JPH06258111A - Electromagnetic flowmeter - Google Patents

Abstract

PURPOSE:To increase excitation current value for excitation by providing various means for detection, signal judgment and switching the first and the second. CONSTITUTION:When the flowrate signal output from a sample hold circuit 4 is below 2V, CPU 6 outputs small judgment signal and when it is over 2V, CPU 6 outputs middle judgment signal and when it is over 4V, CPU 6 outputs large judgment signal. When the judgment signal is small, middle, large, the first switch part 7 outputs an excitation switch current signal of small, middle, large, respectively, and an excitation circuit 5 supplies an excitation coil 1 at this time with current of 4mA, 8mA, 14mA, respectively. On the other hand, depending on the judgment signal of small, middle, large, the second switching part 8 outputs a gain switching signal of large, middle, small. By this, the gain of signal amplifier circuit 3 becomes to be 140 times, 70 times, 40 times, respectively. Therefore, the detecting flowrate is large, the excitation current is increased and the S/N of output signal of detecting the flowrate with the measuring pipe 2 becomes high.

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 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 An electromagnetic flow meter is known as a device for measuring the flow rate of a fluid flowing in a pipe. It is known that an electromotive force corresponding to the flow velocity of a fluid is generated when a fluid having electrical conductivity flows (moves) in a magnetic field, and an electromagnetic flow meter is an application of this principle. When measuring the flow rate at multiple remote locations, install the electromagnetic flowmeter at the place where the fluid flows, record the signal output by the electromagnetic flowmeter, and record it.
Also, the control device for analysis and the like will be placed at a remote place. The electromagnetic flowmeter and the control device are connected by a signal line, and a maximum current of 20 mA is supplied to the signal line. The electromagnetic flowmeter uses 4 mA or less of the supplied current as a power source and uses 4 to 20 mA for signal transmission of data and the like.

[0003]

Conventionally, with the above-mentioned configuration, the exciting current value supplied to the exciting unit for applying the magnetic field was always fixed. Since the exciting current value is 4 mA or less, there is a problem that the power that can be consumed for exciting is extremely small.

The present invention has been made to solve the above problems, and an object thereof is to increase an exciting current value for exciting an electromagnetic flowmeter.

[0005]

According to the electromagnetic flowmeter of the present invention, the magnitude of the flow rate signal detected by the detection means and output and amplified by the signal amplification means is discriminated, and thereby the discrimination signal is outputted. Means, first switching means for outputting a signal for switching the exciting current value according to the determination signal, and second switching means for outputting a signal for switching the signal amplification factor of the signal amplification means according to the determination signal. Is characterized by.

[0006]

When the signal discriminating means determines that the flow rate signal is measuring a large flow rate, the first switching means outputs a signal for increasing the exciting current value, and the second switching means outputs the signal amplifying means. A signal that reduces the signal amplification factor is output.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing the configuration of an electromagnetic flowmeter that is an embodiment of the present invention. In the figure, 1 is an exciting coil for generating a magnetic field, 2 is arranged in the magnetic field generated by the exciting coil 1, and the electromotive force generated by the fluid to be measured flowing in this magnetic field is detected to determine its flow velocity. A measuring tube (detection means) that outputs a proportional flow rate signal, 3 is a signal amplification circuit that amplifies the flow rate signal with alternating current, 4 is a sample hold circuit that converts the alternating current amplified signal into direct current, and 5 is an exciting current for the exciting coil 1. It is an exciting circuit for supplying.

Further, 6 is a CPU having a function of outputting a discrimination signal according to the magnitude of the signal output from the sample and hold circuit 4, and 7 is a first switching for outputting an exciting current switching signal according to the discrimination signal output from the CPU 6. Department,
Reference numeral 8 is a second switching unit that outputs a gain switching signal according to the determination signal output from the CPU 6, 9 is an A / D conversion unit that converts the analog signal output from the sample hold circuit 4 into a digital signal, and 10 is a 24 V power supply. Is a terminal for supplying a data signal and transmitting a data signal. Note that C
The PU 6 controls the output of the flow rate data via the output unit 11 by the signal converted to digital by the A / D conversion unit 9, and controls the sample hold circuit 4, the excitation circuit 5, the first and second switching units 8 and the like. It also controls.

