US2430488A - Adjustable compensated standard - Google Patents

Description

Nov. l1, 1947.

H. T. WILHELM 2,430,488 ADJUSTABLE coMPENsATED STANDARD Filed sept. '2, 1943 3 Sheets-Sheet l POWER SOURCE @y HT. w/HsLM ma@ Nov. 11, 1947. J H.T.wn HE1 M 2.430,488

ADJUSTABLE COMPENSA-TED STANDARD Filed Sept. 2,-1943 3 Sheets-Sheet 2 www W0 ATTORNEY Nov. ll, 1947. H. T. WILHELM 2,430,483

ADJSTABLE COMPENSATED STANDARD FledlSepL 2, 1943y 3 Sheets-Sheer?l 3 l /NVE/VTOR H 7 W/LHELM .Bywmw ya@ ATTORNEY Patented Nov. 11, 1947 ADJUSTABLE COMPENSATED STANDARD Henry T. Wilhelm, Long Island City, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application September 2, 1943, Serial No. 500,936

13 Claims. 1

This invention relates to alternating current bridge circuits and more particularly to compensated admittance and impedance standards linding special applications in alternating current bridges.

One of the difculties which constantly face users of alternating current bridges is that while adjusting one particular admittance or impedance component, other components are also varied by reason of impurities inherent in the bridge standard, thereby complicating the balancing adjustment and greatly increasing the time required to make the measurement. A very desirable advantage would be realized by maintaining constant all components not being adjusted.

It is therefore the object of this invention to provide an alternating current bridge standard for an alternating current bridge which, while any one component thereof is being adjusted, maintains all others constant.

The foregoing object is achieved by this invention by providing in combination an adjustable compensated alternating current bridge standard comprising a pair of terminals for said standard, a multiple position switching means, a plurality of standard circuit elements having undesired circuit components inherent therein, one compensating element for each standard element having components of the same kinds and magnitudes as the undesired inherent circuit components of its standard element, circuits connecting the standard elements, the compensating elements and the switching means to the pair of terminals, said circuits and switching means being adapted to selectively connect the standard elements in a plurality of predetermined combinations between said pair of terminals and to automatically substitute between said terminals the compensating element for each standard element not so connected.

The invention may be better understood by referring to the accompanying drawings, in which:

Fig. 1 discloses a Maxwell type bridge il1ustrative of one of the types of bridges which may utilize this invention;

Fig. 2 discloses a schematic of the essential elements of a practical standard admittance which may be used in the Maxwell bridge of Fig. 1;

Fig. 3 discloses how the standard admittance schematically disclosed in Fig. 2 may be constructed in accordance with this invention;

Fig. 4 discloses one form of switching mechanism which may be employed to practice this invention;

Fig. 5 discloses a decade type conductance standard employing commercially available radial type switches;

Fig. 6 discloses a capacitance decade employing commercially available radial type switches;

Figs. '7 and 8 disclose conductance and capacitance decade units respectively, each employing a drum type switch; and

Fig, 9 discloses the invention applied to an inductance standard.

Fig. 1 shows how the invention may be embodied in a Well-known Maxwell type inductance measuring bridge. A detail description of this bridge and its properties may be found in any standard work on electrical measurements, reference, however, being made to Bell Laboratories Record for November 1940, page 92, for a brief description of the principles of this bridge. In the simple form shown in Fig. 1 the bridge comprises four arms, two opposite arms comprising resistors Rl and R2, while one of the other two arms comprises the standard admittance Ys and the fourth arm the unknown impedance Zx in series with a balancing impedance Zb. A suitable power source I is connected to the B and D corners of the bridge and a suitable detector to the A and C corners of the bridge. Except for the shielding shown on the standard admittance and the balancing impedance, all shielding is deleted for the sake of clarity. Shielding would, of course, be used and may be applied in accordance with established principles. An important advantage of the Maxwell bridge is that an unknown inductance Lx may be measured by using a capacitance standard which is more easily constructed with low losses and with accuracy than is a standard inductance. The unknown inductive impedance ZX may contain an unknown resi-stive component RX, the complex impedance being expressed in the familiar form Rx-l-iwLx. The Maxwell bridge permits the standard to be expressed most conveniently in the form of a complex admittance ys so that the balance equation is:

In a practical bridge structure the product R1R2 is made equal to some'power of ten so that the resistance component Rx is measured by the standard conductance GS and the inductance Lx by the capacitance cs.

