JPH0126491B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electromagnetic flowmeter, and particularly to an electromagnetic flowmeter with low power consumption.

An electromagnetic flowmeter is configured to apply a magnetic field perpendicular to the fluid flow direction, simultaneously detect changes in electrical signals in the fluid flow path, and measure the fluid flow rate based on this. As a method of applying a magnetic field, a method in which an excitation current is passed through an excitation coil is widely used. By the way, the power consumption of an electromagnetic flowmeter is determined mostly by the excitation power, so recently, the excitation current is periodically passed through the excitation coil, and the flow rate is measured by sampling the signal generated between the electrodes at that time. The current practice is to reduce power consumption by not allowing excitation current to flow. However, in order to reduce power consumption, it is necessary to make the period in which the exciting current is not flowing longer than the period in which the exciting current is flowing, but if it is too long, the response and S/N ratio will deteriorate. It's actually not very effective. Furthermore, some methods of applying a magnetic field use permanent magnets. Although methods using permanent magnets can reduce power consumption, they have the disadvantage that output drifts due to the electrochemical potential created between the electrodes and the liquid.

The present invention provides an electromagnetic flowmeter transmitter with a permanent magnet and an excitation coil, performs excitation almost only with the permanent magnet, and allows current to flow through the excitation coil as needed. By eliminating the noise caused by the electrochemical potential contained in the induced voltage generated between the electrodes by using the induced voltage generated between the electrodes when current is passed through the excitation coil, it is possible to eliminate the above-mentioned drawbacks. This realizes an electromagnetic flowmeter with low power consumption.

FIG. 1 is a connection diagram showing an embodiment of the electromagnetic flowmeter of the present invention. In FIG. 1, 1 is an electromagnetic flowmeter transmitter, 2 is an excitation current circuit, and 3 is a signal processing circuit. The electromagnetic flowmeter transmitter 1 includes a pipe 11 through which fluid flows, electrodes 12a and 12b, and cores 13a and 1.
3b, 13c, 13d and permanent magnets 14a, 14
b, 14c, 14d and excitation coils 15a, 1
5b. The cores 13a to 13b and the permanent magnets 14a to 14d are coupled as shown in the figure to form a magnetic circuit that generates a magnetic field perpendicularly within the pipe 11. Note that the part consisting of the permanent magnet 14a, the core 13b, and the permanent magnet 14b, and the part consisting of the permanent magnet 1
4c, the core 13d, and the permanent magnet 14d may each be one permanent magnet. In addition, the excitation coils 15a and 15b are connected to the pipe 11 and the core 13.
a, 13c, and is excited in a direction that demagnetizes (or magnetizes) the magnetic field of the permanent magnets 14a to 14d when the excitation current Iw flows. The excitation current circuit 2 consists of a constant current source 21 and a switch 22, and when the switch 22 is turned on by the control pulse _P1 from the signal processing circuit 3, the excitation coil 15 is turned on.
An excitation current Iw is passed through a and 15b. The signal processing circuit 3 is provided with the voltage e _a induced between the electrodes 12a and 12b of the transmitter 1, and converts the noise due to the electrochemical potential contained in the induced voltage during the period T in which the exciting current Iw is not flowing into the exciting current. The system uses and removes the induced voltage generated during the period t during which Iw is flowing, and outputs a value _Vo related to the flow rate of the fluid.
Sampling switch _S1 and hold capacitor
a circuit ₃₂ that samples and holds the output e _b of the amplifier 31, a differential amplifier 33 that amplifies the difference between the output e _b of the amplifier 31 and the output of the sample and hold circuit 32, and a sampling switch S ₂ and a hold circuit an output circuit 34 that outputs the output e _c of the differential amplifier ₃₃ as Vo, and a pulse P that controls the switch 22 and the sampling switches S ₁ and S ₂ , respectively. An example is shown in which a pulse generating circuit 35 that generates pulses ₁ , _P2 , and _P3 is provided.

The operation of the present invention constructed in this way will be explained below with reference to the time chart of FIG. Normally, the electromagnetic flowmeter transmitter 1 is excited only by permanent magnets 14a to 14d, and the fluid has a magnetic flux density B ₁
A magnetic field is given. On the other hand, the pulse _P1 generated from the pulse generating circuit 35 at the timing shown in FIG.
is turned on and the excitation current Iw is supplied to the excitation coils 15a and 15b for a certain period of time t, demagnetizing (or magnetizing) the magnetic field caused by the permanent magnets 14a to 14d.
Because the fluid is excited in the direction of
A magnetic field of B ₂ (B ₂ ≈0) is applied. As a result, induced voltage _{e a} generated between electrodes 12a and 12b
is as shown in FIG. 2B, and changes by flowing the excitation current Iw. Note that the solid line in FIG. 2B shows the case of demagnetization, and the dotted line shows the case of increase/decrease. Here, if the flow velocity of the fluid is v, the diameter of the pipe 11 is D, and the noise due to electrochemical potential is Ec, then
The value e _a1 of the induced voltage generated during the period T when the exciting current Iw is not flowing and the value e _a2 of the induced voltage generated during the period t when the exciting current Iw is flowing are given by the following equations.

