Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to test instruments, and more specifically to test instruments for the testing of local area network cables. 
     2. Description of the Related Art 
     High-speed data transmission cables are often an integral part of computer networks and telecommunication systems. A local area network (LAN), for example, as illustrated in FIG. 1 will usually include a number of individual computers and peripheral devices  60  communicating to one another through data cables  62 . The performance of the network can be affected by the quality of the data cables  62 , therefore it is important to test the cables to ensure the network is configured correctly. A number of companies have developed hand-held test instruments that allow network installers to quickly and accurately test the cables used to construct the LAN. These test instruments must be electrically reliable under field cable installer and cable test conditions. It is desirable for the instruments to allow for ready replacement in the field of the cable test connector, which, in the case of LAN cables is the RJ-45 connector. The instruments must be mechanically rugged, reliable, and professional in appearance. 
     LAN&#39;s are generally constructed of a twisted wire cable containing a number of twisted wire pairs. Existing hand-held test instruments will run a battery of tests to evaluate the performance and connections of each of the twisted wire pairs within each cable. Representative tests performed by the test instruments include cross talk, attenuation, length of the cable, and noise. Each of these tests relies on the measurement of a high frequency (RF) signal which is transmitted through the wire pair. The actual RF measurements in the test instrument typically take place on an RF measurement Printed Circuit Board (PCB). 
     Some known test instruments separate the test hardware into a main unit and a performance/adapter module such as the instrument disclosed by Moser et al, U.S. Pat. No. 5,677,633, entitled “Cable Test Instrument Having Interchangeable Performance Modules.” The performance/adapter module is an interchangeable module having a compatible connector for attachment to the main unit and a cable connector for attachment to a cable being tested. The above described instrument configuration allows the test instrument to be connected to a variety of different LAN cables by simply replacing the performance/adapter module. 
     The prior art experiences limitations when the test equipment is separated into two pieces of hardware, as described above and illustrated in FIG.  2 . The test equipment illustrated in FIG. 2 includes an adapter housing  70  and a main housing  72  designed to receive the adapter housing  70 . The adapter housing  70  and the main housing  72  each include a mating connector. Upon insertion of the adapter housing  70  into the main housing  72 , the mating connectors engage one another to form electrical and mechanical connections whereby electrical signals are communicated between the main housing  72  and the adapter housing  70 . This connection is often inadequate to provide a reliable electrical and mechanical connection which is necessary for LAN testing. Due to the orientation of the connectors there may be misalignment when inserting the adapter housing  70  into the main housing  72  which could possibly damage the connectors. Moreover, misalignment between the mating connectors can also produce discontinuities in the electrical connection from one piece of the test equipment to the other. 
     A shroud may be used to lock the adapter housing  70  into the main housing  72 . However, this configuration additionally requires a user to engage the connectors while being visually blocked from observing any potential misalignment between the two connectors. Furthermore, if the shroud does not adequately constrain the connector locations just prior to connector mating, the connectors may be damaged by any misalignment. When a straight-in connection orientation is used between the main housing  72  and the adapter housing  70 , as illustrated in FIG. 2, strain can be placed on the mechanical connection from excessive movement or pull on the adapter if the adapter housing  70  is not locked securely into the main housing piece. As a result of this strain on the mechanical connection, the electrical connection between the adapter housing  70  and the main housing  72  may degrade over time and become unsuitable for providing accurate test measurements. 
     In addition to misalignment in the connectors, some prior art designs create a lever arm due to the orientation of the mechanical interface between the mating connectors of an adapter housing and of a main instrument housing when the adapter housing protrudes beyond the outer surface of the main housing. This lever arm puts additional strain on the electrical connection and may therefore affect the accuracy of the measurements being performed. 
     An additional problem experienced with designs where the test equipment is separated into two pieces is that the test signal must propagate through two printed circuit board&#39;s (“PCB”) instead of a single PCB. These PCB&#39;s are typically connected from one module to another with a right angle connector on each module. Bends in the propagation path of an RF signal greatly affect the signal properties. These approximate right angle bends due to the use of a right angle connector introduce discontinuities in the characteristic impedance of the connection in addition to the discontinuity of the connector itself. 