A schematic of the essential elements of a practical standard admittance for the Maxwell bridge is shown in Fig. 2. It is obvious that if the bridge is to balance for an unknown inductive impedance having a negligibly small resistive component Rx, the admittance standard must have a conductance component Gs which is also very small. For practical reasons the construction of such small conductances is not feasible and is avoided by including in the admittance standard a residual conductance GR, usually in the form of a slide wire in series with a resistor which is balanced by the resistive component Rb of the balancing impedance Zt. Also it is impossible to construct any practical alternating current standard admittance or impedance without incurring some spurious unwanted components usually in the form of capacitive susceptances for admittance standards and resistances for impedance standards. In this invention these components are utilized as a part of the residual components of the bridge and are automatically kept constant so as not to continuously upset the balancing adjustment for one component while adjusting another. In this way the undesired components are at all times completely compensated.

In Fig. 2 the residual conductance GR and the residual capacitance Ca are each kept constant. In the practical decade standard the residual conductance comprises a iixed conductance element connected as shown schematically in Fig. 2. However, the residual capacitance CR comprises not only physical capacitors but also the capacitance of the wiringand switch elements of the decade standard. VThe total admittance may then be expressed as YsIGs-i-LUCS: (gs-l-jwcs) (GR--Y'wcl) In the above expression the quantity (GR-HwCR) is the residual admittance constant for any given test frequency, while the quantity (gS-l-jwcs) is the variable admittance equal to ys in Equation 1. It will be obvious to those skilled in the art that the constant quantity (GR-i-y'wCR) is not objectionable as it may be balanced by inserting in the C-D arm a balancing impedance Zb. It is also clear that if this quantity is to be kept constant as is contemplated by this invention, the initial balance of the bridge is in no way upset and any variations which take place in the admittance standard are incurred by reason of the adjustment or the various variable components of the standard unit. The variable components, therefore, are a direct measure of the unknown impedance Zx which is connected to the terminals Xi and X2 of the bridge of Fig. 1.

Referring now to Fig. 3 which discloses the schematic of a practical embodiment of this invention, illustrating how an admittance unit of the general form shown in Fig. 2 may be constructed, the two terminals of this standard admittance carry the reference characters A, B which correspond to the A, B terminals of the bridge in Fig. l. Between 'these two terminals is shown permanently connected the constant conductance GR and capacitance Ca. As previously stated, the constant conductance GR in a practical'st'ructure usually comprises a physical conductance connected between these two terminals as well as the lumped leakage conductance. The constant capacitance Ca represents not only a physical capacitance whichmay be connected between the two terminals but also the total stray capacitance existing between the wiring and the switch terminals of both the conductance and capacitance standard component elements shown in Fig, 3. At this point it may be mentioned that in a practical structure it is preferable that the balancing impedance Zt be made without adjustment in which event the constant capacitance Ca of the admittance standard shown in Fig. 3 may also include a variable condenser to aid in securing the initial balance with terminals Xi and X2 short-circuited. In any event after initial balance is secured the value of the capacitance CR remains invariable.

