JPS61198040A - Optical dew point sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical dew point sensor consisting of a light transmission body connected to a light source and a light measuring device, as well as to a measuring device for this sensor.

[Conventional technology]

Dew point mirror hygrometers for measuring dew point using optical means have been known for some time. This hygrometer includes a metal plate with a mirror surface onto which light from a light source is irradiated. Light reflected from the surface is received by a photodetector facing the surface. When the dew point is reached, moisture condensing from the air deposits on the mirror surface, reducing the intensity of the reflected light. A decrease in light intensity as seen by the photodetector is an indication that the dew point has been dropped. The surface temperature measured at this moment of the metal plate (cooled by the Peltier element) therefore corresponds to the dew point to be measured.

For the sensor for measuring the dew point according to the invention, a light transmission device is used, such as is known from DE 21 17 168, a measuring device using optical fibers for measuring the refractive index of liquids and gases.

According to this optical fiber set refractometer, a heterogeneous light transmission body that can be immersed in a medium is used as a sensor. This inhomogeneity causes a loss in light intensity depending on the type of medium, which is used for measurements. In this measuring device, light in the form of inhomogeneous modes is introduced into a transmitter which is guided through a medium, preferably a liquid. Transmitter inhomogeneities present in the medium transform these disparate modes into a broad spectrum of modes. The intensity of the light transmitted from the other end of the optical transmission body is a measure of the refractive index of the surrounding medium. However, this device is not used for determining or measuring dew point.

A method and device for determining vapors in gases (also used for dew point determination) has been known for some time from US Pat. No. 3,528,278.

In this US patent, the sensor for determining dew point uses a transparent element (eg, a quartz glass rod coated with a highly reflective material). Light enters the rod through its precisely polished front surface. The mantle surface of the rod and the angle of inclination of the front surface with respect to the direction of illumination are determined such that total reflection of the incident light occurs inside the rod as long as the mantle surface of the rod is not wetted by liquid.

In the case of a boundary layer between glass and liquid, the critical angle at which total internal reflection occurs is different from that in the case of a boundary layer between glass and air. This phenomenon is utilized in the device according to the above-mentioned US patent to determine the dew point. Droplets of condensate, i.e., condensation, for example, that adhere to the surface of a glass rod, after reaching the dew point, will scatter a large part of the light incident on the rod, if the rod is dimensioned appropriately. The intensity of the light emitted from the edge is significantly reduced compared to the case at temperatures much higher than the dew point.

In this device, it is necessary to maintain a critical angle, so
The need for precise polishing of the glass material guiding the light beam and precise positioning with respect to the light source increases the cost of the device and makes it more prone to failure.

[Problem that the invention seeks to solve]

It is an object of the present invention to provide a sensor for determining the dew point which serves the same purpose as the glass material according to US Pat. No. 3,528,278 and which is less expensive and less likely to fail.

In order to solve this problem, the Berlin-Otzfenbach, Fau D. Known knowledge about the characteristics of optical transmission bodies is utilized in ``Minutes OFS 84JK'' published by I--Fairark Game M.B.A.

A light transmission body as a sensor whose surface is provided with a defined raster of a predetermined wavelength band is known from this publication. This raster consists of a defined crevice grid which, when moistened, causes a portion of the light incident on the light conduit to exit. The type of moisture molecule can be inferred from the decrease in light intensity.

A prerequisite for this measurement method is a very precisely produced linear or crevice grid.

[Means for solving problems]

Starting from this prior art, the present invention proposes to reduce the dew point of a gas in such a way that the light conduit only has locations on its surface with light-scattering irregularities created by damage, e.g. rough surface areas. Provide a simple sensor to understand.

[Effect]

Because inhomogeneities are so easily created, the intensity of the light emitted from the other end of the light conduit when the dew point is reached is significantly increased compared to conventional sensors. This increase provides an indication of the presence of condensate that can be used for measurement and alarm purposes. The physical cause will be explained in detail later with reference to the drawings.

