US3036263A

US3036263A - Electric impedances of variable value

Info

Publication number: US3036263A
Application number: US750197A
Authority: US
Inventors: Hallas Lister
Original assignee: Telephone Cables Ltd
Current assignee: Telephone Cables Ltd
Priority date: 1957-07-26
Filing date: 1958-07-22
Publication date: 1962-05-22
Anticipated expiration: 1979-05-22
Also published as: GB890945A; CH366330A; DE1131923B; DK108458C; BE569734A; FR1209307A; NL229937A

Description

y 22, 1962 L. HALLAS 3,036,263

ELECTRIC IMPEDANCES 0F VARIABLE VALUE 3 Sheets-Sheet 3 Filed July 22, 1958 United States Patent 3,036,263 ELECTRIC IMPEDANCES 0F VARIABLE VALUE Lister Hallas, Romford, England, assignor to Telephone Cables Limited, a British company Filed July 22, 1958, Ser. No. 750,197 Claims priority, application Great Britain July 26, 1957 5 Claims. (Cl. 32374) This invention relates to an improved variable-value impedance of the kind comprising a number of fixedvalue impedances in association with a group of switches which are operable in sequence to change progressively the total value of impedance connected between two terminals. The invention also relates to such variable impedances which are automatically controllable by groups of sequentially actuating relays, similar to relay counters, and can be used, for instance, in the operation of automatically balancing a bridge network incorporating the variable impedance in one arm of the bridge. By the term impedance, as used in this specification, is meant impedance which is either substantially capacitative or substantially non-capacitative.

The object of the invention is to provide an impedance which is progressively variable in steps of equal value over a given range by means of an advantageously small number of switches and switching operations and which therefore lends itself to being automatically controlled by a correspondingly small number of relays. The invention will usually be applied in connection with the decade system of counting but it is applicable to other systems.

The improved variable impedance in accordance with our invention comprises a number of fixed-value impedances associated in sucha manner with N two-wayswitches that, by movement of the switches one at a time in succession to the operated condition followed by movement of the switches one at a time in succession to the non-operated conditions, the value of impedance con-' nected between two terminals is progressively variable from a minimum to a maximum value in 2N -1 equalvalue steps by the first 2N-1 switching operations and is returned to the minimum value by the next switching operation.

When the impedance is substantially capacitive, the fixed value impedances may consist of N -1 single-unitvalue capacitors and one N-unit-value capacitor with one pole of each capacitor connected to one of the terminals. The other poles of the single-unit-val-ue capacitors are separately connected to the movable contact of one of each of N l of the switches and the corresponding pole of the N-unit-value capacitor is connected to the first side contacts of all the switches. In the non-operated condition of the first N 1 switches, their first side contacts are engaged by their movalble contacts. The second side contacts of all the switches are connected together and, in its unoperated condition, the Nth switch completes a circuit from its second side contact to the other terminal. To vary the capacitance between the terminals from 0 to 2Nl units, in steps of one unit, the first N 1 switches are moved to the operated condition one at a time in sequence, the Nth switch is then similarly changed, and thereafter the first N 1 switches are returned one at a time in sequence to the non-operated condition. By then returning the Nth switch to the non-operated condition ice the value of impedance between the terminals is returned to zero.

Where the imperdance is a variable resistor, it may consist of two series connected chains of N1 singleunit-value resistors and, series connected to the end of one chain, one N-units value resistor. The movable contacts of the first N 1 switches are joined to one terminal and the movable contact of the Nth switch is connected to the other terminal. One series chain of resistors is connected between the first-mentioned terminal and one side contact of the Nth switch, and the other series chain is connected between that terminal and the other side contact of the Nth switch, the N-unit-value resistor being at the end of a chain which is nearest to the Nth switch. The corresponding side contacts of the first N --1 switches are connected to one series chain in such a manner that one single-nnit-resistor is connected between each two such side contacts, and the other side contacts are similarly connected to the other series chain. The resistors may be replaced by inductances to give a variable inductance.

The switches may be operable by a counting chain of N-relays which are energisable one at a time in sequence and a subsequently releasable one at a time in sequence. The relay chain may be of the free-running form in which the relays are energised in the first sequence of oper-a tions and released during the second sequence. The sequence in which the relays are released may be the same as that inwhichthey are energised or it may be such that the first N -l relays will be released in the opposite order to Which they are energised, the Nth relay being released after the others. The variable capacitor is controllable by either arrangement of relays. The variable resistor; or inductance, is made to be controllable by one system or the other by arranging for the largest resistor to be connected between the side contact of the Nth switch and the corresponding side contact of the first of the other switches to be operated by the first released relay.

Where the impedance range extends over several sig-v nificant figures, a number of the improved variable impedances may be used between two terminals, one corresponding to each significant figure, and the values of the units of impedance are appropriately related in ac cordance with the requirements of a decade system of counting. Where such an arrangement is relay controlled, a separate relay chain will be provided for each variable impedance, with means controlled by each relay chain for initiating a change of state of one step in the next higher chain following the completion of a full cycle of operation of the lower chain. Where the variable impedance is the variable arm of a bridge-network the operation of the relay chain may be under the control of means which is responsive to the conditions of balance and unbalance of the bridge. Where the controlling relay system is automatically responsive to the condition of a bridge network, only the lowest value relay chain will be free-running with means for arresting the relay operation at balance. In this case it is preferable to provide means to ensure positively that a cycle of operation of the free-running chain cannot begin before the change of state, which is initiated by the completion of the previous cycle of that chain, has occurred in one or more of the higher value relay chains.