t is a well-known tact that it is very difficult to construct standard circuit elements Without including impurities which are herein termed undesirable components. Although various types of improved construction may be employed to reduce their magnitudes, no construction has been found to eliminate them entirely. In accordance with this invention they need not be eliminated but in so far as adjusting the standard elements is concerned their presence in no way disturbs the initial balance oi the bridge. For the conductance decade gs, shown in Fig. 3, this is accomplished by compensating the conductance elements by connecting in series therewith compensating capacitors such as C1, C2, C3 and C4, the capacitances of which are exactly equal to the spurious capacitances oi their associated conductance elements. It is here assumed that all other spurious components are negligible but should they be appreciable, they may be compensated in exactly the same way. The function oi the switching arrangement is then to either short-circuit the compensating capacitance or short-circuit the standard conductance element which inherently includes the stray capacitance to be compensated. For example, in Fig. 3 the ten-micromho conductance unit must be understood to have inherent therein a capacitance component equal to Ci. Therefore a compensating condenser Ci is connected in series with this conductance unit. A two-position switch with a blade-3 is connected to terminal 6 joining this compensating capacitor C1 and the ten-micromho conductance unit. The switch is caused to engage either switch point 4 or switch point 5. When it is in engagement with point 5, as shown in Fig. 3, the ten-micromho standard element is short-circuited thereby eliminating this conductance standard element from the circuit between the standard terminals A, B. It Will be noted that in this position compensating capacitor C1 is vinserted between these two standard terminals A and B. The eiect is to remove the ten-micromho standard element from the circuit while leaving intact between the two standard terminals the capacitance Ci which corresponds to the undesired inherent capacitance component of the standard ten-micromho element. When this switch blade 3 is switched to point 4, the compensating capacitance C1 is switched out of the circuit and the ten-micromho element is connected to the terminals A and B along with its inherent capacitance component equal to the capacitance of capacitor C1. Each of the two conductance elements also has a similar capacitor connected in series therewith which in each case is exactly equal in capacitance to the stray capacitance inherent in its associated conductance element. It will be understood that by switching switch blades 3 of Vthese conductance units in various combinations, a complete compensated conductance decade may be achieved ranging from `zero to micrornhos in ten micromho steps.

lThe sum of the capacitances of the compensating condensers C1, C2, C3 and C4 is symbolically indicated as being a part of the constant capacitance Cmit being understood that these compensating capacitances together with the wiring capacitances are included in this constant capacitance CR along with any variable capacitance which may be connected between the terminals A and B for initial balance purposes. In the event that any one of the conductance elements is inductive instead of capacitive the compensating capacitor will :be omitted and compensation provided by bridging the standard conductance element with a capacitor of suitable size in accordance with well-known principles.

In the past the capacitance standard has been a somewhat simpler problem. Standard capacitors can be constructed quite easily With very low impurities. However, in order to secure precise adjustment for an inexpensive bridge standard by employing commercially available capacitors, it has been necessary to select capacitors which are slightly less than the nominal value and then pad them out with shunting capacitors to bring them to the exact nominal value. This means that on the average about half of the condensers commercially available have not been used for the construction of this type of standard. In accordance with this invention, however, these oversize capacitors may easily be employed to construct such a standard. For example, in Fig. 3, the capacitance standard cs comprises a plurality of standard capacitors nominally indicated as having the values of 100 micromicrofarads, 200 micromicrofarads, 300 micromicrofarads, and 400 micromicrofarads, respectively. Each of these standard capacitors is assumed to be oversize by an amount equal to the capacitance of its associated compensating capacitor. As an example, the 100-micromicrofarad standard capacitor is assumed to be oversize by an amount equal tothe capacitance C1. In the circuit arrangement shown in Fig. 3, one side of all of the standard capacitors as well as one side of all of the compensating capacitors is connected to the B terminal of the standard, while the terminals 6 of the switch blades 3' are all connected together to the A terminal of the standard. Switch blades 3 are caused to operate between switch points 4' and 5 connected to the standard capacitors and the compensating capacitors, respectively. It will be obvious that when any one of the switch blades 3' is moved between points 4 and 5 the net change in capacitance will be equal to the difference between the capacitance of the standard capacitor and that 0f its associated compensating capacitor. The standard capacitor in each case may be regarded as having inherently therein an admittance component which is undesired and which is eliminated in effect from the standard circuit by reason of the switching arrangement and the compensating capacitor. As in the case of the conductance standard, the sum of all of the compensating capacitors Ci, C2', Ca' and C4 together with the wiring capacitance is included as part of the constant capacitance Ca, schematically shown in Fig. 3. In alternating current bridge practice, the constant conductance and capacitance Ga and CR, respectively, are referred to as the residual conductance and capacitance of the standard. As previously stated, this residual conductance and capacitance are balanced out in the Maxwell type bridge by the balancing impedance Zh in the C-D arm of the bridge as shown in Fig. 1.

