JPH0110573Y2 - - Google Patents

Description

[Detailed description of the invention] The invention includes an excitation coil, excitation current switching means for switching the direction of inflow of excitation current into the excitation coil, constant current means for passing a constant current through the excitation coil, and a DC voltage power supply. This article relates to an excitation circuit for an electromagnetic flowmeter.

Generally, an electromagnetic flowmeter has an excitation coil and electrodes arranged perpendicularly across the conduit in order to measure the flow rate of fluid flowing inside the conduit, and the excitation coil and electrodes are arranged orthogonally, and an excitation current is applied to the excitation coil. By flowing , magnetic lines of force are generated from the excitation coil, and when the fluid crosses the magnetic lines of force in the orthogonal direction, superpower is generated at the electrodes based on Fleming's law, and this generated electromotive force increases the flow rate. The flow rate is measured using the fact that the flow rate is proportional to the flow rate. By the way, in order to eliminate various inconveniences caused by the electrolytic action of the fluid flowing inside the conduit due to the electrodes placed facing the inside of the conduit, the excitation coil placed outside the conduit is shown in Fig. 1. There is one in which a rectangular AC excitation current is caused to flow through an excitation circuit as shown. That is, the excitation circuit of the conventional electromagnetic flowmeter shown in FIG.
4 and 4' are switched to flow the constant excitation current _I0 from the constant current circuit 5 in an alternating current manner. First, from time t ₀ to _{t 1} , when the changeover switches 3 and 3' are closed as shown in FIG. 2, the excitation coil 1 has an excitation electrode _I0 as shown in FIG. begins to flow towards. However, due to the transient characteristics of the excitation coil 1, the predetermined excitation current _I0 cannot be immediately applied to the excitation coil 1, and there is a delay time from time _t0.
A predetermined excitation current I ₀ flows through the excitation coil 1 when TD has elapsed, so in order to measure the flow rate, the time when the excitation current I ₀ is completely stabilized, that is, from time t ₀ to the time when the delay time T ₁ has elapsed TD < T ₁ , and a considerable delay time is required until the flow rate measurement time ΔT is reached. For this reason, the period for sampling the flow rate becomes extremely long, and this method is somewhat lacking in practicality. Note that FIG. 2 is a time chart when the changeover switches 4, 4' are closed from time _t1 to time _t2 , and in this case, the exciting current _I0 flows through the exciting coil 1 from the sign to the sign. .

Further, a technique for shortening the sampling period is disclosed in, for example, Japanese Patent Laid-Open No. 53-20956. In the conventional excitation circuit described in this publication, the sampling period is shortened by transiently increasing the voltage supplied to the excitation coil.

However, in the excitation circuit described in this publication, there are two power sources for excitation, one for high output and one for low output.
It is necessary to provide different types of power supplies, and it is also necessary to switch between the two types of power supplies according to the transient period and steady period of the excitation current.
Since it is relatively large at about 1A, the elements for switching between the two types of power supplies must be configured taking into consideration the effects of heat generation, etc., which makes the configuration complicated and increases the cost. There is a drawback. Moreover, this excitation circuit has the disadvantage that a fairly large, high-output power supply is required to increase the rise of the excitation current quickly.

The purpose of the present invention is to eliminate the above-mentioned drawbacks, shorten the flow rate sampling period, and provide an excitation electromagnetic flowmeter that has a very simple circuit configuration and is therefore excellent at reducing manufacturing costs. The purpose is to provide circuits.

In order to achieve the above-mentioned object, the excitation circuit of the electromagnetic flowmeter of the present invention includes an excitation current switching means that switches the direction of inflow of excitation current into the excitation coil in response to excitation current switching timing, and the excitation current switching means. A single DC power supply for supplying excitation current provided on an excitation current inflow side to the excitation current switching means, and a constant current means provided on an excitation current outflow side from the excitation current switching means, the constant current means comprising: a constant current transistor to which an excitation current input section is connected to an excitation current outflow side of the excitation current switching means; a constant current resistor to which an excitation current output section of the constant current transistor is connected;
A differentiation circuit that includes a charging/discharging capacitor, a charging/voltage dividing resistor, and a response switch that opens and closes in response to excitation current switching timing, and these are connected in series, and a reference power supply and voltage that are connected in series to each other. the voltage dividing resistor is connected to a series circuit connected in parallel to the charge/discharge capacitor, a set voltage input section into which a set voltage is input, and an input section of the constant current transistor. and a control amplifier in which the set voltage input part is connected to a connection part between a charging/discharging capacitor of the differentiating circuit and a voltage dividing resistor of the series circuit.

