CN205003215U - Be applied to printed circuit board's four -wire test circuit - Google Patents

Abstract

The utility model provides a be applied to printed circuit board's four -wire test circuit, the last circuit that awaits measuring that includes of printed circuit board, four -wire test circuit includes: power, first feeder resistance, second feeder resistance, ampere meter and voltmeter, power, first feeder resistance, the circuit that awaits measuring, consecutive the connecing of ampere meter form the electric current supply return circuit, second feeder resistance, await measuring circuit and the consecutive formation voltage survey return circuit that connects of voltmeter. The utility model discloses a test circuit has an electric current supply return circuit and a voltage test loop to every test point, both mutual independence, the voltage measured also almost is the pressure drop of line resistance itself of awaiting measuring, feeder resistance can be neglectd completely, make the line resistance that awaits measuring that records almost be similar to the line resistance itself that awaits measuring, but PCB's small resistance is surveyed in the accurate determination from this, the measuring accuracy of its four -wire test can reach m omega level, compare the great measuring accuracy that has improved with ordinary second line test circuit.

Description

A kind of four line test circuits being applied to printed circuit board (PCB)

Technical field

The utility model relates to printed-wiring board (PWB) test machine, particularly relates to a kind of four line test circuits being applied to printed circuit board (PCB).

Background technology

As everyone knows, all electric equipments or control system all will use printed-wiring board (PWB), and the quality of printed-wiring board (PWB) directly has influence on function and the performance of product.But due to pcb board factory production technology, always there is the series of problems such as the resistance difference caused not as rosin joint, short circuit, copper thickness in the PCB produced.How to detect that these problematic PCB become the first order issue of puzzlement pcb board factory.Two ends test machine in the market also can measure some defective PCB, as the situation that open circuit, short circuit and some resistance comparison in difference are large.Some defect of PCB is found in actual production, as the problems such as having no copper in the holes, cavity, copper is thin, line is thin, circuit breach all can have influence on circuit resistance, when resistance is less than 25 Ω, when testing above defect plate with common open short circuit test method, test result display PASS, but client's resistance after high-temperature soldering changes, and causes open circuit problem to occur, finally cause customer complaint, serious also need is paid an indemnity to client.

Common open short circuit test method is common measure with two cable, and as shown in Figure 1, measure with two cable is a kind of scheme generally applied at present.Measure with two cable only has a loop, and measured impedance is R1+R2+Rpcb, and namely measured impedance is feeder resistances (R1+R2) and circuit resistance to be measured (Rpcb) sum, therefore cannot the low resistance of Accurate Measurement tested PCB.But because the condition of open test is generally 20 Ω, therefore feeder resistances impact is little, negligible.Although the precision of measure with two cable is not high, what be used to judge circuit opens the needs that short circuit can meet the printed wiring board of the overwhelming majority, but measure with two cable technology is only applicable to the test of breaking completely, hole is disconnected completely, tests then helpless for low resistance.

Summary of the invention

The purpose of this utility model is the deficiency making up two ends measuring technology, provides a kind of four line test circuits being applied to printed circuit board (PCB).

The purpose of this utility model is achieved through the following technical solutions.

Be applied to four line test circuits of printed circuit board (PCB), described printed circuit board (PCB) includes circuit to be measured, described four line test circuits comprise: power supply, the first feeder resistances, the second feeder resistances, reometer and voltage table;

Described power supply, the first feeder resistances, circuit to be measured, reometer are connected formation one electric current supply loop successively; Described second feeder resistances, circuit to be measured and voltage table are connected formation one voltage determination loop successively.

Wherein, two the first feeder resistances are included in described electric current supply loop.

Wherein, two the second feeder resistances are included in described voltage determination loop.

Compared with prior art, beneficial effect is the utility model:

Test circuit of the present utility model has an electric current supply loop and a voltage tester loop for each test point, both are separate, because the internal driving of voltage table is very high, be far longer than the feeder resistances (Ω level) in voltage determination loop, most electric current is made to flow through line resistance to be measured, the electric current flowing through voltage table is almost nil, therefore the voltage measured also be almost the pressure drop of line resistance to be measured itself, feeder resistances can be ignored completely, measured line resistance to be measured is made almost to be similar to line resistance to be measured itself, thus can the small resistance of Accurate Measurement tested PCB, the measuring accuracy of its four line test can reach m Ω level.Compared with common measure with two cable circuit, substantially increase measuring accuracy, ensure that product quality.

Accompanying drawing explanation

Fig. 1 is common measure with two cable circuit theory diagrams;

The four line test circuit schematic diagrams that Fig. 2 provides for the utility model embodiment.

Embodiment

In order to make the purpose of this utility model, technical scheme and advantage clearly understand, below in conjunction with drawings and Examples, the utility model is further elaborated.Should be appreciated that specific embodiment described herein only in order to explain the utility model, and be not used in restriction the utility model.

In the present embodiment, each test point tested by four lines has one to encourage line and a detection line, and the two strictly separates, and forms independent loop separately; Require that detection line must be received on a test loop having high input impedance simultaneously, make the electric current flowing through detection line minimum, be approximately zero.Namely excitation line is electric current supply loop, and namely detection line is voltage determination loop, and electric current, voltage two loop are independent separately.Electric current supply loop two-terminal and voltage determination loop two-terminal amount to four terminals, therefore claim four line tests.

Refer to shown in Fig. 1, the four line test circuits that the present embodiment provides comprise: power supply, feeder resistances R1, feeder resistances R2, reometer, line resistance Rpcb to be measured, feeder resistances R3, feeder resistances R4, voltage table.

Wherein, power supply, feeder resistances R1, line resistance Rpcb to be measured, feeder resistances R2, reometer are connected formation electric current supply loop successively; Described feeder resistances R3, line resistance Rpcb to be measured, feeder resistances R4, voltage table are connected formation one voltage determination loop successively.

V ≒ I1xRpcb (obtaining less pressure drop because I2 (small area analysis) is multiplied by small resistor again), because of the internal driving of voltage table very high (M Ω level), be far longer than feeder resistances R3 and the R4 (Ω level) in voltage determination loop, most electric current is made to flow through Rpcb, the electric current I 2 flowing through voltage table is almost nil, therefore the voltage measured also be almost the pressure drop of Rpcb itself, feeder resistances can be ignored completely, measured Rpcb is made almost to be similar to Rpcb itself, thus can the small resistance of Accurate Measurement tested PCB, the measuring accuracy of its four line test can reach m Ω level.

The foregoing is only preferred embodiment of the present utility model; not in order to limit the utility model; all do within spirit of the present utility model and principle any amendment, equivalent to replace and improvement etc., all should be included within protection domain of the present utility model.

Claims (3)

1. be applied to four line test circuits of printed circuit board (PCB), described printed circuit board (PCB) include circuit to be measured, it is characterized in that, described four line test circuits comprise: power supply, the first feeder resistances, the second feeder resistances, reometer and voltage table;

Described power supply, the first feeder resistances, circuit to be measured, reometer are connected formation one electric current supply loop successively; Described second feeder resistances, circuit to be measured and voltage table are connected formation one voltage determination loop successively.

2. four line test circuits as claimed in claim 1, is characterized in that, include two the first feeder resistances in described electric current supply loop.

3. four line test circuits as claimed in claim 1, is characterized in that, include two the second feeder resistances in described voltage determination loop.