In using the standard shown in Fig. 3, the switch blades3 of the conductance standard and 3' of the capacitance standard may be manually switched in various combinations to suit the conductance and capacitance desired. For convenience it is desired to have them vary progressively in one-unit steps from Zero to ten for each of the decade units employed. One form of switching arrangement suitable for this purpose is shown in Fig. 4.

In Fig. 4 a part of the conductance standard of Fig. 3 is shown with two of the switch blades 3, their associated terminals 6 and their switch points 4 and 5. One of the conductance standard elements, the 40-micromho element, with its associated compensating capacitor C4 is also shown. The various switch blades 3 are shown actuated by suitable push-rods I3, I4 which are preferably made of insulating material. These push-rods rise on a series of properly cut cams 8, 9, I0 and II which are in turn mounted to a shaft 'I which may be turned by an index knob I2. As the index knob I2 is turned to the required conductance, the cams 8, 9, I0 and II are rotated to actuate their associated push-rods I3 and I4. In Fig. 4 the push-rods and the switch blades associated with cams 9 and II) have been deleted. Also in Fig. 4 the position of the switch is such as to set'the standard for 40 micromhos which corresponds to the schematic arrangement shown in Fig. 3. It will be noted that this is achieved by causing the switch blade 3 to contact switch point 4 which is caused by push-rod I4 being lifted by a swell on cam I I.

It will be understood that each of the cams have eleven positions corresponding to the conductance settings Zero to ten, inclusive. The positions on the respective cams which contain swells are more fully disclosed by the following table:

Fig. 5 discloses hcw the conductance decade standard elements together with their associated` compensating capacitors may be connected between the A, B standard terminals with a radial type switch commercially available. When using such radial type switches, it is preferable that the switch be of the non-snorting type, that is, the switch blade 3 does not bridge adjacent switch points. Should it bridge these points, it is obvious that certain positions would cause the blade to momentarily short-circuit the A and B terminals of the standard thereby greatly unbalancing the bridge and increasing the difliculty of balancing the bridge. It will be noted that as in Fig- 3, the conductance elements are connected in series with their compensating capacitors between the A and B terminals of the standard. The switch acts merely to short-circuit either the conductance element or the compensating capacitor, it being understood that the conductance element contains an undesired capacitance component equal to the capacitance of its corresponding compensating capacitor. As in Fig. 3 all the switch points4 of the various switches are connected to the B terminal of the standard while all the switch points -of the various vswitchesare connected to the A-terminal of the standard. When using this type of switch, instead of having only one No. 4 and one No. 5 switch point for each switch as in Fig. 3 and Fig, 4, apluralityof-such points must be provided. All the No. 4 points of eachswitch must bestrapped together and Yall the No.5 points must be strapped together as shown schematically in Fig. 5. As all of the standard elements Aand the compensating elements as well as the various switch elements bear-reference characters and numerals corresponding to those shown in Fig. 3, the operation Yof this switch is obvious from the previous description. -It need only be remembered that these four switches are ganged together on a common shaft 'I so that their brush rotors 3 all rotate simultaneously under control of a single knob I2 in a mannersimilar to the four cams in Fig. 4.

A capacitance decade switching arrangement for a capacitance decade standard is shown in F-ig. 6. The same general typeof switch structure is employed here as is employed for the circuit Iof Fig. 5. As in'Fig. 3-one side of each of the standard capacitors .as well as the `compensating capacitors is connected permanently to the B terminal of the standard. All of the switch blades 3 are connected permanently to the A terminal of the standard. For each position of the switch either the standard capacitance or the compensating capacitance is connected directly across the A and B terminals of the standard in just the same manner las previously -described for Fig. 3. The reference numerals and characters employed in this ligure also correspond with the corresponding parts of Fig. 3. While in the case of the conductance standard of Fig. 5 it was preferable that a non-shorting type switch be used, either a non-snorting or a shorting type may be used for the capacitance standard of Fig. 6. Because of the better Contact features of the shorting type switch it is preferred.

