WO1998058481A1

WO1998058481A1 - Telephone line testing device and equipment protector

Info

Publication number: WO1998058481A1
Application number: PCT/US1998/012451
Authority: WO
Inventors: Paul Richard Prince; Kevin R. Prince; Rodney E. Hosilyk
Original assignee: Paul Richard Prince; Prince Kevin R; Hosilyk Rodney E
Priority date: 1997-06-16
Filing date: 1998-06-15
Publication date: 1998-12-23
Also published as: AU8073198A

Abstract

A telephone line testing and power surge attenuating device (131) detects the integrity of a telephone loop connected to a subscriber's modular telephone jack and attenuates potentially damaging power surges. The testing circuit tests the current potential of the line, and, if the current is excessive, presents a visual indication thereof (LED4). If the tip and ring signals of the telephone loop are reversed, reverse polarity is visually indicated (LED1). Otherwise, if the tested current falls within a predefined acceptable range, a visual indication (LED2) that the telephone line is in working order is provided.

Description

TELEPHONE LINE TESTING DEVICE AND EQUIPMENT PROTECTOR

Background of the Invention Field of the Invention

The present invention relates to an inexpensive, reliable phone line test device and phone equipment protector for use while traveling and at home, which indicates whether a phone line is safe for connection with a computer modem or other equipment and which, during use, protects the equipment against power surges that may appear on the telephone line. Description of Related Art

Increasingly, various types of telephone systems are being used today that terminate in a standard wall-type modular jack, such as "RJ-11" standard modular jacks in North America. Other standard phone jacks are used throughout the world. Other, non-standard phone lines, such as those of digital or analog PBX systems, while terminating in a standard phone jack, sometimes provide current capacity that will damage standard equipment. Thus, as people travel with devices that use phone lines, such as portable fax machines and portable computer modems, there is an increasing need for travelers to be able to identify standard telephone lines from non-standard, potentially damaging lines.

There are a variety of conventional telephone line testing devices, most of which are used primarily to determine if a fault condition exists on the telephone line at a given location. However, these do not provide enough information to the traveler who is seeking to protect equipment from dangerous current flow.

Such conventional testers are merely simplified devices, which use red or green light emitting diodes (LEDs) and resistors to indicate the polarity of the telephone line. One such tester is known and commercially available as "BT-71" Deluxe Phone Line Tester, manufactured by Black Point Products, Point Richmond, CA and Radio Shack Catalog Number 43-104 "Phone Line Tester." Other such devices are disclosed in US patents 4,827,498 to Ross, 4,626,633 to Reuhl et al, 4,600,810 to Feldman et al, 4,564,728 to Roman, and 4,920,555 to Ingalsbe. In these devices, high current conditions are not tested. Therefore, if one of these devices is used to test a line that has dangerous current potential, the light emitting diodes (LEDs) of such devices will only indicate that power is present. The user of such a device remains unaware of any dangerous line conditions or excessive current.

More complex examples of telephone line testing circuits have been marketed by IBM and Road Warrior International, and are described as "Modem Saver™" devices. Each of these devices employ full-wave rectifiers to supply circuitry for detecting excessive current or voltage, and a reverse polarity indicating yellow LED. The IBM device (disclosed in US Patent 4,522,864) generally measures the current flow capacity of the telephone line, but has temperature dependent trip point characteristics. The Road Warrior device (Road Warrior International part #MODS0001) presents a relatively high line impedance and a complex interaction between the "danger" indicating red LED initiating voltage and a green "safe to use" LED trip-off circuit. Five one-percent resistors are utilized to attempt to match these circuits, but are also plagued with undue temperature dependence of trip thresholds. Neither of these "Modem Saver™" prior art devices provide safety provisions against high currents associated with PBX syste s or with power lines shorting to telephone lines. Further, neither of these devices can be easily modified to provide different trip points for the safe/alarm threshold.