The invention Will be further described with reference,-

' 3 by way of example, to the accompanying diagrammatic drawings, wherein:

FIGURE 1 is a circuit diagram of a variable capacitor;

FIGURE 2 is a circuit diagram of a group of relays for controlling the variable capacitor; and

[FIGURE 3 is a circuit diagram of a variable resistor which is also controllable by a relay group of the form which is represented in FIGURE 2.

Each relay is represented in FIGURE 2 by a rectangle containing a two-letter designation, see for instance relay CA. Except in FIGURE 3, switches which are controlled by each relay are represented by the same two letters and a suffix number, for instance, relay CA controls four switches CAI-CA4. The relays are adapted to be energised for any convenient source of direct current, such as battery, one terminal of which is permanently earthed and one terminal of each relay is permanently connected to the other terminal the current source which is represented by a negative sign in a circle. Each relay is energisable by completing a circuit from its other terminal to earth, shown conventionally at the bottom righthand corner of FIGURE 2, that is by putting an earth on a relay. All the switches shown in and described with reference to FIGURE 2 will be referred to as relay contacts or merely as contacts. The switches shown in and described with reference to FIGURES 1 and 3 will be referred to as switches although they will in practice also be relay contacts. The switches and contacts are shown in the unoperated condition, that is to say with all the relays de-energised.

The variable capacitor represented by FIGURE 1 is designed to provide between two terminals X and Y a capacitance which is adjustable in unit steps to any value in the range to 199 units. The instrument is in three sections, referred to as the units, tens and hundreds sections, connected in parallel between the terminals X and Y. It incorporates four l-unit condensers Cl and one S-unit condenser C in the units section, four IO-unit condensers C and one SO-unit condenser C50 in the tens section, and one IOU-unit condenser C100 in the hundreds section. The units and tens sections are similarly constructed. The terminal X is permanently connected to one pole of each condenser in the units section. The other poles of the unit condensers C1 are connected to the movable contacts of four two-way switches CA4- CD4. In the unoperated condition of these switches, the movable contacts close on to their side contacts 19 which are permanently connected together, to a side contact b of another two-way switch CBS and to the remaining electrode of the S-unit condenser C5. In the unoperated condition of the switch CES, its movable contact is closed on its other side contact a. The terminal Y is permanently connected to the movable contact of switch CBS, and the remaining side contact a of switch CBS is permanently connected to the remaining side contacts a of switches CA4-CD4. In the unoperated condition of the switches, no condenser of the units section is connected between terminals X and Y.

The tens section is similar to the units section, except as regards the following features. In place of the four l-unit condensers C1 there are provided four 10-unit condensers C10, and in place of the S-unit condenser C5 there is provided a 50-unit condenser C50. The five twoway switches CA4-CD4 and CBS are replaced by similar switches CF4-CI4 and C15. In the unoperated condition of the switches, no condenser of the tens section is connected between the terminals X and Y. The hundreds section consists of a single -100-unit condenser C100 in series with a single-pole switch CK4 between the terminals X and Y. The switch CK4 is open in its unoperated condition, so that in that condition the IOOTunitS condenser is not electrically connected to both terminals X and Y.

The value of the capacitance between the terminals X and Y can be raised to four units in single unit steps by operating, that is changing over the moving contacts of, the four switches CA4 to CD4 one at a time and in that order. In that condition the moving contacts of the four switches CA4-CD4 are in engagement with their side contacts a. By operating the fifth switch CES, the circuit is completed between the terminals X and Y through the S-unit condenser, and the circuit from terminal Y to the side contacts a of switches CA4-CD4 is broken, so that although the four l-unit condensers C1 are no longer in circuit between the terminals X and Y, the capacitance between those terminals has increased to five units, that is to the value of condenser C5. The value of the capacitance between the terminals X and Y can now be increased from five to nine units, in single unit steps, by returning the four switches CA4CD4 one at a time to the unoperated condition. For instance, by returning switch CD4 to the unoperated condition, its associated unit condenser C1 is connected in parallel with the S-unit condenser C5 between the terminals X and Y. If now the remaining two-way switch CB5 is returned to the unoperated condition, the condition of the units section returns to that shown in FIGURE 1 in which the value of capacitance between terminals X and Y is again zero. It will be appreciated therefore that the value of the capacitance connected between the terminals X and Y is progressively variable from zero to nine units in unit value steps by the first nine switching operations and can be returned to zero by the tenth switching operation. It will also be appreciated that the switches lend themselves to be controlled by relays which can be energised to effect the first five steps of the process and released, that is de-energised, to effect the next five steps, so that the ten switching operations can be'controlled by means of only tfive relays. During the first four steps the switches CA4-CD4 can be operated in any order; similarly they may be released to return to the unoperated condition in any order. The switches, however, can be, with particular advantage, controlled by a group of relays in theform of a' free running relay counter and in such case it is preferred to cause all the relays to operate in the sequence 'CA4CD4, CBS and to return in the same order to the unoperated condition.

