JPH05256673A - Excitation malfunction detecting means of electromagnetic flowmeter - Google Patents

Abstract

PURPOSE:To enable a means to detect something wrong with excitation in itself irrespective of type of a magnetic generating means if an alternating field is the case by installing a search coil in a magnetic path of a magnetic field which the magnetic generating means generates, and detecting a variation in the alternating field. CONSTITUTION:When an exciting current Ix flows into two exciting coils 2a and 2b, magnetic flux phi is impressed on a measured fluid flowing in the inner part of a measuring tube 1 vertically with a tube axis of this measuring tube 1 via a core 4. In this case, electromotive force in proportional to a flow velocity and strength of a magnetic field being impressed is produced in this measured fluid. This electromotive force is detected by two electrodes 3a and 3b and, after being amplified by an amplifier 6, signal processing takes place, thus flow information is secured. On the other hand, since the magnetic flux phi impressed onto the fluid is interlinked with a search coil 5 via the core 4, a voltage (e) in proportional to a time differential of variation in a magnetic field is produced at both ends of the search lever 5. Since if the magnetic flux phi is in constant amplitude and constant form at a constant period, the voltage (e) is also in constant amplitude and constant form at a constant period, so that with this voltage (e) monitored, any malfunction in excitation is detectable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an excitation abnormality detecting means for an electromagnetic flowmeter, and more particularly to an excitation abnormality detecting means for an electromagnetic flowmeter which accurately detects various abnormalities.

[0002]

2. Description of the Related Art An electromagnetic flowmeter is a flowmeter to which Faraday's law of electromagnetic induction is applied and detects a generated electromotive force by applying a magnetic field to a fluid. Therefore, detecting an abnormality in the applied magnetic field is important as an abnormality detecting function of the electromagnetic flowmeter. Conventionally, it has been devised to monitor the current flowing in the exciting coil and the voltage across the exciting coil, that is, to detect the abnormality in the excitation by detecting the abnormality in the electric circuit for generating the magnetic field. No. 158558.

[0003]

In the above-mentioned prior art, since the excitation abnormality is detected by detecting the abnormality of the electric circuit for generating the magnetic field, it is impossible to detect the abnormality of the magnetic pole or the magnetic path after the excitation coil. Met. Further, it cannot be applied to a magnetic field generating means using a permanent magnet. Since it is necessary to insert a resistor in series with the exciting coil in order to monitor the exciting current, it is said that the burden of the exciting power source becomes large especially in a low power consumption electromagnetic flowmeter such as a two-wire type electromagnetic flowmeter. There was a problem.

An object of the present invention is to provide an excitation abnormality detecting means for an electromagnetic flow meter, which is capable of essentially detecting an abnormality in excitation regardless of the type of magnetic field generating means if it is an alternating magnetic field.

[0005]

The above-mentioned object is to install a search coil in the magnetic path of the magnetic field generated by the magnetic field generating means,
This is achieved by detecting changes in the alternating magnetic field.

[0006]

[Function] The search coil installed in the magnetic path has a voltage e∝dφ / which is proportional to the time derivative of φ of the magnetic flux passing through the magnetic path.
dt occurs. If φ is a magnetic flux with a constant amplitude and a constant shape, a constant voltage with a constant amplitude and a constant shape is obtained. Therefore, the excitation abnormality can be detected by monitoring the voltage e.

[0007]

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows an embodiment of the present invention. 1 is a measuring tube through which a fluid to be measured flows, 2a and 2b are exciting coils for generating a magnetic field, 3
a and 3b are a pair of electrodes for detecting electromotive force, 4 is a core forming a magnetic pole and a magnetic path, 5 is a search coil, and 6 is an amplifier. When the exciting current Ix flows through the exciting coils 2a and 2b, a magnetic flux φ is applied to the fluid to be measured flowing through the core 4 inside the measuring tube 1 perpendicularly to the tube axis of the measuring tube 1. An electromotive force proportional to the flow velocity and the strength of the applied magnetic field is generated in the fluid to be measured. This electromotive force is detected by the electrodes 3a and 3b, amplified by the amplifier 6, and then signal processed to obtain flow rate information. On the other hand, since the magnetic flux φ applied to the fluid interlinks with the search coil 5 via the core 4, a voltage e proportional to the time derivative of the change in the magnetic field is generated at both ends of the search coil 5. If the magnetic flux φ changes in a sine wave shape, the voltage e becomes a cosine wave, and if the magnetic flux φ changes in a square wave shape, the voltage e has a waveform that steeply rises and disappears like an exponential function, as shown in FIG.
Whether or not the magnetic flux φ has changed can be determined by the presence or absence of this voltage e. In other words, it can be detected as an abnormality when the exciting current has stopped flowing due to the disconnection of the exciting coil, the excitation power source is more than the above, or the magnetic flux does not alternate due to the failure of the direction control mechanism of the exciting current. Further, since the voltage e has information on the frequency of the magnetic flux φ and the timing of change, it can be determined whether or not the magnetic flux φ changes in an intended pattern. Further, in the case of a square wave-shaped magnetic flux, voltage e
By setting the threshold value e1 and monitoring the time t, it is possible to detect a delay in the rise of the magnetic flux due to an abnormality in the magnetic circuit as an abnormality.

Although the magnetic field generating means is an exciting coil here, the present invention is effective even if it is a moving permanent magnet or a combination of a permanent magnet and an exciting coil as long as it is an alternating magnetic field. Further, although the electrode for detecting the electromotive force generated in the fluid to be measured is shown to have a structure in contact with the fluid to be measured, there is no problem even if it is not in contact with the fluid. Further, although the search coil is installed in the side path of the core 4, it does not matter whether it is the magnetic pole or the outer circumference of the exciting coil as long as the magnetic flux φ passes therethrough.

[0009]

According to the present invention, it is possible to essentially detect an electromagnetic flow type excitation abnormality using an alternating magnetic field not only in the excitation circuit but also in the magnetic pole and the magnetic path.

[Brief description of drawings]

FIG. 1 is a structural diagram of one embodiment of the present invention.

FIG. 2 is a waveform diagram of a square-wave magnetic flux and a waveform of a generated voltage of a search coil corresponding to the waveform.

[Explanation of symbols]

1 ... Measuring tube, 2a, 2b ... Exciting coil, 4 ... Core, 5 ...
Search coil.

Claims (1)

[Claims] 1. A non-magnetic measuring tube through which a fluid to be measured flows, a magnetic field generating means provided outside the measuring tube for generating an alternating magnetic field orthogonal to the tube axis of the measuring tube, and a tube of the measuring tube. An electromagnetic flowmeter comprising at least a pair of electrodes arranged so as to face each other orthogonally to the axis and the magnetic field, a search coil for detecting a change in the alternating magnetic field being provided, and an excitation abnormality detecting means for the electromagnetic flowmeter. .