Further, telephone systems in many areas of the world still exhibit a high number of power surges appearing on the line. Such power surges can damage portable computer modems, fax machines, and the like. The user of such a damaged device not only sustains damage to equipment, but often there are no discernable signs of such damage. Therefore, the user ends up spending a considerable amount of time attempting to make such equipment work without the knowledge the equipment has been damaged. This is true because successfully connecting a typical portable computer to a telephone network through a standard modem relies on a variety of hardware and software settings. If the user is having a difficult time connecting successfully, it is likely to be perceived to be a problem with the settings.

In the case of equipment damaged during use, the user believes that the equipment is still functioning normally since it had been working heretofore. As such, there is a considerable need for a device that attenuates dangerous voltage and current surges to a safe level before reaching the delicate equipment used by the traveler. What is therefore needed is a portable, low cost, precision current-measuring system that warns portable equipment users when telephone lines present excessive current capacity that may be hazardous to their modems, other equipment, or to the user of such a device.

What is also needed is to provide safety against smoke and fire or explosion in the event that such excessive current capacity is detected. Such a device would be a universal current test instrument that is precise, safe, and low in cost. The device would also provide a test instrument easily modified for special purpose communication lines or other power sources and special purpose communication or other special purpose equipment in which the safe/alarm threshold is easily adjusted. The ability to indicate and/or test the functioning of the alarm indicating circuitry is also needed in some applications. Further, such a needed device would provide for power surge protection during use of modems or other equipment, and would provide all of the above functions in one compact, easily transported, convenient to use device. Summary of the Invention

The present invention is a telephone line testing and power surge attenuating device which detects the integrity of the line connected to a subscriber's modular telephone jack and attenuates potentially damaging power surges. The device includes a modular connector at one end of a flexible electrically conductive cable, the other end of the cable terminating in a circuit enclosure housing a testing circuit and power surge attenuating circuit. The enclosure further includes a modular jack for connecting the subscriber's telephone equipment through the device to the telephone line. The testing circuit, when connected through the modular connector, the cable, and through a manually or automatically selective switch to the telephone line, presents low impedance to the line, drawing the line "off hook." The testing circuit then tests the current potential of the line, and, if the current is excessive, presents a visual indication thereof. If the tip and ring signals of the telephone loop are reversed, reverse polarity is visually indicated. Otherwise, if the tested current falls within a predefined acceptable range, a visual indication that the telephone line is in working order is provided. When the testing circuit is disengaged through the switch, the telephone line is connected to the modular jack of the enclosure through power surge attenuating circuitry. One embodiment of the invention is a device for testing circuits comprising an input having a first line and a second line. A surge attenuator is coupled to the input. A switch having a first position and a second position is coupled to the surge attenuator. A test circuit is coupled to the surge attenuator when the switch is in the second position. The test circuit has a plurality of indicators which communicate current conditions on the input. An output is coupled to the switch so that the output is coupled to the surge attenuator when the switch is in the first position.

Another embodiment of the invention is a device for testing the current in a telephone line and attenuating power surges on the line while connected to telephone equipment such as a modem. The device comprises an input and a test circuit supported within a housing. The test circuit has at least a first indicator indicating a safe current condition on the input, a second indicator indicating an unsafe current condition on the input, and a third indicator indicating polarity of the current on the input. A surge attenuation circuit having an output is connected to the device input. The device also includes means for switching, having a first position and a second position. When the switching means is in the first position, the switching means electrically connects the telephone equipment input to the output of the surge attenuation circuit. When the switching means is in a second position, the switching means electrically connects the test circuit to the output of the surge attenuation circuit.

Brief Description of the Drawings These and other features and advantages of the invention will become more apparent upon reading the following detailed description and upon reference to the accompanying drawings.

Figure 1 is an exploded perspective illustration of the hardware components according to one embodiment of the invention.

Figure 2 is an exploded perspective illustration of the hardware components according to an alternate embodiment of the invention.

