CN100575960C

CN100575960C - Three measuring range potential difference meter

Info

Publication number: CN100575960C
Application number: CN200710067798A
Authority: CN
Inventors: 方勇; 张春雷; 程军; 李顺定
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-04-03
Filing date: 2007-04-03
Publication date: 2009-12-30
Anticipated expiration: 2027-04-03
Also published as: CN101034103A

Abstract

A kind ofly be used for the three measuring range potential difference meter that dc voltage measurement has three measuring disk, its first step disc is made up of measuring disk and bracket panel, second step disc constitutes measuring disk by 11 * 11 Ω ring resistance nets, constitute bracket panel by 10 0.5 Ω resistance, the 3rd dish is two slide wire discs, is connected with lead between two measuring disk and measurement slip, does not switch by switch, when being measured, potential difference meter do not exist variation and thermoelectric potential influence, resolution to reach 0.1 μ V; And saved the replacement dish of first and second step disc.

Description

Three measuring range potential difference meter

Technical field

The present invention relates to instrument that DC voltage is measured.

Background technology

Current for the potential difference meter that three measuring disk are arranged, in the connection between three measuring disk, telophragma generally adopts switch to switch, and so just produces the variation of contact resistance, brings restriction to resolution.In order to overcome this problem, generally adopt big brush with the increase contact area, and adopt a silver-colored carbon/carbon-copper composite material; Patent No. ZL200520101772.0 has announced that the potential difference meter that three measuring disk are arranged solves the variation new method of switch contact resistance, its first, second step disc respectively has measuring disk, replacement dish and bracket panel are formed, measuring disk is identical with resistance on the replacement dish, resistance of the every increase of measuring disk, the replacement dish just reduces same resistance, because first step disc was declined at 0 o'clock, the total resistance of circuit changed when second step disc was put different indicating value, first step disc was put at 0 o'clock, the total resistance of circuit was constant when second step disc was put different indicating value, first step disc removes for this reason measuring disk, outside the replacement dish, increased bracket panel distinguish step disc put 0 and the circuit of declining 0 two kinds of situations connect, second step disc has also increased bracket panel, has 10 resistance to insert or cut out several resistance respectively above and makes the total resistance of circuit constant.Two measuring disk connect the back and are connected two with slide wire disc and measure between terminals, brush on the step disc switch is got rid of measured outside the loop, do not exist switch to switch between the resistance that three are measured on short, also just do not produce variation; Because first, second step disc all has the replacement dish, has increased first, second step disc switch and has been welded with the number of plies of resistance, thereby increased the volume of instrument, also make switch and apparatus structure become complicated.

Summary of the invention

The objective of the invention is to design a kind of three measuring range potential difference meter that three measuring disk are arranged, telophragma does not switch by switch in the connection of three measuring disk, first, second step disc cancellation replacement dish, and three range conversions are arranged, make resolution reach 0.1 μ V.

Technical scheme of the present invention is taked like this: electric current from the positive pole of potential difference meter 1.5V working power through the setting resistance R of the resistance measurement network on two step discs and the two slide wire disc to 463 Ω _NAnd the lockable adjustable resistance R of 0～0.7 Ω _P2, again through 0～105 Ω adjustable resistance R _P1Get back to the negative pole of working power and form potential difference meter work loop; Standard cell E _NAnodal through being connected to the double-point double-throw switch K of galvanometer G between two normally closed contacts ₂To setting up resistance R _NAnd lockable adjustable resistance R _P2, process 100K Ω current-limiting resistance R is to standard cell E again _NNegative pole is formed the potential difference meter standard loop; Be used to connect measured " U _X" two terminals, behind the resistor network of anodal terminal through two measuring disk and two slide wire discs, again through being connected to the double-point double-throw switch K of galvanometer G between two normally closed contacts ₂Form potential difference meter to the negative pole terminal and measure the loop; First step disc has measuring disk I, it has 0,1,2 ... 22 totally 23 gears, except that between 0,1 contact, directly connecting, connect one of 10 Ω resistance between all the other each grade contacts, other has bracket panel I ' and bracket panel I "; the brush of bracket panel I ' and bracket panel I " brush be connected bracket panel I ' and bracket panel I with lead " 0 contact isolated, all the other all contacts connect with lead; The 3rd dish is two slide wire discs, two slip thickness materials are identical, resistance all is 0.5 Ω, wherein one is measurement slip III, another root is auxiliary slip III ', and the index dial of two slide wire discs divides 10 big lattice, and the resistance of every big lattice correspondence is 0.05 Ω, every big lattice divide 10 little lattice, and the brush on two slide wire resistances is with a slice metallic brush sheet; Second step disc is made up of measuring disk II and bracket panel II ', measuring disk II has 0,1,2 ... 10 totally 11 gears have the resistance of 11 11 Ω, the 1st resistance R above ₁One end welds the 2nd resistance R ₂One end, resistance R ₂The other end welds the 3rd resistance R ₃One end ... welding successively, the 10th resistance R ₁₀The other end and the 11st resistance R ₁₁An end connects is circuit node A, the 11st resistance R ₁₁The other end and the 1st resistance R ₁The other end be connected in 0 point of measuring slip III, 0 that measures slip III is circuit node B, resistance R ₁With resistance R ₂Tie point be connected resistance R through 20 Ω resistance with the 1st contact ₂With resistance R ₃Tie point be connected resistance R through 12 Ω resistance with the 2nd contact ₃With resistance R ₄Tie point be connected resistance R through 6 Ω resistance with the 3rd contact ₄With resistance R ₅Tie point be connected resistance R through 2 Ω resistance with the 4th contact ₅With resistance R ₆Tie point be connected resistance R with the 5th contact ₆With resistance R ₇Tie point be connected resistance R with the 6th contact ₇With resistance R ₈Tie point be connected resistance R through 2 Ω resistance with the 7th contact ₈With resistance R ₉Tie point be connected resistance R through 6 Ω resistance with the 8th contact ₉With resistance R ₁₀Tie point be connected resistance R through 12 Ω resistance with the 9th contact ₁₀With resistance R ₁₁Tie point be connected resistance R through 20 Ω resistance with the 10th contact ₁With resistance R ₁₁The Node B that connects o'clock is connected with 0 contact through 30 Ω resistance, is the resistance of 10 * 0.5 Ω on the bracket panel II ' of second step disc; Bracket panel II ' the 10th contact and 20 Ω range transfer resistance R ₁₄An end be connected in parallel in the positive pole of potential difference meter working power, 0 contact of bracket panel II ' connects bracket panel I " 0 contact; the brush of bracket panel II ' connects bracket panel I " other contact except that 0 contact, the brush of measuring disk II connects the brush and bracket panel I of bracket panel I ' after through 190 Ω resistance " the tie point that is connected of brush; other contacts connection measuring disk I 22nd contact of bracket panel I ' except that 0 contact; measuring disk I the 0th; 1 contact is connected with node A; 0 contact of bracket panel I ' is connected with Node B after through 220 Ω resistance, measurement slip III the 10th o'clock is through 84.5 Ω resistance R ₁₃Back and 1800 Ω range transfer resistance R ₁₆An end be connected range selector K ₁* 10 range contacts, range transfer resistance R ₁₆The other end and range transfer resistance R ₁₅An end connect range selector K ₁* 1 range contact, range transfer resistance R ₁₅The other end and range transfer resistance R ₁₄The other end connect 162 Ω auxiliary resistance R ₁₇Back and range selector K ₁* 0.1 range contact connects range selector K ₁Normally closed contact connect to set up resistance R _NNoble potential one end; Be used to connect measured " U _X" two measure terminal, anodally be connected with measuring disk I brush, negative pole passes through double-point double-throw switch K ₂The back is connected with auxiliary slip III '.

By above technical scheme, first step disc need not the replacement dish, does not all have resistance on the two-layer bracket panel, can be contained in the switch nexine, and measuring disk I is contained in the switch skin; Second step disc need not the replacement dish, 15 ° of angles are rotated in each stepping of switch, and each 11 contact of the bracket panel II ' of second step disc and measuring disk II are distributed in same one deck of switch, and resistance is contained in the switch skin, unload when resistance is overproof and load onto easily, this brings convenience for debugging and maintenance; Make potential difference meter simple in structure like this, volume-diminished has also reduced production cost; On the total circuit partly in potential difference meter internal measurement loop and work loop, there is not switch, so there is not variation influence, when three measuring disk resets of potential difference meter, the potential difference meter working current converges at the B point, what zero potential was measured is B point current potential, in measuring the loop, do not exist working current to flow through lead resistance, so this potential difference meter zero potential is very little; Two slide wire resistance thickness materials are identical, and the thermoelectrical potential equal and opposite in direction of generation, direction are opposite, so this potential difference meter thermoelectrical potential is also very little, therefore, when * 0.1 range, resolution were 0.1 μ V, this potential difference meter is measured also can obtain good repeatability.

