The working principle of measuring resistance by DC bridge
To measure the resistance of a small resistance, a dual arm bridge (Kelvin bridge) is usedBecause of its high accuracy and good stability, the bridge is widely used in electromagnetic measurement, automatic adjustment and automatic controlThe simplest bridge is a circuit consisting of four branches. Each branch is called the arm of the bridgeFigure, an unknown resistance circuit (R2), access U DC power supply a diagonal line, a diagonal galvanometer by adjusting the G. can access the known resistance value makes no current through the G, then the bridge balance, the unknown resistance R2=R1 R4/R3.
The value of the resistor allows no current to pass through the G. The bridge is balanced and the unknown resistance is R2=R1 = R4/R3.Whisden Wheatstone bridge DC Wheatstone bridge is the most basic. Its working principle: suppose four resistor is fixed, when the S is closed, if satisfied: "R3*R2=R1*R4", is equal to the product of the diagonal resistance, then Ucd equals 0, CD is no voltage. Using this principle, when both sides four volume etc. a time for the unknown, if the regulation of the remaining three resistance value can make the equation set up, then use the formula to get the unknown. But in fact as long as the equation on each side of a variable resistor can be adjusted, so the other two resistance is a fixed value, then another it can be obtained.This principle can be used as a resistance measuring box. This principle uses the concept of "bridge", or "balance bridge"
The direct current bridge is the basic electromagnetic measuring instrument for measuring physical quantity by comparing method. There are many kinds of bridge, such as single arm and double arm bridgeResistance measured at medium resistance (10~106 ohms) shall be measured with the Whisden Wheatstone bridge;To measure the resistance of a larger resistance, a high resistance bridge or a ohmmeter is used;