Figure 3 is a schematic diagram of one embodiment of the testing circuit of the invention. Figure 4 is a schematic diagram of another embodiment of the testing circuit of the invention. Figure 5 is a schematic diagram of an alternate embodiment of the testing circuit of the invention. Figure 6 is a schematic diagram of an alternate embodiment of the invention. Detailed Description

Referring to Figure 1, an exploded view of a tester 19 is shown in relation to a section of wall 21 having a suitable telephone jack 23 mounted within a wall plate 25. The jack shown is for insertion of a RJ-11 plug as is typical in North America. By using a different plug, or an adapter, the invention can work well with a variety of jacks, and the RJ-11 configuration shown is but one. The tester 19 has an upper housing 31, which interconnects with a lower housing 33. The upper housing

31 and the lower housing 33 may be snap joined, or joined with screws 35 as shown here, or any combination thereof. A circuit board 37 is secured between the upper housing 31 and the lower housing 33. The circuit board 37 also supports a series of light emitting diodes LED1, LED2 and LED4, which are visible through a series of apertures 38 in the upper housing 31.

The circuit board 37 provides a strain relief tie 39 for a cable 41, which should be able to withstand pulling and twisting forces without sustaining damage. The strain relief tie secures the cable 41 to the circuit board 37. Most of the stress forces will be transmitted from the cable 41 to the circuit board 37 through the stress relief tie 39.

The end of cable 41 contains a modular connector 43 having a rectangular body 45 and lacking a normally present clip connector which would otherwise facilitate holding the tester 19 in place after insertion into the telephone jack 23. In one embodiment, the modular connector may be an RJ-11 phone plug. Lack of the clip connector prevents the device from being left in the telephone jack 23 for an extended period of time and ensures only a test of a momentary duration. Where a modular connector 43 is supplied with a locking clip, it may be easily removed with the use of cutters or other appropriate means.

Referring to Figure 2, an exploded view of a device 50 according to one embodiment of the invention is shown in relation to a section of wall 21 having a suitable telephone jack 23 mounted within a wall plate 25. As with the tester 19, the device 50 has an upper housing 31, which interconnects with a lower housing 33. The device 50 differs from the tester 19 in that the device 50 combines a line tester with a surge attenuator circuit for continuous protection of attached equipment such as a modem. Therefore, a connector jack 52 is mounted on the printed circuit board 37 to accept a plug from attached telephone equipment. A modular connector 43 attached to the electrically conducting cable 41 retains its clip to be securely retained within the telephone jack 23. A switch, which may be activated by a manual button 54, either connects the line tester circuit or the connector jack 52 to the telephone jack 23 through the surge attenuation circuit. The surge attenuation circuit (described below) is coupled between the telephone jack 23 and the switch 54 to protect the modem from any dangerous line surges from the telephone line. The circuit board 37 also supports a series of light emitting diodes LED1, LED2 and LED4, which are visible through a series of apertures 38 in the upper housing 31. The circuit board 37 provides strain relief slots 40 for the cable 41, which should be able to withstand pulling and twisting forces without sustaining damage.

Figure 3 illustrates a schematic diagram of the circuit for the tester 19 according to one embodiment of the invention. Although a telephone jack, such as jack 23 may have other connections, including additional lines and others, the circuitry involves only the two signal lines which sometimes, if found wired properly, occur as red and green lines.

A first line 103 designated as "Red Input," is connected to a first terminal of a 0.145 amp fuse F1. The fuse F1 also protects against smoke, fire and explosion in the event that the line has very high current capacity by quickly opening internally without release of spark, flame or smoke. The fuse F1 is preferably a resetting type, and in one embodiment is a Raychem TR2250-145 resettable fuse. A second terminal of the fuse F1 is connected to the anode of a diode D1 and to the cathode of a zener diode Zl. The zener diode Z1 has a voltage regulation value of approximately 5.1 volts. The anode of the zener diode Zl is connected to a first terminal of a resistor R1 and to a first terminal of a resistor R4. A second terminal of the resistor R1 is connected to the anode of a zener diode Z2 and to the circuit ground. The cathode of the zener diode Z2 is connected to a second input line 105, designated as "Green Input," and to a first terminal of a resistor R2. The zener diode Z2 has a voltage regulation of approximately 5.1 volts.

