JPH0335607B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical liquid level detector, and more particularly to an optical liquid level detector with light source monitoring means of simple construction.

Conventional technology Electric sensors are convenient as a means of detecting the liquid level, but depending on the nature of the liquid to be detected, they may cause electrode contamination,
Since there are problems such as malfunction due to air bubbles and corrosion of the sensor, optical means may be more advantageous.

A conventional optical liquid level detection method will be explained with reference to FIG. Medium M ₁ with absolute refractive index n ₁ and absolute refractive index n ₂
When incident light I enters the interface S with the medium M ₂ at an incident angle θ ₁ , if the incident angle θ ₁ is smaller than the critical angle θ ₁ , a part of the incident light I enters at the reflection angle θ _1. It is reflected and becomes reflected light R, and the other part enters the medium M ₂ with a refraction angle θ ₂ and becomes transmitted light D. When the angle of incidence is equal to the critical angle θc, the incident light Ic becomes a ray parallel to the boundary surface S indicated by the arrow T, and when the angle of incidence is greater than the critical angle θc, the incident light is totally reflected. It becomes reflected light. The critical angle θc is given by the following equation.

sinθc=(n ₁ / n ₂ ) It is known that the critical angle for incident light traveling from glass to air is approximately 42°, and the critical angle for incident light traveling from glass to water is approximately 60°. .

When incident light is applied to the detection surface 2 of the probe 1 shown in Fig. 1 at an incident angle of 45°, when the detection surface 2 is underwater, most of the incident light is smaller than the critical angle. This becomes transmitted light D. On the other hand, when the detection surface 2 is in the air, the incident angle is larger than the critical angle, so most of the incident light undergoes total reflection twice as shown by the dotted line in the same figure, and becomes parallel to the incident light I. Reflected light R
becomes. Therefore, if the presence or absence of reflected light R is detected,
In this case, the liquid level L, which is the water surface, can be detected.

However, in the conventional method described above, if a failure occurs in the light source 3 in Fig. 1 and the incident light I disappears or significantly decreases, the reflected light R will not be detected unless special measures are taken. A problem arises in that the liquid level is detected regardless of its presence or absence. For example, when a liquid level detector is applied to detect the full water level, even if the actual water level is below the full water level, it is judged as full, which is inconvenient. In order to solve this problem, it is conceivable to provide a monitoring detection element 7 beside the light source 3 to monitor the deterioration of the light source 3, as shown in FIG.
This solution requires an extra monitoring detection element 7 and its housing 7a in addition to the original detection element, which has the disadvantage of complicating the structure and increasing costs.

Problems to be solved by the invention Therefore, the problems to be solved by the invention are as follows:
The objective is to simplify the deterioration monitoring of the light source 3 in the optical liquid level detector.

Means for Solving the Problems Referring to FIG. 1, in a preferred embodiment of the present invention, a gap 9 is provided in the light source side optical path 41 of the incident light I of the probe 1 in contact with the input end of the probe.
The end face of the probe entrance end is made into a partially reflecting surface 10, and a portion p of the incident light I is reflected by the partially reflecting surface 10 to become partially reflected light q, which is then reflected onto the optical path 51 of the reflected light R from the detection surface 2. The reflected light R is caused to travel along the optical path 51 along with the reflected light R toward the
The sum of the reflected light q and a part of the reflected light q is detected. The partially reflective surface 10 described above does not necessarily need to be formed by the void 9, and may be formed by a half mirror or other means.

Note that simply connecting the light source side optical fiber 4 shown in FIG.
It is not possible to form a 0.

Operation In FIG. 1, a photodetector element 6 such as a photodiode is arranged in the optical path 51 of the reflected light R to detect the amount of light in the optical path 51. The outputs of the photodetecting element 5 for (partially reflected light q only) and (partially reflected light q + reflected light R from the detection surface 2) are expressed as E ₀ and E 0 in FIG. 5, respectively.
If E ₁ , the presence of the liquid level can be detected by the presence of only the output E ₀ , and the absence of the liquid level can be detected by the presence of the output E ₁ . In case of deterioration or loss of the light source 3, the output E ₀ decreases or disappears, so that it can be distinguished from the presence of a liquid level.

Therefore, according to the present invention, the deterioration of the light source 3 can be monitored by the extremely simple means of forming the partially reflecting surface 10 in the incident side optical path 41.

Embodiment An embodiment of the present invention will be described with reference to FIG. Optical fiber 4 coupled to a light source 3 such as a light emitting diode
By fixing one end of the optical fiber 6 coupled to one end and a photodetecting element 5 such as a photodiode to a hollow holder 8, and fitting the hollow holder 8 to the light source side of the probe 1, the light source side optical fiber 4 is fixed. A gap 9 is formed between the probe 1 and the light receiving end of the probe 1.
Since the light flux emitted from the light source side optical fiber 4 is not necessarily a perfectly parallel light beam, a portion p of the incident light I is reflected by the light receiving end face of the probe 1 and becomes a partially reflected light q. The shape and dimensions of the gap 9 and the mounting positions of the optical fibers 4 and 6 are appropriately selected to direct the partially reflected light q to the optical path 51 of the reflected light R. Thus probe 1
The above-mentioned light-receiving end facet partially functions as a reflecting surface 10.

The illustrated probe 1 is made of quartz glass, and has a cylindrical portion and a conical tip portion formed integrally. The apex angle of the tip is appropriately selected, and its conical surface forms a detection surface 2, and the incident light I traveling parallel to the axis of the cylindrical portion is incident on the detection surface 2 at an incident angle of about 45°. When the interface between the air K and the liquid W to be detected, that is, the liquid level L, is above the detection surface 2, most of the incident light I travels into the liquid W to be detected as refracted light D.
There is little reflected light on the detection surface 2. Detected liquid level L
is below the probe 1 and the outside of the detection surface 2 is only air K, the incident light I is reflected twice by the detection surface 2 as shown by the dotted line in FIG.
The incident light R is parallel to .

