US3441093A

US3441093A - Jet perforating gun arming switch and circuitry

Info

Publication number: US3441093A
Application number: US646973A
Authority: US
Inventors: Gene T Boop
Original assignee: PROFITABLE RESOURCES Inc
Current assignee: PROFITABLE RESOURCES Inc
Priority date: 1967-06-19
Filing date: 1967-06-19
Publication date: 1969-04-29
Anticipated expiration: 1986-04-29

Description

April 29, 1969 G. T'. BOOP 3,

JET PERFORATING GUN ARMING SWITCiI AND CIRCUITRY Filed June 19, 1967 Sheet ,2 of 2 GENE T. 800/ INVENTOR.

BY M/IAL'L/S L. 54755 United States Patent US. Cl. 175-455 Claims ABSTRACT OF THE DISCLOSURE A sequentially fired jet perforating gun and circuit having a sub which connects two adjacent charge carriers together. The sub houses an explosive responsive switch, and includes a piston having a deformable washer associated therewith. The force of a detonated charge forces the piston into fluid tight engagement with the sub, while at the same time deforms the washer into electrical contact with the sub to thereby form a circuit path between the piston and the sub, thus arming the explosive charge located in the next adjacent charge carrier. The circuit is of the single wire type which relies upon a grounded return path to the surface of the earth where the device is controlled, and includes series arranged resistors having a branch circuit between each resistor for each charge and explosive responsive switch, with a diode associated with each charge, and with adjacent diodes being arranged in reversed polarity with respect to each other. Proper polarity current explodes the bottom most charge, whereafter the current polarity must be reversed as each charge of the gun is sequentially fired.

Cross reference to related application Gene T. Boop application filed Oct. 22, 1965; Ser. No. 501,518, for Jet Perforating Gun, now Patent Number 3,327,792, issued June 27, 1967.

Background Perforating guns used in perforating well pipes, and particularly jet perforating guns which utilize a shaped charge for penetrating well pipes, are known in the art. The guns of the past art generally require a multiplicity of wires in order to activate, explode, or fire the various charges associated with the perforating gun, In order to eliminate the multiplicity of wires required to selectively fire the explosive charge located in each charge carrier of the jet perforating gun, various complex selector switching arrangements have been attached in series relationship with the gun in order to permit a single current carrying wire to be connected from the selector switch to the surface of the earth. One example of such a select switch arrangement is exemplified by applicants Patent Number 3,208,378, filed Dec. 26, 1962. Select switch arrangements of this nature require a complex selective switching means wherein the switching device selectively connects various individual charges of the gun to the current source. Many of the select fire switch arrangements of the past art are more troublesome to maintain than the perforating gun itself.

Summary It is therefore a primary object of the present invention to provide a jet perforating gun having a single wire system which selectively fires the various charges associated with the gun.

Another object of the present invention is to provide a switch which is actuated by the explosive force of one of the charges in order to arm the next adjacent charge.

Another object of the present invention is to provide a sub-assembly which interconnects two adjacent charge P ce carriers of the gun, and which also carries a switch device which arms the explosive charge of one charge carrier when the charge in the next adjacent charge carrier is detonated.

A still further object of the present invention is to provide a pressure actuated switch for a jet perforating gun which is actuated in response to the discharge of an explosive charge device.

A still further object of the present invention is the provision of a switch device that enables a single wire system to be used in conjunction with a jet perforating gun in a manner to selectively fire the charges associated with the various charge carriers of the gun.

A still further object of the present invention is the provision of a perforating gun circuit which selectively permits the various charges associated with the gun to be sequentially fired.

The above objects are attained in accordance with the present invention by the provision of a multiplicity of series arranged resistors having a source of current provided at one end thereof, and with a parallel branch circuit disposed across each resistor wherein the branch circuit includes a diode, charge, and a normally open switch, with the normally open switch being moved to the closed position to provide a circuit path to ground whenever an adjacent charge carrier is detonated. The switch means includes a deformable member which is deformed into electrical engagement with the sub as a result of the explosive force received from the detonation of an adjacent charge to thereby form a current conducting path to ground which arms the next adjacent charge.

Brief description of the drawings FIGURE 1 is a perspective view of an assembled jet perforating gun made in accordance with the present invention with some parts being cut away in order to conserve space.