Two types of switch structures have already been described as sui-table for the practice of this invention. Figs. l and 8 disclose still another familiar type of switch structure which may be employed. In Fig. '7, for example, a conductance decade standard is shown utilizing a drum type switch. As in the previous figures the conductance standards are connected in series with their respective compensating capacitors and each of these series connections ispermanently connected between the A and B terminals of thestandard. As vis well known either the drum may rotate relative to stationary brushes or the brushesmay be moved with respect to stationary drums. In Fig. '7 it is intended that the drum strips I5,-I6, Il and I8, which are developments of strips which may be mounted on an insulating cylinder, are caused to rotate and thereby move past their contacting brushes 19,20, 2l, 22, 23, 24, 25 and. 26. Brushes-21 and '29 maintain connections between .strips I5 and Il and the A terminal of the standard while brushes 28 and30 maintain connection between strips IS and I8 to the B 1terminal ofthe standard. `It will be noted that the brushesA I9 to 2S, inclusive, are offset with respect .to their associated brushes. For example, brush I9 is offset so as to break connection with strip I5 before brush 2U will make contact with drum I5. This provides the non-shorting feature previously mentioned with respect to the other. switches. A

`suitable index strip 3l integrallymounted to` Gil .dex 52.

drum strip I5 carries numerals 0 to 10, inclusive, which correspond to the various settings of the decadeunits zero to micromhos, inclusive. This index strip l.3Irotates with the drum past a stationary-index 32 schematically illustrated in Fig. 7 as-an arrow Except for the different type of switch structure, the switching operation is identical with those previously described for the other type switches and further description is therefore unnecessary.

InFig. 8, the capacitance decade type of standard is disclosed utilizing a drum type switch similar to the drum type switch previously described for the conductance standard of Fig. 7 except that the non-snorting feature which is unnecessary for the capacitance standard is not shown. As in the case of the previously described capacitancestandard, one side of each of the standard and compensating capacitors is permanently connected to the'B-terminal of the standard, while each of the'drum strips 33, 34, 35 and l3G is permanently connected to theA terminal of the standard through brushes 45, 45,41 and 48, respectively. v,Each of the capacitors whether standard or compensating has connected to itsr free terminal a brush '.31 rto"44,'inclusive. The switching action of this vdrum type switch is identical with the switching-action of the other'types previously described. As in Fig, 7, so also in Fig. 8an index stripll isintegrally attached to drum strip 33 and carries the numerals 0 to 10, inclusive. This index strip is caused to move past astationary index schematically illustrated as an arrow 50.

In all of the previous iigures the invention has been applied exclusively to the construction of an admittance standard. However, the invention is equally Vapplicable to an impedance standard whichmay contain unwanted or undesired impedance components. This is illustrated for an inductance Ystandard in Fig. 9. When an inductance standard is constructed for measuring inductance,l it is usually used in a bridge of the comparison type in which case the standard would ordinarily be connected between the A and D corners, vwhile the A-Band B-C arms would beemployed as ratio arms of the bridge. The `unknown as in Fig. l would be between the C and D corners of the bridge. In.Fig..9 the switching is accomplished by .means of radial type switches of the type previously illustrated in Fig.

I5. In /Fig.r9 this type of. switch is shown ina developed form. VAll the switch blades 3 are V.ganged together and caused to move around the switch` simultaneously as previously .described for Fig. 45. :These .are actuated manually through a knob (not shown) which carries with it an in- This index 52 moves adjacent to a, stationary scale 5I inscribed from 0 to l0, inclusive.

fWhile 'this index strip 5I is shown developed straight in Fig. 9 it Will be understood that for a radial type switch it isnecessary that it be curved `or arcuate in form.

.an undesired lresistance component. For example, the-inductance element L1 may be expressed as having the complex form Ri-I-y'wLi. rFor each of the inductance elements the switch blade 3 is caused-to either short-circuit the standard in- -ductance element or its compensating resistor. VIfthe inductance element is to be included in standard circuit.

those skilled in the use of this type of alternat-.

. blade 3 is caused to short-circuit the inductance element leaving in the circuit the compensating resistor. Referring to Fig. 9 it will be seen that this will take place each time a switch blade 3 engages a switch point 5, while each time the blade 3 engages a switch point 4, the associated inductance element is switched into the circuit.