According to another feature of the invention, the light-scattering inhomogeneities are also created by cutting the fibers, if the light transmission body consists of fibers.

Using the sensor of the present invention, a highly sensitive device is obtained which emits a signal solely due to the presence of condensate.

Further features of the sensor according to the invention are indicated in claims 3 and 4.

According to claim 5, this sensor is also suitable as a measuring device for measuring the entire dew point of a gas. In this case, the damaged area of the surface is provided with a cooling device connected to a control device and a temperature sensor connected to a temperature measuring device. According to claim 6, the cooling device known per se may consist of a Vertier element.

A preferred embodiment of the invention will now be described in more detail with reference to the drawings.

〔Example〕

FIG. 1 shows the basic configuration of a measuring device suitable for the sensor according to the invention. In this example, light is emitted by the light emitting diode 1, and this light is guided to the light receiver 2 (photodiode) through the entire optical transmission body 3. Transmission body 6 arranged between connector couplings 3a + 3b
is exposed in whole or in part to the medium to be examined for measurement purposes. As shown in the sectional view of FIG. 1a, the transmission body 3 made of glass or synthetic resin includes an inner core portion 6c and a mantle 3d surrounding this core portion and also made of glass or synthetic resin. and is surrounded on the outside by an elastic protective covering 3e made of rubber or synthetic resin.

In the measuring device according to the present invention, as shown in FIG.
A damage 3f (exaggeratedly shown in FIG. 4) is created on the surface of the transmission layer.

In a fiber whose surface is not damaged, the supplied light (incident light) is guided from the light emitting diode 1 to the receiver 2 by total internal reflection with almost no loss inside the transmitter 6, where the light is Strength can be measured. In that case, total reflection occurs regardless of whether the transmitter 6 is wetted with liquid or surrounded by gas.

This state will be explained according to the transition of the light flow shown in FIG. In addition, in FIG. 2, in order to simplify the illustration, a part of the core 3 of the fiber is not taken into consideration, without taking into account the water film (refractive index nw) surrounding the fiber mantle and the transmission body 3.
Only the light stream of c (refractive index n.) is shown. Total reflection occurs at the interface between the water film surrounding the transmitter 6 and the surrounding air, and the water film surrounding the transmitter only causes refraction of the emitted light rays.

The meanings of the symbols generally used for the critical angle of total internal reflection are as follows.

α= arc cell n/nc n=refractive index nc=transmission layer refractive index n5=refractive index of air nW=refractive index of water The thin water film surrounding the core portion 3ct of the transmitter 3 is:
Two interfaces extending parallel to each other are defined, namely, an interface between the transmitter 6 and water and an interface between water and air. By applying the known refraction law twice, we obtain a refraction law applied to a single interface between the transmitter 3 and the air. However, this means that the water film does not optically affect total internal reflection at all. The reason why a water film is optically invalid is 2.
The two interfaces extend parallel to each other.

The exact situation is illustrated in FIG. 3a.

In the transmission body 3, there is an inner core part 3c and a negative side mantle 3d. The surface of the core portion 3c is undamaged. In this case, as in FIG. 2, total internal reflection produces the light source shown.

Therefore, this transmitter 3 is not suitable as a sensor for measuring dew point.

The situation is different if, according to the invention, the surface of the transmission body is suitably damaged, for example made rough. This is the 4th ~
This is used in the embodiment shown in FIG.

3b and 3c, the transition of the light flow in the area where the surface of the transmitter 6 is damaged will be explained. Damage to the surface of the transmitter layer, shown by the irregular contours in Figures 3b and 3c, for example a rough surface, represents a number of surfaces with different orientations, and the incident light is refracted diffusely by these surfaces and partly is reflected.

Surprisingly, the loss of light intensity is greater when there is no condensation on a transmitter with a damaged surface than when there is condensation. The cause of this is 3b, 3
The trap is explained by the loss of light flow, as shown for the two cases in Figure c.

