RU2266525C2 - Fluid level indicator - Google Patents

Abstract

FIELD: test engineering; measurement technology.

SUBSTANCE: indicator can be used as detector of presence of fluid in containers, in particular, in high-voltage discharge conduits of different purpose diesel engine. Indicator has housing, radiation source, reflector, radiation receiver and signal processing unit. There is working cavity in central part of the case. Reflector is disposed inside the cavity onto frame with two parallel channels. Radiation source is disposed in one channel and radiation receiver - in the other one. Radiation source and radiation receiver are connected with signal processing unit fastened to top part of plate. Plate is disposed inside case under frame. There hole for feeding fluid at lower part of side wall of working cavity. There is drainage hole in top part side wall of working cavity. Top cap of the cavity is made in form of screw. Frame is connected with case by thread.

EFFECT: simplified design; reduced cost.

2 dwg

Description

The invention relates to measuring technique and can be used as a sensor for the presence of liquid in containers, a component in various automated control and monitoring systems, for example, in high pressure discharge pipelines of diesel engines for various purposes.

Known level gauge for liquid [1]. It contains a radiator, a photodetector, a guide tube in which the float is placed. Along the light guide tube, optical fibers are arranged in pairs, intended for supplying an optical signal processing element mounted on the float. The height of the optical element for processing the light signal is made greater than the step of vertical placement of the optical fibers.

The disadvantage of this device is that this design does not allow its use, for example, for recording the presence of fuel in the discharge pipelines of diesel engines, in particular marine diesel engines.

Known liquid level gauge [2], adopted as a prototype. It contains a source and a receiver of directional radiation, optically coupled through input and output units with a moving body in the form of a float with a reflector, and the radiation receiver is electrically connected through an amplifier to the input of a digital switch, the output of which is connected to the radiation source and the input of the frequency meter, the output of which is paired with a computer. Inside the cylindrical body there is a calibration channel optically connected to the radiation source through a beam splitter, a rotary mirror and a return prism with a second radiation receiver.

The disadvantages of the device are the design complexity and high cost.

The invention solves the problem of simplifying the design and its assembly, as well as reducing the cost of the device.

The problem is solved due to the fact that in the liquid level switch comprising a housing, a radiation source, a reflector, a radiation receiver, a signal processing device, in accordance with the invention, a working cavity with a lid is located in the central part of the housing, in which a reflector is located on a frame with two parallel vertical channels, in one of which a radiation source is installed, and in the second - a radiation receiver connected to the signal processing device, which is mounted on the board, inside the housing under the rim, and the axis of the radiation source and radiation receiver are equally distant from the geometric axis of symmetry of the reflector made of a material whose refractive index is equal to the refractive index of the liquid, while a hole for supplying liquid is made in the lower part of the side wall of the working cavity, and its upper part has a hole for draining the liquid, and the upper cover is made in the form of a screw, and the frame is connected to the housing using a threaded connection.

The invention consists in the following. The liquid level switch is based on the use of the effect of loss of total internal reflection at the boundary of two optical media with different refractive indices.

The effect is as follows. Let a beam A be incident on the boundary of two optical media with refractive indices n and n '(called the refractive surface) from a medium with refractive index n, whose unit vector is the angle ω with the normal to the given surface at the point of incidence. According to Snell's law of refraction, at the boundary of the indicated optical media, there will be a change in the direction of the unit vector of the beam A in such a way that the unit vector of the emerging beam will make the angle ω 'with the normal. In this case, the condition of the law of refraction must be satisfied

Показатель преломления воздуха относительно пустоты (вакуума) мало отличается от единицы n_в=1,00027. Поэтому в оптотехнике принято определять показатели преломления не относительно пустоты, а относительно воздуха. При этом показатель преломления воздуха принимается равным единице.The product of the refractive index by the sine of the angle formed by the beam with the normal at the point of incidence remains constant when the beam interacts with the refracting surface. It follows from formula (1) that, upon transition from an optically less dense (n <n ') medium to a medium, a denser ray, being refracted, bends to the normal. Otherwise (if n> n ') the beam, on the contrary, deviates from the normal and therefore

The refractive index of air relative to the void (vacuum) differs little from unity n _in = 1,00027. Therefore, in optical engineering it is customary to determine the refractive indices not relative to the void, but relative to air. In this case, the refractive index of air is taken equal to unity.