FIGURE 2 is a cross-sectional view of one of the sub assemblies of the device seen in FIGURE 1, with some additional parts being illustrated.

FIGURE 3 is a cross-sectional view of a modification of the device seen in FIGURE 2.

FIGURE 4 is a partial cross-sectional View of a modification of the device seen in FIGURES 2 and 3.

FIGURE 5 is a schematical representation of a firing circuit which may be used to detonate the various explosive charges associated with the device seen in FIG- URE 1, which includes the sub-assembly of FIGURES 2, 3, or 4.

Brief description of the preferred embodiments Looking now to FIGURE 1, in conjunction with the remaining figures, wherein there is seen, generally illustrated by the arrow at numeral 10, a jet perforating gun which is suitably suspended by any means 12, which usually is a collar locator having a cable coupling device at one end and another end which threadedly engages a charge carrier 14. One of the ends may be provided with a swivel and attached to a cable 16. The cable 16 is provided with an internally located insulated wire for providing a source of current from above the surface of the ground to the circuitry of the perforating device. Each charge carrier 14 houses a shaped charge and detonator means located behind a button 18 in the usual manner, with each charge carrier being connected together by a connector or sub 20. A guide means 22, sometimes called a bull-plug, is provided at the depending free end of the gun.

Each of the subs 20 is comprised of a main body 24 having a pair of circumferentially extending grooves 26 about the outer periphery of each shouldered end thereof for receiving an O-ring 28 therein. The O-ring provides a positive seal which hermetically seals the interior of the gun. A multiplicity of threaded apertures 30 each receive a bolt 31 which rigidly maintains adjacent charge carriers secured together in the illustrated manner of FIGURE 2.

Each sub is provided with a first counterbore 33 which communicates with a larger oppositely located and centrally aligned counterbore 34 by a smaller aligned passageway 35 to thereby provide a centrally arranged passageway through the sub. A piston 36 having a piston rod 38 connected thereto is reciprocatingly received within the small passageway of the main body of the sub-assembly in the illustrated manner of FIGURE 2. The piston 36 is provided with a threaded counterbore 48. The threaded counterbore receives a centrally drilled-through packing nut 42 therein. The depending free end of the piston rod is threaded at 44 and threadedly engages a nut 46 to thereby maintain the device in assembled condition. The annulus between the piston rod 38 and the passageway 35 is filled with a plastic coating 48 which is provided on the outside peripheral surface of the piston rod prior to assembly of the device. A resilient insulating washer 50 is held compressed between a washer 52 and the main body 24. Multiple resilient

insulating washers

54 and 56 are compressed between the piston 36 and the main body 24.

A drilled passageway 58 extends through the piston and the piston rod and is of a sufficient size to receive a Teflon insulated electrical conductor 60 therethrough. A Teflon seal 62 having a passageway 64 therethrough is compressed into the converging portion formed by the passageway 66 as it reduces in size into the before mentioned passageway 58.

A circular resilient clip 68 is attached to the threaded depending end portion 44 of the piston rod to provide an electrical connection for the conductor 70. A resistor 72 is electrically connected to the before mentioned wire 60 and conductor 74. Conductor 76 is attached to conductor 74 with the shaped charge and detonator 78 being electrically connected between

conductors

70 and 76 in the illustrated manner of FIGURES 2 and 5.

Looking in particular to the details of FIGURE 3, wherein a modification of the device previously seen in FIGURE 2 is disclosed, and wherein corresponding numerals 120, for example, agree with the corresponding or like parts of the other figures, such as 20 and 220, for example. As seen in FIGURE 3, the packing nut 142 bears against a deformable washer 143, wherein the washer 143 has been curved outwardly against the pressure which is to be provided by the explosion which results from detonation of the shaped charge. The washer 143 has an outside diameter which is greater than the inside diameter of the passageway 134. However, as seen in the illustration of FIGURE 3, the outside peripheral edge portion of the washer 143 does not contact the side wall 134 since the washer has been curved or dished toward the direction from which explosive force is received, an amount to produce a free annular area between the outside periphery of the washer 143 and the inside peripheral wall surface of passageway 134.

