|Publication number||USRE29499 E|
|Application number||US 05/584,065|
|Publication date||Dec 20, 1977|
|Filing date||Jun 5, 1975|
|Priority date||Oct 13, 1970|
|Publication number||05584065, 584065, US RE29499 E, US RE29499E, US-E-RE29499, USRE29499 E, USRE29499E|
|Inventors||Lucian W. Spencer|
|Original Assignee||Reliance Telecommunication Electronics Company|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (16), Referenced by (5), Classifications (12)|
|External Links: USPTO, USPTO Assignment, Espacenet|
There are many existing telephone loops that, due to their length, difficulty of access, or circuit makeup, are expensive to maintain. It is quite often the case, when a repairman visits a subscriber premises following a trouble report, that it is found that the telephone loope tests out satisfactorily and the compliant was caused by no one to answer the telephone, was due to a temporary equipment overload, or the telephone equipment, other than the loop itself, on the subscriber's premises was at fault. Thus, the repairman has made a trip to an extreme end of a telephone exchange for naught. In recent days, it is becoming more and more prevalent for subscribers to install and maintain their own on premise equipment, e.g., TWX, PBX, telephone equipment (hand sets) and the like. Thus, reports of "telephone" trouble by a subscriber to a telephone company are beginning to be mixed bag, i.e., troubles regarding equipment to the telephone company is responsible for (mainly the telephone loop) and troubles that the subscriber is responsible for (on premise equipment). The hereinafter disclosed invention allows telephone company personnel to make the distinction as to where the reported trouble is and whose responsibility it is, without a repairman leaving the maintenance depot.
The instant invention, a telephone loop tester, is a device that permits a telephone line to be tested (whether it is operable or not) from a telephone central office without the expense of a repairman`s visit to a subscriber's premises. Such a device is especially valuable when a telephone loop consists of a carrier system because conventional capacitor charge tests techniques are inapplicable. Additionally, the telephone loop tester, as hereinafter disclosed, is also applicable to voice frequency circuits as well as circuits involving carrier.
When a subscriber reports trouble, telephone company personnel can transmit an audio tone of a frequency, within a telephone circuit pass band from a central office towards a subscriber's premises. This tone activates the invention (telephone loop tester), which is on the subscriber's premises. The on premise telephone loop tester contains a tuned detector, which upon receiving a tone, activates a timing circuit. This timing circuit, in turn, operates a relay circuit, which places a circuit across the plus and minus (tip and ring) sides of the telephone line. It is this circuit that simulates the electrical condition of a telephone instrument in the "off hook" position. This circuit is held for a predetermined length of time by a timer, and causes the central office line equipment to operate, thereby indicating to personnel in the central office that the telephone loop (circuit) is complete from the central office to the subscriber's premises and return.
Power of operation of the detector, timer and relay circuit is supplied by a nickel candium rechargeable battery, this battery being trickle charged from the telephone line, and generally located at the subscriber's premises. Alternatively, the detector, timer and relay circuit can be powered from commercial power available at the subscriber end or other means that are well known.
The most practical frequency to use for activating the detector in the on premise telephone loop tester is 1,000 hz., available in most telephone central offices as a milliwatt supply; however, any frequency within the pass band of the telephone circuit may be used. In fact, several units, each tuned to a different frequency, may be used on the same line, if ever required, such as a party line application or in cases where the invention is used for telemetering. In order to prevent actuation of the detector by voice energy, a diode switch is provided to disconnect the detector of the loop tester from the telephone circuit when the telephone circuit is in use.
For the purpose of illustration of the instant invention, there is shown in the accompanying drawing, a circuit which makes up the on premise telephone loop tester. It is to be understood, however, that this drawing is for the purpose of example only and the invention is not limited thereto.
FIG. 1 is a schematic diagram of an on premise telephone loop tester circuit showing a detector, timer and relay circuit along with a power source rechargeable from the telephone line itself; and
FIG. 2 is a schematic diagram of a telephone transmission system containing the telephone loop tester circuit shown in FIG. 1.
The on premise telephone loop tester is generally indicated at 26 in FIG. 2.
Making reference to FIG. 1, all transistors in the idle condition are cut off, i.e., not conducting; relay RY1 is released and the battery is being trickle charged by a current flowing in a path from the plus side of the telephone line 1 to the minus terminal side of the line. See elements 1 and 2 as well as the designations tip and ring in FIG. 1. Also see U.S. Pat. No. 3,510,584 for disclosure regarding trickle charging a battery from a telephone line, said disclosure herein incorporated by express reference.