     As illustrated in FIG. 3, the use of a right angle connector  80  in a removable cable adapter assembly  82  and a mating connector  81  in a main instrument housing  86  in the prior art may introduce at least four right angle bends. Two of these right angle bends are at areas  88  and  90  on the removable cable adapter assembly  82 . The first right angle bend  88  consists of horizontal board traces from a PCB  91  meeting the connector via a right angle. The second right angle  90  is either a full right angle or a short radius that is part of the connector  80 . The right angles  88 ,  90  in the cable adapter assembly are mirrored in the main instrument housing by a third and fourth right angles  92 ,  94 , adding to the signal measurement degradation. 
     In addition to the impedance disruptions caused by these bends in the signal path, the areas of the second and third right angles  90 ,  92  are not fully shielded. This leads to undesired cross talk between signal pairs. These errors contribute additional error in instrument test measurements. 
     It will be appreciated that the electrical and mechanical connection orientations of present test instruments in the field limit the accuracy and reliability of the tests performed on a cable. The electrical limitations become more apparent at higher test frequencies and the mechanical limitations lead to reliability issues. It would therefore be advantageous to develop a test instrument with improved electrical and mechanical connection orientations to provide a more secure connection between a main housing piece and an adapter housing piece and to increase accuracy of cable test measurements. 
     SUMMARY OF THE INVENTION 
     The systems and methods of the present invention have several features, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this invention as expressed by the claims which follow, its more prominent features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description of the Invention” one will understand how the features of this invention provide several advantages over traditional test instruments. 
     One aspect of the present invention is an apparatus for performing testing of local area network cables. The apparatus comprises an adapter module having a cable or connector located proximate to one end, a first printed circuit board connected to the adapter module to form a first wire connection, and a first connector connected to the first printed circuit board on a first surface of the first printed circuit board. The first connector includes a mating surface which is substantially parallel to the first surface of the first printed circuit board, and wherein there are substantially no bends in an electrical path from the first wire connection to the first mating surface. The apparatus further comprises a main instrument housing having an internal recess configured to receive the adapter module, a second printed circuit board connected to the housing to form a second wire connection, and a second connector connected to the second printed circuit board on a second surface of the second printed circuit board. The second connector includes a second mating surface which is parallel to the second surface, and wherein there are substantially no bends in an electrical path from the second wire connection to the second mating surface. The first connector engages the second connector on the first and second mating surfaces upon insertion of the adapter module into the main instrument housing. 
     Another aspect of the invention is a method of manufacturing a cable test instrument. The method comprises connecting a first printed circuit board having a first surface to a first connector having a first mating surface such that the first mating surface is substantially parallel to the first surface of the first printed circuit board. The method further comprises inserting the first printed circuit board and first connector in an adapter housing. The adapter housing is connected to a cable or connector located proximate to one end. The method further includes connecting a second printed circuit board having a second surface to a second connector having a mating surface such that the second mating surface is parallel to the second surface of the second printed circuit board. A main instrument housing is provided having an internal recess configured to receive the adapter housing. Finally, the second printed circuit board and the second connector are inserted in the main instrument housing such that the first connector engages the second connector on the first and second mating surfaces upon insertion of the adapter housing into the main instrument housing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram illustrating an exemplary layout of a LAN. 
     FIG. 2 is a perspective view illustrating the orientation of an adapter module during insertion into a handset module of a prior art test instrument. 
     FIG. 3 is a side view of the PCB assembly of a prior art adapter module to a PCB assembly of a main instrument housing. 
     FIG. 4 is a perspective view illustrating an adapter module assembly stack of the invention. 
     FIG. 5A is a perspective view illustrating the adapter module of FIG. 4, and showing the locking tabs in an open position. 
     FIG. 5B is a perspective view illustrating the adapter module of FIG. 4, and showing the locking tabs in a closed position. 
     FIG. 6 is a perspective view illustrating a handset module of the invention. 
     FIG. 7 is a perspective view illustrating the orientation of the adapter module of FIG. 4 during insertion into the handset. 
     FIG. 8 is a perspective view illustrating the adapter module of FIG. 4 inserted into and locked in the handset module. 
     FIG. 9 is a cross-sectional view of the adapter module as locked into the handset module, taken along lines  6 — 6  of FIG.  8 . 