As in the previous gures it will be observed that with only four standard elements of l-millihenry, 2-rnil1ihenry, 3-millihenry and Llr-millihenry inductance, a complete decade with 1- millihenry steps from to 10 millihenries may be achieved. Also it will be observed that the total resistance component of the standard inductance will always be equal to the sum of the four compensating resistors R1, R2, R3 and R4. In this manner whether or not any particular inductance element is switched in or out of the circuit, the total resistance component of the entire standard is always the same.

It will be obvious that while several different types of specific switching structures have :been disclosed embodying the invention, the same principle is used in every case, that is to say, either the standard element containing the undesired components is switched into the circuit while its corresponding compensating element is switched out or the standard element is switched out while the compensating element is switched into the It will be appreciated by all ing current bridge that this invention greatly increases the speed with which measurements may be made. It will also be appreciated that various other speciiic types 0f switching structures may be employed to accomplish the same switching` scheme and therefore may be used to practice this invention. Each of these switching schemes should be regarded as equivalent to those specically herein disclosed. It may also be pointed out that the switching circuit disclosed in Fig. 3 for the conductance component gs may be interchange'd with the circuit disclosed for the capacitance component Cs but the circuits as selected for these two components in Fig. 3 are preferred. For low frequencies there would be little advantage in either circuit but at higher frequencies there is a real advantage in selecting them as illustrated schematically in Fig. 3. Should the circuit shown for the capacitance componentin Fig. 3 be used for the conductance component, the conductance elements would be open when `switched out of the circuit instead of being shortcircuited. Nevertheless, at higher frequencies the stray capacitance between the free terminal of the conductance element and various switch parts would couple the conductance element into the standard circuit which, without extra shielding, would introduce an uncontrollable error rendering the standard useless for accurate measurements. For this reason the short-circuiting arrangement for the conductance component gs is preferred as shown in Fig. 3, using non-shorting type switches as previously described.

For the capacitance component Cs a similar objection arises. conductance component be used for the capacitance component and the measurements be made at higher frequencies the contact resistance of the shorting switches may become an uncontrollable factor which would again render the, standard Should the circuit shown for the l0 useless for accurate measurements. Therefore, the switching scheme as shown in Fig. 3 for the capacitance component is preferred.

Attention is also called to the obvious fact that this invention may be applied to compensating a standard element for more than the one undesired component specifically disclosed herein, the additional compensating elements being connected in the same manner as the ones illustrated. This, however, is ordinarily unnecessary.

What is claimed is:

1. An adjustable compensated alternating current bridge standard of the decade type comprising a pair of terminals for said standard, a multiple position switching means, a plurality of standard circuit elements less than ten in number and having undesired circuit components inherent therein, one compensating element for reach standard element having components of the same kinds and magnitudes as the undesired inherent circuit components of its standard element, circuits connecting the standard elements, the compensating elements and the switching means to the pair of terminals, said circuits and switching means being adapted to selectively connect the standard elements in a plurality of predetermined and arbitrary combinations between said pair of terminals and to automatically substitute between said terminals the compensating element for each standard element not so connected.`

2. An adjustable compensated alternating current bridge standard of the decade type comprising a'pair of terminals for said standard, a plurality of standard circuit elements less than ten in number and each having undesired circuit components inherent therein, one compensating element for each standard element, said cornpensating element having components of the same kinds and magnitudes as the undesired inherent circuit components of its standard element, a multiple-position switch for each standard circuit element and its associated compensating element, circuits connecting the standard elements, the compensating elements and the switches to the pair of terminals, said circuits for each switch being adapted to alternately connect either the standard element or its associated compensating element in circuit between said pair of terminals, control means for operating all of said switches in a predetermined and arbitrary sequence whereby said standard elements are selectively connected in predetermined and arbitrary combinations between .said pair of terminals and said compensating elements are caused to replace between said terminals any corresponding standard element not so connected.