A pulse generating circuit 11 shown in FIG. 1 applies a driving pulse to a light source 3 such as a light emitting diode, and generates a light flux, that is, incident light I in a pulsed manner.

The light in the optical path 51 of the reflected light R, that is, the above-mentioned reflected light R and partially reflected light q, is applied to a photodetecting element 5 such as a photodiode via an optical fiber 6 and converted into an electric signal. The detection circuit 12 analyzes the output of the photodetection element 5 to detect the liquid level L, and displays the detection result on the display 13. When the detection circuit 12 consists only of the amplifier circuit 20 shown in FIG. 4, the output at the amplifier output terminal A becomes as shown in FIG. That is, by detecting the output E ₀ for only the partially reflected light q, it is determined that the liquid level L is at or above the position of the probe 1, and this is displayed as necessary. Output for (partially reflected light q + reflected light R from detection surface 2)
By detecting _E1 , it is determined that the liquid level L is below the probe 1, and this is displayed as necessary. Deterioration or damage to the light source 3 can be determined by detecting the absence of the output E ₀ for only the partially reflected light q, and this can also be displayed if necessary.

In order to prevent malfunctions when the above output E ₁ is a disturbance, the presence of multiple pulse-like outputs E ₁ is counted and determined, and a counter (not shown) is provided for this purpose. The detection circuit 12 may have a different configuration.

Referring to Figure 5, the disturbance E ₂ (partially reflected light q
+Reflected light R from the detection surface ₂ Similarly, the detection circuit 12 can include a changeover switch 21 synchronized with the pulse of the pulse generation circuit, a positive/negative conversion circuit 22, and an integration circuit 23. Since the changeover switch 21 inverts the output only during the period when there is no incident light I, as shown in FIG. 4, only the disturbance _E2 is inverted.

Therefore, when the reflected light R exists, that is, when the liquid level L is below the probe 1, the detection circuit 1
2 produces a finite output Vi as shown in FIG. 7 after a suitable integration time Ti. On the other hand, when there is no reflected light R, that is, when the liquid level L is at or above the position of the probe 1, the detection circuit 12 generates a significant output as shown in FIG. 8 even after an appropriate integration time Ti. do not. This makes it possible to accurately detect the liquid level even when the disturbance is large.

Effects of the Invention As explained above, since the optical liquid level detector of the present invention provides a partial reflection surface in the optical path of the incident light of the probe, it has the following effects.

(a) A photodetector element for monitoring light source deterioration and its housing can be omitted.

(b) Deterioration of the optical transmission line as well as the light source can be monitored.

(c) By incorporating a positive/negative conversion circuit and an integration circuit, the influence of disturbances on detection can be removed.

[Brief explanation of drawings]

FIG. 1 is a schematic illustration of an optical liquid level detector according to the present invention, FIG. 2 is an illustration of a critical angle, FIG. 3 is a schematic illustration of a conventional optical liquid level detector, and FIG. 4 is a schematic illustration of a conventional optical liquid level detector. is a circuit diagram of the detection circuit, and FIGS. 5 to 8 are diagrams explaining the operation of the detection circuit. I...Incoming light, R...Reflected light, p...Part of incident light, q...Partially reflected light, K...Air, L...Liquid surface, W...Liquid to be detected, 1... Probe, 2...Detection surface, 3...Light source, 4, 6...Optical fiber, 5...
...Photodetection element, 7...Detection element for monitoring, 8...Holder, 9...Gap, 10...Partially reflective surface, 11
...Pulse generation circuit, 12...Detection circuit, 13...
. . . Display device, 20 . . . Amplification circuit, 21 . . . Changeover switch, 22 .

Claims (1)

[Claims] 1. An optical system in which the angle of incidence of light from inside the probe to its detection surface is greater than the critical angle between the probe material and air and smaller than the critical angle between the probe material and the liquid to be detected. In the liquid level detector having a system, a partial reflection surface provided in the optical path on the probe entrance side so as to reflect a part of the incident light onto the optical path of the reflected light from the detection surface, and a part of the reflection surface from the detection surface. An optical liquid level detector comprising a single photodetecting element that receives the sum of light and reflected light from the partially reflecting surface. 2. In the optical liquid level detector according to claim 1, an optical path of the incident light on the light source side is provided with an air space that is in contact with the input end of the probe, and the end surface of the input end of the probe is arranged so that the end surface of the input end of the probe is Optical liquid level detector that acts as a slope. 3 An optical system in which the angle of incidence of the incident light from inside the probe to the detection surface is larger than the critical angle between the probe material and air and smaller than the critical angle between the probe material and the liquid to be detected, and the above incident light is intermittently transmitted. a light source that projects the light onto the probe; a partial reflection surface that is appropriately provided in the optical path of the incident light on the probe and reflects a part of the incident light onto the optical path of the reflected light from the detection surface; a photodetecting element that is appropriately provided in the optical path of the light and generates an electrical output proportional to the sum of the reflected light from the detection surface and the reflected light from the partially reflective surface;
Suitably connected to the output of the photodetector element via a reversing switch synchronized with the intermittent projection of the light source to generate an output of the same polarity as the output of the photodetector element when the incident light is projected, and An optical liquid level detector comprising: an inverting circuit that generates an inverted output of the output of the photodetecting element during non-projection; and an integrating circuit connected to the output of the inverting circuit.