JPH0545196A - Exciting circuit of electromagnetic flowmeter - Google Patents

Abstract

PURPOSE:To smooth the switching of voltage, and also solve the inconvenience to reset the standard voltage by calibers, kinds, etc., by detecting whether an exciting current is at the saturation voltage or not to switch high voltage and low voltage. CONSTITUTION:The polarity and the existence of the excitation of an exciting current If are controlled by an excitation switching element FS1, and the current is allowed to flow to an exciting coil L. A switch Q4 becomes off and the exciting voltage applied from a power source element PS1 becomes low voltage VL, because the control signal Vc at this time is smaller than a standard voltage ES3. However, an operational amplifier Q5 operates so that a transistor Q6 is saturated because the impedance Zc of the coil L increases in an excessive state for the current If to be reversed. On the other hand, in a voltage switching element VS1 a comparator CO compares the voltage Vc with the voltage ES3, detects the saturation of a constant current control circuit CC1, makes the switch Q4 on, and applies the high voltage VH adding the increase portion between junctions CN1 and CN2 to the low voltage VL, to the exciting coil L.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exciting circuit of an electromagnetic flow meter in which the rising of exciting current is made steep, and the exciting current can be switched with a particularly simple structure to facilitate high-frequency excitation. The present invention relates to an exciting circuit of an electromagnetic flowmeter improved so that.

[0002]

2. Description of the Related Art As an exciting circuit of an electromagnetic flowmeter in which a high voltage is applied in a transient state to a voltage applied in a steady state so that the rising of an exciting current is accelerated, for example, Japanese Patent Laid-Open No. 53-53-
No. 20956 is disclosed. FIG. 5 is a circuit diagram showing the structure of the excitation circuit of this electromagnetic flow meter. Below, FIG.
About the outline.

A tap is provided in the middle of the secondary side of the transformer T to which the commercial frequency AC voltage is applied to the primary side, and the input end of the diode bridge D _B is connected between this intermediate tap and the ground point. The low voltage DC voltage E _L
To get This DC voltage E _L is smoothed by the capacitor C _L.

Further, an anode of a diode D ₂ is connected to the secondary side of the transformer T, and a capacitor C _H is connected to the cathode of the transformer D to rectify and smooth the rectified and smoothed DC voltage E at both ends. _{Get h} This like transformer T, the diode - Doburijji D _B, diode - de D _2, the capacitor C _H, is C _L like a DC voltage source E is configured.

This DC voltage E_HIs the transistor Q₃Through
Then switch S₁, S₂, S₃, S _FourYellowtail formed by
It is applied to one end of the input end of the edge BG. And that
An exciting coil L is connected to the output end of the. Also, direct
Current voltage E_LM Diode D₁Bridge BG via
It is applied to one end of the force end.

A transistor Q ₁ is provided at the other end of the bridge BG.
And a resistor R ₄ connected in series. The reference voltage E _S1 is applied to the non-inverting input terminal (+) via the resistor R ₁ and the output terminal of the operational amplifier OP1 is connected to the base of the transistor Q ₁ via the resistor R ₂ and its emitter is connected to the resistor. R ₃
Is connected to the inverting input terminal (-) of the operational amplifier OP1 via. The steady value of the exciting current is set by the reference voltage E _S1 .

The above transistor Q ₁ and resistor R ₁
The constant current circuit CCS is composed of R ₄ , the operational amplifier OP1, the reference voltage E _{S1 and the} like. Furthermore, the other end of the bridge BG the inverting input terminal of the operational amplifier OP2 to the reference voltage E _S2 is applied to the non-inverting input terminal (+) - is connected to, the output terminal of the transistor Q ₂ base () - scan It is connected to the.

