...... Switch, BT₁~ BT₈...... Control circuit, PC₅,
PC₇, PC₈...... Photo coupler, Q₁~ Q_Four……Tiger
Register, T₁, T_Two...... Power supply terminal, T_Three, T_Four...... Out
Force terminal.

Claims (2)

[Scope of utility model registration request] 1. A side of a bridge is formed by four switches whose opening and closing are controlled by a control circuit which is supplied with a timing signal and controlled by the timing signal, and an exciting voltage is applied to its power supply terminal to output the same. In the exciting circuit of the electromagnetic flow meter, in which the exciting coil is connected to the terminal and the polarity of the exciting current flowing in the exciting coil is reversed by opening and closing at the same time with the switches on the opposite sides of the bridge as a set, the first capacitors are connected in parallel. A first series circuit of a Zener diode and a resistor connected in parallel to the power supply terminal, and a second series circuit of a Zener diode and a resistor in which a second capacitor is connected in parallel is provided to one of the power supply terminal and the output terminal. A third series circuit of a Zener diode, in which a third capacitor is connected in parallel, and a resistor is connected to one of the power supply terminal and the output terminal. Are connected between the other terminal, the excitation circuit of the electromagnetic flow meter, characterized in that the power supply of said control circuit with a voltage by the charge accumulated in this like capacitors. 2. A side of a bridge is formed by four switches whose opening and closing are controlled by a control circuit which is supplied with a timing signal and controlled by the timing signal, and an exciting voltage is applied to its power supply terminal to output the same. In the exciting circuit of the electromagnetic flow meter, in which the exciting coil is connected to the terminal and the polarity of the exciting current flowing in the exciting coil is reversed by opening and closing at the same time with the switches on the opposite sides of the bridge as a set, the first capacitors are connected in parallel. A first series circuit of a Zener diode and a resistor connected in parallel to the power supply terminal, and a second series circuit of a Zener diode and a resistor in which a second capacitor is connected in parallel is provided to one of the power supply terminal and the output terminal. , One of the control circuits is supplied with an independent power source, and the timing signal is applied to the one of the control circuits. One of the two control circuits is driven to control the remaining control circuit with a timing signal which is a DC signal isolated from the timing signal formed by this control circuit, and a voltage generated by the charges accumulated in the first and second capacitors. An exciting circuit for an electromagnetic flow meter, wherein the exciting circuit is used as a power source for the rest of the control circuit.