     FIG. 10 is a perspective view illustrating an alternate embodiment of the adapter module from FIG. 4, which includes an internal receptacle for receiving a connector plug. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is best described in reference to the Figures wherein like elements are designated with like numerals throughout. 
     Referring initially to FIG. 4, an assembly stack configuration of an adapter module  100  is shown for use as a plug in assembly for a cable test instrument. The module  100  includes an adapter housing  102  that is comprised of an inner cover  104  and outer cover  106  to shield enclosed electronics. The inner cover  104  is secured to the outer cover  106  by four securing screws  108 . The four securing screws  108  pass through holes  109  in an upper face  110  of the inner cover  104  and extend outward to be received in one of four receivers  112  located on an inner surface  114  of the outer cover  106 . 
     A PCB  116  includes apertures  118  through which the securing screws  108  extend. When securing screws  108  are received and tightened into fixed position within the receivers  112 , an upper portion  120  of each receiver  112 , having a reduced diameter from that of the rest of the receiver  112 , extends through each aperture  118 . The location where the upper portion  120  connects to the rest of the receiver  112  forms a shoulder  122 . The shoulder  122  applies force to the PCB  116 , urging it into contact with a shoulder (not shown) within the inner cover  104  so as to secure the PCB  116  in position. The PCB  116  includes a straight through RF connector  124  connected to the PCB  116  using any of the connection methods known to those in the art. The RF connector  124  includes a connector housing  125  which contains electrical contacts (not shown). These contacts provide an electrical connection from the PCB  116  to a mating connector (not shown). Located on the connector housing  125  are locating pins  126  for use in alignment of the mating connector with a first mating surface  127  which will be discussed further hereafter. The mating surface  127  is substantially parallel with the PCB  116 . 
     Located below the PCB  116  is a latch  128  with locking tabs  130 . The latch  128  is secured in the adapter housing  102  by contact forces between the inner surface  114  of the outer cover  106  and an inner edge surface (not shown) of the inner cover  104  when the inner and outer covers  104 ,  106  are assembled with the securing screws  108 . The latch  128  is moveable in direction  132  such that the locking tabs  130  can be moved into and out of a locking position by a means discussed hereafter. Cable strain relief is provided by a pliable sleeve  140  and a more rigid strain relief apparatus  142  through which a cable can be connected to the adapter module  100 . The strain relief apparatus  142  extends through opening  146  in a wall  144  of the outer cover  106  and is fastened against wall  144  by a strain relief nut  148 . 
     A locking button  150  includes prongs  152  which extend from the locking button  150  and towards the latch  128 . Attached to each prong  152  is a lip  153 . The locking button  150  contacts an outer surface (not shown) of the outer cover  106  while the prongs  152  extend through a slot  154  in the outer cover  106 . The prongs  152  further extend through a slot  156  in the latch  128  whereby each lip  153  contacts a surface of the latch  128 . The lips  153  and prongs  152  apply an outward force to the latch  128  which secures the locking button  150  to the latch  128 . Once secured, the position of the locking button  150  controls the position of the locking tabs  130 . In the embodiment shown in FIG. 4, the locking button  150  is moveable with respect to the outer cover  106  in the same direction  132  as the latch  128  in order to control the position of the locking tab  150  with respect to the locking position. The locking mechanism will be described further hereafter with respect to FIGS. 5A and 5B. 
     The locking button on the adapter can be any kind of sliding or toggle locking mechanism that uses fixed tabs, ridges, or sockets on or in the adapter well in the handset and a sliding mechanism in the adapter housing. 
     Still referring to FIG. 4, the adapter housing  102  is also equipped with vertical guide wells  160  on outer side surfaces  162  of the inner cover  104  to ensure alignment when the adapter module  100  is inserted into a main handset as will be discussed further hereafter. 
     The assembled adapter module  100  is shown in FIG. 5A with the locking button  150  in the open position and the locking tabs  130  in a retracted position  200 . FIG. 5B shows the adapter module with the locking button  150  in the closed position and the locking tabs  130  in an engaged position  202 . The locking mechanism will be discussed further hereafter. 
     In FIG. 6, a main handset  300  of the testing instrument is shown. The handset  300  includes a housing  306  with a mating adapter well  302  located on one end of an outer surface  304  of the housing  306 . The mating adapter well  302  is configured to receive the adapter module  100  previously shown in FIG.  5 A. Inside the adapter well  302  and located on a base surface  305  is a mating RF connector  308  for receiving the RF connector  124  on the adapter module  100 . In the adapter well  302  there are guide ribs  310  located on inner side surfaces  312  which are configured to engage the guide wells  160  on the adapter housing  102 . The mating RF connector  308  includes a connector housing  316  and two mechanical locating pin sockets  314  extending into the connector housing  316 . The locating pin sockets  314  define a second mating surface  315  which is substantially perpendicular to the locating pin sockets  314 . To facilitate insertion of the adapter module  100 , the locating pin sockets  314  align with the locating pins  126  on the RF connector housing  124  of the adapter module  100  to ensure that the RF connectors  124 ,  308  are properly aligned prior to engagement. Once aligned, the adapter module  100  is completely inserted into the adapter well  302  in the main handset  300  which couples the RF connectors  124 ,  308  together. 
     In the adapter well  302  on the main handset  300  there are bosses  320  extending from the inner side surfaces  312  of the adapter well  302 . The bosses  320  restrain the locking tabs  130  of the adapter module  100  when the adapter module  100  is inserted in the adapter well  302 . The locking tabs  130  are moved into the locking position  202 , shown in FIG. 5B, via the locking button  150 , which slides the locking tabs  130  underneath the bosses  320 . The bosses  320  are then in contact with both the locking tabs  130  and the inner surface  114  of the outer cover  106  of the adapter module  100 , thereby securing the adapter module  100  in the adapter well  302  of the main handset  300 . 
     For additional ease of removal of the adapter  100  from the main handset  300 , finger access notches  330  are included through the inner side surfaces  312  in the main handset  300  as seen in FIG.  6 . The access notches  330  give the user a non-protrusive gripping area for removal of the adapter module  100  from the adapter well  302  on the main handset  300 . By providing a gripping area on the adapter housing, no unnecessary strain is placed on the cable or strain relief sleeve  140  to remove the adapter module  100  from the adapter well  302 , thereby reducing the chance of damaging the adapter components. 
     The orientation of insertion of the adapter module  100  into the main handset  300  is shown in FIG.  7 . As the adapter module  100  is inserted into the adapter well  302  in the main handset  300 , the guide features of the assembly, guide wells  160  on the adapter housing  102  and guide ribs  310  on the main handset  300 , ensure proper alignment. The locating pins  126  on the adapter module  100  mate with the pin sockets  314  in the adapter well  302  just prior to the mating of the RF connectors  124 ,  308  to ensure alignment of the connectors. 
     The flush design of the total unit is shown in FIG. 8 where the adapter module  100  is fully installed in the main handset  300  and the locking mechanism is engaged with the locking button  150  in the closed position. 
     As can be seen in FIGS. 7 and 8, the cable connection to the test measurement unit is at a right angle to the direction of insertion of the adapter  100  into the handset  300 . Therefore tension on the cable or strain relief sleeve  140  has little effect on the electrical connection contained within the locked housing connection between the adapter module  100  and the main handset  300 . The adapter module  100  and the adapter well  302  in the main handset  300  incorporate guide features that pre-align the connector upon insertion of the adapter module  100  into the adapter well  302 . These guide features also pre-align the mating RF connectors  124 ,  308  into proper connection alignment to reduce the possibility of damage to the RF connectors  124 ,  308  in the case of misalignment. The alignment features include, but are not limited to, mating ribs  310  and locating pins  126  to guide the adapter module  100  into the adapter well  302  on the main handset  300 . The alignment features also assist the locking mechanism in stabilizing the adapter module  100  in the adapter well  302 . 
     FIG. 9 illustrates a cross-sectional view from FIG. 8 of the adapter module  100  and the main housing unit  300  when the two are engaged and locked together. The main handset  300  includes a PCB  506  attached to the RF connector  308  with a malleable material, for example, solder. Thus, the adapter module  100  and handset PCB&#39;s  116 ,  506  are visible in the figure along with their respective RF connectors  124 ,  308 . 
