JPS6041496B2 - Optical fiber transmission system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transmission system in which a central device collects on/off signals of at least two switches in one or more terminals.

Collecting on and off signals of a large number of switches in a central device is required for collecting control signals in process control systems, such as those in steel. Conventionally, this type of transmission system uses a transmission system that transmits electrical signals.

However, in factories where this type of transmission system is used, there is generally an extremely large amount of electrical noise, so expensive shielding measures are taken for the transmission system, and the electrical signal
A high voltage signal of about 0V is used. As a result, it is poorly compatible with electronic computers typically located in central equipment.

It is also extremely difficult to simplify the wiring harness by connecting this transmission system in a star or tee configuration. In order to eliminate these drawbacks, this invention introduces an optical fiber transmission system and uses reflected light within the optical fiber as the switch on/off signal so that the terminal switch is not affected by electrical noise at all. west,
The transmission system as a whole is extremely resistant to electrical noise, and each switch and the central device can be easily connected in a tee or star configuration to simplify the wiring harness and the central device. FIG. 1 shows one embodiment of the present invention, where M is a central device, T is an optical transmitter,
R is the optical receiver, SWI~SW3 are the terminal switches, 1~
4 is an optical branch circuit, and 5 to 11 are optical fibers.

In the optical transmitter T of the central device, there are a light emitting circuit TI that sends out an optical pulse of wavelength input 1 to the optical fiber, a light emitting circuit T2 that sends out an optical pulse of wavelength input 2 to the optical fiber, and wavelength input 1 and ^2. It includes a multiplexing circuit that multiplexes light and transmits it to an optical fiber. The optical pulses at wavelengths 1 and 2 are synchronously sent out to the optical fiber at the same time. On the other hand, optical receiver R
It consists of an optical demultiplexer R3 that separates and extracts the light of wavelengths ^1 and 2, and a light receiving circuit that independently receives the light of each wavelength. Switches SWI to SW3 of the terminal reflect only the light of the input 1 when the switch is on, and reflect the light of the input 2 when the switch is off.
It is designed to reflect only the light of In FIG. 1, the light entering 1 is shown as a solid line with an arrow, and the light entering 2 is shown as a broken line with an arrow. Wavelength transmitted from optical transmitter T^
The optical pulses 1 and ^2 reach the SWI via the optical fiber 5, the optical branch circuit 2, and the optical fiber 6. As shown in FIG. 1, when the SWI is off, it reflects only the incoming light. The reflected input optical pulse reaches the optical receiver R via the optical fiber 6, the optical branch circuit 2, the optical fiber 5, and the optical branch circuit 1. This optical pulse is received by the light receiving circuit of the demultiplexer R3 in the optical receiver. At this moment, no optical pulse is incident on the RI receiving circuit. Based on the arrival time difference between the optical pulse output from the optical transmitter T and the optical pulse with the wavelength of the input 2, the optical receiver R discriminates that the optical pulse of the input 2 is from SWI, and further distinguishes the optical pulse of the wavelength input 2 Since only the optical pulse of 1 is received, it is determined that this is a switch off signal. FIG. 2 shows an example of the configuration of a terminal switch that can be used in such an optical fiber transmission system. 6 is an optical fiber, 13 is a switch handle, FI is a filter that reflects wavelengths other than 1, and F2 is a filter that reflects wavelengths other than 2.

It will be easily understood that when the switch is off, the light with wavelength input 2 is reflected, and when the switch is on, the light with wavelength input 1 is reflected. Now, since the optical fiber transmission system according to the present invention uses light of two or more wavelengths, it is possible to easily distinguish between, for example, a reflected light pulse from an optical fiber connection point and a reflected light pulse that is a signal from a switch. . That is, in general, reflection from a connection point, etc. has almost no wavelength selectivity, so it is possible to distinguish the reflected light pulse signal from the terminal switch by imparting wavelength selectivity as described above. FIG. 4 schematically shows the received waveforms of the two wavelengths input 1 and 2 in the optical receiver R in the embodiment shown in FIG.
Since optical pulses 2 and S3 have wavelength selectivity, they are signals from the switch, but since optical pulses P1, P2, P3, and P4 occur simultaneously at two wavelengths, it is determined that they are not signals from the switch. As described above, according to the present invention, a switch that is completely immune to electrical noise as shown in Fig. 2 is used as a terminal switch while using an optical fiber in the transmission path, so a transmission system that is extremely resistant to electrical noise is realized. Not only is this possible, but the terminal optical switch can be discriminated based on the propagation time of the reflected light pulse, so it can be realized with a simple optical fiber connection as shown in FIG. Also, since two wavelengths are used,
Terminal switch signals and noise from unknown reflection points can be easily distinguished, and a highly reliable transmission system can be constructed. In the above embodiment, the optical fiber is connected in a tee shape and the wavelengths used are two wavelengths, but the present invention can also be realized by a transmission system with a so-called star connection. By using a wide light emitting element, essentially two wavelengths can also be used.

As described above, the optical fiber transmission system according to the present invention can be constructed without intervening electrical signals at all except for the central device, can realize a transmission system that is extremely resistant to electrical noise, and can distinguish between each switch by relying on the wiring. Since this can be done without any problem, it is possible to easily connect the wires in a tee shape or a star shape, thereby simplifying the wire connections and the central device.

Furthermore, by using two or more wavelengths, unknown optical noise at optical fiber connection points can be suppressed, and a highly reliable transmission system can be realized.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing an example of the configuration of a terminal switch that can be used in the present invention, and FIG. 3 is a diagram showing an example of a received signal received by the central device. FIG. In the figure, 1 to 4 are optical branch circuits, 5 to 8 are optical fibers, M is a central device, T is an optical transmitter, R is an optical receiver, SWI to SW3
is the terminal switch. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. In a transmission system where a central device collects the on/off signals of at least two or more switches in one or more terminals, the central device and each switch of the terminals are connected by optical fiber, and the central device has , one or more optical transmitters that send light of at least two or more wavelengths to each switch through an optical fiber, and each switch can detect the amount of reflection for each wavelength and also detect the position where the reflection is occurring. An optical receiver is included, and the terminal also has a switch on and off.
An optical fiber transmission system comprising an optical circuit that reflects light transmitted through an optical fiber by changing the amount of reflection for each wavelength of the same optical fiber depending on whether the optical fiber is turned off.