JPH11101741A - Fiber liquid detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fiber sensor capable of simply detecting a liquid highly stably in a non-contact state. SOLUTION: One end of two branched bundle fibers is attached to a scanning device 9 to two dimensionally scan the waterdrop placed on a copper plate 18. Exciting light and fluorescence are split by a beam splitter 10 and the exciting light is detected by a photodetector (exciting light) 15 having sensitivity only to exciting light to obtain an output signal. The fluorescence is condensed by a lens 12 to pass through a filter 19 removing only exciting light and only a fluorescence signal is detected by a photodetector 13. The obtained voltage signal is amplified by a signal amplifier 14 to obtain an output signal 17. By calculating the ratio of the obtained output signals 16, 17, the attenuation of fluorescence can be estimated and a waterdrop and other liquid can be discriminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting and detecting liquid adhering to an object in a non-contact manner mainly by using an optical fiber.

[0002]

2. Description of the Related Art Conventionally, a method of detecting a liquid adhering to an object has been performed by directly contacting an optical fiber as a probe and measuring attenuation due to leakage of light guided in the fiber. Are known. Techniques such as OTDR (optical pulse radar in fiber) are used to remotely measure the attenuation of light, but this method requires a complicated device and performs signal processing by computer processing.

[0003]

However, in the conventional method, since the probe is constantly in contact with the liquid to be measured, it is difficult to repeat the measurement, and only the attenuation due to light leakage is measured. Then, it is difficult to identify the liquid.

[0004]

According to the present invention, it is possible to discriminate and detect a liquid by using a target absorption spectrum specific to the liquid to detect the liquid.
Also, non-contact detection is enabled by using reflected light.

[0005]

[Function] Each liquid has its own absorption spectrum. In particular, many liquids have a strong absorption spectrum in the near infrared to mid-infrared range.

When an optical crystal doped with a rare earth metal ion such as Er ³⁺ or Tm ^{3+ is} excited by a light source having a specific wavelength, it emits fluorescence from the near infrared region to the mid infrared region.

By appropriately selecting a combination of fluorescence emitted from such a crystal and a light source used for excitation, there are two types of excitation light, fluorescence that is absorbed by the absorption spectrum of the liquid and excitation light that is not absorbed. Using the difference in the absorptivity of liquid to light, only specific liquid is detected.

An optical fiber is used for remote, non-contact detection of a liquid attached to an object. This fiber not only guides the fluorescence and the excitation light, but also functions as a measurement probe that receives the reflected light from the measurement target.

While the probe fiber is scanned by the fiber scanning device, the ratio between the intensity of the received excitation light and the intensity of the received fluorescence is calculated, thereby canceling the coupling loss between the two lights to the fiber and the temporal fluctuation in the intensity of the light source. It is possible to measure only the decay of the fluorescence absorbed in the liquid.

[0010] A digital voltmeter or an oscilloscope is used to measure the fluorescence attenuation.

By controlling the scanning probe fiber while measuring the fluorescence attenuation, the size and position of the liquid can be measured simultaneously with the detection of the liquid.

A computer can be used for the signal processing and the fiber scanning control.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a liquid detecting device according to the present invention and its application will be described in detail.

FIG. 1 is an overall configuration diagram showing an embodiment of the present invention. The light emitted from the light source 1 is passed through the fiber liquid detector 2 and the signal processor 3.

FIG. 2 is a block diagram of a moisture sensor for showing one embodiment of the present invention in detail. LD as excitation light source
(Laser Diode) Light emitted from the light source 5 is
Irradiates the Tm ³⁺ : YAG crystal 7 through the through-hole, and ^guides the obtained fluorescence and excitation light to a two-branch bundle fiber 8 which is a scanning probe. In order to improve the S / N ratio of the output signal, the injection current of the LD is modulated by an AC signal from the signal generator 4, and the optical output of the excitation light and the fluorescence is also AC modulated.

Fluorescence and excitation light are guided into the fiber so that the light intensity distribution in the output end face of the two-branch bundle fiber becomes uniform.

One end of the two-branch bundle fiber is attached to a scanning device 9 driven by a stepping motor, and can two-dimensionally scan a water drop placed on the copper plate 18.