3. An adjustable compensated admittance standard of the decade type comprising a pair of terminals for said standard, a multiple-position switching means, a plurality of standard admittance elements less than ten in number and having undesired admittance components inhervent therein, one compensating admittance element for each standard, said compensating element having components of the same kinds and -magnitudes as the undesired inherent compobeing adapted to selectively connect the standard elements in a plurality of predetermined and arbitrary combinations between said pair of terminals and to vautomatically substitute between said terminals the compensating element for each standard element not so connected.

4. An adjustable compensated admittance standard ofthe decade type comprising a pair of terminals for said standard, a plurality of standard admittance elements less than ten in number and each having undesired admittance components inherent therein, one compensating admittance element for each standard element, said compensating element having components of the same kinds and magnitudes as the undesired inherent componentsof its standardr elementy a multiple-'position switch for each standard element and its associated compensating element, circuits connecting the standard elements, the compensating elements and the switches to the pair of terminals, said circuits for each switch being adapted to alternately connect either the standard element or its associated compensating element in circuit between said pair of terminals, control means for operating all of said switches in a predetermined and arbitrary sequence whereby said standard elements are selectively connected in predetermined and arbitrary combinations between said pair of terminals and said compensating elements are caused to replace between said' terminals any corresponding standard element not so connected.

An adjustable compensated conductance standard of the decade type comprising a pair of terminals for said standard, a multiple-position switching means, a plurality of standard conductance elements less than ten in number and having undesired admittance components inherent therein, one compensating element for each standard element having components of the same kinds and magnitudes as the undesired inherent components of its standard element, circuits connecting the standard conductance elements, the compensating elements and the switching means to the pair of terminals, said circuits and switching means being adapted to selectively connect the standard conductance elements in a plurality of predetermined and ar bitrary combinations between said pair of terminals and to automatically substitute between said terminals the compensating element for each standard conductancev element not so connected.

6. An adjustable compensatedv conductance standard of the decade type comprising a pair of terminals for said standard, a plurality of standard conductance elements less than ten iny number and each having undesired admittance components inherent therein, one compensating element for each standard element, said compensating element having components of the same kinds and magnitudes as the undesired inherent components of its standard element, a multiple-position switch for each standard element and its associated compensating element, circuits connecting the standard elements, the compensating elements and the switches to the pair of terminals, said circuits for each switch being adapted to alternately connect either the standard element or its associated compensating element in circuit between said pair of terminals, control means for operating all of said switches in a predetermined and arbitrary sequence, whereby said standardv conductance elements are selectively connected in predetermined and arbitrary combinations between said pair of terminals and said compensating elements are caused to replace between said terminals any corresponding Standard element not so connected. i

'7. An adjustable compensatedY conductance standard oi'theldecade type comprising' a pair of terminals for said standard, a plurality of-standard conductance elements less than ten in number and each having undesired admittance components inherent therein, one compensating element for each' standard element, said compensating element having components of the same kinds and magnitudes as the undesired inherent components oi its standard element, a multipleposition switch for each standard element and its associated compensating element, circuits connecting each standard element in a series circuit with its corresponding compensating element, other circuits connectingeach of said series circuits to its corresponding multiple-position switch, said switch and said other circuits being such as to alternately short-circuit either the standard conductance element or its associated compensating element, a circuit connecting all of said series circuits in parallel between said pair of terminals, control means for simultaneously operating all or said switches in a predetermined and arbitrary sequence, whereby said standard elements are selectively connected in predeter mined and arbitrary combinations between said pair of terminals and saidcompensating elements are caused'to replace between'said terminals any corresponding standard element not so connected.

8. An adjustable compensated capacitance standard ofthe decade type: comprising a pair of terminals for said standard; a'multiple-pcsition' switchingl means, a plurality of standard capacitance elements less than ten' in number andhavingundesired admittance components inherent therein, one compensating element for each standard element having components of the same kinds and magnitudes'as-'the undesired inherent admittance' components oi its standard element, circuits connecting` the standard clements, the compensating elements and the switching means to the pair of terminals, said circuits and switching means being adapted to selectively connect the standard elements in a plurality of predetermined and arbitrary combinations between said pair of terminals and to automatically substitute between saidv terminals thecompensating element for each standard element not so connected.