Looking now to the details of FIGURE 4 wherein there is disclosed a sub 220 which has a body 224 fabricated essentially identically to the sub 20/ and 120, respectively, of FIGURES 2 and 3, respectively; but, differs therefrom in that a modified switch assembly is included which is comprised of a piston 236 having a hollow piston rod 238 depending therefrom. The hollow rod receives an insulated bolt 260 therethrough, with the bolt being rigidly held in an insulated manner from the piston and rod by insulated

washers

250, 254, and 256. Bolthead 261 is compressed against spacer 262 with the terminal end of the lower conductor 60 held therebetween. The threaded end portion of the bolt receives nut 268 thereon with the terminal end of the upper conductor 60 held therebetween, to thereby provide a current flow path from upper conductor 60, through rod 260, spacer 262, and to the lower conductor 60. The free end of piston rod 238 threadedly engages nut 270 which compresses

insulators

250, 254, and 256 against body 224. Conductor 70, having diode 80 connected in series relationship therein, is directly connected to nut 270, which is spaced apart and insulated from nut 268 by washer 271. Bolts 242, 242' compress a deformable member 243 against the exposed face of piston 236. The deformable member is deformed outwardly into electrical contact with the inside periph eral wall surface of chamber 234 when the explosive device, or charge, associated therewith is detonated, to thereby provide an electrical path to ground for the diode 80 of FIGURE 4, for example.

FIGURE 5 illustrates the preferred circuitry used in conjunction with the device illustrated in the foregoing figures. The circuitry of FIGURE 5 is provided with a source of current, 83 and 83', with each current source being reversed in polarity with respect to each other. The current source is grounded at 81 and provided with normally

open switches

82 and 82'. The switches are connected to a common conductor 84. A current limiting device 85 provides a controlled current source at 74.

Numerals

86, 88, and represent the circuit components and explosive charges which are located in each of the separate charge carriers. Each charge carrier is connected in the illustrated manner as indicated by numeral 88, for example, with

numerals

20 and 36 representing components of one of the before described subs. Looking to the details of circuitry 86, for example, there is seen the before mentioned conductor 76 which is electrically connected between conductor 74 and diode 80. It should be understood that the diode, or rectifier, can be any electrical device which permits current of proper polarity to flow in the illustrated direction, while preventing the same polarity current to flow opposite to that indicated by the arrow. Rectifier 80 is connected to explosive device 78 which includes a shaped charge, the usual Primacord, and the detonator. The details of the shaped charge and detonation means therefor are known by those skilled in the art and accordingly need not be described in detail herein (see Boop; 3,173,992; issued May 16, 1965, for details). The explosive device 78 is electrically connected to the deformable member, 43 for example, of one of the subs. Member 43, along with member 20, provides the explosive responsive switch means illustrated in the foregoing figures. The last charge carrier 90 differs from the remaining charge carriers for the explosive charge associated therewith is connected directly to ground because it is the first of the sequentially fired charges to be detonated, and accordingly it is armed before entering the hole.

Operation The assembled perforating gun of FIGURE 1 is to run into the hole on a wire line 16 and the various charge carriers 14 are positioned relative to the well casing by using the collar locater 12 in the usual manner. The cable 16 has an insulated conductor 74 centrally located therein that provides a source of current to the various charge carriers in accordance with the circuitry of FIGURE 5, which will be explained in more detail later on. Each of the charge carriers 14 are connected together by subs 20 with the subs 20 carrying the explosive responsive switch means of the device.

The switch means of FIGURES 2 and 3 are assembled by first lacing a length of Teflon insulated wire 60 through the passageway 58 after which the seal 62 is placed into the cavity 66 of counterbore 40, and the packing nut 42 is then screwed into the illustrated assembled position to thereby press the

deformable washer

43 and 143 against the

piston

36 or 136, while at the same time pressing the Teflon seal 62 and 162 into its fluid tight position to thereby seal passageway 58 from the passageway 34. The piston and piston rod is then placed into the position illustrated in FIGURES 2 and 3 with the