The tens section can be operated similarly to the units section and provides for the value of capacitance to be varied fromzero to ninety units in ten-units steps. In the process of increasing the capacitance to a value in excess of ten units, the first and each subsequent switching operation of the tens section is arranged to occur each time switch CES of the units section is returned to its unoperated condition. Moreover after each such operation all theswitches OF4-CI4, 015 of the tens section are required to remain unaltered during the next cycle of operation of the units section. The relay group for controlling the tens-section must therefore be dilferent from that for controlling the units section. The relay arrangement to be described below will be such as to cause the switches OF4-CI14, 0J5 to operate one at a time and in that order and to be released in the order CI4-CF4, C15. After the units and tens sections have connected 99 units of capacitance between the terminals X and Y, the capacitancevalue can be increased by one unit by simultaneously releasing switches CBS and C15 to the unoperated condition, thereby clearing the units and tens sections, and closing switch CK4 in the hundreds section to complete the circuit between the IOU-unit condenser C100 and terminal Y. The switch CK4 will remain closed during ten following cycles of operation of the units section and one cycle of the tens section, at the end of which 199 units of .capacitan cewill be connected between the terminals X and Y. It will be seen that by altering one switch of the tens-section after every switching cycle of the units section, and by closing the hundreds-section switch after the first switching cycle of the tens section, the value of capacitance between the terminals X and Y can be raised in unit steps from 1 to 1-99.

Also, the range can be increased by one or more significant figures by inserting, in parallel with the sections described, one or more sections similar to the units-section and with appropriate values of component condensers.

FIGURE 2. represents a system of relays for controlling the variable capacitor which has been described with reference to FIGURE 1. There have been previously proposed several forms of apparatus for automatically effecting, and printing the results of, tests on the quads of telephone cables, in which each test involves the automatic adjustment of a capacity bridge and the result to be printed is the amount by which the variable arm of the bridge is adjusted to balance the bridge. In such proposals, the variable arm of the bridge may comprise a number of separate condensers which can be automatically connected into the bridge network by a group of relays arranged to be energised automatically one after another. The relays are provided with additional contacts for selecting circuits to printing devices whereby the value of the capacitance adjustment etfected by the relays can be automatically recorded. Such an arrangement incorporates means which is responsive to the condition of the bridge network'in such manner that the capacity adjusting action of the relays can be initiated and continued while the bridge is unbalanced and automatically stops when a balanced condition is achieved. Such means also ensures that the relays which have been energised will remain energised until released by other means. Such other means will include a device which automatically releases the relays when the recording process is complete.

The arrangement herein described with reference to FIGURE 2 is applicable in such a testing and recording system. For the purpose of describing the present invention, it is only necessary to indicate the devices which interconnect the capacity adjusting relays with the means which is responsive to the condition of the bridge network and with the means which is responsive to the completion of a recording.

The capacity adjusting relays comprise a units group of fi-ve relays CA-CE, a tens group of live relays CF-CJ and a hundreds group comprising one relay CK. There are also auxiliary relays PA-PB and PQ the purposes of which will be indicated below. The earth connection for energising holding and releasing all the relays is taken from a bus-bar 1. The earth connection to the bus-bar 1 is completed through a two-way switch PQ1 and normal closed contacts PMl. The contacts PMll are controlled by a relay or other means, not shown, which causes the contacts PM1 to open when a previous capacity value has been recorded, thereby releasing all the capacity controlling and auxiliary relays. The central contact arm of the two-way switch PQ1 is connected to earth by contacts i PMl. The switch PQ1 is controlled by an excess value relay PQ in such a manner that if the apparatus endeavours to increase the variable capacity beyond the range provided by the apparatus, relay PQ is energised and switch PQ1 is operated to break the earth connection to the bus-bar 1 and to complete a holding circuit for relay PQ through an indicator lamp L.

The earth connection to the units relays CA-CE is provided by a two-way switch P11 under the control of a relay, not shown, which is energised when the bridge network, with which the illustrated apparatus is to be used, is unbalanced. In the FIGURE 2 the switch P11 is shown in the position which corresponds to the bridge being in a balanced condition. Contacts PKl, shown open in FIG- URE 2, require to be closed to set the relay system in operation.

The units relays CA-CB are energisable one after another and in that sequence from a relay-operating line 2 which can be connected to the bus-bar 1 through contacts PBZ, PC2, CB4 and PKl and switch P11. Relay PA causes the first unit relay CA to be energised by closing contacts PAZ. Relay CA operates make-before-break contacts CA1 to complete its own holding circuit to the hold line 3, operates make-before-break contacts CA2- to prepare a similar holding circuit for the next units relay CB and closes contacts CA3 to provide an energising connection from the relay-operating line 2 through makebefore-break contacts CB1 to relay CB. The remaining units relays CC, OD and the five-units relay CE are associated with circuit and contact arrangements similar to relays CA and CB. When relay CE is energised, its makebefore-break contacts CB2 are operated to transfer the holding circuit for unit relay CA from the hold line 3 to the auxiliary hold line 4, and also contacts CB4 are opened to interrupt the operating earth connection to the relay operating line 2. When relay CA releases the contacts CA2 are released to transfer the holding circuit for relay CB from the bold line 3 to the auxiliary hold line 4. The holding circuits for the remaining relays CB-CB are similarly controlled. So long as the associated bridge network is unbalanced the auxiliary hold line 4 is isolated, at switch P11, from the bus-bar 1 so that as soon as any relays are connected to the line 4 they will be automatically released. When the bridge is balanced, switch P11 returns to the unoperated position as shown. This applies an earth to the auxiliary hold line 4, thus preventing the release of any relays connected to that :line, and interrupts the earth connection to the relay operating line. It will be seen therefore that the condition of the relays CA-CE of the units section is retained, after switch P11 moves into the unoperated position, until the earth connection to the bus-bar 1 is interrupted at contacts PMIl or switch PQ1.

When relay CE operates it also closes contacts CB3 to initiate the operation of a two-state pair of relays PB and PC. The purpose of this relay group is to initiate and control the cycle of operations of the tens group of relays CF-CJ. A change of state of the relay PB occurs for every opening of contacts CB3, that is for every release of relay CE. When contacts CB3 are closed an earth is applied to the relay PC through the unoperated makebefore-break contacts PCI. Relay PC energises and operates contacts PCI to apply its own holding earth connection to busbar 1 and interrupt its energising circuit through contacts CB3. Contacts PC]. also complete an energising circuit for relay PB but this is prevented from operating by a shunt circuit provided through contacts CB3 and FBI. When relay CE eventually releases, contacts CB3 open and interrupt the shunt circuit of relay PB which is therefore energised through contacts PCl. When relay CE next energises, during another cycle of the unitsrelay group, contacts CB3 close to short circuit relay PC through operated contacts PBl. Relay PC releases and contacts PCl return to the unoperated condition in which the holding circuit for relay PB is transferred to operated contacts CB3. When relay CE eventually releases, contacts CB3 open to interrupt the holding circuit for relay PB which therefore releases and contacts PBl return to the unoperated condition. It will be seen therefore that with successive opening of contacts CB3, relay PB is alternately energised and de-energised.

The series circuit for initiating the operation of the units relay group CA-CE includes a pair of two-way contacts PBZ and PC2. and it is apparent that this circuit can only be complete when both contacts are either simultaneously operated or unoperated. When relay CE is first energised, contacts PC2 operate to interrupt that series circuit. This ensures that no units relay energising circuit can be completed during the release of relays CA-CE in the second half cycle of operation of the units relay group. When relay CB releases, contacts PBZ operate to complete the alternative series circuit through contacts PC2 and PB2 in preparation for the initiation of the next cycle of operation of the units relay group. The next time relay CB operates, contacts PC2 are released to again interrupt the series circuit and when relay CE .next releases contacts PBZ are also released so that the series circuit is again completed by the return of contacts PBZ and PC2 to the position shown in FIGURE 2.

The tens section of the variable capacitor is controlled by the tens group of relays CF-CJ which are energised one at a time and in that Order and are then released in the order CI-CF, CI. The arrangement is such that one step in the change of state of the tens group. occurs at the completion of each cycle of operation of the units group of relays, that is each time the last relay CE of the units group releases.

The tens group of relays CF-CI are divided into a group of odd number relays OF, CH, C] and a group of even number relays CG and CI. The odd number relays CF, CH and C] are energisable by a connection to earth through two-way contacts PB4 in one position and an operating line 7 which is interrupted at two positions by contacts C63 and C13. Similarly the even number relays CG, C1 are energisable by a connection to earth through the same contacts P134 in the other position and another operating line 8 which is also interrupted in two positions by contacts CF3 and CH3. The energising circuit for each relay is completed by make-before-break contacts which are operable by the energised relay itself to interrupt the energising circuit after completing a holding circuit. The contacts which operate in that manner are contacts CFl-CJI. Moreover neither of the operating lines 7 and 8 is extended, after the energising of a relay from that line, to operate another relay from the line, until a further relay has been energised from the other line. For instance, after relay CF has been energised from line 7, relay CH cannot be energised from line 7 until contacts CG3 have been closed by the energising of relay CG from line 8. The two-way contacts PB4, controlled by relay PB and having the centre contact connected to the busbar 1, serve to apply the earth connection from the busbar to lines 7 and 8 alternately. By this arrangement it is ensured that only one of the tens group of relays CF-CJ will be energised at the end of each cycle of operations of the units group of relays. When first energised, each relay CFCI will be held by a connection to a

release line

5 or 6 connected to the busbar 1 by contacts C12 in the case of line 5 and contacts CM- in the case of line 6. Except in the cases of relays CI and OJ these holding circuits will be transferred direct to the busbar 1 when a subsequent relay is energised. For instance, relay CF will be held by its own contacts OF1 to line 5, until the energising of the'next relay CG transfers the holding connection direct to the busbar 1 through contacts CG2. Contacts CH2 and C12 are provided for a similar purpose in connection with relays CG and CH. In the case of relay a holding circuit to busbar 1 will be prepared at contacts CFZ when the first relay, CF, of the group, is energised. In the case of relay CI it is not necessary, as will appear below, to transfer its hold connection from line 6. Two-way contacts CF3 interrupt the circuit from contacts PB4 to the even number relay operating line 8 until relay CF is energised and this cannot occur until contacts P134 move to the operated condition at the end of the first cycle of the units relay group.

The functions of relay CI differ from those of the previously operated relays CF-CI of this group because, when relay CI is energised, provision has to be made for all five relays to release one at a time in sequence, and for the hundreds relay CK to operate when relay CI releases. Contacts C13 will open and remain open to render the contacts P34 ineffective so long as relay CI is energised. Relay PB also controls two-way contacts PB3 which operate simultaneously with contacts PB4 but without effect up to this stage. It will be seen that, in the upper position, contacts PB3 connect one release line to the busbar 1; but when relay CI is not energised, there is a parallel connection at the contacts C12 so that the connection between the line 5 and the busbar 1 remains unaffected when contacts PB3 move into the lower position. While relay CI is being energised, contacts PB3 will be in the lower position, and contacts C12 will move into the lower position so that the release line 5 will be disconnected from the busbar 1, but without effect on relays CF and CH because their holding circuits will have been transferred to the busbar 1 at contacts CGZ and C12. Also, in the lower position, contacts PB3 will have connected the release line 6 to the busbar 1 before contacts C14 have opened to disconnect an alternative circuit from the release line 6 to the busbar ll. This last mentioned switching operation will be ineffective on relay CG because its holding circuit will have been previously transferred from the release line 6 to the busbar 1 by contacts CH2. In the case of relay Cl, however the only holding circuit is tothe release line 6 through its own contacts C11. It will be seen from FIGURE 2 that when contacts PB3 are in the lower position they can also supply a' holding circuit from relay CI to' the busbar 1 when contacts C11 are operated and contacts CFl are unoperated but so long as relay CF is energised this circuit will be interrupted by the operated contacts CF2.

The arrangement of the tens group of relays is such that they will be released in sequence, upon successive operations of relay CE, in the order CI, CH, CG, CF and CJ. The next operation of relay CE, after the relays in the tens group have been energised, causes contacts PB3 to move into the upper position and interrupts the holding circuit for relay Cl which was completed from the busbar 1 through contacts PB3 in the lower position, release line 6 and switch C11. When contacts C12 return to the unoperated position, the holding circuit for relay CH will be transferred back to the release line 5 after this line 5 has been connected to the busbar 1 by contacts PB3 in the upper position. When contacts PB3 again move to the lower position, at the next operation of relay CE, the last mentioned holding circuit for relay CH is interrupted. When contacts CH2 open, the holding circuit for relay CG will be re-transferred to the release line 6 which is connected to the busbar 1 by contacts PB3 in the lower position. At the next operation of relay CE, contacts PB3 will move into the upper position to break the holding circuit for, and so release, relay CG. The re-opcnin'g of contacts CGZ will retransfer the holding circuit for relay CF to the release line 5 which in turn will be connected to the busbar 1 through contacts PB3 in the upper position. At the next operation of relay CE, contacts PB3 will again move into the lower position, and so will break the holding circuit for, and release, relay CF.

The arrangements for the release of relay C] are as follows. Although relay CI is an odd number relay and is energisable from the same line 7 as the other odd number relays CF and CH, its hold and release control is effected through the release line 6 which is associated with the even number relays CG and CI. When relay CF is released, the holding circuit for relay CI is transferred, by contacts CF2, from the busbar l to the release line 6, so that when contacts PB3 next move to the upper position, the earth is removed from the release line 6, so that relay CJ releases.

In the lower part of FIGURE 2 there is showna'two state relay pair PD and PE, which is similar to the previously described relay pair PB and PC. In the case of relays PD and PE, a change of state of relay PD occurs every time relay CI, of the tens groups of relays, releases and returns contacts CI'Z from the operated to the unoperated condition. The sequence. of control and operation of the relay pair PD and PE is identical with that of relays PC and PB, and in this respect it is immaterial that contacts CJZ constitute a two-way switch. The relay pair PD and PE, by controlling the two-position contacts PDZ, serve to energise relay CK when relay CI is first released, to connect the IOO-units capacitor C into the variable capacitor, and, if relay CI is released again in the same sequence of operations, to energise relay PQ to indicate that the capacitance range of the apparatus has been exceeded.

The operative steps to vary the value of capacitance,

connected between the terminals X and Y in FIGURE 1, from zero to 199 units are as follows:

' With all the switches and contacts except PM in the condition shown in the drawings, contacts PKl are closed. If the associated bridge network is in an unbalanced condition, contacts P11 will be operated to energise relay PA, close contacts PAZ and apply an earth to the first relay CA of the units group of relays. Relays CA, CB, CC and CD are energised in succession to increase the capacitance value to 4 units; then relay CE is energised to add the S-unit capacitor C5 and remove the tour single capacitors. Relays CA-CD are now released in the same sequence to increase the capacitance in unit steps to 9 units and eventually relay CE is released to return the capacitance value to zero.

When relay CE is released, relay PB is energised, and remains energised, to complete an operating circuit through contacts C13 and PB4 to the first relay CF of the tens group of relays. This relay'CF being energised inserts the -unit capacitor Cltl between terminals X and Y. The relay CF completes its holding circuit at contacts CPI and prepares, at contactsCFS an energising circuit for the next relay CG of the tens group of relays. While this operation has been in progress the following conditions have been present to prevent premature operation of'the units group of relays. When the S-uni't'"capacitor-controlling relay CE was energised, contacts-CB4 opened to open the earth connection to the relay operating line' 2. When CE was released, contacts CB4 reclosed, but contactsPCZ were operated to maintain' the break in the earth connection which was eventua'lly completed at contacts PBZ when relay PB operated.

To ensure that the first relay C1 of the tens group of relays will change its state before the first relay CA in the units group is energised, the energising of relay PA, which is now connected to earth through contacts CB4, PC2. and PB2, is delayed by the capacitor C connected in parallel with the relay. The relay PA is not energised, so that con tacts PA2 are not closed until the capacitor C has been charged to the operation potential of the relay PA and this chargin period is made longer than the time required for the first relay CF of the tens group of relays to be energised when contacts PR4 are moved into the operated position.

The complete cycle of operations of the units group of relays is now repeated and when relay CE again releases, the contacts PB4 return to the lower position to energise the second relay CG of the tens group of relays. These operations continue until there is obtained the condition in which 59 units of capacity are connected between the terminals X and Y. In this condition all the relays of the units group have been released with the exception of relay CE, and all the relays of the tens group are energised. Relay CE now releases causing contacts PB3 to move to the upper position and causing relay CI, in the tens group, to be released because contacts C14 have been opened by the energisation of relay C1. The value of capacitance has now been increased to 60 units. The cycle of opera-- tions is again repeated causing relays CH, CG, CF of the tens group to be released one at a time and in that order.