The DC flow rate signal output from the sample and hold circuit 4 changes in voltage in proportion to the detected flow rate. For example, when the exciting current is 4 mA,
If the fluid in the measuring tube 2 is not flowing, the voltage of the flow rate signal output from the sample hold circuit 4 is 0 V, 50 m ³ /
The flow rate signal output when the flow rate is 2.5 V, and the flow rate signal voltage when the flow rate of the fluid is 100 m ³ / hour is 5 V
(Maximum value). When the output of the sample hold circuit 4 is 0V, the output unit 11 outputs a 4mA data signal (flow rate signal), and when it is 5V, a 20mA data signal is output. In the range where the current equal to or lower than the data signal is used as the exciting current, the data signal representing the flow rate is not affected. Therefore, in the present invention,
When the current of the data signal is 4 mA or more, the exciting current is increased to 4 mA or more according to the current value.

When the flow rate signal output from the sample hold circuit 4 is less than 2V, the CPU 6 judges the signal "small".
Is output, and when the voltage is 2 V or more, the determination signal “middle” is output,
When the voltage is 4 V or more, the judgment signal "large" is output. When the determination signal “small” is output, the first switching unit 7 outputs the excitation current switching signal “small”, and the excitation circuit 5 keeps the current supplied to the excitation coil 1 at 4 mA. When the determination signal "medium" is output, the first switching unit 7 outputs the excitation current switching signal "medium", whereby the excitation circuit 5 switches the current supplied to the excitation coil 1 to 8 mA. When the determination signal "large" is output, the first switching unit 7 outputs the excitation current switching signal "large", whereby the excitation circuit 5 switches the current supplied to the excitation coil 1 to 14 mA.

On the other hand, the second switching section 8 outputs the gain switching signal "large" in response to the judgment signal "small", and the gain of the signal amplifying circuit 3 becomes 140 times. When the determination signal "medium" is output, the second switching unit 8 outputs the gain switching signal "medium", whereby the gain of the signal amplification circuit 3 becomes 70 times. And the judgment signal "large"
Is output, the second switching unit 8 outputs a gain switching signal “small”, whereby the gain of the signal amplification circuit 3 becomes 40 times. When the exciting current is doubled, the flow rate signal for detecting the same flow rate is also doubled. At this time, therefore, it is necessary to halve the gain of the signal amplification circuit 3.

As described above, as shown in FIG. 2, when the flow rate to be detected is large, the current value (excitation current value) supplied to the exciting coil 1 becomes large and the gain of the signal amplifying section 3 becomes small. On the other hand, when the flow rate to be detected is small, the value of the current supplied to the exciting coil 1 becomes small and the gain of the signal amplification section 3 becomes large. Therefore, when the flow rate to be detected is large, the exciting current value is increased, so that the S / N ratio of the signal that the measuring tube 2 detects and outputs the flow rate becomes high.

When switching between the electromagnetic current value and the gain, hysteresis may be provided as shown in FIG. This prevents frequent switching. Also,
In the above embodiment, the gain switching is performed in three stages, but the present invention is not limited to this and may be performed in two stages or four stages.

[0014]

As described above, according to the present invention, the exciting current value can be increased when the flow rate of the fluid to be measured is large with respect to the exciting means for generating the magnetic field.
This has the effect of improving the detection sensitivity.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of an electromagnetic flowmeter that is an embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining a switching state of an exciting current.

FIG. 3 is an explanatory diagram for explaining a switching state of an exciting current.

[Explanation of symbols]

 1 Excitation Coil 2 Measuring Tube 3 Signal Amplifying Circuit 4 Sample Hold Circuit 5 Excitation Circuit 6 CPU 7 First Switching Section 8 Second Switching Section 9 A / D Conversion Circuit 10 Terminal 11 Output Section

Claims (1)

[Claims] 1. The magnitude of a flow rate signal output by the detection means arranged in the magnetic field generated by the exciting means by the flow rate detection and amplified by the signal amplification means is discriminated, and the discrimination signal is output accordingly. A signal discriminating means, a first switching means for outputting a signal for switching the exciting current value supplied to the exciting means according to the discriminating signal, and a signal for switching the signal amplification factor of the signal amplifying means by the discriminating signal. And a second switching means for controlling the electromagnetic flowmeter.