The second terminal of the resistor R2 is connected to the anode of a light emitting diode LEDl, which preferably outputs yellow light. The cathode of the light emitting diode LED1 is connected to ground.

The cathode of the diode D1 is connected to a first terminal of a resistor R3, to a first terminal of a capacitor C1, and to a terminal pin 8 of a comparator U1. A terminal pin 5 of the comparator U1 is connected to ground. The comparator U1 includes an internal voltage reference and is commercially available as part number RH338/KP, and is readily available from AR Industries, Santa Ana, CA. The terminal pins 5 and 8 provide the power to operate the comparator 111. A second terminal of the resistor R3 is connected to the anode of a light emitting diode LED2 and to the anode of a light emitting diode LED4. The light emitting diode LED2 preferably outputs a green light and the light emitting diode LED4 preferably outputs a red light. The cathode of the light emitting diode LED2 is connected to the anode of a light emitting diode LED3. The cathode of the light emitting diode LED3 is connected to ground. The light emitting diode LED3 is normally not visible when circuit 101 is enclosed within the upper and lower housings 31, 33.

A second terminal of the capacitor C1 is connected to ground. A second terminal of the resistor R4 is connected to a first terminal of a capacitor C2 and to a first terminal of a resistor R5. A second terminal of the capacitor C2 is connected to ground. A second terminal of the resistor R5 is connected to a first terminal of a resistor R6, and to an input terminal pin 3 of the comparator 111. A second terminal of the resistor R6 is connected to a hysteresis feedback terminal pin 2 of the comparator U1.

A terminal pin 1 of the comparator U1 is preferably connected to ground. A terminal pin 6 may be connected to a terminal pin 7. A terminal pin 4 is connected to the cathode of the light emitting diode LED4. When the voltage at the terminal pin 3 exceeds a predetermined level, the terminal pin 4 sinks current. When the voltage at the terminal pin 3 is below the predetermined level, the terminal pin 4 presents a high impedance to the light emitting diode LED4.

In one embodiment of the present invention, the components in Figure 3 have the following values:

TABLE 1 Typical Values for the Elements Shown in Figure 3

In operation, a user inserts the modular connector 43 into the telephone wall jack 23. Current flows into the first line 103 or the second line 105. If the polarity of the telephone line is correct, current flows from the first line 103, through the fuse F1, through the zener diode Z1, through the resistor R1, through the zener diode Z2, and back out the second line 105. The higher the current is into and out of the leads 103, 105, the higher the voltage is developed across the resistor R1.

When the current exceeds a predetermined value, the voltage created across the resistor R1 becomes high enough and causes the comparator U1 to sink current at the terminal pin 4. The voltage across the zener diode Z1 causes current to flow through the diode D1, through resistor R3, through the red light emitting diode LED4, into the terminal pin 4 and to ground. This current flow illuminates the red light emitting diode LED4 indicating a high current condition on the telephone line. In the event that the precision threshold voltage is slightly exceeded and the comparator U1 switches to the "alarm" state, the hysteresis provided through the resistor R5 slightly raises the voltage at the input terminal pin 3 of the comparator U1, insuring the "alarm" state is maintained.