то по закону преломления

Поэтому, если увеличивать угол ω, то будет расти и угол ω', который всегда больше угла ω. При некотором значении ω₀ угла ω угол ω' станет равным 90°, а его синус - единице. То есть преломленный луч скользит по преломляющей поверхности. Подставив это значение в закон преломления, найдем угол ω₀ So, if the beam passes from a medium with a large refractive index into a medium with a lower refractive index, i.e.

then by the law of refraction

Therefore, if we increase the angle ω, then the angle ω 'will also increase, which is always greater than the angle ω. At a certain value ω _{0 of the} angle ω, the angle ω 'becomes equal to 90 °, and its sine - to unity. That is, the refracted beam glides over the refractive surface. Substituting this value into the law of refraction, we find the angle ω ₀

If the beam forms an angle of incidence exceeding ω ₀ , then all the radiation is completely reflected from the refracting surface, as from an ideal mirror, despite the fact that the refracting surface is transparent. This phenomenon is called total internal reflection, and the angle ω ₀ defined by formula (2) is called the limiting angle of total internal reflection. If total internal reflection occurs at the glass-air interface, then

With the often used glass of the K8 grade, for the green line of the spectrum n = 1.5163 and ω ₀ ≈41 ° 16 '. Therefore, if we take the prism of the BR - 180 ° and direct the radiation of the LED at an angle of 45 ° to the inclined faces, the radiation flux will not go beyond them, but, reflected from them, will exit through the hypotenuse face of the prism in the opposite direction.

In our case, this stream will be partially received by the photodetector (phototransistor or photodiode) and can be detected. If the faces of the prism are immersed in a liquid, for example, diesel fuel having a refractive index of about 1.6, then the phenomenon of total internal reflection will be disrupted and the entire radiation flux (with the exception of a negligible fraction of the reflected component) will come out of the prism and will be absorbed in the fuel itself. The radiation incident on the photodetector will be negligible in this case, and the signal from the photodetector will decrease many times. This effect is used to make a decision about the presence of fluid in the analyzed volume.

In the known system, an assessment is made of a certain level of signal decrease when lowering the prism into the liquid (or, which is the same, when the liquid level rises), which allows us to judge the achieved liquid level. Therefore, such sensors are called level switches. In our case, the analyzed volume is filled from below and the fact of the presence of liquid (fuel) is recorded in the controlled pipeline of the emergency circuit of the diesel engine power system.

The proposed constructive solution of the device allows to minimize the number of necessary structural elements, which greatly simplifies the design and allows to reduce its cost. In addition, the use of a threaded connection for mounting a frame with a reflector, as well as a top cover, the role of which is played by a special screw, simplifies the assembly process of the device, as well as its maintenance and prevention.

Figure 1 shows a General view of the liquid level switch.

Figure 2 shows a diagram explaining the principle of operation of the level switch.

The liquid level switch comprises a housing 1, a reflector in the form of an optical prism 2 (in this particular case BR-180), a top cover in the form of a screw 3 with a ring 4, a vertical cylindrical working cavity 5. Inside the housing 1, a frame 6 is mounted on the thread, in vertical the channels of which are placed a radiation source 7 and a radiation receiver 8, made, for example, on a phototransistor. The axes of the radiation source 7 and radiation receiver 8 are equally spaced from the geometric axis of symmetry of the prism 2. The side wall of the working cavity 5 is provided in the lower part with an opening 9 for supplying fuel, and in the upper part with an opening 10 for draining fuel. Inside the housing 1, a board 11 is fixed using screws 12. A signal processing device is attached to the board 11 (not shown in FIG. 1). In the lower part of the housing 1, a plug 13 is installed on the thread, provided with a gasket 14.

The device operates as follows. Since in this case the liquid level switch is used as a fuel leakage sensor and is designed to detect the presence of fuel in high pressure discharge pipelines of diesel engines for various purposes, then in normal mode, i.e. in the absence of liquid fuel in the working cavity 5 (see Fig. 2), the light flux from the radiation source 7 enters the lateral face of prism 2 at an angle of 45 °, does not extend beyond the boundaries of the prism, but is reflected from the lateral faces, exits through the hypotenuse face of the prism in the opposite direction, is perceived by the radiation receiver 8 and the presence of a signal is detected by the signal processing device. If there is fuel in the emergency circuit of the pipeline, liquid fuel begins to flow through the opening 9 into the working cavity 5 and fills it. In this case, the optical prism 2 is immersed in liquid fuel. In this case, the phenomenon of total internal reflection will be violated and the entire luminous flux from the radiation source 7 will come out of the prism 2 and will be absorbed in the fuel itself. The radiation incident on the receiver 8 will be negligible in this case, and the signal from the receiver 8 will decrease many times, and the signal processing device generates an alarm (accident).

Literature

1. RU 2183316 C1, 11/08/2000, G 01 F 23/00.

2. RU 2161782 C2, 03/05/1999, G 01 F 23/292 (prototype).

Claims (1)

A liquid level switch comprising a housing, a radiation source, a reflector, a radiation receiver, a signal processing device, characterized in that a working cavity is made in the central part of the housing, in which a reflector is located, mounted on a frame with two parallel vertical channels, one of which is installed a radiation source, and in the second, a radiation receiver connected to a signal processing device, which is mounted on a board located inside the case under the rim, and the axis of the radiation source and the radiation receiver is equally removed from the geometric axis of symmetry of the reflector made of a material whose refractive index is equal to the refractive index of the liquid, while a hole for supplying liquid is made in the lower part of the side wall of the working cavity, and a hole for draining the liquid is made in its upper part, the upper the cavity cover is made in the form of a screw, and the frame is connected to the housing using a threaded connection.

Images