-When the value of inserted capacitance has become 99 units, relay CE is on the point of being released and when this occurs relay C1 in the tens group is also released.

When relay C1 was energised, contacts C12 moved into the lower position to complete an energising circuit for relay PE which in turn completed its holding circuit at contacts PEI. Although contacts PEI complete an energising circuit tor relay PD, this is short circuited through contacts PD1 and C12. When relay C1 is eventually re leased, contacts C12 return to the upper position thus removing the short circuit from relay PD which is energised. This changes over contacts PDZ to energise the IOO-unit relay CK which completes its holding circuit at contacts CK1 and connects the 100-unit capacitor C100 between the terminals X and Y.

The relays PD, PE and CK remain energised while the complete cycle of operations of the units group and tens group of relays is repeated. At the end of that complete cycle 199 units of capacitance are inserted between the terminals X and Y. The apparatus will not increase this value of capacitance. When relay C1 was energised for the second time it applied, through contacts C12 and PD1, a short circuit to relay PE which was consequently released. Relay PD was not released because the return of the make-before break contacts PEI provided a holding circuit for the relay through contacts C12. In the event of the cycle of operations of the units group of relays tending to be repeated this will immediately result in the release of relay C1 causing the holding circuit for relay PD to be broken at contacts C12. Contacts PD2 are thus returned to the non-operated condition and provide an energising circuit for relay PQ through the closed contacts CK2. As previously indicated the contacts PQl are altered to provide a holding circuit for relay PQ through the indicator L and to release all the other relays.

It is required to ensure that, when relay CK is to be energised to connect the IOU-unit capacitor C between terminals X and Y, the initiation of the next cycle of operation of the units group of relays will be delayed until that step has been completed by the closing of switch CK l. This can be provided for by short-circuiting the relay PA through contacts CK3, PB2, CF3, P134 and C13. In the unoperated condition as shown in FIGURE 2 the short circuit is incomplete at contacts CK3 and PE2. The energising of relay C1, at the end of the first half-cycle of operation of the tens group of relays, will energise relay PE, as described above, and thereby change the state of contacts PEZ so as to tend to complete the short circuit for relay PA. However, at this stage, the energising of relay CF has provided another break in the short circuit at con tacts CPS and also the energising of relay C1 has opened contact C13 to provide another break. When the circuit for releasing relay C1 is just completed, relay OF has already been released so that contacts CF3 are again in the position shown, and contacts PB4 are also in the position shown. The contacts C13 close, when relay C1 actually releases, to complete the short circuit for relay PA. The short circuit is eventually opened when relay CK is energised and changes over the contacts CK3. The cycle of operations of the units group of relays then recommences by the energising of the first relay CA after the time delay provided by the capacitor/ resistance circuit associated with the relay PA.

If at any time the bridge-network, incorporating the variable capacitor, becomes balanced, contacts PI]; will revert to the position shown in FIGURE 2, the earth connection will be removed from the relay operating line 2, so that any non-energised relays of the units group will remain in that condition, and the release line 4 will be connected to earth, by contacts P11, so that any energised relays of the group will be held in that condition. No further changes of state of the tens group of relays CF-CJ nor of the hundreds relay CK can occur, because all such changes of state are only initiated by the release of the units group relay CE.

FIGURE 3 illustrates a variable resistor which can be controlled by the group of relays already described with reference to FIGURE 2, to provide between terminals X and Y a value of resistance which is variable in unit steps from zero to 199 units.

In FIGURE 3 the two-way switches RCA4-RCD4, RCES, RCFd-RCM, ROI 5 and RCK4 correspond in number and in their order of operation to the two-way switches already described with reference to FIGURE 1. By changing-over switches RCA4-RCD4 one at a time and in that order the resistance inserted between the terminals X and Y is increased in unit steps from zero to 4 units. By then changing over switch RCES the resistance value is increased to 5 units. Bythen restoring to the initial condition switches RCA4-RCD4 one at a time and in the same order the value of resistance is increased in unit steps from to 9 units. The next switching operation, comprising returning switch RCES to the initial condition restores the value of the inserted resistance to zero. By means of the relay arrangement already described the final switching movement of the units section is accompanied by the first switching movement of the tens section. In this section the operation of the switches RCF4-RCI4 one at a time and in that order raises the resistance between terminals X and Y from zero to 40 units in tenunit steps. By changing over switch RCJS the value of the inserted resistance is increased to 50 units and by then releasing the first four switches of this section one at a time and in the order RCI4-RCF4 the resistance is increased to 90 units. Then by returning switch RG15 to the initial condition the resistance is again reduced to zero except that, by means of the relay arrangement already described, switch RCK4 is operated to insert 100 units of resistance into the circuit.

