1. Field of Invention
The present invention relates to modular overload protectors for communication systems, and in particular, to modules that include; overvoltage protection utilizing solid state devices and line identification.
2. Discussion of the Relevant Art
In communication systems, such as telephone systems, it is necessary to position overload protectors at various positions to protect sensitive parts of the system and to protect equipment connected to the line from lightning strikes or other causes of overvoltage appearing on the communication lines. Typically these overvoltage protection devices incorporated the carbon block type which provided parallel air gaps. However, the carbon block protector during normal operation on the communication line could cause static to appear on the line and thus, the gas tube type surge protectors replaced them. These devices generally used back up protection, which utilized thermally sensitive plastics that were assembled with spring pressure on them and thus, when overheated would yield and short the communication terminal line to ground.
With the inherent desire to protect the communication equipment several different types of protectors have been used over the years, each including thermally active members, which when overheated cause the line terminals to short to ground. Initially the thermally sensitive material was a low temperature melting solder pellet, which when melted because of the extreme heat caused by an overvoltage, would permit the assembly in some manner to short the line terminal to ground. Further improvements in the state of the art replaced the solder pellet used with the gas filled tube. Still further improvements of the protection devices, which proved to be more reliable, utilized a back-up air gap together with the thermally sensitive material for overheating protection in the assemblies that provides provide protection of the line if the gas tube associated therewith for some reason vented its gas.
However, all of the devices known in the prior art required that the technician in replacing any of the components after a lightning strike or overvoltage condition to carefully replace the components as it was originally assembled so that the protection would be restored. This type of assembly work performed in the field proved to be a handicap and thus, it was found more desirable to provide a device which is completely sealed and when it has provided its useful protection, is just thrown away and replaced with a new unit. This, of course, became feasible only with the advent of inexpensive thermally sensitive plastics and/or inexpensive solid state protection devices together with a new type of construction which reduced the cost of the protection device.
However, it has been determined that the sealing material sometimes referred to as a potting or encapsulating material, generally composed of some type of epoxy compound was found to interfere with the operation of the solid state surge arrester thereby making the apparatus less reliable so that a protective housing was needed to protect the solid state surge arresters from contamination.
Therefore, it is an object of the present invention to provide a miniature station protector module for communication systems which is completely sealed and may be disposed of once it has served its purpose for protecting the communication line.
It is another object of the present invention to provide a miniature station protector module which combines all of the features of the earlier type devices including fail-safe shorting, highly stable and efficient, as well as being inexpensive to manufacture.
It is still a further object of the present invention to provide a miniature station protector module which utilizes a solid state protector device.
It is yet another object of the present invention to provide a miniature station protector module, as described above, which further includes a protective housing to protect the solid state surge protector from contamination because it comes into contact with the sealing or potting material.
The foregoing and other objects and advantages will appear from the description to follow. In the description reference is made to the accompanying drawing which forms a part hereof and in which is shown by way of illustration a specific embodiment in which the invention may be practiced. These embodiments will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the spirit and scope of the invention. The following detailed description is, therefore, not to be taken in a limited sense, and the scope of the present invention is best defined by the appended claims.