AC Bridge Circuits :: Papers

AC Bridge Circuits As we saw with DC footstepment circumferences, the circuit configuration known as a noseband put up be a very useful way to measure unknown values of resistance. This is true with AC as well, and we can go through the very same principle to the accurate measurement of unknown impedances. To review, the tie circuit track downings as a pair of two-component potential dividers affiliated across the same source voltage, with a null-detector rhythm movement machine-accessible between them to indicate a condition of balance at home in volts IMAGE Any one of the foursome resistors in the above bridge can be the resistor of unknown value, and its value can be placed by a ratio of the other three, which be calibrated, or whose resistances are known to a precise degree. When the bridge is in a equilibrate condition (zero voltage as indicated by the null detector), the ratio works out to be this IMAGE One of the advantages of using a bridge circuit to measure resistance is that the voltage of the power source is irrelevant. Practically speaking, the high the supply voltage, the easier it is to detect a condition of imbalance between the four resistors with the null detector, and thus the more sensitive it give be. A greater supply voltage leads to the possibility of increased measurement precision. However, there will be no fundamental error introduced as a import of a lesser or greater power supply voltage unlike other types of resistance measurement schemes. Impedance bridges work the same, only the balance equation is with complex quantities, as both magnitude and phase across the components of the two dividers must be equal in order for the null detector to indicate zero. The null detector, of course, must be a device capable of detecting very small AC voltages. An oscilloscope is often used for this, although very sensitive electromechanical meter movements and eve n headphones (small speakers) may be used if the source frequency is inside audio range. One way to maximize the effectiveness of audio headphones as a null