Although the number of switches used in the variable resistance is the same as that in the variable capacitor other modifications of the circuit are required due to the essentially difierent natures of the impedance elements. For instance in the variable capacitor the capacitance is changed by altering the number of unit capacitors connected in parallel whereas in the variable resistor the re sistance is altered by changing the number of the unit resistors connected in series. a I

In the arrangement shown in FIGURE 3 the movable contacts of the switches controlling the unit resistors R1 are permanently connected to one terminal X to which is also permanently connected one end of each of two sets of four series connected unit resistors R1. The other end of one of these series connected sets of unit resistors is permanently connected tothe side contacts a of the first switch RCA4- and the last switch RCES. The side contacts a of the remaining three switches RCB4-RCB4 are permanently connected to intermediate points between those unit resistors in such a way that between each adjacent side contacts a there is permanently connected a unit resistor R1. The other side contact b of the first switch RCA i is permanently connected to the otherwise free 'end of the second set of series connected unit resistors R1 and the side contacts b of the three switches RCB4- RCB4 are permanently connected to intermediate points in the set in such a way that a single unit resistor R1 is connected between each pair of adjacent side contacts b. The arrangement is. also such that there is a unit resistor R1 connected between the side contact a of the fourth switch RCB4 and the terminal X and also another unit resistor R1 connected between the side contact b of that switch and the terminal X. A S-unit resistor R5 is connected between the side contacts b of the firstswitch RCA4 and the fifth switch RCES. The movable contact of the fifth switch RCES constitutes the other terminal of this units section. In the unoperated condition, shown in FIGURE 3, there is a short circuit between. the two terminals through the movable contact and side contact a of switch RCESand the side contacta and movable contact of the first switch RCA4. The first step, eifected by the energizing of relay CA in FIGURE 2, comprises the movement of the central contact of switch RCA4 out of engagement withits side contact a and into engagement with its side contact b. This removes a short circuit from the unit resistor R1 connected between the side contacts a of the switches RCA4 and RCB4 so that this resistor is now connected in series between the terminals 12 RCA4 which itself short circuits the set of four series connected unit resistors R1 of which one end is connected to the side contact b of switch RCA4. By re turning switches RCA4-RCD4 one at a time and in that order to their unop-erated condition the last mentioned set of unit resistors R1 are brought one at a timeinto the series circuit between the terminals of the section. The final return of RCES to its initial connection breaks that series circuit and recloses the short circuit through its side contact a and the side contact of the first switch RCA4.

The tens section of the variable resistor diifers from the units section in the following respects. In place of the unit resistors R1 there. are now used IO-unit resistors R10 and a 50-unit resistor R50 is used in place of the 5- unit resistor R5. Whereas in the unit section the S-unit resistor R5 was connected between the side contacts b of switch RCES and the first switch RCA4, the SO-unit resistor R50 in the tens section is connected between the side contacts b of the fifth switch RCJS and the fourth switch RCI4. Furthermore, the part circuit containing a unit resistor R1 connected between the terminal X and the si-decontact b of the fourth switch RCD4 in the units section has no counter-part in the tens section, but a 10-unit resistor R10 is permanently connected between the corresponding terminal of the tens section and the side contact b of the first switch RCF4. It 'will be seen that the arrangement of the switches and separate resistors in the tens section is such that the resistance between the two terminals of this section, that is between the centre contacts of switches RCES and RCJ5, will be increased in IO-unit steps from zero to units by moving the switches one at a time into the operated condition in the order RCF4'-RCI4 and RCJ5 and thereafter returning the first four switches into the unoperated condition in the order of RCI4-RCF4. By thereupon returning the switch RG15 into the non-operated position the inserted resistance is again at zero. It will also be seen that this sequence of switching operations can be efiected by the tens group of relays already described with reference to FIGURE 2.

Finally the hundreds section of the variable resistance comprises a l00 unit resistor R short circuited by a normally closed switch RCK4. This can be operated by means of the relay CK in the hundreds section of the arrangement shown in FIGURE 2 to remove the short circuit from the resistor R100 and thus insert a IOU-unit of resistance between the terminals X and Y of the variable resistance. 7

Both the variable capacitor and resistor can be expanded to cover a range of values extending overmore than three significant figures by adding one or more sections corresponding in each case to the tens section. Each such added section, which will be series connected with the other sections in the case of the variable resistance and parallel connected in the case of the variable capacitor, will include units of resistance or capacitance appropriately related to its position in relation to the other sections. Each such added section can be controlled by a group of relays which is similar to the tens section group of relays which has been described. I

A variable inductance can be constructed in a manner similar to that of the variable resistance, the resistors being replaced by screened inductances and the relay controlling arrangements remaining the same.

One advantage of the improved variable impedance lies in the use of an arrangement of switches which is such that the full range of adjustment is obtainable by a cycle of switching operations at the end of which the device is returned to the initial condition by a simple switching operation instead of it being necessary to reset a comparatively large number of switches to an initial condition. In combination with that advantageis the factthat a comparatively small number of switches are required and the numher and type of such switches are particularly. adapted for automatic control by groups of relays. In the case of 13 the variable capacitor, there is the added advantage that only a comparatively small number of fixed-value condensers is required. In all the cases described, variation through a range of ten equal value steps is obtainable with only five relay-operated switches and in the case of the variable capacitor only five fixed-value condensers are required.

What I claim as my invention is:

1. A variable impedance comprising A(N1) separate equal-value impedances, where A is a whole number less than 3 and N is any whole number greater than unity, and a separate impedance of N-times that value, N twoway switches of which each switch comprises a first side contact and a second side contact and a central movable contact which is in conductive engagement with the first side contact in an unoperated condition of the switch and with the second side contact in an operated condition of the switch, each of Nl of the two-way switches controlling the insertion of the value of one of the smaller separate impedances in circuit between two terminals of the variable impedance and the Nth two-way switch controlling the insertion of the value of the larger separate impedance between those terminals, and the switch contacts and separate impedances being interconnected with the two terminals to provide for the total value of impedance in circuit between the two terminals to be progressively varied in 2Nl equal-value steps from a minimum to a maximum value by 2N-1 changes of conditions of the switches and to be returned to the minimum value in the next 2Nth step by a subsequent change of condition of one of the switches, the 2N changes of condition of the switches comprising a change of state of all the switches one at a time in succession to the operated condition and thereafter one at a time to the unoperated condition.

