JPH0445110Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] The present invention is a crime prevention alarm device that uses light (near infrared rays) used outdoors. The present invention relates to a case and a structure of a near-infrared transmitting window of an alarm device that detects the passage of a person or an object by blocking the passage of the same.

[Conventional technology]

In infrared security alarm systems used outdoors, frost builds up on the outer surfaces of the emitter and receiver windows due to radiation cooling on clear nights in winter, reducing the infrared transmittance and reducing the amount of light that reaches the light receiving element of the receiver. In some cases, the amount decreased to the same extent as when a person or object passed by, resulting in a malfunction. Conventionally, to prevent this, a hood as shown in FIG. 2 was provided on the top surface of the emitter/receiver, or a hole was made in a part of the near-infrared transmitting window. Other methods have been considered, such as heating the window material or using something like a wiper.

[Problem that the invention attempts to solve]

In the conventional method, there are the following three problems.

1. When using a hood, there is a problem in terms of the design as a security device, and at the same time, the direction of the light beam is easily detected, which is undesirable due to the characteristics of security equipment.

2. Drilling a hole in a part of the window material is effective against frost, but it poses a problem because insects and other insects can enter through the hole. Installing a security device In some cases, ants can enter through small gaps and build nests inside, so it is best to avoid creating more openings than necessary.

3 In order to apply heat or operate the wipers to prevent frost formation, the energy required for this must be supplied to the emitter and receiver, and the power supply capacity of a normal power supply for security equipment is limited. This is a problem.

[Structure of the idea]

In order to solve the above problems, the present invention utilizes the effect of the hood and has no problems in terms of design.
The present invention aims to provide a window structure for an infrared security device that does not require energy supply from another source.

(Example 1) FIG. 1 shows a cross section of a light receiver embodying the present invention. The light receiving element 5 receives the infrared pulsed light x (wavelength
0.94μ) and converts it into an electrical signal. The output of this light receiving element 5 is amplified by the electric circuit section 6.
After processing, when the amount of received light falls below a certain level, a relay or the like is driven to output it to the outside as a contact output (not shown). In this receiver, a cover 1 as shown in the figure is provided in front of an infrared transmitting window 2. This cover does not extend to cover the entire infrared beam. As a result, the section a shown in the figure becomes a part where frost is difficult to adhere due to radiant cooling. In other words, radiative cooling at night in winter occurs mainly by radiating heat towards the sky, so frost will adhere to the front and top surface of the cover 1, but the a of the infrared transmitting window will The area no longer looks up at the sky and radiates less heat, which prevents frost from forming. Generally, in a security alarm system that uses a light projector and a light receiver, the light receiver is set to receive light that is much stronger than the limit of the amount of infrared light required to issue an alarm, thereby maintaining a state of alert. This is because the amount of infrared rays that passes through the atmosphere changes depending on the weather, so even in fog or rain, the attenuation of light in the atmosphere will prevent an alarm from triggering. Specifically, the design is such that the light receiver can receive tens to hundreds of times more pulsed light than the limit for emitting a detection signal on clear skies, and the spacing between the light emitter and receiver is determined. Therefore, even if frost builds up on a clear winter night and blocks 90% of the effective area of the optical system, if there is 10% of the area where frost does not adhere as in the present invention, an alarm will be activated. This can be avoided.

(Example 2) Fig. 3 shows an example of the present invention in which the optical system is made rotatable, and the cover 1 is arranged along the cylindrical transmission window, which is advantageous in terms of design. Better than traditional hoods. The structure shown in this embodiment is advantageous because it makes it difficult to determine the direction of the infrared pulsed light, that is, the warning direction.

(Example 3) In the example shown in Fig. 4, the covers are 1-a, 1-
It is divided into parts b. The infrared transmitting window located at the rear of this divided gap has a smaller angle of view toward the sky than if there was no cover, making it difficult for frost to adhere to it. Furthermore, by providing this vertical division in other parts, it is possible to reduce the part of the infrared transmitting window 2 that radiates heat toward the sky. Acrylic resin is effective as the material for the infrared transmitting window and the cover 1. By selecting an appropriate acrylic resin, visible light and far infrared rays will not pass through, and a transmittance of 90% or more at a wavelength of infrared rays of around 0.94μ can be obtained at a thickness of approximately 1 mm. Therefore, even if the light beam is blocked halfway by the cover 1, the effect will be almost eliminated. Conversely, the effect of attenuation of visible light increases,
Another advantage is that it is less susceptible to the effects of sunlight and light emitted by lighting devices.

Although the above embodiments have been described with respect to a light receiver, it goes without saying that similar effects can be obtained with a light projector.

[Effect of idea]

As described above, the present invention has an excellent design and does not allow the intrusion of insects, etc., and can prevent malfunctions of security alarm devices due to frost buildup without receiving energy from the outside. Significant effects can be obtained by reducing the influence of illumination light.

[Brief explanation of the drawing]

FIG. 2 is a diagram showing a conventional example, and FIGS. 1, 3, and 4 are diagrams showing an embodiment of the present invention.

Claims (1)

[Scope of utility model registration request] It consists of a projector that emits near-infrared pulsed light, and a receiver that receives this near-infrared pulse and issues an alarm signal when it is interrupted, and is equipped with a near-infrared transmitting window on the front side of the optical system of the projector and receiver, An infrared security alarm device characterized in that a cover made of a material with high near-infrared transmittance and low far-infrared transmittance is placed close to the front of the alarm, extending from above into the beam of pulsed light.