Transistor Q whose emitter is grounded₂of
Collector,Resistance R_FiveThrough transistor Q₃The base
Connected to the base, this base has a resistance R₆Through the transition
Star Q₃Connected to the collector. With the above configuration
The timing circuit (not shown)₁, S
₂, S ₃, S_FourWhen the conduction state of is reversed, the exciting current becomes steady
Transistor Q because it changes from the value₁The collector voltage of
Reference voltage E_S2Transistor Q becomes lower than the value of₂Turn on
And

Therefore, a current flows through the resistors R ₅ and R ₆ ,
The transistor Q ₃ turns on. As a result, the cathode terminal of the diode D ₁ becomes a direct current voltage E _H having a high voltage, the high voltage is applied to the bridge BG, the diode D ₁ becomes reverse biased, and the low direct current voltage E _L becomes Be cut.

After that, when the exciting current changes and reaches a steady value, the collector voltage of the transistor Q ₁ becomes the reference voltage E.
_It becomes higher than the value of _S2 and turns off the transistor Q ₂ . As a result, the transistor Q ₃ also turns off, and the diode D
_A low DC voltage E _L is applied to the bridge BG from the cathode terminal of ₁ . The above operation is performed by the switch S ₁ ~
It is performed every time S ₄ is switched, and a high voltage is applied during the transient period of the exciting current and a constant voltage is applied during the steady period.
Will be applied to. As described above, when switching the exciting current, the switching is promptly executed.

[0011]

However, in the exciting circuit of the electromagnetic flowmeter as described above, the exciting power source is switched depending on the value of the analog voltage such as the collector voltage of the transistor Q ₁ , so that the switching is smooth. In addition, when the exciting current is selected and changed depending on the diameter and model, if the reference voltage E _S1 is changed in accordance with the exciting current value, the reference voltage E _S2 must be reset accordingly. There is a disadvantage that it does not happen, and it has a drawback that it becomes a complicated structure as a whole.

[0012]

In order to solve the above problems, the present invention applies a magnetic field to a fluid to be measured by periodically repeating an exciting current having two or more steady values. It relates to the exciting circuit of the electromagnetic flowmeter that detects the generated voltage. It connects the exciting coil to the output terminal of the power supply that supplies two voltages, the high voltage and the low voltage, and the bridge that has the changeover switch on each side. A bridge circuit that inverts the direction of the exciting current flowing in the exciting coil by opening and closing the changeover switch, and a current detection element and a control element are connected in series between the input terminal of this bridge circuit and the previous power source. A control signal that controls the internal resistance of the previous control element by comparing the detection voltage generated in the detection element with a predetermined voltage and that the excitation current is a non-saturation voltage in the steady state and a saturation voltage in the transient state. A constant current control means having an amplifier for outputting the voltage, and a voltage switching means for detecting whether or not the control signal is the previous saturation voltage and switching to the low voltage in the previous steady state and to the high voltage in the previous transient state. It was done.

[0013]

[Operation] The bridge circuit inverts the direction of the exciting current flowing in the exciting coil by opening and closing the changeover switch on each side. In this case, the amplifier of the constant current control means is connected to the input end of this bridge circuit and the front end. The detection voltage generated in the current detection element connected in series with the power supply is compared with a predetermined voltage to control the internal resistance of the control element connected in series to the current detection element, and the excitation current is in the steady state. It outputs a control signal which is a kind of ON / OFF signal which is a non-saturated voltage and a saturated voltage in the transient state. The voltage switching means detects whether this control signal is the previous saturation voltage or not, and supplies two voltages, a high voltage and a low voltage, such that the control signal is a low voltage in the steady state and a high voltage in the transient state. Switch the power supply.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention.

PS1 is a power supply unit, VS1 is a voltage switching unit, and C
C1 is a constant current control circuit, FS1 is an excitation switching unit, and L is an excitation coil. Power unit PS1 transformer T, diode - de D _3, D _4, and is constituted by a capacitor C _1, C _2. An AC voltage or an intermittent DC voltage in the case of a switching power supply is applied to the primary winding of the transformer T, and a tap T ₃ is provided in the middle of the terminals T ₁ and T ₂ of the secondary winding. the T ₃ diodes - de D ₃
The node of is connected.

A capacitor C ₁ is connected between the cathode of the diode D ₃ and the terminal T ₁ , and a connection point CN ₁ between the cathode of the diode D ₃ and the capacitor C ₁ is smoothed. Generated low voltage V _L. Further, the terminal of the diode D ₄ is connected to the terminal T ₂ , and the capacitor C ₂ is connected between the cathode of the diode D ₄ and the connection point CN 1, and the cathode of the diode D ₄ is connected. Connection point CN with capacitor C ₂
A smoothed high voltage V _H is generated at 2.

