CN1793974A - Direct current petential difference meter of bimeasuring range conversion using conversion branch - Google Patents

Abstract

A two-range switching DC potential difference meter applying transposition branch is prepared as using 20x 2 omega as the first measuring disc, 10x 0.22 omega as the second measuring disc and 0-2.42 omega slide wire disc as the third measuring disc; using conductive wire to connect two measuring end buttons directly to three measuring discs to exclude contact resistance and variation as well as thermo voltage from measuring-stepping switch out of measuring result and to carry out compensation by large negative potential if zero potential is big; applying two resistances of 50 omega and 450 omega to execute range changeover by utilizing transposition branch.

Description

A kind of DC potentiometer that adopts the conversion of branch two ranges

Technical field

The present invention relates to measure the instrument of DC voltage.

Background technology

The potential difference meter of current production, when measuring disk has three when above, measure between terminal for two and have switch contact resistance and variation, therefore, even working current is little of 0.1mA, the silver-bearing copper compound substance is not only adopted in the brush of switch and contact, contact area is also done very greatly, variation is brought influence when reducing measuring switch stepping switching, this just makes the instrument volume become big, nonetheless, can not make potential difference meter resolution little to 0.1 μ v, the thermoelectrical potential that also has switch in addition with contact variable thermoelectric potential influence.

Summary of the invention

The problem to be solved in the present invention is, when the step switch that is used for measure portion in the potential difference meter has five, and contact resistance and variation that the measuring switch stepping is switched, the switch thermoelectrical potential does not influence measurement result, makes instrumental resolution reach 0.1 μ v.When range was changed, range conversion was the resistance that one digit number or two figure places are taken advantage of 10 integral number power with resistance.

Technical scheme of the present invention is such: working current is regulated resistance R P ₁, RP ₂, standardization time sampling is connected in the potentiometer circuit with setting resistance and metering circuit; It is characterized in that measuring partly with two slide wire disc of two step discs, first step disc is by respectively having 20 * 2 Ω I measuring disk and I ' replacement dish to form, second step disc is by the II that 10 * 0.22 Ω are respectively arranged " the replacement dish forms; this advances two brushes of dish and interconnects, the promptly two slide wire discs of the 3rd dish, and two resistance wire resistances are identical; be all 0～2.42 Ω; its indicating value index dial has 11 big lattice, and the corresponding resistance of every lattice is 0.22 Ω, and 110 little lattice are arranged; Another root of work III measuring disk slip is made III ' replacement dish slip in two slips, and the brush on two slide wire resistances of this dish is from getting off with a slice metal upper punch; I ' replacement is coiled at the 20th and is connected 8.58 Ω resistance R ₁The back is coiled at the 10th with II ' replacement and is connected, 0 resistance R that connects 4.22 Ω of II measuring disk ₂The back is connected with 0 of I measuring disk, and this coils the 20th connection III measuring disk does not hold, and it is 507.58 Ω resistance R that III ' replacement slip top connects a resistance ₃The back is connected with 0 on I ' replacement dish; I ' replacement dish brush and 50 Ω resistance r ₁Be connected in parallel on the metering circuit positive pole, resistance r ₁450 Ω resistance r connect ₂, tie point meets double-point double-throw switch K _1-1* 0.1 range contact, resistance r ₂Measure brush with I and be connected in the single-pole double-throw switch (SPDT) * 1 range contact, the normally closed contact of single-pole double-throw switch (SPDT) is connected the metering circuit negative pole;

By above technical scheme, the measuring disk that two step discs and slide wire disc are used for measure portion connects with lead, contact resistance and variation, not in measuring the loop, the just potential difference meter work loop of influence always hinders, because total resistance resistance is very big, so variation can be ignored, the thermoelectric potential influence of several μ V be supply voltage, supply voltage be the volt, how many μ V are thermoelectrical potential be, both differ 10 the 6 power orders of magnitude, and therefore influence can be ignored, even so, even contact resistance variation and thermoelectrical potential are big to the degree of can not ignore, can be by standard is adjusted RP ₂Resistance obtain revising, zero potential can increase between slide wire disc and the I measuring disk lead resistance to be revised, Just because of this, reduced requirement to switch, after adopting small-sized measurement step switch, it is many that whole instrument overall dimensions reduce, and makes the measurement data of instrument obtain good repeatability.Because the range conversion is that one digit number or double figures are taken advantage of 10 integral number power with resistance, available interim standard resistance is revised with resistance range conversion, has improved the accuracy of potential difference meter range ratio.

Description of drawings

Accompanying drawing is a principle of the invention circuit.

Embodiment

In the drawings, by " U _x" anodal through each measuring disk, pass through change-over switch K again ₂To " U _x" negative pole is to measure the loop, by positive source through measuring step switch to setting resistance R N and temperature compensation dish RP ₄, arrive resistance R then ₀, adjustable resistance RP ₃, RP ₂And RP ₁After, getting back to power cathode is the work loop, anodal through change-over switch K from standard cell EN ₂, to setting up resistance R N and temperature compensation dish RP ₄, be standard loop to the standard cell negative pole again.When five dishes are all thrown " 0 ", left side resistance equals 55 Ω between two brushes of first step disc, and the right resistance equals 550 Ω, and total resistance is 50 Ω between two brushes of first step disc, therefore 10/11 on the left side of total current flows between two brushes of first dish, and 1/11 flows on the right.