resilient washers

54 and 56 placed between the piston and body 24, and with the resilient washer 50 being held between the body and metallic washer 52 by the nut 46. The nut 46 is tightened sufficiently to provide a seal between passageway 34 and passageway 33. The surface of the piston rod is provided with a Teflon coating 48 which permits a close tolerance fit between the piston rod 38 and the drilled passageway 35, while at the same time completes the insulation of the piston and piston rod from the main body 24. A resilient split clip 68 provides a source of current between conductors 70 and the piston rod. The sub is next placed into a charge carrier where the O-rings provide a high pressure seal to prevent leakage of fluid from the well and into the charge carriers. Bolts are next run through apertures provided in the charge carriers where the threaded end of the bolt threadedly engages the drilled and tapped bolt holes 30 which rigidly maintain the charge carriers to the sub 20. The circuit components of the next charge carrier is then made up as schematically illustrated in FIGURES 2, 4, and 5 and the next sub is then placed into position until a string of charge carriers and subs are built-up to the required number to perform a particular perforating job. After the gun has been loaded in the above described manner, the circuitry of FIGURE 5 will have been constructed, with the subs, charge carriers, and circuitry being schematically illustrated as exemplified by the arrow at

numerals

86, 88, and 90. It should be understood that, for convenience, only three charge carriers and two subs are illustrated in FIGURE 5, and that there would generally be about fifteen charge carriers associated with a string of perforating guns, with the upper practical limit of the number of charge carriers probably exceeding thirty-five or forty.

After the charge carrier has been run into the well, the circuitry seen above conductor 74 of FIGURE 5 will be located above the ground level, while the circuitry below the conductor 74 will be located within the perforating gun.

When it is desired to fire or detonate the lowermost charge 90, the current source 83 or 83' is adjusted to provide the proper voltage for the gun. The selected voltage will depend upon the number of charge carriers as well as the length of the conductor 74. For example, in a gun having fifteen charge carriers therein, it is usually desirable to maintain sufiicient voltage to provide a five volt drop across each of the resistors 72. Therefore, in this instance the current source will be adjusted to provide at least seventy-five volts at the first gun 86. This will provide five volts across each of the resistors 72 which is sufficient voltage at normal amperage to cause the shaped charge 78 of the bottom-most gun to detonate or fire.

After selection of the proper voltage, switch 82 is closed and current will flow from the negative side of the voltage source 83 along conductor 84, through current limiting device 85, where the before mentioned voltage drop will occur, to thereby provide a controlled current source at conductor 74. Since diode 7 8 of sub 86 is arranged to pass negative polarity current, and since the explosive responsive switch is in opened condition, the latter of these factors prevents current from detonating the explosive charge 78, and accordingly, current will only flow through the resistor 72, then through the sub assembly 20', where the current will continue to flow in the same manner through each of the charge carriers until the current reaches the bottom most charge carrier 90, which is directly grounded, and accordingly, the shaped charge associated with the last charge carrier 90 will be detonated. Detonation of the explosive device at 90 causes the normally open switch associated with sub 20' of FIGURE 5 to assume the closed, or current conducting position. The details of the switch actuation to the closed position will be discussed in greater detail later on.

After detonation of charge carrier 90, switch 82 is opened and switch 82 closed whereupon a positive source of current is provided along the same before described path until the current reaches charge carrier 88, to thereby provide a voltage drop across the illustrated resistor (assuming the conductor 60 to have shorted to ground), as well as a source of current to the detonator itself. In this respect it is pointed out that when the switch of any sub assumes a closed position, the conductor connected thereto will always be grounded, and accordingly, the detonator will be provided with a current source. The conductor 60 may not always be grounded to the sub since it is possible for the wire to be fused to open circuit by the explosive blast without being fused to the packing nut 42 of FIG- URE 2, for example. The next adjacent explosive device will therefore detonate so long as the switch associated therewith assumes the closed position, regardless of whether conductor 60 is fused to the open circuited position, grounds to the charge carrier itself, grounds to the sub, or grounds to the packing nut 42, for the reason that the voltage drop across the resistor will be available to fire the gun so long as the switch associated with a charge carrier assumes the closed position. Should the switch fail to assume the closed position, the next adjacent charge carrier 86, for example, cannot be detonated since there will be no flow path of current through the detonator of the charge and the charge will accordingly remain unarmed.

After the switch associated with sub 20 has assumed the closed position, a negative potential is imposed upon the circuitry by switch 82', and the explosive device 88 will be detonated thereby closing the switch associated with charge carrier 20. This enables the explosive device 86 to be detonated by imposing a negative charge of current by closure of switch 82. Accordingly, each adjacent charge carrier can be detonated sequentially by merely closing

switch

82 and 82' to thereby impose the proper polarity of current upon the explosive device.