According to the above configuration, the set voltage of the control amplifier of the constant current means is transiently increased in response to the switching timing of the excitation current, so that the excitation current flowing through the excitation coil is quickly adjusted to the desired value. This will result in an increase to the period value. Moreover,
Unlike the conventional excitation circuit described in JP-A No. 53-20956, there is no need to switch the excitation power source or high voltage, so the configuration is simplified accordingly. .

Next, the above configuration of the present invention will be specifically explained using examples.

FIG. 3 is an electric circuit diagram of one embodiment of the present invention, and FIG. 4 is a time chart for explaining the operation of the circuit. The excitation circuit of this embodiment consists of an excitation coil L, an excitation current switching circuit ESC, and a constant current circuit CS.
, a first DC voltage power supply _E1 as a DC power supply for supplying excitation current, a timing circuit TC, and a monostable multivibrator MMV.

The excitation current switching circuit ESC is configured by connecting in parallel a series component of the first and fourth changeover switches A and B' and a series component of the second and third changeover switches A' and B. , an excitation current inflow portion I ₁ which is a common connection portion of the first and third changeover switches A and B, and an excitation current outflow portion I ₂ which is a common connection portion of the second and fourth changeover switches A′ and B′. , an excitation current inflow/outflow part _I3 to the excitation coil which is a common connection part of the first and fourth changeover switches A and B', and an excitation coil which is a common connection part of the second and third changeover switches A' and B. It has an excitation current inflow/outflow part _I4 for. The constant current circuit CS includes a control amplifier CA, an NPN type constant current transistor Q whose base is connected to the output section of the control amplifier CA via a base current limiting resistor _R1 , and an emitter of the constant current transistor Q. It includes a constant current resistor _R5 , a differentiating circuit DC connected to the setting voltage input section _IN1 of the control amplifier CA, a discharge resistor _R2 , a voltage dividing resistor _R3, etc., and an excitation current I from the excitation current switching circuit ESC. ₀
The collector of the constant current transistor Q is connected to _the inflow part _I5 , and _{the emitter thereof is connected to the inflow part I5 through} the constant current resistor _R5 . Connected to the outlet I ₆ . The differential circuit DC connects in series a charging/discharging capacitor C, a charging/voltage dividing resistor R ₄ , and a first response switch S ₁ whose opening/closing is controlled in response to the output pulse of a monostable multivibrator MMV, which will be described later. The discharging resistor R ₂ is connected in parallel to the charging/discharging capacitor C of the differential circuit DC, and is controlled in the same way as the first response switch S ₁ [However, the first response switch S ₁ is The opening and closing directions are reversed. ] A series circuit with a second responsive switch S ₂ is inserted. A series circuit of a voltage dividing resistor R ₃ and a second DC voltage power source E ₂ as a reference power source is inserted in parallel with the discharge/voltage dividing resistor R ₄ of the differentiating circuit DC.

Timing circuit TC is excitation current switching circuit ESC
The monostable multivibrator outputs a predetermined timing signal in response to the excitation current switching timing operation of the monostable multivibrator.
Monostable multivibrator by sending to MMV
Trigger MMV. The triggered monostable multivibrator MMV is the first of the constant current circuit CS,
Pulse outputs are sent to both switches S ₁ and S ₂ to open and close the second response switches S ₁ and S ₂ .

Explain the operation.