The excitation light and the fluorescence transmitted through the water droplet and reflected on the surface of the copper plate are guided again in the two-branch fiber 8, and are divided into two directions by the beam splitter 10 placed on the output end side.

Fluorescence separated by the beam splitter 10,
The excitation light passes through the fundal fiber 11 and is detected by a photodetector (excitation light) 15 having sensitivity only to the excitation light, and an output signal 16 is obtained.

The other light is condensed by the lens 12 and passes through the filter 19 for removing the excitation light, and the photodetector 13 detects only the fluorescence signal. The obtained voltage signal is amplified by the signal amplifier 14 to obtain an output signal 17.

The ratio of the obtained output signals 16 and 17 (signal 1
7 / Signal 16) is calculated to determine the fluorescence signal decay.

FIG. 3 is a waveform example of the obtained output electric signal ratio. When the probe fiber scans over the water droplet, the fluorescence signal is attenuated because the fluorescence is absorbed by the water, and the voltage ratio with the excitation light not absorbed by the water drops significantly.

FIG. 4 shows the obtained output signal 1 with respect to the relative position of the probe fiber scanned on the water drop to the center of the water drop.
It is a measurement example which shows the relationship between the ratio of 6 and 17. Good agreement between measured and calculated values is seen.

FIG. 5 is a measurement example showing the identification and detection of a water drop. This is a result of two-dimensionally scanning the probe fiber for water droplets, oil, discoloration due to rust on the surface, and the like on the copper plate. The decay of the fluorescence can be estimated from the height of the contour line with respect to the signal intensity ratio of the fluorescence and the excitation light, and it is confirmed that the water droplet can be distinguished from another liquid.

On the same principle, not only water but also oil and alcohol can be detected. The object to be measured is not limited to a copper plate, and any object can be measured as long as reflected light can be obtained. In particular, a feature of the present apparatus is that it can be detected separately from the surface shape of the measurement target and other liquids.

Since the liquid detecting apparatus according to the present method uses the ratio of the light intensity of the reflected light, errors due to temporal intensity fluctuations of the light source and coupling loss to the probe fiber can be reduced.

According to the present invention, with a simple configuration,
Liquid detection with high stability and excellent discrimination becomes possible. This is not realized by the conventional fiber sensor measurement technology, and has a wide application range as a new measurement technology.

[Brief description of the drawings]

FIG. 1 is an overall view for explaining an embodiment of a measuring device according to the present invention.

FIG. 2 is a configuration diagram for explaining an embodiment of a fiber liquid sensor according to the present invention.

FIG. 3 is a diagram showing an embodiment of an electric output signal according to the present invention.

FIG. 4 is a diagram showing an embodiment of a fiber liquid sensor according to the present invention.

FIG. 5 is a diagram showing an embodiment of a fiber liquid sensor according to the present invention.

[Explanation of symbols]

Reference ^Signs List 1 light source 2 fiber liquid detection device 3 signal processing unit 4 signal generator 5 excitation light source 6 lens 7 Tm ³⁺ : YAG crystal 8 2-branch bundle fiber 9 fiber scanning device 10 beam splitter 11 bundle fiber 12 lens 13 photodetector 14 signal amplifier 15 Photodetector 16 Excitation light output signal 17 Fluorescence output signal 18 Copper plate 19 Excitation light removal filter

Claims (1)

[Claims] 1. A light source comprising: an excitation light source having a wavelength not included in an absorption band of an object to be measured; and a luminous body such as a crystal for generating fluorescence having a wavelength included in an absorption band of the object to be measured by the excitation light source. The light generated from the light source is incident on the optical fiber, the output light from the fiber output end is irradiated onto the liquid to be measured while spatially scanning the fiber end, and the reflected light transmitted through the measurement target is taken in from the same fiber end and taken in. It has a device that extracts light from another fiber end, separates the excitation light source wavelength into wavelength components that are absorbed by the object to be measured, and measures the light intensity, and has a signal processing device that calculates the respective intensity ratios. An apparatus for displaying the calculated value as a function of the position of the fiber output end.