-It will now be realized by those skilled in the art that the purpose of the diodes or rectifiers is to prevent the gun from going automatic; that is, without the rectifiers 80 being included in the circuit in the illustrated manner of FIGURE 5, closure of either switch 82 or 82 would sequentially detonate each of the explosive devices in an uncontrolled manner except for the control of the current to the device.

Looking again to the details of FIGURE 2, and having now read the above description, it will be realized by those skilled in the art that the actuation of the switch associated with any sub is brought about by the explosive energy of the charge carrier with which the

deformable member

43, 143, 243 is associated. Upon detonation of the explosive charge associated with passageway 34, for example, the piston 36 is driven upwardly with tremendous force. This causes the resilient washers, 54 and 56, to be compressed to thereby prevent flow of gas 0r liquid between the piston rod 38 and passageway 36. At the same time, the deformable washer 43 is compressed against the piston 36 with sufficient force whereby it spreads outwardly because of the great force imposed upon it to thereby expand into current conducting contact with the inside peripheral wall 34, to provide a current conducting path between the piston and the main body 24. When the deformable washer 43 is caused to expand in this manner, a current flow path is formed from conductor 70, through diode 80 and clip 68, into the piston rod 38, through piston 36, through washer 43, and then into the main body 24 where a return circuit is formed since the gun is always in grounded condition, either through the well fluid and well casing, or through the outer supporting portion of the cable or wire line 16.

Looking to the modification of FIGURE 3, the washer 143 is fabricated into an outwardly depending dished configuration, whereby the explosive force of its associated explosive device deforms the washer 143 against the piston and sub to thereby ground the device with less force than is required for the deformable washer 43 of FIGURE 2. In this respect, it is pointed out that

washer

43 or 143 may be of mild steel, copper, or any other malleable, metallic, or current conducting material which is sufiiciently deformable by the force provided by the blast from the explosive device; yet which will not melt under the intense heat of the explosion.

Looking now to the operation of FIGURE 4, in conjunction with the circuitry of FIGURE 5, and assuming a lower subadjacent charge carrier has armed the a jacent charge carrier of sub 220, application of proper polarity current at upper conductor 74 will provide a current flow along the following path: from 74, resistor 72, upper conductor 60, nut 268, bolt 260, spacer 262, to the lower conductor 60, whereupon the armed adjacent charge Will detonate to thereby provide an explosive force which will drive piston 236 in an upward direction while at the same time deforming member 243 sufficiently whereby its outer peripheral edge will contact the inside peripheral wall of chamber 234.

The lower conductor 60 will either be fused to open circuit or to ground; but, regardless of the effect of the explosion upon the conductor, the switch means associated with the sub assumes the closed position to provide a flow path as follows: 74, 76, 78, 70, 80, 270, 238, 236, 243, 224. Reverse polarity can now be applied at 74 in order to detonate the explosive device 78, thereby arming the next adjacent unexploded charge, assuming FIGURE 4 not to be the last (uppermost) charge of the series.

This invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as described in the appended claims.

I claim:

1. In a perforating gun having multiple charge carriers, each being connected to another by a sub having a passageway therethrough, the improvement comprising:

a normally open explosive responsive switch including piston means located in the passageway and associated with first and second adjacent charge carriers, seal means associated with said piston means to prevent fluid flow through the sub, and means forming a passageway through said piston means;

said switch including a current conducting deformable member associated with said piston means and adapted to be deformed into engagement with said passageway of said sub and into current conducting condition upon detonation of said first adjacent charge carrier associated therewith to thereby form a current conducting path for a charge located in the second adjacent charge carrier;

and a current conducting member located in the passageway of said piston means to provide a source of current to the said adjacent charge carrier.

2. The improvement of claim wherein said piston means includes a rod extending through the passageway of the sub, with said piston means having a face opposite said rod with said face being directed to receive the explosive force of a detonated charge;

means attaching said deformable member to the face of said piston means;

the passageway of the sub being adapted to receive said piston means including said deformable washer, with the diameter of said deformable washer being less than the diameter of the piston means receiving portion of the passageway; whereby, detonation of the explosive charge causes said member to outwardly deform into engagement with the passageway of the sub to thereby permit current flow from the rod, through the deformable member, and into the sub.