The voltage switching unit VS1 has hysteresis.
Comparator CO, transistor Q _Four, Reference voltage E_S3Na
The input terminal of the comparator CO is controlled at one end.
Signal V_CHowever, at the other end, the reference voltage E_S3Is applied,
Output signal V generated at the output end₀Is the connection points CN1 and CN
The drain and source are connected between 2 and
Field-effect transistor Q_FourTo the gate
Is being applied.

The constant current control circuit CC1 includes an operational amplifier Q ₅ ,
It is composed of a reference voltage E _S4 , a detection resistor R ₇ , an impedance variable field effect transistor Q ₆ , a diode D ₅ , and the like. One end of the series circuit in which the detection resistor R ₇ and the transistor Q ₆ are connected in series is connected to the connection point CN 1, and the connection point of these detection resistor R ₇ and the transistor Q ₆ is connected to the common potential point COM. ing. Further, a diode D ₅ is connected in parallel with the transistor Q _{6 in the} opposite polarity to the direction of the exciting current I _f .

Operational amplifier Q_FiveIs the detection resistance R₇From both ends of
Generated detection voltage and reference voltage E_S4And the exciting current is
Control signal V so that it becomes a predetermined value_CTransistor Q₆
Output to the gate of and to the input end of the comparator CO
Also outputs. The other end of the series circuit and the terminal T of the power supply unit PS1₁
An excitation switching unit FS1 is connected between the and. this
The excitation switching unit FS1 is a switch S_FiveAnd S₆In series, S₇
And S ₈Are connected in series, and these series circuits are connected in parallel.
Connected to form a bridge circuit.

An exciting coil L is connected between the connection point between the switches S ₅ and S ₆ and the connection point between S ₇ and S ₈ . These switches are switched by a timing signal output from a timing circuit (not shown). In addition, these switches S ₅ , S ₆ , S ₇ , S ₈
Diodes D _{6 to} D ₉ are connected in parallel with each other.

Next, the operation of the embodiment configured as described above will be described with reference to the waveform chart shown in FIG. Figure 2
(A) is a waveform of the exciting current I _f ′ flowing in the exciting coil L,
FIG. 2B shows the ON / OFF state of the switch Q ₄ , FIG.
(C) has shown the waveform of the applied voltage _Vf to the constant current control CC1, respectively.

The excitation current I _f ′ is controlled by the excitation switching section FS1 to control its polarity and the presence / absence of excitation, and is applied to the excitation coil L with a waveform as shown in FIG. 2 (a), for example. In this case, the control signal V _C of the operational amplifier Q ₅ controls the gate voltage of the transistor Q ₆ so that the steady-state value I _fc of the exciting current I _f ′ becomes E _S4 = I _fc · R _7. Q ₆ of the drain / source - between the nest Inpi - to adjust the dance.

At this time, the control signal V _C is the reference voltage E _S3
Since it fluctuates with a smaller value, its output voltage V ₀ is low level, and therefore the switch Q ₄ is in the off state (OFF) as shown in FIG. 2B. Therefore, the excitation voltage V _f applied from the power supply unit PS1 is as shown in FIG.
As shown in (c), the low voltage V _L is applied. This low voltage V _L is V _L > (R ₇ + Z _Q6 + R _C ) I _fc . Here, Z _Q6 is the impedance between the drain and the source of the transistor Q ₆ under constant current control, R
_C is the resistance of the exciting coil L.

However, in the transient state in which the exciting current I _f ′ (FIG. 2A) is reversed, the exciting current flowing through the exciting coil L fluctuates, so that the impedance Z _C of the exciting coil L increases. Therefore, the operational amplifier Q ₅ is a transistor Q ₆
The control voltage V _C to the gate of the transistor Q ₆ is controlled so that the drain-source impedance Z _Q6 of the transistor Q ₆ is minimized so that the transistor Q ₆ is saturated.

On the other hand, the voltage switching unit VS1 includes a comparator C.
O compares the control voltage V _c with the reference voltage E _S3 to detect the saturation of the constant current control circuit CC1 and turns on the switch Q ₄ (FIG. 2 (c)). When the switch Q ₄ is turned on, a high voltage V _H (FIG. 2C) obtained by adding the constant voltage V _L and the increase between the connection points CN1 and CN2 is applied to the exciting coil L.

The exciting current I _f ′ at this time _rises up to | I _f ′ | = I _{fc with} I _f ′ = V _H [1-exp (t / τ)], where τ is the time constant of the exciting coil L. , The rise time is shortened. When the exciting current I _f ′ reaches a predetermined steady value I _fc , the saturation of the operational amplifier Q ₅ is released, the switch Q ₄ is turned off, and the exciting current from the low voltage V _L to the exciting coil L is a steady value I _fc.
Supplied with.

FIG. 3 is a block diagram showing another first embodiment of the present invention. In this case, as shown in FIG. 1, instead of adding the increased voltage component in series to the low voltage V _L to form the high voltage V _H , the power supply unit PS2 separates the low voltage V _L and the high voltage V _H from each other. The configuration is such that it is taken out through a rectifier circuit. The high voltage V _H is smoothed by the capacitor C ₃ .

FIG. 4 is a block diagram showing another second embodiment of the present invention. In this case, the switch Q ₄ and comparator as a voltage switching unit VS2 - is obtained by a structure in which to insert the Fuotokapura PC between the motor CO. In the case of the present invention, since the ON / OFF signal is transmitted in about msec only when the exciting current is switched, control by the photocoupler becomes possible. According to this configuration, the switch Q ₄ and the constant current control circuit CC1 side can be separated in terms of direct current, and there is an advantage that the circuit design is facilitated.

[0029]

As described above in detail with the embodiments, according to the present invention, the control of the switch for switching between the high voltage and the low voltage is controlled by the saturated and non-saturated output from the constant current control circuit. Since the switching is performed in relation to the control signal that substantially functions as an on / off signal having a state,
This eliminates the inconvenience of having to reset the reference voltage in response to the exciting current value even when the exciting current is selected and changed depending on the diameter and model, as well as smooth voltage switching. Further, since a high voltage is applied to the constant current control circuit only when the exciting current is raised, unnecessary power loss in the constant current circuit section can be reduced.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram illustrating the operation of the embodiment shown in FIG.

FIG. 3 is a block diagram showing a first modified example of the present invention.

FIG. 4 is a block diagram showing a second modified example of the present invention.

FIG. 5 is a configuration diagram showing a configuration of an excitation circuit of a conventional electromagnetic flow meter.

[Explanation of symbols]

T transformer E DC voltage source CCS constant current circuit OP1, OP2 operational amplifier BG bridge PS1, PS2 power supply unit VS1, VS2 voltage switching unit CC1 constant current control circuit FS1 excitation switching unit L excitation coil CO comparator PC photo coupler V _H high voltage V _L low-voltage Q ₅ operational amplifier

Claims (1)

[Claims] 1. A high voltage and a low voltage in an exciting circuit of an electromagnetic flowmeter for detecting a voltage generated by applying a magnetic field to a fluid to be measured by periodically repeating an exciting current having two or more steady values. And a power supply that supplies two voltages of
A bridge circuit that connects an exciting coil to an output end of a bridge having a changeover switch on each side and opens and closes each changeover switch to reverse the direction of an exciting current flowing through the exciting coil, and an input end of the bridge circuit and the above-mentioned A current detection element and a control element are connected in series between a power supply and a detection voltage generated in the current detection element is compared with a predetermined voltage to control the internal resistance of the control element and the exciting current is in a steady state. Is a non-saturated voltage and has a constant current control means having an amplifier that outputs a control signal that is a saturated voltage in the transient state, and detects whether this control signal is the saturated voltage or not, and detects the low voltage in the steady state. An exciter circuit for an electromagnetic flow meter, comprising: a voltage switching means for switching to the high voltage in the transient state.