If the current available from the telephone line is within tolerances, such as below 120 milliamps, a lower amount of current will flow through the resistor R1. This presents a voltage lower than the predetermined value at the terminal pin 3 of the comparator U1. Because the voltage at the terminal pin 3 is below the predetermined value, the terminal pin 4 presents a high impedance to the light emitting diode LED4. The voltage across the zener diode Z1 then causes current to flow through the diode D1, through resistor R3, through the green light emitting diode LED2, through the light emitting diode LED3, and to ground. This current illuminates the green light emitting diode LED2 indicating a within tolerances condition on the telephone line. If the current is below approximately 8 milliamps, the light emitting diode LED2 will not illuminate, indicating insufficient line current.

When the polarity across the telephone lines is reversed, the voltage at the second line 105 is higher than the voltage at the first line 103. This causes current to flow from the second line 105, through the zener diode Z2, through the resistor R1, through the zener Z1, through the fuse F1, and back to the first line 103. The current flowing through the zener diode Z2 presents a voltage across the zener diode Z2. This causes current to flow through the resistor R2, through the yellow light emitting diode LED1, and to ground. This current illuminates the yellow light emitting diode LED1 indicating a reverse current condition on the telephone line. This indication of reversed polarity directs the user to make use of a polarity-reversing adapter, which is available separately.

The comparator U1 accurately measures current flow in the current loop to define either "safe" or "alarm" by causing either illumination of the green light emitting diode LED2 or the red light emitting diode LED4 respectively. The other circuit components, also readily available, are commonly known by those skilled in the art. Resistor R1 may be changed to adjust the alarm trip point according to the relationship: Trip Current ~ 10 + (1150 + R1) milliamps. In alternate embodiments not shown, a series of resistors, selectable with a rotary switch for example, may be employed to allow users to set precision multiple or customized trip current values.

When the circuit 101 is connected to a subscriber telephone loop line, a temporary high voltage condition may be present. This high voltage may be caused by a variety of factors, including a noisy environment or having significant energy stored within the inherent capacitance of the line or the capacitance of any associated connected telephone equipment or subscriber equipment. The line may also be in the presence of a high voltage ring signal. If this transient high voltage condition is allowed to trip the comparator U1 to the "alarm" state, the hysteresis will contaminate the precision current measurement between "safe" and "alarm" states. Such a false trip upon connection to the line is avoided through the low pass filtering function of the capacitor C2 in combination with the resistors R1 and R4. When the capacitor and resistor values of Table 1 are used, this low pass filter has a time constant of approximately 30 milliseconds.

Standard comparator operation, well known by those skilled in the art, provides either a high impedance or a current sink at the terminal pin 4, based upon the difference between an internal reference to an external voltage at the terminal pin 3. When the "alarm" state is detected, the comparator U1 sinks current from the resistor R3 and through the light emitting diode LED4, illuminating the light emitting diode LED4 and starving the light emitting diode LED2 of its current. The light emitting diode LED3 is employed in a bias function to allow substantially all current flowing through the resistor R3 to flow through the light emitting diode LED4 when in the "alarm" state. When an operator uses the embodiment of Figure 3, the green light emitting diode LED2 or the yellow light emitting diode LED1 will usually be illuminated at startup. This is due to current flow before activation of the comparator U1. When the tester is used on telephone lines within tolerances, the red light emitting diode LED4 may never illuminate. This may cause the user to question whether the light emitting diode LED4 is operational. Figure 4 illustrates a circuit 111 with additions to the circuit 101 of Figure 3 to briefly illuminate and therefore test the light emitting diode LED4 upon initial connection of the tester to the telephone line Referring to Figure 4, the cathode of the diode D1 is additionally connected to a first terminal of a capacitor C3 and to a first terminal of the resistor R7. A second terminal of the capacitor C3 and a second terminal of the resistor R7 are connected to a gate of an N-channel MOSFET transistor Q1. The gate of the N- channel MOSFET transistor Q1 is also connected to a first terminal of a resistor R8. A second terminal of the resistor R8 is connected to the cathode of zener diode Z2. A drain of the transistor Q1 is connected to the cathode of the light emitting diode LED4. A source of the transistor Q1 is connected to ground. All other components of the circuit 111 of Figure 4 are the same as the circuit 101 of Figure 3.

