Filter contact assembly

Abstract: A contact assembly for installation in an electrical connector, provides effective electromagnetic filtering in a simple, compact, and rugged construction that facilitates in-field replacement of a damaged contact assembly. The contact assembly includes a signal conductor, a diode for diverting high voltages on the signal conductor to ground, and a "pi" filter for filtering out unwanted frequencies. The "pi" filter includes a ferrite bead inductor coupled to the signal conductor and a first capacitor coupling a location of the signal conductor on a first side of the inductor to ground. The other capacitor of the "pi" filter is formed by the capacitance of the diode, with the diode connected to a signal conductor location on a second side of the inductor, and with the capacitance of the diode similar or equal to that of the first capacitor. The diode is mounted in a notch of the signal conductor, the ferrite bead inductor lies immediately forward of the notch, and the first capacitor lies immediately forward of the ferrite bead. A ground conductor has a sleeve portion that immediately surrounds both the first capacitor and the ferrite bead, and has a finger contacting the diode. Solder holds the finger of the ground conductor in place both mechanically and electrically. A quantity of epoxy fills the remaining notch area and forms the middle of the assembly with a cylindrical periphery to facilitate insertion and removal from a long narrow hole in the connector.

Description: This invention relates to electrical connectors and filter contact assemblies for use therein. In many applications, it is desirable to design electrical connectors so their contact assemblies divert to ground any high voltage pulses induced by high energy electromagnetic pulses or static electricity, and also filter out frequency signals of unwanted frequencies induced by electromagnetic energy in the environment. Such unwanted signals are often referred to as EMP (electromagnetic pulse), ESD (electrostatic discharge), EMI (electromagnetic interference), and RFI (radio frequency interference), all of which may be referred to as EMX. While diodes and capacitive/capacitive-inductive filters have been connected to contacts of connectors to cancel the effects of EMX, the resulting contact assemblies have been relatively complex, which increases their cost, and have been relatively cumbersome. The cumbersome contact assemblies are difficult to replace by simply pulling out a defective one (which may be due to mechanical or electrical damage) from a long thin hole in the connector and inserting a new one in its place. U.S. Patent 4,747,789 by Gliha shows a connector filter contact assembly with a diode and inductor/capacitor filter connected to a signal conductor. The assembly, especially the filter which includes a plurality of capacitors in addition to the diode, is bulky and cumbersome, having a diameter many times greater than that of the signal conductor and not capable of easy replacement in the same manner as a simple signal contact. U.S. 4,746,310 by Morse shows an attempt to make a relatively compact contact assembly, with the diode lying in a notch in the signal conductor and with the inductor comprising a ferrite sleeve closely surrounding the signal conductor. However, the connector requires two large capacitors which are not part of the contact assembly so that replacement of the contact assembly does not replace the capacitors. A contact assembly which minimised the number of components while providing effective filtering and transient suppression, and which resulted in a compact contact assembly with all filtering and suppression elements included in a thin and rugged assembly that could be easily inserted and removed from a small diameter hole in the connector for in-field replacement, would be of considerable value. According to the present invention there is provided a filter contact assembly for installation in a connector housing, the contact assembly comprising a signal conductor with first and second ends, an inductor/resistor element coupled to the signal conductor, a ground conductor, a diode connected between the signal and ground conductors and capacitor means connected between the signal and ground conductors, characterised in that the capacitor means consists of a single capacitor which is connected to the signal conductor on a side of the inductor/resistor element opposite to that of the diode and which has a capacitance substantially equal to the inherent capacitance of the diode. The use of the capacitance of the diode in the filter facilitates inter alia an economy in the number of components of the assembly. In carrying out the invention, a largely balanced "pi" filter may formed by the inductor and capacitor in conjunction with the capacitance of the diode. The diode lies on a side of the inductor opposite the capacitor and has a capacitance equal to that of the capacitor. The inductor may comprise a ferrite sleeve or bead surrounding a location on the signal conductor, while the capacitor may also be sleeve-shaped and surrounding the signal conductor. A ground conductor includes a sleeve portion surrounding the capacitor and connected thereto, the ground conductor including a portion extending by but spaced from the ferrite bead, and also including a finger extending against a face of the diode. The notch in the signal conductor which holds the diode, as well as adjacent portions of the contact assembly, are potted with a flowed but hardened plastic material such as epoxy which forms the middle of the contact assembly substantially cylindrical to facilitate insertion of the contact assembly into a thin hole in a connector. The present invention will be better understood from the following description of exemplary embodiments thereof when read in conjunction with the accompanying drawings in which: Figure 1 is a partial sectional side view of a connector constructed in accordance with a first embodiment of the present invention; Figure 2 is a front elevation view of the connector of Figure 1; Figure 3 is a schematic diagram of the circuitry of the contact assembly of the connector of Figure 1; Figure 4 is a sectional side view of the contact assembly of the connector of Figure 1; Figure 4A is a sectional view taken on the line 4A-4A of Figure 4; Figure 5 is an exploded perspective view of the contact assembly of Figure 4. Figure 6 is a schematic diagram of the circuitry of a contact assembly of another embodiment of the invention, which includes a resistor in its filter; Figure 7 is a sectional view of the contact assembly appertaining to Figure 6; and, Figure 8 is a partial exploded perspective view of the contact assembly of Figure 7. Figure 1 illustrates a connector 10 mounted on an electrically-grounded mounting plate 12. The connector includes a housing 11 with a metal shell 14 held to the mounting plate 12 by a locking nut 16. Several contact assemblies of the form shown at 20 are mounted within the shell and extend through a front insulator 22 and a rear insulator 24, a grommet 26 backing up the rear insulator. A face seal 28 seals the front of the contact assembly and is itself sealed by a peripheral seal 30. A metal ground plane 32 is electrically connected to the shell 14 by an outer ground spring 34 and is electrically connected to the contact assembly by an inner ground spring 36 contacting ground conductor 80. The rear 40 of the contact assembly is connected through conductors (not shown) with most of the contact assemblies carrying electrical signals. The contact assembly is held in the connector by a retention clip 42 which abuts a shoulder 44 on the contact assembly. The contact assembly can be replaced in the field by the use of an extraction tool which spreads the fingers of the retention clip 42 and effects withdrawal of the contact assembly. A new contact assembly can be installed in the narrow largely cylindrical hole 46 in the connector by moving the connector assembly forwardly into the hole until the retention clip 42 springs behind the shoulder of the new contact assembly. An insertion tool is sometimes used to aid in installation. Figure 3 is a schematic diagram of the circuitry of the contact assembly of Figure 1, showing it as having front and rear ends 50,52 connected through a signal conductor 54 (which may carry signals and/or current for powering devices), and a ground 56. In many applications it is highly desirable to safeguard the contact assembly against EMP (electromagnetic pulses) that produce high voltages in the signal conductor, and against EMI (electromagnetic interference) which results in unwanted high frequency signals in the signal conductor. The high voltages are avoided by a diode 60 such as a Zener type, which may be unipolar or bipolar depending on the protection required. The opposite terminals or sides 86,88 of the diode are connected respectively to ground 56 and to the signal conductor 54. EMI is avoided by a filter 62 which is a low pass filter that passes only signals below a certain frequency. One of the most effective simple filters is a balanced "pi" filter which includes an inductor 64 coupled to the signal conductor 54, and two capacitors 66,68 connecting locations along the signal conductor on opposite sides of the inductor 64, to ground. Best results are obtained when the filter is balanced when the two capacitors 66,68 have substantially equal capacitance. (Even better filtering is obtained by placing a resistor between the inductor and one of the capacitors, as will be described later herein.) The number of capacitors that have to be included in the contact assembly is minimised by using the capacitance that accompanies the diode 60 as one of the capacitors, and using a first capacitor 68 so its capacitance matches the capacitance of the diode. The entire diode with its diode function and capacitance is indicated as 76. The opposite terminals 67,69 of the first capacitor 68 are connected, respectively, to ground and to the signal conductor. It should be noted that instead of an inductor 64, it is possible to use a resistor instead, as the inductor/resistor element, although this results in larger losses. Thus, the part 64 can be referred to as an "inductor/resistor" element. Figures 4 and 5 illustrate details of the contact assembly 20. To facilitate explanation, one direction F is considered to be the forward direction; however, the opposite could be considered the forward direction. The signal conductor 54 is formed with a forward end portion 70 in the shape of a pin with a small diameter cylindrical outer surface. The first capacitor 68 is an annular bead capacitor, and the inductor 64 is an annular ferrite bead, and both annular devices are mounted on the forward end portion 70 of the signal conductor. The signal conductor also includes a middle portion 72 forming a notch 73 with a platform 74 on which the diode 76 is mounted. A ground conductor 80 contacts the outer terminal of the first capacitor 68 and one side of the diode 76, to connect both to ground (through the inner ground spring 36 of Figure 1). However, the ground conductor 80 is out of contact with the inductor 64. The ground conductor 80 includes a forward sleeve portion 82 which surrounds the first capacitor 68, and includes a rearwardly-extending finger 84 that contacts the diode. The opposite faces 86,88 of the diode can be soldered to the platform 74 of the signal conductor, and to the finger 84 of the ground conductor. The first capacitor 68 has terminals on its radially inner and outer surfaces, and can be mechanically and electrically connected to the signal conductor 54 and the sleeve portion 82 of the ground conductor by soldering thereto. The ferrite bead inductor 64 is formed so that its inside fits very closely around the signal contact portion 70 to closely couple them (the bead ferrite inductor does not have to be mechanically or electrically connected in series with the signal conductor. Its physical location on the signal conductor produces the desired electrical effect). After the diode 76, inductor 64, first capacitor 68 and ground conductor 80 are installed on the signal conductor, it is preferred to encapsulate them with a mass 90 of flowable and hardenable polymer, such as epoxy. The middle portion 72 of the signal conductor with elements mounted thereon is placed in a substantially cylindrical mould, and epoxy is flowed into the mould to fill substantially all empty spaces. The epoxy includes a portion 92 lying in the notch 73 of the signal conductor around the diode 76 and finger 84, and also includes a portion 94 which lies between the inductor 64 and middle locations or parts 96 of the ground conductor 80 that lie directly around the inductor. Thus, the contact assembly 20 includes a diode for dissipating pulses and an effective filter for dissipating high frequency currents, in a relatively simple and compact assembly that can fit in the narrow holes formed in the connector into which contact assemblies can be inserted and removed. In one specific design of contact assembly, the signal conductor 54 has a forward end of diameter A of 0.7617 mm (30mil) (one mil equals one thousandth inch) and a maximum diameter B of 2.0312 mm (80mil), and the diode 76 has a width and length each of 0.93943 mm (37mil) and a height of about 0.2539 mm (10mil). The capacitance of the diode is about 2000 picofarads and the first capacitor 68 has a capacitance of 2000 picofarads. The diode includes a mass of diode material and terminals at its opposite sides, with a capacitance of over 100 picofarads for most diodes of this type. The inductor 64 has an inductance of 10 microhenrys. The diode 76 is a Zener diode which has a breakdown voltage of ±6 volts. The filter formed by the inductor 64, the first capacitor 68, and the capacitance of the diode 76 provide an attenuation of signals passing through the signal conductor 54 of 10 decibels at 10 megahertz. Substantial attenuation occurs only above about 1 megahertz, and therefore for this design the contact assembly is useful for carrying signals of a frequency up to about 1 megahertz. While a simple "pi" filter with a pair of capacitors coupling opposite sides of an inductor to ground is effective in blocking high frequency currents, even greater effectiveness is obtained with an RLC circuit, similar to a "pi" filter but with a resistor in series with the inductor. Figure 6 illustrates a filter circuit 