JPS5811864A - Eddy current type measurement system - Google Patents

Abstract

PURPOSE:To detect the position of a detection part 1 accurately by detecting the detection part reaching a reference position on the basis of the output of the detection part, and detecting the extent of movement of the detection part from the reference position. CONSTITUTION:Before a detection part 1 is inserted into a guide tube 3, the primary coil 11 of the detection part 1 is energized by an energizing signal source 4. Output voltages E1 and E2 of secondary coils 12 and 13 are observed to detect the detection part 1 reaching a prescribed reference position in the tube under the liquid level of a fluid to be measured. Assuming that the fluid to be measured is stationary, a flow velocity signal obtained by rectification and smoothing is integrated to find the extent of movement.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an eddy current measurement system that measures the temperature, flow velocity, porosity, etc. of a conductive fluid to be measured (for example, sodium) based on eddy currents generated in the fluid to be measured. Specifically, when inserting the detecting section constituting such a system into the guide tube, the position of the detecting section within the guide tube can be detected with high accuracy.

Some nuclear reactors use liquid metal sodium (hereinafter referred to as sodium) as a coolant and are configured so that the sodium enters the reactor vessel from the bottom, passes through the reactor core, and exits the reactor vessel from the top. In such a nuclear reactor, a plurality of guide tubes are arranged in the upper part of the reactor core along the flow direction of sodium, and a detection section in which a secondary coil is arranged is inserted so as to sandwich a primary coil in each guide tube. The flow velocity, temperature, porosity, etc. of sodium in the upper part of the reactor core are being measured. Based on these measurement results, the operating state of the reactor is monitored and abnormalities in the reactor core are detected.

Incidentally, these measurements must be carried out with the detection section placed at a predetermined position at the distal end within the guide tube. For this purpose, it is necessary to detect that the detection section is placed at a predetermined position within the guide tube.

As a method for detecting the position of such a detection section, a method such as that disclosed in Japanese Patent Application Laid-Open No. 52-439462 has been proposed. In this method, sections with different conductivities are machined at predetermined positions in the guide tube, and changes in the output of the secondary coil of the detection section or changes in the self-impedance of the primary coil are detected. It is designed to detect that the guide tube is placed at a predetermined position within the guide tube.

However, in such a method, since the reactor enters the operating state, the relative position between the detection part and the parts of the guide tube with different conductivities is affected by the difference in linear expansion coefficient of the constituent materials and the difference in the coefficient of linear expansion of the guide tube. It may change due to vibration, etc.

As a result, the electromagnetic symmetry of the secondary coil and its surroundings with respect to the primary coil/K of the detection section is impaired, which is undesirable as it tends to cause measurement errors.

In order to solve these drawbacks, the present invention inserts a detection section in which a plurality of coils are arranged along the axial direction into a guide tube arranged in the fluid to be measured along the flow direction of the fluid to be measured. When placing the b
The position of the detection part in the pipe (3) is detected by detecting that the detection part has reached the reference position to be measured in the pipe, and also detecting the amount of movement of the detection part from the reference position in the pipe. It is something.

From this K, even if the reactor enters the operating state, the detection unit 1
The electromagnetic symmetry of the secondary coil and its surroundings with respect to the secondary coil is not impaired, and no measurement errors occur.

Hereinafter, it will be explained in detail using the drawings.

FIG. 1 is a configuration explanatory diagram showing an example of essential parts of a system according to the present invention, and FIG. 2 is an equivalent circuit diagram of FIG. 1.

In the drawings, 1 is a detection unit, 2 is a lead wire, 3 is a guide tube, 4 is an excitation signal source, and L□ to L3 are liquid level positions of the fluid to be measured. The detection unit 1 includes a primary coil 11 and a primary coil 11.
The secondary coils 12 and 13 are arranged along the axial direction so as to sandwich the secondary coils 12 and 13.

The primary coil 11 is AC excited by the excitation signal source 4 . The guide tube 5 is made of stainless steel, for example.
It is arranged in the fluid to be measured along the flow direction F of the fluid to be measured. The detection section 1 is inserted into the rice guide tube 3 .

(4) The operation of the system configured as described above will be explained. In the following description, it is assumed that the wall thickness of the guide tube 1 is uniform over its entire length.

Before inserting the detection section 1 into the guide tube 3, the primary coil 11 of the detection section 1 is excited by the excitation signal source 4. The output voltage iE□ of the secondary coil 12 located on the upstream side,
Assuming that the output voltage of the secondary coil 13 located on the downstream side is k E2, the output voltage while the detection section 1 is sufficiently in front of the liquid level of the fluid to be measured is E1'F E2. When the detection unit 1 approaches the liquid level LIK, an eddy current flows in the fluid to be measured and
As K cancels out the magnetic flux caused by the secondary coil 11, the magnetic flux interlinking with the secondary coil 12 decreases, resulting in E□<E2.

OK to insert the detection part 1 into the guide tube 3 below the liquid level L2 of the fluid to be measured. Therefore, El decreases more and more, and when the center of the primary coil 11 is well below the liquid level L2, El becomes almost is a constant value.