In operation, the transistor Q1 couples the red light emitting diode LED4 to ground upon application of a positive voltage to circuit 111. This allows current to flow through and illuminate the red light emitting diode LED4. The transistor couples the light emitting diode LED4 to ground by virtue of a gate bias supplied from the capacitor C3, which is normally held discharged by the resistor R7. The resistor-capacitor circuit comprised of the capacitor C3 and the resistor R8 has a time constant of approximately 200 milliseconds using the values of Table 2. After the resistor R8 discharges capacitor C3 toward the second input line 105, the transistor Q1 turns off, allowing the comparator U1 to define the state of the light emitting diode LED4. The time duration of the red light emitting diode LED4 check in one embodiment of the invention is approximately 0.25 to 0.75 second. The following Table 2 lists the values of the components in Figure 4.

TABLE 2 Typical Values for the Elements Shown in Figure 4

In addition to checking the operation of the red light emitting diode LED4, it may be desirable to check the proper operation of the comparator U1. This may be necessary when telephone lines need to be checked in more demanding medical or emergency applications. To check the operation of the comparator U1, a circuit 121 of Figure 5 is used. Here the schematic differs more significantly from the schematic of Figure 3.

Taken as a departure from Figure 3, the second terminal of the resistor R5 is connected to the source of the N-channel MOSFET transistor Q1. The gate of the transistor Q1 is connected to a first terminal of a resistor R8, to the first terminal of the capacitor C3, and to the first terminal of the resistor R7. The second terminal of the resistor R7 and the second terminal of the capacitor C3 are connected to the cathode of the zener diode Z2 and the first terminal of the resistor R2. A second terminal of the resistor R8 is connected to the cathode of the diode D1 and to a first terminal of a resistor R9. A second terminal of the resistor R9 is connected to the first terminal of the resistor R6, to the drain of the transistor Q1, and to the input terminal pin 3 of the comparator U1. The following Table 3 lists the values of the components in Figure 5. TABLE 3 Typical Values for the Elements Shown in Figure 5

The operation of the circuit 121 is similar to that of the circuit 111 except that the state of the transistor Q1 changes from open to conducting rather than conducting to open. After a short time set by the time constant of the resistor-capacitor circuit comprised of the resistor R8 and the capacitor C3, the transistor Q1 connects the resistor R5 to the input terminal pin 3 of the comparator U1. This allows the comparator U1 to perform substantially according to the description associated with the circuit 101 of Figure 3. Prior to conduction of the transistor Q1, the comparator U1 senses the voltage defined by the combination of the resistor R9 and the hysteresis resistor R6, which causes the red light emitting diode LED4 to illuminate briefly as a substantially thorough alarm detection test.

Figure 6 illustrates the components of the invention incorporating a surge protector and tax impulse filters. The circuit 131 of Figure 6 differs from the circuit 101 of Figure 3 in several areas. A surge attenuator 107 is connected between the first line 103 and the second line 105. The surge attenuator 107 consists of a surge absorber SA1 and the fuse F1. In case of high voltage power surges, the surge absorber SA1 limits transient voltage to the modem. In one embodiment, the surge absorber SA1 is a Panasonic model ERZ- V07D361 surge absorber. The fuse F1 limits lower frequency surge currents to the modem. In one embodiment, the fuse F1 is a Raychem TR2250-145 resettable fuse.