Description of drawings

Accompanying drawing is a principle of the invention circuit.

Embodiment

Among the figure, measuring disk II is 11 the 11 end to end resistance rings of Ω between node A and Node B, when measuring disk II puts " 5 " or puts " 6 ", the brush of measuring disk II is to being that 5 11 Ω resistance are in parallel with 6 11 Ω resistance between the Node B, back in parallel resistance is 30 Ω to the maximum, other contact of measuring disk II all is connected to 30 Ω to the resistance value between the Node B and is as the criterion, and corresponding point directly are connected on 5,6 contacts and the resistance ring; When measuring disk II put " 4 " or puts " 7 ", the brush of measuring disk II was to being that 4 11 Ω resistance are in parallel with 7 11 Ω resistance between the Node B, and back in parallel resistance is 28 Ω, so 4,7 contacts are connected with corresponding point on the resistance ring through 2 Ω resistance; When measuring disk II put " 3 " or puts " 8 ", the brush of measuring disk II was to being that 3 11 Ω resistance are in parallel with 8 11 Ω resistance between the Node B, and back in parallel resistance is 24 Ω, so 3,8 contacts are connected with corresponding point on the resistance ring through 6 Ω resistance; When measuring disk II put " 2 " or puts " 9 ", the brush of measuring disk II was to being that 2 11 Ω resistance are in parallel with 9 11 Ω resistance between the Node B, and back in parallel resistance is 18 Ω, so 2,9 contacts are connected with corresponding point on the resistance ring through 12 Ω resistance; When measuring disk II set or when putting " 10 ", the brush of measuring disk II is to being that 1 11 Ω resistance is in parallel with 10 11 Ω resistance between the Node B, and back in parallel resistance is 10 Ω, so 1,10 contacts are connected with corresponding point on the resistance ring through 20 Ω resistance; When measuring disk II reset, the brush of measuring disk II is between the Node B being the connections of 30 Ω resistance.

The first step disc reset, second step disc are put " n " (n=0,1,2,3 ... 10) time, the brush of bracket panel I ' is that two resistance that are both 220 Ω are in parallel with resistance value between the Node B, is 110 Ω therefore.

First step disc is put " n " (n=0,1,2,3 ... 22), during the second step disc reset, the brush of bracket panel I ' is that two resistance that are both 220 Ω are in parallel with resistance value between the Node B, is 110 Ω therefore.

When first, second step disc during not reset, except that second step disc was put " 10 ", the brush of bracket panel I ' and the calculating of the resistance value between the Node B need be carried out triangle-star conversion.

During the second step disc set, the calculating of resistance value between the brush of bracket panel I ' and the Node B: establish resistance (R ₂+ R ₃+ ... + R ₉+ R ₁₀) and resistance R ₁₁The both sides resistance is equivalent to resistance r ₁, resistance R ₁₁With resistance R ₁The both sides resistance is equivalent to resistance r ₁' resistance (R ₂+ R ₃+ ... + R ₉+ R ₁₀) and resistance R ₁The both sides resistance is equivalent to resistance r ₁", be equivalent to resistance r ₁, r ₁', r ₁" intersection point is Q ₁:

R then ₁=(R ₂+ R ₃+ ... + R ₉+ R ₁₀) * R ₁₁/ (R ₁+ R ₂+ ... + R ₁₀+ R ₁₁)=9 * 11 * 11/11 * 11 Ω=9 Ω

r ₁’＝R ₁×R ₁₁/(R ₁+R ₂+…+R ₁₀+R ₁₁)＝11×11/11×11Ω＝1Ω

r ₁”＝(R ₂+R ₃+…+R ₉+R ₁₀)×R ₁/(R ₁+R ₂+…+R ₁₀+R ₁₁)＝9×11×11/11×11Ω＝9Ω

Resistance value equals (210 Ω+r between the brush of bracket panel I ' and the Node B ₁) * (190 Ω+20 Ω+r ₁")/(2 * 219) Ω+r ₁'=219 Ω/2+1 Ω=109.5 Ω+1 Ω=110.5 Ω

When second step disc is put " 2 ", the calculating of resistance value between the brush of bracket panel I ' and the Node B: establish resistance (R ₃+ R ₄+ ... + R ₉+ R ₁₀) and resistance R ₁₁The both sides resistance is equivalent to resistance r ₂, resistance R ₁₁With resistance (R ₁+ R ₂) the both sides resistance is equivalent to resistance r ₂' resistance (R ₃+ R ₄+ ... + R ₉+ R ₁₀) and resistance (R ₁+ R ₂) the both sides resistance is equivalent to resistance r ₂", be equivalent to resistance r ₂, r ₂', r ₂" intersection point is Q ₂:

R then ₂=8 Ω r ₂'=2 Ω r ₂"=16 Ω

Resistance value equals (210 Ω+r between the brush of bracket panel II ' and the Node B ₂) * (190 Ω+12 Ω+r ₂")/(2 * 218) Ω+r ₂'=218 Ω/2+2 Ω=109 Ω+2 Ω=111 Ω.

In like manner, when second step disc was put " 3 ", resistance value was 111.5 Ω between the brush of bracket panel I ' and the Node B,

When second step disc was put " 4 ", resistance value was 112 Ω between the brush of bracket panel I ' and the Node B,

When second step disc was put " 5 ", resistance value was 112.5 Ω between the brush of bracket panel I ' and the Node B,

......

When second step disc was put " 10 ", resistance value was 115 Ω between the brush of bracket panel I ' and the Node B.Because the every stepping of measuring disk II increases by 0.5 Ω, so the every stepping of bracket panel II ' reduces by 0.5 Ω, makes the total resistance of circuit constant; When the first or second step disc reset, the brush of bracket panel I ' and the resistance value between the Node B are 110 Ω, and 10 * 0.5 Ω resistance of bracket panel II ' all enter circuit.

* 10, * during 1 range, the 10th of bracket panel II ' is 115.5 Ω through Node B to the resistance between the 10th of the measurement slip III, adds 84.5 Ω resistance R ₁₃Totally 200 Ω, the 10th of bracket panel II ' through resistance R ₁₄, resistance R ₁₅Resistance also be 200 Ω, resistance R ₁₆Changed the position in two ranges, the circuit resistance is constant, and when * 0.1 range, the resistance that parallel connection reduces is by series connection 162 Ω resistance R ₁₇Come the holding circuit resistance constant.

When * 10 ranges, the 10th of bracket panel II ' is 115.5 Ω through Node B to the resistance between the 10th of the measurement slip III, adds 84.5 Ω resistance R ₁₃Totally 200 Ω, the 10th of bracket panel II ' through resistance R ₁₄, resistance R ₁₅To resistance R ₁₆To range selector K ₁* 10 range contacts are 2000 Ω, and the electric current the during standardization of potential difference meter working current is 2.2mA, and the 2mA electric current flows through the 10th the process Node B of bracket panel II ' to range selector K ₁* 10 range contacts, 0.2mA flows through resistance R ₁₄, resistance R ₁₅, resistance R ₁₆To range selector K ₁* 10 range contacts; Measuring disk II puts " n " (n=1,2,3 ... 9) time, I is to being equivalent to resistance r for the brush of bracket panel I ' process measuring disk _n, r _n', r _n" intersection point Q _n(n=1,2,3 ... 9) with through 190 Ω resistance R ₁₂To intersection point Q _nResistance value equates that when measuring disk II put " 10 ", I was to the resistance value of node A and through 190 Ω resistance R for the brush of bracket panel I ' process measuring disk ₁₂Resistance value to node A all equals 210 Ω, so flow through measuring disk I and 190 Ω resistance R ₁₂Electric current respectively be 1mA.