At time _t10 , the first and second changeover switches A and A' of the excitation current changeover circuit ESC are closed by switch driving means (not shown). Then, an excitation current I ₀ starting from the sign to the sign begins to flow through the excitation coil L while changing as shown in FIG. 4 and 5. Here, the high level part of Fig. 4 1 [time
_t10 to _t20 ], the first and second changeover switches A,
A' indicates the period when it is closed, and the _high level portion in _FIG . By the way, at time _t10 , the timing circuit TC
A trigger pulse is sent to the monostable multivibrator MMV from , which causes the monostable multivibrator MMV to generate a rectangular pulse output as shown in Fig. 4. Therefore, the constant current circuit CS
The first and second responsive switches S ₁ and S ₂ are in an open and closed position opposite to that shown, ie, the first responsive switch S ₁ is closed while the second responsive switch S ₂ is open. Therefore, a transient current flows into the charging/discharging capacitor C of the differentiating circuit DC from the second DC voltage source E ₂ , so that the charging/voltage dividing resistor R ₄ receives:
4 A differential pulse voltage as shown in FIG. 4 appears. As a result, the set voltage input section IN ₁ of the control amplifier CA receives the normal set voltage e _s , that is,
A transient set voltage e _s ' that is larger than the voltage obtained by dividing the DC voltage of the second DC voltage power source E ₂ by the voltage dividing resistor R ₃ and the charging/voltage dividing resistor R ₄ is applied. This will control the amplifier
CS operates as a circuit so that a large excitation current I ₀ flows through the constant current resistor R ₅ in response to the transient set voltage e _s ′. As a result, a phase advance occurs in the excitation current I ₀ and a predetermined excitation current I ₀ begins to flow through the excitation coil L after a delay time T _D from time t ₁₀ in FIG. 4 .

Since the delay time T _D according to the present embodiment is shorter than the delay time T _D according to the prior art, the present embodiment naturally makes it possible to shorten the sampling period for flow rate measurement.

Furthermore, in the excitation circuit of this embodiment, the set voltage of the control amplifier CA is transiently increased using a differentiating circuit DC.
- Like the conventional excitation circuit described in Publication No. 20956,
There is no need for two types of power sources, and there is no need for a complicated configuration for switching between these two types of relatively high voltage power sources. Furthermore, in this invention, by selecting the constant of the differential circuit DC,
The rise of the excitation current can be easily accelerated.

In addition, the charge charged in the charging/discharging capacitor C of the differential circuit DC is a monostable multivibrator.
When the pulse output from the MMV disappears [time T _D has elapsed from time t ₁₀ in Figure 4] and the first and second response switches S ₁ and S ₂ return to the open/close positions shown, the discharge resistor R ₂ , which completes the differentiation circuit DC's preparation for the next sampling.

In the above embodiment, although the charging/discharging capacitor C is used in the differentiating circuit DC, the first
voltage dividing resistor by opening and closing response switch _S1
Another voltage dividing resistor may be inserted in parallel with _R3 .

As described above, according to the present invention, the set voltage of the set voltage input section of the control amplifier of the constant current means is increased transiently in accordance with the excitation current switching timing, thereby shortening the sampling period of the flow rate. In addition, the circuit configuration for this purpose is relatively simple, and costs can be reduced.

[Brief explanation of the drawing]

Figure 1 is an electrical circuit diagram of the prior art, Figure 2 is:
FIG. 3 is an electric circuit diagram of an embodiment of the present invention, and FIG. 4 is a time chart for explaining the circuit operation. L...Exciting coil, ESC...Exciting current switching circuit, CS...Constant current circuit, _E1 ...First DC voltage power supply, DC...Differentiating circuit, CA...Control amplifier, TC...Timing circuit, MMV...Monostable multivibrator.

Claims (1)

[Claims for Utility Model Registration] Exciting current switching means for switching the direction of inflow of excitation current into an excitation coil in response to excitation current switching timing; and a unit provided on the excitation current inflow side to the excitation current switching means. a DC power source for supplying excitation current, and a constant current means provided on the excitation current outflow side from the excitation current switching means, the constant current means providing excitation current on the excitation current outflow side of the excitation current switching means. a constant current transistor to which a current input section is connected; a constant current resistor to which an excitation current output section of the constant current transistor is connected; a charging/discharging capacitor, a charging/voltage dividing resistor, and opening/closing in response to excitation current switching timing. A differential circuit including a response switch and connected in series with each other; a reference power source and a voltage dividing resistor connected in series with each other; and the voltage dividing resistor is connected in parallel to the charging/discharging capacitor. a set voltage input section into which a set voltage is input, and an output section connected to the input section of the constant current transistor, and the set voltage input section is configured to charge and discharge the differentiating circuit. An excitation circuit for an electromagnetic flowmeter, comprising a control amplifier connected to a connection between a capacitor and a voltage dividing resistor of the series circuit.