The circuit 131 also contains a switch S1. The switch S1 selectively connects the line 105 to either the test circuitry or to the device output of the connector jack 52. In one embodiment of the invention, the switch S1 is a manual push button switch, with the connection to the test circuitry being made while the button is pushed and held. If the button is not pushed, the switch S1 connects the input line 105 to the device output -1 flat the connector jack 52, which is the default position of the switch S1. Of course, other types of switches, including toggles or automatic electric switches may be used. To test the circuit, the user pushes the button and checks the light emitting diodes LED1, LED2, and LED4. When the user is satisfied that the telephone line is safe for connection to his attached telephone equipment, the user releases the button of the switch S1. This connects the surge attenuator 107 to the device output to operate the attached equipment, while maintaining surge attenuation protection for the attached equipment. At any time during operation of the equipment, if the user suspects loss of line current, the user may depress the button of the switch S1 to observe the light emitting diodes LED1, LED2, and LED4 indicating the status of the telephone line.

In addition to the circuit 101 described above with reference to Figure 3, the test circuit 131 includes the cathode of a zener diode Z4 connected to the first terminal of the fuse F1. The anode of the zener diode Z4 is connected to a first terminal of a resistor R10. A second terminal of the resistor R10 is connected to the second terminal of the resistor R4. If a high voltage condition appears on the input lines 103, 105, the combination of the zener diode Z4 and the resistor R10 allow the comparator U1 to indicate a fault condition even if the fuse F1 trips. This allows the use of an automatic resettable fuse F1 which may limit current through internal heating. Such current limiting is detected by the zener diode Z4 and the resistor R10 causing an "alarm" indication.

The circuit 131 also includes the cathode of a zener diode Z3 connected to the first terminal of the resistor R1. The anode of the zener diode Z3 is connected to the second terminal of the resistor R1. If an abnormally high current is present, for example approximately 1-2 amperes, the zener diode Z3 appears as a low impedance to the telephone lines 103, 105. The zener diode Z3 limits the voltage presented to the terminal pin 3 of the comparator U1 to the breakdown voltage of the zener diode Z3 and allows very rapid tripping of the current surge protector fuse F1.

The circuit 131 includes tax impulse filters 64, 66 to even further protect a connected modem from harm. In some countries, tax impulse signals are transmitted over the telephone lines to meter usage of the telephone lines and ensure taxes are properly paid. However, these impulse signals may cause damage to modems. Generally, these signals are sent at either 12 kilohertz (kHz) or 16kHz.

The 12kHz tax filter 64 comprises an inductor L2 and a capacitor C4. A first terminal of the inductor L2 is connected to the second terminal of the fuse F1, to a first terminal of the capacitor C4, and to a red lead 70 of the connector jack 52. A second terminal of the inductor L2 is connected to a second terminal of the capacitor C4 and to a black lead 74 of the connector jack 52.

The 16kHz tax filter 66 comprises an inductor L1 and a capacitor C5. A first terminal of the inductor L1 is connected to the second terminal of the switch SI, to a first terminal of the capacitor C5, and to a green lead 72 of the connector jack 52. A second terminal of the inductor L1 is connected to a second terminal of the capacitor C5 and to a yellow lead 76 of the connector jack 52. When the switch S1 is in the default position, the tax filters 64, 66 are available for use. If a user merely plugs an RJ-11 jack into the connector jack 52 which connects across the red lead 70 and the green lead 72, the tax filters 64, 66 are bypassed. However, by using an adapter to connect across the black lead 74 and the yellow lead 76, the tax filters 64, 66 are incorporated into the circuit 131. In this circumstance, any signals coming from the telephone lines 103, 105 must pass through the tax filters 64, 66. Each tax filter 64, 66 blocks the current components of the signal at the appropriate tuned frequency. By tuning the tax filter 64, 66 to 12kHz and 16kHz, those components of the signal on the telephone lines will not substantially flow through the modem. The following Table 4 lists the values of the additional components in Figure 6 according to one embodiment of the invention.

TABLE 4 Typical Values for the Elements Shown in Figure 6

For more precise tuning of the tax filters 64, 66, the inductors L1 and L2 or the capacitors C4 and C5 may be adjustable.