Damage to the surface of the transmission body, for example a rough surface, results in a number of partial surfaces with different slopes. In the case of such a surface, the respective angle of incidence of the light rays incident on the interface necessarily changes compared to a microscopically smooth surface. It therefore depends on chance whether the incident light beam is reflected at the transmitter or is emitted as divergent light. The microscopically roughened dry surface of the transmitter has a large number of such facets with different slopes, so that the majority of modes as a whole are at the critical angle of total internal reflection,
That is, all the modes at the angle α<43° are exceeded and the light is emitted from the transmitter as scattered light, so that the intensity of the light at the other end of the transmitter decreases.

On the other hand, if condensation occurs on the surface of the transmitter as shown in Figure 6c, the third
It is as explained with reference to figure a. That is, the surface tension of water causes a film of water to form over the damaged surface area or roughened surface features, and this film of water does not extend parallel to the individual facets of the damaged surface area. , extends parallel to the axis of the transmission body.

between the rough surface of the transmitter and the water film that forms in this area.
Statistically speaking, both of the facets, which are not flat, have a relatively large limit angle for total reflection at the interface between the transmitter and the water, so that most modes, that is, all modes at α〈66°, are transferred to the water film. Scatter it inside. Furthermore, the water film only allows a portion of these modes to pass through the water film-air interface.

The mode that undergoes total internal reflection at the interface between water and air will reach the transmitter again if the transmitter has a refractive index lower than that of the wetting liquid (for example, in the case of glass fiber and hydrogen). . As a result, in the case of a liquid-wetted transmission body of the type of the invention, a greater number of modes remain in the transmission body than in the case of a non-liquid-wetted transmission body. This means that the intensity, which is subsequently detected by the detector of the emitted light stream, is significantly greater than in the case of an unwetted transmission body.

An indicating device for ascertaining liquid phase and therefore dew point using the sensor of the present invention is shown in Figures 4 and 5. For example, in the device shown in FIG. 4, light from the light emitting diode 1 is supplied to the transmission body 6 (which has a damage 6f). The transmission body 3 is
A photodiode for measuring the intensity of received light is provided at the light transmitting end as a light receiver 2. If the rough surface is not wetted and therefore no condensed phase is present, a significant portion of the incident light will be transmitted from the damage 3f, and only a small amount of photocurrent will be transmitted from the photodiode 2. It is. On the contrary, if the damage 3f is wetted by being below the dew point, the photocurrent of the photodiode 2 increases significantly.

This difference in photocurrent can be used as a quantitative indication of liquid deposition. This configuration can also be used to monitor liquid levels in containers.

A modification of the embodiment shown in FIG. 4 is shown in FIG.

In this example as well, the light from the light emitting diode 1 is guided to the transmission layer via one leg 6g of the transmission body 3 and a light splitter in the shape of the Y-shaped splitter 4.

The transmitter 3 according to this example has a cutting point 3f in place of the damage 3f.
This cutting point has the same effect as the damage 3f, as will be described later with reference to FIG. 5a.A mirror surface 5 is formed at the tip of the transmission body 6, reflects the arriving light, so this light passes through the cutting point 3f' of the transmitter 3 again and is finally guided to the photodiode via the Y-shaped divider 4 and the leg 6h of the transmitter 3. The operation of this embodiment is basically the same as that shown in FIG.

However, the operation of the embodiment of FIG. 5 is more sensitive than that of the embodiment of FIG. 4 because the light is coupled twice at the cutting point 3 f'. This example is also not used for measurement, but merely for quantitative indication of moisture adhesion.

As can be seen from the course of the light beam shown in FIG. 5a, the light beam is propagated into the core portion 3C without loss due to total internal reflection.

In the region of the intentionally formed cutting point 3 f', the protective coating 3e has been removed. As long as this cutting point 3f' is not connected by a film of water, the light is emitted as in the case of a rough surface as described with respect to FIG. 3b. If, on the other hand, the cutting point 3f' is covered by a film of water 8 as schematically shown in FIG. 5a, total internal reflection will occur as explained in connection with FIG. 3c.

