JPS6127697B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inductive level gauge for detecting the level of liquid metal such as liquid sodium.

As a liquid level gauge for detecting the level of liquid sodium or the like in a nuclear reactor system, there is an inductive level gauge as shown in FIG. This induction type liquid level gauge 1 houses a coupled inductance in which a primary coil 4 and a secondary coil 5 are wound coaxially around a bobbin 3 in a sheath 6, and when the primary coil is excited with an alternating current 7, the The voltage 8 induced in the secondary coil detects the liquid level of the liquid metal 2 around the sheath because of the relationship between the linear voltage V ₂ and the liquid level L as shown in FIG. . Although this type of liquid level gauge has a simple and robust structure, the induced voltage in its secondary coil is V ₂
The disadvantage is that the value of is affected by the ambient temperature. That is, when the secondary core induced voltage is V ₂ and the liquid level of the liquid metal is L, it is expressed as V ₂ =A−BL (1). (However, A and B are constants) When the ambient temperature of the liquid level gauge changes, the conductivity of the liquid metal and sheath changes, so the pattern of the size, phase, distribution, etc. of the eddy current induced inside them changes. . As a result, the constants A and B in the above equation (1) change. That is, since the constants A and B change depending on the temperature, the secondary coil induced voltage V ₂ is also affected by the temperature change. If the induced voltage of the secondary coil is affected by the ambient temperature in this way, it is difficult to accurately detect the liquid level, especially in a nuclear reactor system. However, the relationship between the ambient temperature, e.g., 200℃, 400℃, 600℃, and the AC frequency, e.g., 1KHz to 100KHz, which excites the primary coil, is as shown in Figure 3.
If it is ₁ or ₂ , the liquid level detection error of the liquid level gauge due to temperature changes can be minimized. In other words, the transfer impedance ΔZ of the liquid level gauge can be made substantially constant.

However, the temperature distribution in the longitudinal direction of the liquid level gauge has a large temperature difference between the depth of the liquid, that is, the temperature near the liquid surface and the deep position far from the liquid surface, and the rate of change is strong near the liquid surface, so it is not possible to use conventional methods. With the liquid level gauge, the temperature range in which the transfer impedance ΔZ remains approximately constant was exceeded, making it impossible to accurately measure the liquid level.

The present invention was made in view of the above circumstances, and its purpose is to accurately detect the liquid level of liquid metal even in the face of changes in ambient temperature and non-uniformity in temperature distribution of the liquid level gauge. The present invention provides an inductive liquid level gauge.

The present invention is characterized in that the alternating current power frequency that excites the primary coil of the level gauge is adjusted so that the difference in transfer impedance of the level gauge when liquid metal is present and when there is no liquid metal around the level gauge Set the value to be approximately constant against changes in ambient temperature. Divide the secondary coil connected to the above primary coil, and connect the secondary coil between the two halves of the secondary coil to the position of the liquid metal level to be detected. The above objective is achieved by fixedly arranging the center portions to coincide with each other.

The present invention will be explained below with reference to the drawings.

FIG. 4 shows an example of an inductive level gauge to which the present invention is applied. Since the main parts other than those shown in FIG. 4 are the same as the liquid level gauge shown in FIG. 1, the explanation will be made with reference to FIG. 1.

The inductive liquid level gauge 11 of the present invention has a bottomed cylindrical stainless steel sheath 16 immersed in a liquid metal, for example, liquid sodium 12. The bobbin 13 disposed within the sheath 16 includes
A primary coil 14 is wound, and this primary coil 1
4, there are a pair of upper and lower secondary coils 15a,
15b are wound coaxially. Primary coil 1
4 is excited by an AC power source 17, as shown in FIG. Also, a pair of secondary coils 15a, 15
b is differentially connected, and from its differential output terminal ₂₀ , the _{difference △V 2 (} =V
_2a −V _2b ) is obtained. The relationship between the induced voltage difference ΔV ₂ and the liquid level L of the liquid sodium 12 is as shown in FIG. That is, the pair of secondary coils 15a, 15
When the liquid level of the liquid sodium 12 reaches the contact surface a-a' of b, the difference ΔV ₂ between the induced voltages between the secondary coils 15a and 15b reaches its peak. Therefore, by detecting this peak, the a-
Reaching the a′ plane can be detected. In this liquid level gauge 11, the induced voltage difference ΔV ₂ is a function only of the constant B in equation (1). For that purpose, the constant Ohma function meter 1
Even if it depends on the ambient temperature T in step 1, the detection of the liquid level is not affected. The above constant B is expressed as B=ΔZ·I ₁ (2). However, ΔZ is the difference in the transfer impedance of the liquid level gauge 11 when liquid sodium 12 is present around the liquid level gauge 11 and when it is not present. In this liquid level gauge 11 as well, if the frequency of the current I ₁ of the primary coil 14 is set such that △Z remains approximately constant with respect to temperature changes, the liquid sodium 1 can be adjusted regardless of changes in the ambient temperature T. Surfaces can be detected accurately. That is, the secondary coil a-
Since the temperature distribution in the range of the a′ plane is substantially uniform because the coil length in the longitudinal direction is short, accurate liquid level detection can be performed within a predetermined temperature range using a predetermined frequency.

According to the present invention described in detail above, the AC power frequency that excites the primary coil of the induction type level gauge is transmitted to the level gauge when liquid metal exists or does not exist around the level gauge. The impedance difference is set to a value that is approximately constant with respect to changes in the ambient temperature of the liquid level gauge, and the secondary coil is divided and fixedly placed at the detection site to detect the liquid level at one point. In addition, a peak value detector with a simple configuration is used because the peak value of the detected signal does not change even when the ambient temperature of the liquid level gauge changes or even if there are uneven parts in the temperature distribution. However, the level of liquid metal can be detected accurately.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view showing an example of a conventional inductive liquid level gauge, Fig. 2 is a characteristic showing the relationship between the liquid level and the secondary coil induced voltage in the liquid level gage of Fig. Figure 1 is a characteristic curve diagram showing the relationship between the frequency of the primary coil current and the transfer impedance difference ΔZ with ambient temperature as a parameter in the liquid level gauge, and Figure 4 is a characteristic curve diagram showing the relationship between the frequency of the primary coil current and the transfer impedance difference ΔZ in the liquid level gauge to which the present invention is applied. FIG. 5 is a longitudinal sectional view showing the main part of the surface meter, FIG. 5 is a circuit diagram thereof, and FIG. 6 is a characteristic curve diagram showing the relationship between the output terminal and liquid level in FIG. 5. 1, 11... Inductive liquid level gauge, 2, 12... Liquid level sodium, 1, 14... Primary coil, 5, 15a, 1
5b... Secondary coil, 6, 16... Sheath, 7, 17
...AC power supply, 8...Voltage detector.

Claims (1)

[Claims] 1. A sheath, a primary coil and a secondary coil housed within the sheath and arranged coaxially with each other, and an AC power source that excites the primary coil with an alternating current, the frequency of the AC power source being The difference in transfer impedance between the presence and absence of the liquid metal around the sheath is set to a value that is approximately constant with respect to changes in the ambient temperature around the sheath, and the transfer impedance is induced in the secondary coil. In the inductive liquid level gauge that detects the liquid level of the liquid metal around the sheath from the voltage applied to the sheath, the secondary coil is divided into two, and each of the two divided coils is coaxially wound above and below the primary coil. , and the two divided coils are connected differentially, and the secondary coil is fixedly arranged so that the center position between the two divided coils coincides with the position of the liquid level of the liquid metal to be detected. An inductive liquid level gauge characterized by: