CN1991376A - Two-range portable potentiometer utilizing branch line - Google Patents

Abstract

The invention provides a portable potentiometer with two measurement ranges employing diverting branch double range switching for DC voltage measurement, wherein 20X2 Omega is used as a No:1 measuring disc, 10X0.22 Omega is used as a No:2 measuring disc, 0-2.42 Omega is used as a No:3 measuring disc, wherein the STANDARD-UNKNOWN switch does not influence measurement result, the two measuring junction knobs and the three measuring discs are connected directly with cables, the contact resistance of the measurement step switch, the variable difference and thermoelectrical potential are eliminated outside the measurement result, and the zero potential can further raise negative potential for compensation, two resisters of 5 Omega and 40.5 Omega are utilized for measurement range switch by employing diverting branch method.

Description

A kind of portable two-measurement range potential difference meter that adopts diverter branch

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 the measuring switch stepping and switching, and this just makes the instrument volume become big, 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 be used in the potential difference meter measure portion two step switch and a slide wire disc are arranged the time, contact resistance and variation that the measuring switch stepping is switched, the switch thermoelectrical potential does not influence measurement result, when range was changed, range conversion was the resistance that one digit number is 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, reduce supply voltage fixed resistance R ₀Sampling is connected in the potentiometer circuit with setting up resistance and metering circuit during standardization; 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 I measuring disk and 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 big 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 3.08 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 452.58 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 5 Ω resistance r ₁Be connected in parallel on the metering circuit positive pole, resistance r ₁The other end connect triac device K _1-1* 0.1 range contact, K _1-1* 1 range contact connects I measuring disk brush, and and K _1-2* 0.1 range contact short circuit, K _1-2* 40.5 Ω resistance r are passed through in 0.1 range contact ₂Back and K _1-2* 1 range contact is connected the negative pole of metering circuit, the K of triac device _1-1And K _1-2The mutual short circuit of two-layer normally closed contact.

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 is taken advantage of 10 integral number power with resistance, available standards 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 49.5 Ω between two brushes of first step disc, and the right resistance equals 495 Ω, and total resistance is 45 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 * 0.1 range, be connected in parallel on the resistance r between two brushes of first step disc ₁Resistance be between two brushes of first dish resistance 1/9, so flow through the electric current of measuring disk and be * the 1st, 1/10 of range, therefore the amount limit be reduced to * 1 range 1/10, parallel resistance r ₁After, the metering circuit resistance is reduced, resistance r has just connected in circuit ₂, make the total resistance of potentiometer circuit constant.

The 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 203 Ω with the resistance of setting up resistance R N, and 0～1 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 ₁-5/11×2×(20-n ₁)-5/11×0.22

×(10-n ₃)(mv)

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

＝10n1+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 31 Ω, adjustable resistance PR ₁=2.4 Ω, PR ₂Be to regulate in 0～Ω scope.

Triac device K _1-3To 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 portable two-measurement range potential difference meter that adopts diverter branch, it has working current to regulate resistance R P ₁, RP ₂, reduce supply voltage fixed resistance R ₀Sampling is connected in the potentiometer circuit with setting up resistance and metering circuit during standardization; 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 I measuring disk and 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 big 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 3.08 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 452.58 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 5 Ω resistance r ₁Be connected in parallel on the metering circuit positive pole, resistance r ₁The other end connect triac device K _1-1* 0.1 range contact, K _1-1* 1 range contact connects I measuring disk brush, and and K _1-2* 0.1 range contact short circuit, K _1-2* 40.5 Ω resistance r are passed through in 0.1 range contact ₂Back and K _1-2* 1 range contact is connected the negative pole of metering circuit, the K of triac device _1-1And K _1-2The mutual short circuit of two-layer normally closed contact.