JPH04370715A - Two-wire type electromagnetic flowmeter converter - Google Patents

Abstract

PURPOSE:To obtain a device enabling supply of a current of 4mA to an exciting circuit without enlarging a sampling interval. CONSTITUTION:An exciting circuit 20 for driving an electromagnetic flowmeter and a processing circuit 60 of a signal generated from a pipeline 3 are provided in series. Therefore a current used in the exciting current 20 is all reused by the signal processing circuit 60, and therefore the current supplied through a line 1 can be used wholly without any waste. Since a large current can be made to flow through a coil 2, accordingly, a detection signal being excellent in S/N and responsiveness can be obtained.

Description

[Detailed description of the invention]

0001

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

0002

2. Description of the Related Art Conventionally, it has been known that when a fluid flows in a magnetic field, an electromotive force is generated corresponding to the flow velocity of the fluid, and an electromagnetic flowmeter is an application of this principle. This device records and analyzes transducers placed in locations where fluid flows and the signals generated from them.
The converter consists of a processing device located at a remote location. And, although this is connected by a signal line,
A current of 4 to 20 mA is supplied there. On the other hand, the converter includes an excitation circuit that causes current to flow through an excitation coil for generating a magnetic field, and a signal processing circuit that amplifies the generated electromotive force and 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, so either divide the current supplied to each circuit or provide a rest period. During this time, the capacitor was charged and discharged intermittently to supply the necessary current.

0004

However, when the current supplied to the excitation circuit is reduced, the generated electromotive force is reduced, resulting in poor signal-to-noise ratio and unstable flow rate signals. On the other hand, when an excitation current is supplied intermittently, the interval at which the flow rate signal is sampled increases, resulting in poor responsiveness and susceptibility to electrochemical noise generated between the fluid substance and the electrode material. Ta. The present invention has been made in view of this situation, and it is an object of the present invention to provide a device that can supply a current of 4 mA to an excitation circuit without increasing the sample interval.

[0005]

[Means for Solving the Problems] In order to solve such problems, the present invention provides an excitation circuit for applying current to an excitation coil and a signal processing circuit for processing a detection signal to the transmission line. are connected in series.

[0006]

[Operation] Since all of the current flowing through the signal line is supplied to the excitation circuit and the signal processing circuit, the required amount of current flows through both circuits.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, 1a and 1b are two-wire transmission lines, and an excitation circuit 20 and a signal processing circuit 60 are connected in series to the transmission lines 1a and 1b. The excitation circuit 20 further includes a constant voltage circuit 30 connected in series with the signal processing circuit 60, and a constant current circuit 40 connected in series with the excitation coil 2 with respect to the constant voltage circuit 30. Note that 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 configured as described above, the current supplied via the transmission lines 1a and 1b is supplied to the constant voltage circuit 30.
and flows through the signal processing circuit 60. As a result, a predetermined constant voltage is generated across the constant voltage circuit 30, and based on the voltage, a current limited to a constant current by the constant current circuit 40 is supplied to the exciting coil 2. As a result, the conduit 3 is excited.

At this time, all of the current that has flowed into the excitation circuit 20 flows into the signal processing circuit 60, so that the excitation current is used again in the signal processing circuit 60 and is used without wastage.

FIG. 2 is a circuit diagram showing details of the circuit of FIG. 1. In FIG. 2, a constant voltage circuit 30 is composed of a Zener diode, resistors 32 to 34, a differential amplifier 35, and a transistor 36, and generates a constant voltage across the transistor 36 with a value determined according to the characteristics of the Zener diode 31. . The generated voltage is then 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.
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 frequency division from a reference oscillator. On this occasion,
Since the signal processing circuit and the switching section have different reference potentials, it is necessary to pass the signal through an isolation circuit. The switching elements 47a, 47d and 47c, 47b are shown in FIG.
The polarity is switched to be opposite as shown in (a) and (b). As a result, a current waveform as shown in FIG. 3(c) 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, and supplies a constant voltage to the electrodes 3a and 3b of the conduit 3, which is supplied from the signal processing circuit. The transistor 69 is driven via the differential amplifier 68 in accordance with the flow rate signal sent to the line 1a.
, 1b is varied in the range of 4 to 20 mA. The flow rate signal is input through a resistor 62 from the output of a signal processing circuit driven by the power supply of the low voltage circuit 61, and a constant current circuit composed of a differential amplifier 68 and a transistor 69 generates a current proportional to the flow rate signal. Outputs within a range of 20ma.

[0014]

Effects of the Invention As explained above, in the present invention, the excitation circuit that drives the electromagnetic flowmeter and the signal processing circuit generated from the pipe are connected in series, so that all the current used in the excitation circuit is reused by the signal processing circuit. Therefore, all the current supplied via the line can be used without wasting it, and a large current can be passed through the excitation coil, resulting in a good S/N ratio.
It also has the effect that a detection signal with good responsiveness can be obtained.

[Brief explanation of drawings]

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

[Figure 2] Circuit diagram showing details of the circuit in Figure 1

FIG. 3 is a diagram showing the relationship between the signal that drives the switching circuit 47 in FIG. 2 and the signal supplied to the coil.

[Explanation of symbols]

1 Transmission line 2 Excitation coil 3 Pipeline 3a, 3b electrode 20 Excitation circuit 30 Constant voltage circuit 40 Constant current circuit 60 Signal processing circuit

Claims (1)

[Claims] Claim 1: In a two-wire electromagnetic flowmeter that transmits signals and supplies power through two transmission lines, an excitation circuit provides current to an excitation coil and a signal processing circuit performs signal processing of a detection signal. A two-wire electromagnetic flowmeter converter, characterized in that: is connected in series to the transmission line.