On the other hand, the output voltage E2 of the secondary coil 13 also decreases as it approaches the liquid level, and becomes an almost constant value when inserted into the guide tube 3 at a depth sufficient for the liquid level L3 of the fluid to be measured. ,
E1 is now E2 again. FIG. 3 is a characteristic diagram showing the relationship between the insertion scale of the detection unit 1 and the output voltage of the detection unit 1, with the horizontal axis representing the insertion scale and the vertical axis representing the output voltage. (,) indicates the change in each output voltage E1+E2,
(b) shows the change in the differential voltage E2-El, and (C) shows the change in the sum voltage E2+H□. As is clear from these FIG. 3, the output voltage E2. By observing at least one of the differential voltage E2-E1 or the sum voltage E2+E□, it is possible to detect that the detection unit 1 has reached a predetermined reference position in the pipe below the surface of the fluid to be measured. Here, the liquid level position of the fluid to be measured can be accurately measured using a separately installed liquid level gauge or the like. Further, the distance Ht between the liquid level L3 and the center position of the primary coil 11 in FIG. 2 can be determined in advance through experiments or the like. Furthermore, the amount of movement of the detection unit 1 from the reference position in the pipe below the liquid level is:
Since the flow velocity signal of the fluid to be measured is proportional to the relative velocity between the fluid to be measured and the detection unit 1, assuming that the fluid to be measured is stationary, the rectified and smoothed flow velocity signal can be integrated.
You can ask for help. FIG. 4 shows an example of a circuit for determining such a movement amount. In FIG. 4, 5 is a rectifying and smoothing circuit, 6 is an integrator, and 7 is an output terminal.

In this way, based on the output signal of the detection unit 1, the detection unit 1 detects that the fluid to be measured has reached a predetermined reference position in the pipe below the liquid level, and also detects that the measured fluid has reached a predetermined reference position in the pipe below the liquid level. By detecting the amount of movement of the detection section 1, the position of the detection section 1 within the tube can be detected with high accuracy, and the detection section 1 can be inserted and arranged at a desired position within the tube.

In the above embodiment, it is assumed that the fluid to be measured is stationary, and a series of position detections are performed while keeping the excitation frequency of the primary coil 11 constant. However, if the fluid to be measured is moving, If there is a difference, measurement errors will occur. In such a case, when the detection unit 1 detects that it has reached a predetermined position in the pipe below the surface of the fluid to be measured, the penetration depth of the eddy current δ (δ = 1/, F 1,000) is determined. It is sufficient if the excitation frequency is changed to correspond to the wall thickness of the guide tube 3. Here, d is the magnetic permeability, ω is the angular excitation frequency, and σ is the conductivity of the guide tube 3. By doing so, the eddy currents flow only through the guide pipe (7) 3 and are independent of whether or not the fluid to be measured moves. Accurate position detection is possible.

In the above embodiment, the reference position in the guide tube 5 is defined as the liquid level position of the fluid to be measured, the distance t between the liquid level determined in advance through experiments, etc., and the center position of the primary coil 11 of the detection unit 1. Although an example has been described in which the liquid level is changed, if the liquid level of the fluid to be measured fluctuates or if the thickness of the guide tube 5 below the liquid level is uneven, measurement errors will occur. In order to solve such a drawback, it is possible to provide a portion of the tube wall of the guide tube 3 with a changing portion having different electromagnetic characteristics from other portions, and to use this changing portion as a reference position. The changing portion can be formed by providing a recess, a welding member, or a material having a different electrical conductivity or magnetic permeability from the tube wall. In addition, it is desirable that this changing part is provided in a place that does not cause any trouble in measuring the fluid to be measured and is close to the position where the detection part 1 is to be placed. The changing portion formed in this way can be detected based on a change in the voltage induced in the secondary coil 12.13 of the detection portion 1 (8) or a change in the self-impedance of the primary coil 11. Alternatively, a search coil may be fixedly disposed coaxially with the detection section 1 at a fixed interval along the axial direction of the detection section 1, and detection may be performed based on a change in the self-impedance of this search coil. . By using such a search coil,
Another advantage is that the changing section can be provided at a position such that the magnetic fluxes of the primary coil 11 of the detecting section 1 are not interlinked.

Further, in the above embodiment, the primary coil 11 is sandwiched between the secondary coils 12.1 as the detection unit 1 along the axial direction.
Although we have described an example in which at least two coils are arranged along the axial direction, these coils can be switched complementary to each other as a primary coil and a secondary coil. You may also K.

Furthermore, in the above embodiment, an example in which the detection section is inserted into the guide pipe of a nuclear reactor has been described, but it goes without saying that similar effects can be obtained with other pipes.

As described above, according to the present invention, it is possible to realize an eddy current measurement system that can accurately detect the position of the detection section within the guide tube with a relatively simple configuration, and has great practical effects.

[Brief explanation of drawings]

FIG. 1 is a configuration explanatory diagram showing an example of the essential parts of the system according to the present invention, FIG. 2 is an equivalent circuit diagram of FIG. 1, and FIG. FIG. 4 is a circuit diagram showing an example of a circuit for determining the amount of movement of the detection section within the tube. 1... Detection unit, 2... Lead wire, 3... Guide tube,
4... Excitation signal source, 5... Rectifier and smoothing circuit, 6...
Integrator, 7...output terminal.

Claims (1)

[Claims] When inserting and arranging a detection section in which a plurality of coils are arranged along the axial direction into a guide tube placed in the fluid to be measured along the flow direction of the fluid to be measured, detection is performed based on the output signal of the detection section. What is claimed is: 1. An eddy current measurement system that detects the position of the detection part within the pipe by detecting that the detection part has reached a reference position within the pipe and also detecting the amount of movement of the detection part from the reference position within the pipe.