JPH079375B2 - 2-wire electromagnetic flowmeter converter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-wire type electromagnetic flowmeter converter which supplies a power source through a pair of signal lines and also transmits a flow rate signal through the same signal line.

[0002]

2. Description of the Related Art Conventionally, it has been known that an electromotive force corresponding to the flow velocity of a fluid is generated by flowing a fluid in a magnetic field, and an electromagnetic flowmeter is an application of this principle. This device consists of a transducer placed in the place where the fluid flows and a processing unit placed away from the transducer for recording and analyzing the signals generated from it. Then, during this period, a signal line is used for connection, and a current of 4 to 20 mA is supplied thereto. On the other hand, the converter amplifies the generated electromotive force and the exciting circuit that causes the exciting coil to generate a magnetic field.
And a signal processing circuit that generates a flow rate signal.

The minimum current that can be supplied to this device is 4 mA, and it must be supplied to both the excitation circuit and the signal processing circuit. Therefore, the current supplied to each circuit is shunted or a rest period is provided. During that time, the capacitor was charged with electric charge and discharged intermittently to supply the necessary current.

[0004]

However, if the current supplied to the exciting circuit is made small, the electromotive force generated becomes small, so the S / N becomes poor and the flow rate signal becomes unstable. On the other hand, when the exciting current is intermittently supplied, the interval for sampling the flow rate signal becomes large, resulting in poor responsiveness and weakness in electrochemical noise generated between the fluid substance and the electrode material. It was The present invention has been made in view of such a situation, and provides an apparatus capable of supplying a current of 4 mA to an exciting circuit without increasing the sampling interval.

[0005]

In order to solve such a problem, the present invention provides an exciting circuit for applying a current to an exciting coil and a signal processing circuit for performing signal processing of a detection signal to the transmission line. Are connected in series with.

[0006]

Since all the current flowing through the signal line is supplied to the exciting circuit and the signal processing circuit, a required amount of current flows through both circuits.

[0007]

1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, 1a and 1b are two transmission lines, and the excitation circuit 20 and the signal processing circuit 60 are connected in series to the transmission lines 1a and 1b. The exciting circuit 20 further includes a constant voltage circuit 30 in series with the signal processing circuit 60, and a constant current circuit 40 in series with the exciting coil 2 with respect to the constant voltage circuit 30. The signal processing circuit 60 supplies a constant voltage to a circuit that amplifies the electromotive force detected by the electrodes 3a and 3b of the conduit 3.

In the circuit thus constructed, the current supplied through the transmission lines 1a and 1b is constant voltage circuit 30.
And the signal processing circuit 60. As a result, a predetermined constant voltage is generated at both ends of the constant voltage circuit 30, and a current limited to a constant current by the constant current circuit 40 based on the voltage is supplied to the exciting coil 2. As a result, the conduit 3 is excited.

At this time, all the current flowing into the exciting circuit 20 flows into the signal processing circuit 60, so that the exciting current is used again in the signal processing circuit 60 and is used without waste.

FIG. 2 is a circuit diagram showing details of the circuit of FIG. In FIG. 2, the constant voltage circuit 30 includes a Zener diode, resistors 32 to 34, a differential amplifier 35, and a transistor 36, and generates a constant voltage having a value determined according to the characteristics of the Zener diode 31 across the transistor 36. . Then, the generated voltage is supplied to the constant current circuit 40.

The constant current circuit 40 includes resistors 41 to 46, a differential amplifier 48, a transistor 46 and a switching element 47.
It is constituted by a to 47d, and the current value supplied to the exciting coil 2 is determined by the resistor 45.

The switching elements 47a to 47d are switched by a timing signal generated by a signal processing circuit. This timing signal may be generated by the CPU or may be generated by dividing the reference oscillator. At this time, since the signal processing circuit and the switching portion have different reference potentials, it is necessary to pass the isolation circuit. The switching elements 47a, 47d and 47c, 47b are switched to have opposite polarities as shown in FIGS. 3 (a) and 3 (b). As a result, a current waveform as shown in FIG. 3C appears in the coil 2.

The signal processing circuit 60 is composed of a constant voltage circuit 61, resistors 62 to 67, a differential amplifier 68, and a transistor 69, which supplies a constant voltage to the electrodes 3a and 3b of the conduit 3 and is supplied from the signal processing circuit. The transistor 69 is driven via the differential amplifier 68 according to the flow rate signal to
The current flowing through a and 1b is changed within the range of 4 to 20 mA. As the flow rate signal, the output of the signal processing circuit driven by the power source of the low voltage circuit 61 is input through the resistor 62, and the constant current circuit configured by the differential amplifier 68 and the transistor 69 generates a current proportional to the flow rate signal from 4 to 4. Output in the range of 20 ma.

[0014]

As described above, according to the present invention, the exciting circuit for driving the electromagnetic flowmeter and the signal processing circuit generated from the conduit are connected in series. Therefore, all the current used in the exciting circuit is reused by the signal processing circuit. Therefore, all the current supplied through the line can be used without waste, and a large current can be passed through the exciting coil, resulting in a good S / N ratio.
Further, there is an effect that a detection signal with good responsiveness can be obtained.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing details of the circuit of FIG.

FIG. 3 is a diagram showing a relationship between a signal driving a switching circuit 47 of FIG. 2 and a signal supplied to a coil.

[Explanation of symbols]

 1 Transmission Line 2 Excitation Coil 3 Pipe 3a, 3b Electrode 20 Excitation Circuit 30 Constant Voltage Circuit 40 Constant Current Circuit 60 Signal Processing Circuit

Claims (1)

[Claims] 1. A two-wire type electromagnetic flow meter for supplying power with two transmission lines together with signal transmission, an excitation circuit for applying a current to an excitation coil, and a signal processing circuit for performing signal processing of a detection signal. A two-wire type electromagnetic flowmeter converter, characterized in that: is connected in series to the transmission line.