Coil L1 and capacitor C2 are tuned to a predetermined frequency, for example 1,000 hz. Capacitor C1 is used to provide for A.C. coupling and D.C. blocking. Resistor R11 is selected in value to provide a proper amount of trickle charge to battery B1. Resistor R3 has a value so that transistor Q1 will present a high impedance to the tuned circuit (Coil 1 and C2).
When 1,000 hz, the previously mentioned tone, is transmitted from the central office 20 (See Fig. 2) over the telephone pair 22 (See FIG. 2) it is received at the plus minus terminals (tip and ring). This signal then flows through a path comprising resistor R1, diode D1, capacitor C1, the L1-C2 coil capacitor combination to the negative side of the line (ring). Since coil capacitor combination L1, C2 is tuned to this frequency, a voltage is developed across them, which, on positive peaks of the formentioned tone, will cause transistor Q1 to conduct. On each pulse, a collector of Q1 is made negative due to the voltage drop occurring across R2. This negative voltage is applied to the base of transistor Q2 causing it to become conductive. In this electrical state, capacitor C3 causes the base of transistor Q2 to remain negative between pulses and effectively acts as a filter. While transistor Q2 is conducting, its collector becomes positive and through resistor R5, causes transistor Q3 to conduct.
When transistor Q3 conducts, capacitor C4 is being charged, thereby supplying a voltage across current limiting resistor R6. This voltage is high enough to cause zener diode D2 to conduct, placing the base of transistor Q4 at a negative potential, thus causing transistor Q4 to conduct. The base of transistor Q4 remains negative for a length of time determined by the values of capacitor C4, resistor R7, diode D2 and resistor R8, such selection of values obviously being within the purview of one of only ordinary skill in the art. When transistor Q4 conducts, the collector becomes positive which, when applied to the base of transistor Q5 through resistor F10, causes transistor Q5 to conduct. This completes the path for the winding of relay RY1, thereby causing the contacts of RY1 to close.
When the contacts of relay RY1 close, resistor R1 is thereby placed across the ± (tip and ring) sides of the line causing a high current to flow over the talking pair. This high current flow causes an "off hook" signal to be sent towards the central office. This "off hook" signal remains a length of time determined by the time constants in the previously described circuitry. At the same instant that relay RY1 contacts close, D1 becomes back biased and therefore nonconducting. Consequently, the tone input is removed from the detector. After the tone is removed, each transistor, beginning with transistor Q1, returns to the nonconducting state. Q5 will remain in a conducting state for a period of time primarily determined by the RC time constant of C4-R7. Under normal conditions (non-testing) a telephone 24 (See FIG. 2), which is connected across the tip and ring (±) side of the telephone line defined by the telephone pair 22, is placed in the "off hook" condition, the voltage across tip and ring sides of the line drops to a point, below that of an unterminated loop condition, to where diode D1 is back biased and therefore nonconducting. Under this condition, the detector is disconnected from the line and cannot be operated by speech energy during a conversation. Of course, it is possible to replace relay RY1 with equivalents, such as a transistor. Furthermore, battery B1 can be replaced by a power source at, on or near that of the subscriber's premises.
The preceding disclosure has addressed itself to a situation where there is no open or short in the telephone loop. However, if there is an "open" with the telephone loop, the "off hook" signal is not received at the central office after the tone is transmitted therefrom because the "open" prevents the tone from completing its required electrical path. Obviously, if no tone is received at the on premise detector, it is not activated. When this situation exists, telephone company personnel know that trouble, whatever the nature or cause, is in the telephone loop and not in that equipment on the subscriber's premises. Other loop faults, i.e., "short," balance to ground, etc., are readily determined by existing telephone C0 testing routines. The invention described herein is ideally suited to determining those faults which degrade transmission without showing a definite DC fault, and more especially to carrier derived circuits to which routine DC testing techniques are not applicable. In the situation where a telephone company is responsible for both telephone loop and on premise equipment, the instant invention permits repairmen to eliminate either the loop or the equipment, thus permitting these repairmen to concentrate their efforts on that element of a telephone circuit that is causing trouble.
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|U.S. Classification||379/8, 379/29.01, 379/393|
|International Classification||H04B3/46, H04M3/30, H04M1/24|
|Cooperative Classification||H04B3/46, H04M1/24, H04M3/301|
|European Classification||H04M1/24, H04M3/30C, H04B3/46|