e _a1 =B ₁ vD+Ec (1) e _a2 =B ₂ vD+Ec (2) The induced voltage e _a from the oscillator 1 is amplified by the amplifier 31 and then sent to one input terminal (+) of the differential amplifier 33.
added to. Further, the output e _b of the amplifier 31 is also given to a sample and hold circuit 32 . When _the switch _S1 is turned on by the sampling pulse _P2 generated at _the timing shown in FIG. Hold as compensation value. Output of sample hold circuit 32
e _b2 is applied to the other input terminal (-) of the differential amplifier 33. Therefore, the output e _c of the differential amplifier 33 is
The period during which the permanent magnet is excited (excitation current
During T (period in which Iw is not flowing), e _c = k ₂ (e _b1 − e _b2 ) = k ₁ k ₂ (B ₁ − B ₂ ) vD (3) where, k ₁ = gain k ₂ of amplifier 31 = gain of the differential amplifier 33, the noise component Ec including the electrochemical potential is removed, and the value becomes proportional only to the flow rate of the fluid. The output e _c of the differential amplifier 33 is sent to the output terminal OUT via the output circuit 34 as an output voltage Vo. The output circuit 34 is driven by a pulse _P3 generated at the timing shown in FIG.
Switch S ₂ turns off during period t when Iw is flowing.
Accordingly, the output e _c of the differential amplifier 33 during the period T during which only the permanent magnet is excited is sent to OUT.

In this way, in the present invention, the magnetization is performed almost exclusively by the permanent magnet, and the excitation current is occasionally applied, so power consumption can be reduced and the S/
The N ratio and responsiveness do not deteriorate, and the noise component caused by electrochemical potential, which is a problem with excitation using a permanent magnet, can be effectively eliminated.

In the above description, the signal processing circuit 3 is constructed using an analog circuit, but it may also be constructed using a microprocessor as shown in FIG. That is, in FIG. 3, the induced voltage e _a from the oscillator 1 is amplified by an amplifier 31, converted to a digital value D _i by an A/D converter 36, and given to a microprocessor 37. . The microprocessor 33 generates a pulse _P1 that turns on the switch 22 of the excitation current circuit 2, and turns on the A/D converter 3 according to the induced voltage value e _a2 at that time.
The digital value from 6 is stored in the acquisition register as the compensation value D _i2 . During a normal period when the pulse _P1 is not generated, the digital value from the A/D converter 36 corresponding to the value e _a1 of the induced voltage generated by excitation of only the permanent magnet is used as the measured value D _i1 at each measurement cycle. The following equation is calculated between the captured value and the compensation value D _i2 previously stored in the register to obtain the output value Do from which the noise component due to the electrochemical potential has been removed.

Do=K (D _i1 - D _i2 ) where K is a proportional constant (4) The output value Do of the microprocessor 37 is given to the D/A converter 38 as needed and sent to the output terminal OUT as an analog value Vo. Sent out.

In addition, when the permanent magnets 14a to 14d are affected by temperature changes and the magnetic flux density _B1 changes, the fourth
As shown in the figure, the electromagnetic flowmeter transmitter 1 is provided with a Hall element 16 for magnetic flux detection, and the detection voltages e _d1 and e _d2 generated in the Hall element 16 when the magnetic flux densities are B ₁ and B ₂ are respectively amplified by an amplifier 39. After that, A/D converter 3
6 to the microprocessor 37,
If _Do , which is calculated by equation (4), is divided by the difference (D _d1 − D _d2 ) between the digital values D _d1 and D _d2 corresponding to e _d1 and e d2 and output, the change in magnetic flux density can be It is also possible to eliminate the effects of In FIG. 4, the multiplexer MP combines the output from the amplifier 31 and the output from the amplifier 39.
This is for switching the output from the microprocessor 37 and applying it to the A/D converter 36, and is driven by the pulse _P4 from the microprocessor 37. Further, in FIG. 4, the change in magnetic flux density is compensated for by division by the microprocessor 38, but the difference in detection voltage (e _d1 - e _d2 ) is constant, that is, the difference in magnetic flux density (B ₁ The magnitude of the excitation current Iw may be controlled so that -B ₂ ) remains constant.

As explained above, in the present invention, an electromagnetic flowmeter transmitter is provided with a permanent magnet and an excitation coil,
Normally, measured values are obtained by exciting only a permanent magnet, and current is passed through the excitation coil only when obtaining a compensation value to compensate for the noise component due to the electrochemical potential included in the measured value. An electromagnetic flowmeter that consumes less power and is not affected by noise components due to electrochemical potential can be obtained.

[Brief explanation of drawings]

Fig. 1 is a connection diagram showing one embodiment of the electromagnetic flowmeter of the present invention, Fig. 2 is an explanatory diagram of its operation, and Figs. 3 and 4 are connection diagrams showing other embodiments of the electromagnetic flowmeter of the present invention. . DESCRIPTION OF SYMBOLS 1... Electromagnetic flowmeter transmitter, 14a-14d... Permanent magnet, 15a, 15b... Excitation coil, 16... Hall element, 2... Excitation current circuit, 3... Signal processing circuit,
31...Amplifier, 32...Sample and hold circuit, 3
3...Differential amplifier, 34...Output circuit, 35...Pulse generation circuit, 36...A/D converter, 37...Microprocessor, 38...D/A converter, 39...Amplifier.

Claims (1)

[Claims] 1 An electromagnetic flowmeter transmitter is equipped with a permanent magnet and an excitation coil, and normally only the permanent magnet is used for excitation, and if necessary, current is passed through the excitation coil to excite both the permanent magnet and the excitation coil. In addition, the noise included in the voltage induced between the electrodes when excitation is performed only by a permanent magnet is reduced between the electrodes when excitation is performed by both a permanent magnet and an excitation coil. An electromagnetic flowmeter characterized by being equipped with a signal processing circuit that outputs after compensating using an induced voltage.