9. An adjustable compensated capacitance standard of the decade type comprising a pair of terminals for said standard, a pluralityv of standard capacitance elements less thanY ten innumber and each having undesired admittance components inherent therein, one compensating element for each standard element, said compensating element' having components of the same kinds and magnitudes as the undesired inherent admittance componentsfof its standardA element, a multiple-position switch for eachk standard capacitance element and its associated compensating element, circuits connecting the standard elements, the compensating elements and the switches to the pair of terminals, said circuits for each switch being adapted to alternately connect either the standard element or its associated compensating element in circuit between said pair of terminals, control means for operating all of said switches in a predetermined and arbitrary sequence, whereby said standard elements are selectively connected in predetermined and arbitrary combinations between said pair of terminals and said compensating elements are caused to replace between said terminals any corresponding standard element not so connected.

10. An adjustable compensated capacitance standard of the decade type comprising a pair of terminals for said standard, a plurality of standard capacitance elements less than ten in number and each having undesired admittance components inherent therein, one compensating element for each standard element, said compensating element having components of the same kinds and magnitudes as the undesired inherent admittance components of its standard element, a two-position switch for each standard element and its associated compensating element, said two-position switch comprising two switch points and a blade, a connection from each standard capacitance element to one of the switch points or" its associated two-position switch, a similar connection from each compensating element to the other switch point oi its associated two-position switch, a circuit connecting all of said switch blades to one of the terminals of said pair of terminals, another circuit connecting all of said standard and compensating elements to the other terminal of said pair of terminals, said switches and said connections to each standard and compensating element being adapted to alternately connect either the standard element or its associated compensating element in circuit between said pair of terminals, control means for operating al1 of said switches in a predetermined and arbitrary sequence whereby said standard elements are selectively connected in predetermined and arbitrary combinations between said pair of terminals and said compensating elements are caused to replace between said terminals any corresponding standard element not so connected.

11. An adjustable compensated inductance standard of the decade type comprising a pair of terminals for said standard, a multiple-position switching means, a plurality of standard inductance elements less than ten in number and having undesired circuit components inherent therein, one compensating element for each standard element having components of the same kinds and magnitudes as the undesired inherent circuit components of its standard element, circuits connecting the standard elements, the compensating elements and the switching means to the pair of terminals, said circuits and switching means being adapted to selectively connect the standard elements in a plurality of predetermined and arbitrary combinations between said pair of terminals and to automatically substitute between said terminals the compensating element for each standard element not so connected.

l2. An adjustable compensated inductance standard of the decade type comprising a pair of terminals for said standard, a plurality of standard inductance elements less than ten in number and each having undesired circuit components inherent therein, one compensating element for each standard element, said compensating element having components of the same kinds and magnitudes as the undesired inherent circuit. components of its standard element, a two-position switch for each standard circuit element andi its associated compensating element, circuits connecting the standard elements, the compensating: elements and the switches to the pair of termi-- nals, said circuits for each switch being'adapted to alternately connect either the standard element or its associated compensating element in circuit between said pair of terminals, control means for operating all of said switches in a predetermined and arbitrary sequence whereby said standard elements are selectively connected in predetermined and arbitrary combinations bctween said pair of terminals and said compensating elements are caused to replace between said terminals any corresponding standard element not so connected.

13. An adjustable compensated inductance standard of the decade type comprising a pair of terminals for said standard, a plurality of standard inductanoe elements less than ten in number and each having undesired circuit components inherent therein, one compensating element for each standard element, said compensating element having components of the same kinds and magnitudes as the undesired inherent circuit components of its standard element, a two-position switch for each standard element and its associated compensating element, a' circuit connecting the standard elements and the compensating elements in series between said pair of terminals, circuits connecting each two-position switch to its associated standard inductance and compensating element, said circuits for each switch being adapted to alternately short-circuit either the standard element or its associated compensating element in circuit between said pair of terminals, control means for operating al1 of said switches in a predetermined and arbitrary sequence whereby said standard elements are selectively connected in predetermined and arbitrary combinations between said pair of terminals and said compensating elements are caused to replace between said terminals any ycorresponding standard element not so connected.

HENRY T. WILHELM.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Hague, Alternating Current Bridge Methods; Pitman Publishing Co., New York, 1938.

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