100 of this type, which includes a resistor 102 in addition to the inductor 64 (or instead of the inductor), first capacitor 68, and diode capacitor 66 which represents the capacitance of the diode 60. For a filter with capacitance and inductance values as described above, a resistor 102 having a resistance on the order of magnitude of 5000 ohms may be appropriate. Of course, the signal conductor 54 has a resistance, but this is negligible, while an effective filter resistance must be a plurality of ohms. Figure 7 illustrates another contact assembly 110 very similar to that of Figure 4, except that it includes a resistance device 112 in series with forward and rearward parts 114,116 of the signal conductor 118. The resistance device 112 includes a substantially cylindrical dielectric element 115 (Figure 8) with a resistive layer 117 thereon forming the resistor 102 and with conductive layers 119, 120 thereon. In constructing the device, the resistance layer 117 is first deposited on the dielectric element 115, and then the conductive layers 119,120 are deposited with at least a portion of each conductive layer lying over the resistive layer. Each of the signal conductor parts 114,116 is formed with a hole 122,124 that closely receives an end of the dielectric element. The conductive layers 119,120 are soldered respectively to the forward and rearward parts 114,116, to thereby electrically connect the resistive layer in series with the conductive parts, and also to provide some mechanical connection. The ground conductor 80A is similar to that of Figure 4, except that the finger 84A may be somewhat longer to account for the resistive device 112. After assembling the components, the assembly is encapsulated as with epoxy 90A, so that the parts are held together with a substantially smooth cylindrical outside is provided that is formed partially of a quantity of flowed and hardened plastic material. Thus, the invention provides a contact assembly which is relatively simple and compact, to provide ruggedness and low cost and to facilitate in-field replacement of a defective contact assembly. The contact assembly includes a diode for dissipating pulses, and a filter which includes an inductor and which also includes capacitances coupling opposite sides of the inductor to ground, with one of the capacitances being that of the diode. The inductor and first capacitor can be in the form of beads surrounding a cylindrical portion of the signal conductor, while the ground conductor can be formed as a sleeve closely surrounding the bead capacitor, and extending across but out of contact with the inductor and with a finger contacting the diode. The assembly can be encapsulated with a quantity of a flowed but hardened plastic material such as epoxy, and with a substantially cylindrical exterior along the middle of the contact assembly, to hold all the parts together and enable the assembly to be easily replaced in the field.

Claims: A filter contact assembly for installation in a connector housing, the contact assembly comprising a signal conductor with first and second ends, an inductor/resistor element coupled to the signal conductor, a ground conductor, a diode connected between the signal and ground conductors and capacitor means connected between the signal and ground conductors, characterised in that the capacitor means consists of a single capacitor (68) which is connected to the signal conductor (54,118) on a side of the inductor/resistor element (64) opposite to that of the diode (60,76) and which has a capacitance substantially equal to the inherent capacitance of the diode. A filter contact assembly as claimed in claim 1, characterised in that the capacitor (68) is a bead-like annular element and substantially surrounds the signal conductor (54,118), in that the diode (60,76) lies on the signal conductor at a side of the inductor/resistor element (64) which is opposite to the capacitor (68), and in that the ground conductor (80,80A) surrounds and contacts the capacitor (68) and extends across but out of contact with the inductor/resistor element and has a finger (84) that contacts the diode. A filter contact assembly as claimed in claim 2, characterised by a quantity (90,90A) of flowed and hardened plastic material filling the space between the ground conductor (80,80A) and the inductor/resistor element (64), substantially surrounding the ground conductor finger (84) and diode (60,76), and bonded to the signal conductor (54,118), to hold the ground conductor securely out of contact with the inductor/resistor element (64) and in contact with the diode (60,76). A filter contact assembly as claimed in claim 2, characterised in that the signal conductor (118) includes forward and rearward parts (114 and 116) and a resistance device (112) forming the inductor/resistor element (64,112) and having a resistance of a plurality of ohms electrically connecting the signal conductor parts, the diode (76) lying on and connected to one of the signal conductor parts (116) and the capacitor (68) being connected to the other of the signal conductor parts (114). A filter contact assembly as claimed in claim 1, characterised in that the signal conductor (54) has a pin-like cylindrical forward portion (70), a rearward portion (52), and a middle portion (72), a bead capacitor (68) lying closely around and electrically connected to the forward portion (70) of the signal conductor (54), a bead ferrite element (64) lying closely around the forward portion (70) of the signal conductor, behind the capacitor (68), a diode (76) having a first face (88) lying against the middle (72) of the signal conductor (54), and a second opposite face (86) , the ground conductor (80) having a sleeve-shaped forward portion (82) closely surrounding the capacitor (68), a rearward portion forming a finger (84) in contact with the second face (86) of the diode (76), and a middle portion (96) extending across but out of contact with the ferrite element (64). A filter contact assembly as claimed in claim 5, characterised by a quantity of flowed and hardened plastic material (90) disposed about the ground conductor finger (84), the diode (76) and a portion of the signal conductor middle that lies behind the ground conductor forward portion (82), the plastic material forming part of a largely cylindrical exterior surface at the middle of the signal conductor, whereby to hold the parts together to facilitate rearward removal of a defective contact assembly and the forward insertion of a new one in its place. A filter contact assembly as claimed in claim 1, characterised in that the signal conductor (54,118) has forward and rearward end portions in that a ferrite bead (64) surrounds and is closely coupled to the forward portion (70) of the signal conductor, in that the capacitor is a bead capacitor (68) lying forward of the ferrite bead (64) and the signal conductor forward portion and has first and second terminals (69,67) coupled respectively to the signal conductor (54,118) and to the ground conductor (80), in that the diode (76) comprises a mass of diode material with opposite sides (86,88) and first and second terminals at the opposite sides, the mass of diode material allowing current to flow without appreciable resistance between the diode terminals when the voltage between the diode terminals exceeds a predetermined level, and in that a capacitance of over one hundred picofarads is provided between the diode terminals. A filter contact assembly as claimed in claim 7, characterised in that the signal conductor (118) includes separate forward and rearward parts (114,116), and in that the assembly includes a resistive device (112) having a predetermined resistance and electrically connecting the parts (114,116) of the signal conductor, the resistor lying between the ferrite bead (64) and the diode (76). A filter contact assembly as claimed in claim 7, characterised in that the ground contact (80) includes a sleeve portion (80A) mounted on and surrounding the bead capacitor (68) and electrically connected thereto, a middle ground contact portion (96) extending beside but spaced from the ferrite bead (64), and a finger portion (84A) in contact with a terminal (86) of the diode (76). A filter contact assembly as claimed in claim 9, characterised in that a quantity of hardened epoxy-like plastic (90) is disposed about the diode (76) and the ground conductor finger (84), and between the ferrite bead (64) and the middle ground contact portion (96), and forms at least part of a substantially cylindrical periphery. A filter contact assembly as claimed in claim 1, characterised in that the inductor/resistor element (64) is of tubular construction and closely embraces the signal conductor. A filter contact assembly as claimed in claim 1 or claim 11, characterised in that the capacitor (68) is of tubular form and closely embraces the signal conductor (70). A filter contact assembly as claimed in claim 1, 11 or 12, characterised in that the section of the contact assembly embodying the inductor/resistor element capacitor and diode has a uniform cross-section throughout its length. An electrical connector having a housing, characterised by a plurality of filter contact assemblies according to any preceding claim fitted into the connector housing.

Inventors: CLYATT CLARENCE LESTER III, MOORE JOHN ROBERT, NIEMAN GERALD RAY, PAULUS ERIC JAMES, RAGL ALBERT NMN, ZEHRUNG SCOTT ALLEN, CLYATT, CLARENCE LESTER III, MOORE, JOHN ROBERT, NIEMAN, GERALD RAY, PAULUS,ERIC JAMES, RAGL,ALBERT (NMN), ZEHRUNG,SCOTT ALLEN
Applicants: ITT, ITT INDUSTRIES INC.
Application year: 1990
Main classification: H01R13
IPC codes: H01R13