While the present invention has been described in terms of a tester and equipment protector for a telephone line, one skilled in the art will realize that the structure and techniques of the present invention can be applied to many similar devices. The present invention applied in any situation where quick testing is needed to prevent harm to equipment.

Numerous variations and modifications of the invention will become readily apparent to those skilled in the art. Accordingly, the invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The detailed embodiment is to be considered in all respects only as illustrative and not restrictive and the scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

WHAT IS CLAIMED IS:

1. A device for testing circuits comprising: an input having a first line and a second line; a surge attenuator coupled to the input; a switch having a first position and a second position, said switch coupled to the surge attenuator; a test circuit coupled to the surge attenuator when the switch is in the second position, the test circuit having a plurality of indicators which communicate current conditions on the input; and an output coupled to the switch, wherein the output is coupled to the surge attenuator when the switch is in the first position.

2. The device of Claim 1, wherein the switch is a manual switch normally resting in the second position.

3. The device of Claim 1, wherein a first indicator of the plurality of indicators communicates a safe current condition on the input.

4. The device of Claim 1, wherein a second indicator of the plurality of indicators communicates an unsafe current condition on the input.

5. The device of Claim 1, wherein a third indicator of the plurality of indicators communicates the polarity of the current on the input.

6. The device of Claim 1, wherein the test circuit further comprises a comparator which compares the current on the input to a predetermined level.

7. The device of Claim 1, wherein the input is coupled to a modular plug.

8. The device of Claim 7, wherein the output is coupled to a modular jack adapted to receive a telephone plug.

9. The device of Claim 8, wherein the plug is an RJ-11 telephone plug.

10. The device of Claim 1, further comprising at least one impulse filter coupled between the input and the output when the switch is in the first position.

11. The device of Claim 10, wherein the at least one impulse filter is tuned to 12kHz.

12. The device of Claim 10, wherein the at least one impulse filter is tuned to 16kHz.

13. A device for testing the current in a telephone line and attenuating power surges on the line comprising: an input and an output; a surge attenuation circuit connected to the input; a test circuit supported within a housing, the test circuit having at least a first indicator indicating a safe current condition on the input, a second indicator indicating an unsafe current condition on the input, and a third indicator indicating polarity of the current on the input; and means for switching having a first position and a second position, the switching means when in the first position selectively electrically connecting the surge attenuation circuit to the output, and the switching means when in a second position electrically connecting the surge attenuation circuit to the test circuit.

14. The device of Claim 13, wherein the switching means includes a manually operated momentary switch, the switch normally resting in the first position.

15. The device of Claim 13, further including a modular jack electrically connected to the output, the modular jack supported by the housing and at least partially exposed through an open end of the housing.

16. The device of Claim 13, wherein the device further comprises means for filtering which selectively attenuates the magnitude of signals of a pre-determined frequency on the telephone line at the output.

17. The device of Claim 13, further comprising a cable having a first end electrically coupled to the input and having a second end coupled to a connector having two terminals, wherein the cable electrically couples the inputs to the two terminals of the connector.

18. The device of Claim 17, wherein the cable has a first pair of electrical conductors and a second pair of electrical conductors being selectively connected to the surge attenuation circuit.

19. The device of Claim 17, wherein the cable is secured to the device by strain relief slots.

20. A method for protecting electrical equipment comprising the acts of: providing surge attenuation protection for the equipment; electrically disconnecting the equipment; applying a substantially short-circuit to an input; measuring the magnitude of the current through the substantially short-circuit; and measuring the polarity of the current through the substantially short-circuit.

21. The method of Claim 20, further comprising the act of indicating whether the magnitude of the current is above or below a predetermined level.

22. The method of Claim 20, further comprising the act of indicating the polarity of the current.

23. The method of Claim 20, further comprising the act of selectively blocking frequency impulses.

24. The method of Claim 20, wherein the surge attenuation protection suppresses transient high voltages.

25. The method of Claim 20, wherein the surge attenuation protection blocks high current.