When * 1 range, between two brushes of first step disc all-in resistance by 10 times to self resistance resistance r ₁With resistance r ₂Therefore parallel connection flows through that total current is 10/11 of a potential difference meter working current between two brushes of first step disc, flows through resistance r ₁With resistance r ₂Electric current be 1/11 of potential difference meter working current; When * 0.1 range, resistance resistance in series r between two brushes of first step disc ₂After, with 10 times to resistance r ₁Resistance and resistance r ₁Parallel connection makes resistance r ₁On electric current be that electric current between two brushes of 10/11, the first step disc of potential difference meter working current is 1/11 of a potential difference meter working current, so electric current is reduced to 1/10 on the measuring disk, the amount of making limit is reduced to 1/10.

5.5mA working current is to determine like this, at " U _x" two of two ends measure terminals and connect normal voltage near full scale, K switch by polarity ₂Throw to the left side, the measuring disk indicating value is identical with standard voltage value, regulates resistance R P by regulating working current ₁And RP ₂, make the galvanometer nulling, again with K switch ₂Throw to the right, sampling is 185 Ω with the resistance of setting up resistance R N, and 0～0.5 Ω adjustable resistance RP has connected ₃, regulate RP ₃, make galvanometer nulling once more, again with K switch ₂Throw to the left side, regulate RP ₂Make the galvanometer nulling, again with K switch ₂Throw to the right and regulate RP ₃Make the galvanometer nulling, when switch points to the left side and the right and do not regulate the equal nulling of galvanometer, the standardization of potential difference meter working current is described, promptly set up ohmically pressure drop and equate, at this moment with RP with the electromotive force of unsaturated standard cell EN ₃Locking, this potential difference meter is from now on just as standard.After the working current standardization, the I measuring disk is thrown n when * 1 range ₁, the II measuring disk is thrown n ₂, the III measuring disk is thrown n ₃, the IV measuring disk is thrown n ₄, K switch ₂Throw to the left side, be positioned at this moment that voltage is between two terminals of measurement

Ux＝50/11×0.22n ₂+50/11×(4+0.22)+50/11×2n ₁-5/11×(20-n ₁)×2-5/11×(10-n ₃)×0.22(mv)

＝n ₂+200/11+1+100n ₁/11-200/11+10n ₁/11-1+0.1n ₃(mv)

＝10n ₁+n ₂+0.1n ₃(mv)

More than the resistance of III dish calculate n by big lattice ₃Be expressed as an integer and add the radix point back and have one-bit digital to refer to little lattice in the big lattice, little lattice indicating value unit is 10 μ V during * 1 range, is 1 μ V when * 0.1 range.

Convenient in order to measure, the III dish has a big lattice negative potential.

Circuit work power is 1.5V, can work in the 1.4V-1.65V scope in order to make operating supply voltage, gets fixed resistance R ₀Equal 23 Ω, adjustable resistance PR ₁=20 * 2.2 Ω, PR ₂Be to regulate in 0～2.4 Ω scope.

Double-point double-throw switch K _1-2To resistance R ₄And resistance R ₅Switch in difference amount limit, purpose is to mate in different range input impedance for galvanometer G.

Claims (1)

1. A kind of DC potentiometer that adopts the conversion of branch two ranges, it has working current to regulate resistance R P ₁, RP ₂, standardization time sampling is connected in the potentiometer circuit with setting resistance and metering circuit; It is characterized in that measuring partly with two slide wire disc of two step discs, first step disc is by respectively having 20 * 2 Ω I measuring disk and I ' replacement dish to form, second step disc is by the II that 10 * 0.22 Ω are respectively arranged " the replacement dish forms; this advances two brushes of dish and interconnects, the promptly two slide wire discs of the 3rd dish, and two resistance wire resistances are identical; be all 0～2.42 Ω; its indicating value index dial has 11 big lattice, and the corresponding resistance of every lattice is 0.22 Ω, and 110 little lattice are arranged; Another root of work III measuring disk slip is made III ' replacement dish slip in two slips, and the brush on two slide wire resistances of this dish is from getting off with a slice metal upper punch; I ' replacement is coiled at the 20th and is connected 8.58 Ω resistance R ₁The back is coiled at the 10th with II ' replacement and is connected, 0 resistance R that connects 4.22 Ω of II measuring disk ₂The back is connected with 0 of I measuring disk, and this coils the 20th connection III measuring disk does not hold, and it is 507.58 Ω resistance R that 11I ' replacement slip top connects a resistance ₃The back is connected with 0 on I ' replacement dish; I ' replacement dish brush and 50 Ω resistance r ₁Be connected in parallel on the metering circuit positive pole, resistance r ₁450 Ω resistance r connect ₂, tie point meets double-point double-throw switch K _1-1* 0.1 range contact, resistance r ₂Measure brush with I and be connected in the single-pole double-throw switch (SPDT) * 1 range contact, the normally closed contact of single-pole double-throw switch (SPDT) is connected the metering circuit negative pole.