3. The improvement of claim 1, and further including a firing circuit means having a DC. power source for providing a source of current to each charge carrier by means of a single conductor series connected to each said current conducting member located in the passageway of said piston means, and a return current flow path through a grounded connection;

a multiplicity of series arranged resistors;

a branch circuit between each resistor;

said branch circuit including a diode, detonator means associated with the charge carrier, and said normally open switch;

and each diode of each branch circuit being reversed in polarity with respect to each adjacent diode whereby adjacent diodes of adjacent branch circuits conduct current of opposite polarity.

4. In combination with an electrically fired perforating apparatus having separate chambers, each chamber containing electrically actuated explosive perforating means, with the apparatus having a bore interconnecting adjacent chambers, and a single electrical wire conductor for sequentially establishing a source of current for each explosive perforating means, the improvement comprismg:

a multiplicity of series arranged resistors for providing a voltage drop thereacross;

a branch circuit connected between each series arranged resistors for firing one electrically actuated perforating means;

each branch circuit including a series arranged diode, an electrically actuated explosive perforating means, and a normally open explosive responsive switch means, with said switch means being connected to provide a current path to ground when it is moved to the closed position by detonation of an adjacent charge.

5. The device of claim 4 wherein said switch means includes a piston means located in the bore interconnecting adjacent chambers, and seal means associated with said piston means to prevent fluid flow through the bore, and means forming a passageway through said piston means;

means including a current conducting deformable member associated with said piston means and adapted to be deformed into current conducting condition upon detonation of an adjacent charge carrier to thereby form a current conducting path for a charge located in the other adjacent charge carrier;

said single electrical wire conductor including a current conducting member located in the passageway of said piston means to provide a source of current to said other adjacent charge carrier.

6. The device of claim 5 wherein said piston means includes a rod extending through the bore, with said piston means having a face opposite said rod with said face being directed towards said other adjacent charge carrier so as to receive the explosive force of a detonated charge;

means attaching said deformable member to the face of said piston means;

the bore being adapted to receive said piston means including said deformable member, with the diameter of said deformable member being less than the diameter of the portion of the bore which receives said piston means;

whereby, upon detonation of the explosive charge, deformation of said deformable member causes current to flow from the rod, through the member, and into the perforating apparatus.

7. In a perforating gun having multiple charge carriers arranged in series relationship and connected together by means having a passageway therethrough, with each charge carrier having an electrically detonated explosive charge contained therein, the improvement comprising:

seal means associated with each said passageway for sealing each charge carrier from one another;

explosive responsive switch means associated with each charge carrier and including circuit means extending from one into another adjacent charge carrier for arming one adjacent charge carrier upon deto- 9 10 nation of the explosive charge located in said another said deformable member being attached to said piston charge carrier associated with the switch means; and spaced apart from said inside wall surface; said switch means further including a permanently dewhereby:

formable electrical conducting member spaced apart the deformable member outwardly expands into contact from and arranged in close proximity to a grounded with the wall upon detonation of the charge located conducting member whereupon detonation of the in the charge carrier which is in communication with charge associated with said another charge carrier the member. provides an explosive force which deforms said (16- 10. The improvement of claim 9 wherein said deformformable member into electrical contact with the bl member i dished-shaped ith th outer periphery grounded Condu ting memb r to th re y pr ide a thereof depending outwardly away from the piston and closed circuit for arming the one adjacent charge. 10 towards the explosive charge located in the charge carrier 8. The improvement of claim 7 wherein said switch hi i i communication i h h b means includes a piston located in the passageway, and means forming a passageway through said piston; References Cited said current conducting deformable member being associated with said piston and adapted to be deformed 15 UNITED STATES PATENTS against said piston and into current conducting con- 3,010,396 1961 Coleman 175--4.55 dition upon detonation of the recited charge carrier 3,1 6,964 3/1964 La Rue 175-455 to thereby form the recited current conducting path. 3,246,707 4/ 1966 Bell 175-454 9. The improvement of claim 7v wherein said switch 20 3,246,708 4/1966 Harrigan et al 175--4.55 means includes a piston located in and electrically insulated from the passageway; DAVID H. BROWN, Primary Examiner.

said conducting member including the inside peripheral wall surface of the passageway and in communica- US. Cl. X.R.

tion with a charge carrier; 166-55; 200-82