2. A variable impedance comprising N 1 separate equal-value impedances, where N is any whole number greater than unit, and an Nth separate impedance of N times that value, N two-way switches of which each comprises a first side contact and a second side contact and a central movable contact which is in conductive engagement with the first side contact in an unoperated condition of the switch and with the second side contact in an operated condition of the switch, a permanent connection between all the first side contacts of Nl of the switches, the second side contact of the Nth switch and one terminal of the larger separate impedance, a second permanent connection between the remaining side contacts of all the switches, a third permanent connection between the second terminal of the larger separate impedance and one terminal of each of the smaller separate impedances, and N -l permanent connections each joining the second terminal of one of the smaller impedances to the central contact of one of the said N-1 of the switches, whereby the total value of the impedances connected in parallel between the central contact of the Nth switch and the said third permanent connection is progressively variable in 2N-1 equal-value steps from a minimum to a maximum value and in the next 2Nth step to the minimum value by changing the state of all the switches one at a time in succession to the operated condition and thereafter one at a time to the unoperated condition.

3. A variable impedance comprising 2(N-1) separate equal-value impedances, where N is any whole number greater than unit, and separate impedance of N times that value, permanently connected in the form of a first and a second series chain of N 1 of the smaller impedances with the larger impedance at the end of the second chain, N two-way switches each comprising a first side contact, a second side contact and a central contact which is in conductive engagement with the first side contact in an unoperated condition of the switch and with the second side contact in an operated condition of the switch, a first permanent connection between one end of each chain of 14 impedances and the central contacts of N l of the switches, a first set of permanent connections each between the first side contact of one of N 1 of the switches and a point between two adjacent smaller impedances in the first chain, and a second set of permanent connections each between the second side contact of one of said N l of the switches and a point between two adjacent smaller impedances in the second chain, a second permanent connection between the first side contacts of one of said N l of the switches and of the Nth switch and a third permanent connection between the second side contact of the Nth switch and the terminal of the larger impedance at the end of the second chain, whereby the value of the impedances connected in series between the central contact of the Nth switch and the said first permanent connection is progressively variable in ZN-l equal-value steps from a minimum to a maximum value and in the next 2Nth step to the minimum value by changing the state of all the switches one at a time in succession to the operated condition and thereafter one at a time in succession to the unoperated condition.

4. A variable impedance comprising A(Nl) separate equal-value impedances where A is a whole number less than 3 and N is any whole number and a separate impedance of N-times that value, N two-way switches each comprising a first side contact and a second side contact and a central movable contact which is in conductive engagement with the first side contact in an unoperated condition of the switch and with the second side contact in an operated condition of the switch, each of N 1 of the two-Way switches controlling the insertion of the value of one of the smaller separate impedances in circuit between two terminals of the variable impedance and the Nth two-way switch controlling the insertion of the value of the larger separate impedance between those terminals, and the switch contacts and separate impedances being interconnected with the two terminals to provide for the value of impedance in circuit between the two terminals to be progressively varied in 2N-1 equal-value steps from a minimum to a maximum value and to be returned to the minimum value in the next 2Nth step by changing the state of all the switches one at a time in succession to the operated condition and thereafter one at a time to the unoperated condition, and there being provided a chain of N relays, the central contacts of the two-way switches being movable to the operated condition by energization of said relays, and said relays being energizable one after another in succession to produce the first N changes of state of the switches and being releasable one after another in succession to produce the second N changes of state of the switches.

S. A variable impedance comprising A(N1) separate equal-value impedances where A is a whole number less than 3 and N is any whole number greater than unity, and a separate impedance of N-times that value, N twoway switches each comprising a first and a second side contact and a central movable contact which is in conductive engagement with the first side contact of the switch in an unoperated condition and with the second side contact of the switch in an operated condition, each of Nl of the two-way switches controlling the insertion of the value of one of the smaller separate impedances in circuit between two terminals of the variable impedance and the Nth two-way switch controlling the insertion of the value of the larger separate impedances between those terminals, and the switch contacts and separate impedances being interconnected with the two terminals to provide for the value of impedance in circuit between the two terminals to be progressively varied in 2N 1 equal-value steps from a minimum to a maximum value and to be returned to the minimum value in the next 2Nth step by changing the state of all the switches one at a time in suctwo-Way switches being movable to the operated condition by energization of said relays, said relays being energizable one after another in succession to produce the first N changes of state of the switches and being releasable one after another in succession to produce the second N changes of state of the switches, and those of said relays of state being releasable in the reverse order to produce the N-l-lth to 2N1th changes of state.

References Cited in the file of this patent which are energizable to produce the first N-1 changes 10 2,762,038

UNITED STATES PATENTS Howe Aug. 17, 1920 Eaves Apr. 22, 1924 Bush June 26, 1956 Lubkin Sept. 4, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,036,263 May 22, 1962 Lister Hallas It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 3, for "imperdance" read impedance -5 column 3, lines 61, 62, 63, and 68, column 4, lines 7, l9, and 64, column 9, lines 20, 73, and 74, column 10, line 22, and column 12, lines 15 17, 24, 42, and 46, for "-unit", each occurrence, read -units column 4, line 57, for "CF4- CI 14" read CF4-CI4 column 9, line 59, for "CG, read CG and column 13, lines 37 and 66, for "unit", each occurrence, read unity Signed and sealed this 9th day of October 1962.

(SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents