Electrical connectors – With coupling movement-actuating means or retaining means in... – Coupling part with relatively pivotable concentric...
Reexamination Certificate
2003-08-22
2004-10-26
Leon, Edwin A. (Department: 2833)
Electrical connectors
With coupling movement-actuating means or retaining means in...
Coupling part with relatively pivotable concentric...
C439S332000, C439S578000
Reexamination Certificate
active
06808407
ABSTRACT:
BACKGROUND OF THE INVENTION
Through custom and convenience, the preferred connector for general purpose use on many items of test equipment is BNC female (BNC stands for Bayonet Navy Connector). The BNC female connector has a female shell, or cylindrical shield, whose outer surface carries two opposing bayonet pins that engage respective spiral grooves and detents in a bayonet latch that is part of the male BNC connector. The actual RF connection is made between male and female center conductor portions and between male and female cylindrical shield portions. To connect the center conductors, a male pin has a reduced diameter portion that extends beyond a shoulder. The male pin enters a female socket whose outer diameter matches that at the shoulder of the male pin. In this way the mated male and female center conductor portions exhibit no change in outer diameter, provided that they are indeed fully mated. In a similar manner the cylindrical shield around the male pin has an outer diameter that just fits inside the larger cylindrical shield over the female pin. The larger (female) cylindrical shield has an interior step to a reduced diameter that matches the inside diameter of the smaller (male) cylindrical shield over the male pin. When the center conductors are fully mated the smaller cylindrical shield will enter and exactly bottom out against the step in the larger cylindrical shield, and any change in shield inside diameter will vanish, with the result that both the center conductor and the surrounding cylindrical shield each appear to have constant diameters. This mechanical arrangement of overlapping penetration is such that the center conductor and shield are held in rigid coaxial alignment, despite the presence of a mechanical joint. In an ordinary BNC connector, a spring in the back of the BNC latch provides a modest amount of force to cause the full mating of the center pin and the shields. One end of this force is anchored by the detent of the bayonet latch engaging the bayonet pins, and allows the mated parts to be forced together. (This rather abbreviated discussion of the BNC connector technique does not address all issues associated with the BNC design over it long history, such as the use of Teflon, axial slits in the male cylindrical shield, and cable attachment methods. But it is sufficient to raise the issues we are interested in.)
A disadvantage to the original BNC design is that the spring can weaken with age and severe use, and that anything, such as the weight of a long cable or of a probe pod or other housing at the male end, that pulls the male connector away from the panel by overcoming the spring will also cause the mated center conductors and mated shields to each separate to a greater or lesser degree. The resulting diameter variations introduce abrupt changes in characteristic impedance, causing undesirable reflections for signals at high frequencies.
U.S. Pat. No. 6,609,925 issued 26 Aug. 2003 and entitled Precision BNC Connector discloses an arrangement wherein the aforementioned spring is replaced by a deliberate (non-resilient) displacement produced by the rotation of a knurled outer shell engaged by threads to the BNC latch. When the knurled outer shell is turned in the proper direction after an initially mating of the connector, the male pin and its surrounding cylindrical shell are driven forward to fully mate with their female counterparts. As before, the bayonet pins serve as an anchor for the force involved.
Now, it is not that the arrangement described in U.S. Pat. No. 6,609,925 does not work: it does. But there are situations where an aspect of its operation is inconvenient. That is, it is at odds with a human usage model arising out of expectations formed by using other connectors. We shall describe one such situation in order to illuminate a desired property of the improved connector to be described in due course.
Suppose that the instrument or item of test equipment has an input channel using a panel mounted female BNC connector. It is conventional that such connectors are quite rigidly attached to the panel, and do not translate, pivot or rotate once installed. Now let a similar connector be on the panel, some distance away. The second connector is the source of a calibration signal that the user of the instrument wishes, from time to time, to apply to the input channel. The manufacturer of the instrument supplies a high quality (and expensive!) “calibration cable” that is to be used to make the interconnection. The calibration cable might be a length of rigid “hard line” coaxial cable, or semi-rigid cable. Or, it might be flexible, in that it can be bent somewhat, but will resist (and not undergo without damage)torsional rotation, or twisting. (There are other, non-calibration situations where test equipment sometimes has an externally made connection, such as applying by a short coaxial cable either an internally generated or externally supplied standard frequency, or other signal, to an input that uses it. It will be appreciated that these other situations are also represented by the “calibration” example we are about to pursue.)
Suppose, as point of departure, that such a calibration cable was in the shape of a shallow broad U and had conventional BNC male connectors at each end. It is typically fairly short, say, six to twelve inches. It might bend, but not with a small radius, and the two 90° bends of the U shape mean that the length of the cable is already fairly well consumed just to give it that shape. To attach it, one would likely grasp, between thumb and forefinger, each male BNC latch with different hands and align the cable mounted connectors with their panel mounted counterparts. Because the bayonet pins are located some distance back from the end of the panel mounted female connector, some coaxial engagement is possible before further engagement along the axis requires that the bayonet pins actually enter the grooves in the BNC latch on the male connector. Engagement of the bayonet pins with the grooves requires rotational alignment. The BNC latch is typically allowed to rotate freely, so that such alignment is possible. Typically, the operator rotates the BNC latch with wrist motion or by rolling it between the thumb and forefinger. Once the bayonet pins enter the grooves of the latch, a forward motion and further twisting of the latches will connect the calibration cable. The “only” problem here is the low quality of the connection formed by a conventional non-precision BNC connector. Unfortunately, for a calibration signal in the gigahertz region, unsatisfactory connectors can make it appear that the instrument does not meet its specifications. It is for that and other reasons that there are such things as precision BNC connectors.
Now, let's repeat the same operation with the precision BNC connector of U.S. Pat. No. 6,609,925. Suppose, for the moment, that the connectors are cable borne BNC male connectors (that is, they are directly attached to the calibration cable instead of being cross series adapters as shown in the patent). It won't work unless the cable can be twisted as it leaves the connector, or, unless after the 90° bend that is half of the U-shaped bend, the cable can be further bent to make the U into a W, and then (later on) un-bent back into a U again. This is because the back side of that connector (the part that attaches to the cable or that carries the “adapter part”) cannot be rotated relative to the BNC latch. (For those that care to look at
FIG. 3
of U.S. Pat. No. 6,609,925, it is because dogs
40
can only slide, and not rotate, in slots
41
of male shell
39
, and because element
50
—representing the cable or adapter—screws tightly into shell
39
.) So, in order to engage the bayonet pins of, say, the left-hand pair of connectors, one would have to rotate the left-hand BNC shell about 90° clockwise (as seen from behind) in order to get the spiral portion of the grooves to traverse over the bayonet pins until those bayonet pins enter the detents. That means that a cabl
Agilent Technologie,s Inc.
Leon Edwin A.
Miller Edward L.
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