For ten one the 11 Ω end to end resistance rings of measuring disk II between node A and Node B, resistance R during measuring disk II set ₁To be all 11 Ω resistance in parallel with 10 resistances, flows through resistance R ₁₁Electric current be 1/11mA, the voltage U between node A and the Node B _AB=1/11 * 11mV=1mV; Resistance (R when measuring disk II puts " 2 " ₁+ R ₂) to be all 11 Ω resistance in parallel with 9 resistances, flows through resistance R ₁₁Electric current be 2/11mA, the voltage U between node A and the Node B _AB=2/11 * 11mV=2mV; (n=1,2,3 when in like manner, measuring disk II puts " n " ... 10) voltage U between resistance nodes A and the Node B _AB=n mV; When measuring disk I and measuring disk II reset, electric current is without resistance R ₁₁, U _AB=0mV; When not reset of measuring disk I, the electric current that flows through measuring disk I is superimposed upon on the measuring disk II at the 10mV voltage between node A, the B, replaces the resistance between 0,1 contact, and during the working current standardization, first step disc is put n ₁, second step disc puts n ₂, the 3rd dish puts n ₃(n ₃Represent big lattice indicating value) " U at this moment _x" two measure that voltage is between terminal:

U _x＝1×10n ₁+1×n ₂/11×11+2×0.05n ₃(mV)

＝10n ₁+n ₂+0.1n ₃ (mV)

During * 1 range, the 10th of bracket panel II ' through Node B to the resistance R of having connected of 115.5 Ω resistance between the 10th of the measurement slip III ₁₃, resistance R ₁₆Sum is 2000 Ω and its parallel resistor R ₁₄, resistance R ₁₅Sum is 200 Ω, and the 0.2mA electric current flows through the 10th the process Node B of bracket panel II ' to measuring slip III the 10th point, when first step disc is put n ₁, second step disc puts n ₂, the 3rd dish puts n ₃(n ₃Represent big lattice indicating value) " U at this moment _x" two measure that voltage is between terminal:

U _x＝1n ₁+0.1n ₂+0.01n ₃ (mV)

During * 0.1 range, the 10th of bracket panel II ' through Node B to the resistance R of having connected of resistance between the 10th of the measurement slip III ₁₃, resistance R ₁₆And resistance R ₁₅Sum is 2180 Ω and its parallel resistor R ₁₄Be 20 Ω, resistance value ratio is 109 times, so 2.18mA current flowing resistance R ₁₄, the 0.02mA electric current flows through the 10th the process Node B of bracket panel II ' to measuring slip III the 10th point, when first step disc is put n ₁, second step disc puts n ₂, the 3rd dish puts n ₃(n ₃Represent big lattice indicating value) " U at this moment _x" two measure that voltage is between terminal:

U _x＝0.1n ₁+0.01n ₂+0.001n ₃ (mV)

The 3rd dish n ₃1 μ V be 1 big scale value, every little lattice are 0.1 μ V.

The electromotive force of every series-produced standard cell disperses, and between 1.0188V～1.0196V, standardized working current is 2.2mA, therefore sets up resistance R _NGet 463 Ω, add the lockable adjustable resistance R of 0～0.7 Ω _P2, variation range that can the coverage criteria cell emf.

Electromotive force was about 1.65V when dry cell was new, had used electromotive force old just to descend, and can both make the working current of potential difference meter be adjusted to standardization in order to make dry cell under new, former affection condition, got adjustable resistance R _P1Be 0～105 Ω.

Normalized current is to determine like this: 200mV standard signal voltage is pressed polarity and potential difference meter " U _x" two measure terminal and connect, it is identical with the standard signal magnitude of voltage that potential difference meter respectively coils total indicating value, double-point double-throw switch K ₂Throw to the left side, regulate adjustable resistance R _P1, make galvanometer G nulling; Again with double-point double-throw switch K ₂Throw to the right, regulate adjustable resistance R _P2, make galvanometer G nulling, at this moment adjustable resistance R _P2Locking; When using from now on, potential difference meter is standard according to this.