     As can be seen from the orientation of the connectors  124 ,  308  for the main handset and adapter module in FIG. 9, the number of right angle turns from one PCB to the other is reduced to just two in this case. The first right angle  600  occurs in the transition from the PCB  116  to the RF connector  124  in the adapter module  100 . The second right angle  602  occurs in the transition from the RF connector  308  to the PCB  506  in the main handset  300 . It can also be seen that the signal path through the RF connectors  124 ,  308  is completely shielded from one PCB to the other by the connector housings  125 ,  316  respectively. By using this straight through connection along with the complete shielding of the connectors, the RF signal measurement error in the test instrument is greatly reduced from that experienced in the prior art. 
     FIG. 10 illustrates an alternate embodiment of an adapter module  500  for use with the main handset  300  of FIG.  6 . The adapter module  500  includes a support plate  502  installed in a wall  144  of an outer cover  106 . The support plate  502  forms an aperture  504  in the adapter module  500 . Installed through the aperture  504  and into the adapter module  500  is a receptacle  506 . The receptacle  506  mechanically and electrically connects with the adapter module  500 . The receptacle  506  is configured for insertion of a cable test connector plug, for example, an RJ-45 test plug as shown in FIG.  10 . In alternate embodiments, the receptacle  506  is configured to receive a BNC coaxial connector or a pair of fiber optic connectors. Further, the adapter module  500  can also include multiple internal receptacles for connection to multiple connector plugs. Alternatively, different internal receptacles, for example, an RJ-45 and BNC receptacles, can be incorporated into the adapter module  500  to allow a single adapter module  500  to connect with different connector plugs. 
     In alternate embodiments of the invention different types of RF connectors other than straight through connectors are used. An example alternate connector is an edge-wise surface mount connector which connects the signal path straight from one PCB to the other. The use of edge-wise connectors would eliminate all right angle transitions of the electrical signal. However, the types of surface mount edge-wise connectors available commercially are typically less mechanically rugged. 
     In alternate embodiments of the invention, the adapter module can incorporate cable test connector plugs for different types of cable connections other than the male RJ-45 connector plug, such as a BNC coaxial connector. Having different adapters with different connector capabilities enables the user to test cables with different types of connector plugs using the same handset. The use of an interchangeable adapter module is also advantageous due to the fast wear of the RJ-45 test plug. The adapter PCB assembly is an expendable assembly and can be replaced when the RJ-45 test plug wears out. 
     In still an additional embodiment of the invention incorporates an EEPROM or other electronic data storage device onto the PCB of the adapter module. The data storage device can store data such as adapter unit identification and calibration data for the specific adapter unit or the type of adapter unit. This data can be accessed by the handset module to provide the calibration of a variety of adapter types of adapter modules. 
     The mechanical design of the adapter module  100  plugging into the main handset  300  in the manner shown in FIGS. 7 and 8 results in a mated design that is flush with the overall outlines of the handset  300  test instrument. This flush design results in less of a lever arm between the adapter module  100  and the main handset  300 . This is because the adapter stacks over or under the measurement PCB instead of mating length-wise. The reduction in lever arm reduces the chances of inducing mechanical strain on the RF connectors  124 , and  308 . The flush design further improves the overall handling and appearance of the test instrument when the adapter module is installed. 
     The use of a flush test instrument and the adapter insertion design disclosed herein improves the performance of the equipment by eliminating lever arms and direct strain on the electrical connection between the two modules. The design allows easy interchange of adapters  100  to allow the user to test cables with different types of connector plugs or different characteristics, or quick replacement of an adapter  100  with a worn or faulty connector plug. The straight through electrical connection from one PCB to the other from the adapter module  100  to the main handset  300  improves the accuracy of RF measurements by reducing the number of right angle turns the high frequency signal must propagate through. Also eliminated with the straight through connection is the propagation of the RF signal in free space by eliminating the right angle bend in the connectors that was not shielded in the prior art. The design of the invention greatly improves the performance of the cable test instrument in both the mechanical and electrical areas of reliability. 
     While a preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention. Those skilled in the art will appreciate that while the preferred embodiment of the test instrument is designed for the testing of LAN cables, the test instrument may also be used for portable testing of cable or networks in other environments.

Technology Category: 5