To measure the dew point (the temperature at which a mixture of gas and vapor is completely saturated by the amount of vapor present, below which supersaturation and condensation of the vapor occur), It will be necessary to use the equipment shown in Figures 6 and 7. According to this embodiment, the damaged surface of the transmission body is
As is known per se, it is present directly on the cooling element 7, for example in the form of a Peltier element. By means of a temperature sensor integrated into the surface of the cooling element 7, the associated temperature can be ascertained when the dew point is exceeded.

In other respects, quantitative determination of dew point is carried out according to known methods, for example as detailed in US Pat. No. 3,528,278.

The circuit of the measuring device according to the invention is shown in the block diagram of FIG. 8 and essentially consists of two interleaved control circuits cooperating with an optical dew point sensor.

By means of the condensation regulator 12, a target value for causing condensation is intentionally determined via the light intensity ascertained by the receiver of the sensor. This setpoint value is compared at summing point 13 with the temperature ascertained or measured by temperature sensor 6 (temperature measuring device) in the damaged area of the surface. At this time K.

Cooling device 7 (or heating device) by temperature control device 10
is set so that the target value and current value match. When the target value and the current value match, the dew point temperature is achieved, and this temperature is displayed on the display section 11 or stored.

[Brief explanation of the drawing]

FIG. 1 is an exploded side view showing a measuring device equipped with a transmitter, a light emitting diode, and a photodetector, and FIG.
2 is an explanatory diagram showing the state of total reflection that occurs at the interface between the transmitter and water and air when the surface of the transmitter is not damaged. Figures 3a to 60 are the transmission Figure 3a shows the evolution of the light flow on the surface area of the body, where Figure 3a shows the undamaged surface area with no condensation, Figure 3b shows the damaged surface area with no condensation. FIG. 3c is an explanatory diagram showing the course of the respective light flows for a surface area that is damaged and has condensation, and FIG. 4 shows a measuring device according to the first embodiment having a sensor according to the invention FIG. 5 is an exploded side view showing a measuring device according to a second embodiment having a sensor according to the present invention; FIG. FIG. 6 is an exploded side view showing the gas dew point measuring device according to the first embodiment, and FIG. FIG. 8 is an exploded side view showing the gas dew point measuring device according to the second embodiment. FIG. 8 is a schematic block diagram of the electric circuit of the measuring device shown in FIGS. 6 and 7. Explanation of symbols 1... Light emitting diode (light source), 2... Photodetector,
6... Optical transmission body, 3f... Damaged. Agent Patent Attorney Masatoshi Sato FIG, 2 FIG, 3

Claims (7)

[Claims] (1) An optical dew point sensor consisting of a light transmitting body connected to a light source and a light measuring device, wherein the light transmitting body (3) covers a surface of a light scattering irregularity created by damage. An optical dew point sensor comprising: (2) The optical dew point sensor according to claim 1, wherein the surface damage is created by roughening the surface. (3) The optical dew point sensor according to claim 1, wherein the damage to the surface is created by cutting the fiber. (4) The light source (1) and the light measurement device (2) are connected to the transmission body (3)
The optical dew point sensor according to any one of claims 1 to 3, characterized in that the optical dew point sensor is disposed at opposite ends of the dew point sensors. (5) The light source (1) and the optical measurement device (2) are arranged on separate legs of a Y-shaped splitter or a Y-shaped optical transmission body (3, 4), and the common axis portion of the optical transmission body 5. Optical dew point sensor according to any one of claims 1 to 4, characterized in that (3) bears a damaged, particularly rough part of the surface and has an internal mirror (5) at the tip. (6) Claim 1 for measuring the dew point of gas
Measuring device comprising an optical dew point sensor according to any one of clauses 1 to 5, wherein the cooling device (7) is coupled to a control device and the temperature sensor (6) is coupled to a temperature measuring device.
A measuring device characterized in that: and are disposed in a surface damage area. (7) The measuring device according to claim 6, characterized in that the cooling device (7) comprises a Bertier element.