Claims

A kind of three measuring range potential difference meter that three measuring disk are arranged, electric current from the positive pole of potential difference meter 1.5V working power through the setting resistance R of the resistance measurement network on two step discs and the two slide wire disc to 463 Ω _NAnd the lockable adjustable resistance R of 0～0.7 Ω _P2, again through 0～105 Ω adjustable resistance R _P1Get back to the negative pole of working power and form potential difference meter work loop; Standard cell E _NAnodal through being connected to the double-point double-throw switch K of galvanometer G between two normally closed contacts ₂To setting up resistance R _NAnd lockable adjustable resistance R _P2, process 100K Ω current-limiting resistance R is to standard cell E again _NNegative pole is formed the potential difference meter standard loop; Be used to connect measured " U _X" two terminals, behind the resistor network of anodal terminal through two measuring disk and two slide wire discs, again through being connected to the double-point double-throw switch K of galvanometer G between two normally closed contacts ₂Form potential difference meter to the negative pole terminal and measure the loop; It is characterized in that first step disc has measuring disk I, it has 0,1,2 ... 22 totally 23 gears, except that between 0,1 contact, directly connecting, connect one of 10 Ω resistance between all the other each grade contacts, other has bracket panel I ' and bracket panel I "; the brush of bracket panel I ' and bracket panel I " brush be connected bracket panel I ' and bracket panel I with lead " 0 contact isolated, all the other all contacts connect with lead; The 3rd dish is two slide wire discs, two slip thickness materials are identical, resistance all is 0.5 Ω, wherein one is measurement slip III, another root is auxiliary slip III ', and the index dial of two slide wire discs divides 10 big lattice, and the resistance of every big lattice correspondence is 0.05 Ω, every big lattice divide 10 little lattice, and the brush on two slide wire resistances is with a slice metallic brush sheet; Second step disc is made up of measuring disk II and bracket panel II ', measuring disk II has 0,1,2 ... 10 totally 11 gears have the resistance of 11 11 Ω, the 1st resistance R above ₁One end welds the 2nd resistance R ₂One end, resistance R ₂The other end welds the 3rd resistance R ₃One end ... welding successively, the 10th resistance R ₁₀The other end and the 11st resistance R ₁₁An end connects is circuit node A, the 11st resistance R ₁₁The other end and the 1st resistance R ₁The other end be connected in 0 point of measuring slip III, 0 that measures slip III is circuit node B, resistance R ₁With resistance R ₂Tie point be connected resistance R through 20 Ω resistance with the 1st contact ₂With resistance R ₃Tie point be connected resistance R through 12 Ω resistance with the 2nd contact ₃With resistance R ₄Tie point be connected resistance R through 6 Ω resistance with the 3rd contact ₄With resistance R ₅Tie point be connected resistance R through 2 Ω resistance with the 4th contact ₅With resistance R ₆Tie point be connected resistance R with the 5th contact ₆With resistance R ₇Tie point be connected resistance R with the 6th contact ₇With resistance R ₈Tie point be connected resistance R through 2 Ω resistance with the 7th contact ₈With resistance R ₉Tie point be connected resistance R through 6 Ω resistance with the 8th contact ₉With resistance R ₁₀Tie point be connected resistance R through 12 Ω resistance with the 9th contact ₁₀With resistance R ₁₁Tie point be connected resistance R through 20 Ω resistance with the 10th contact ₁With resistance R ₁₁The Node B that connects o'clock is connected with 0 contact through 30 Ω resistance, is the resistance of 10 * 0.5 Ω on the bracket panel II ' of second step disc; Bracket panel II ' the 10th contact and 20 Ω range transfer resistance R ₁₄An end be connected in parallel in the positive pole of potential difference meter working power, 0 contact of bracket panel II ' connects bracket panel I " 0 contact; the brush of bracket panel II ' connects bracket panel I " other contact except that 0 contact, the brush of measuring disk II connects the brush and bracket panel I of bracket panel I ' after through 190 Ω resistance " the tie point that is connected of brush; other contacts connection measuring disk I 22nd contact of bracket panel I ' except that 0 contact; measuring disk I the 0th; 1 contact is connected with node A; 0 contact of bracket panel I ' is connected with Node B after through 220 Ω resistance, measurement slip III the 10th o'clock is through 84.5 Ω resistance R ₁₃Back and 1800 Ω range transfer resistance R ₁₆An end be connected range selector K ₁* 10 range contacts, range transfer resistance R ₁₆The other end and 180 Ω range transfer resistance R ₁₅An end connect range selector K ₁* 1 range contact, range transfer resistance R ₁₅The other end and 20 Ω range transfer resistance R ₁₄The other end connect after through 162 Ω resistance R ₁₇With range selector K ₁* 0.1 range contact connects range selector K ₁Normally closed contact connect to set up resistance R _NNoble potential one end; Be used to connect measured " U _X" two measure terminal, anodally be connected with measuring disk I brush, negative pole passes through double-point double-throw switch K ₂The back is connected with auxiliary slip III '.