# bridge circuit

Bridge circuits are electrical circuits that are mainly used in measurement technology. Because of the circuit arrangement of the individual bridge components, bridge circuits are also called H-circuits.

Bridge circuits are symmetrically constructed and consist of two parallel voltage dividers, the bridge arms, with the impedances R1 and R2 as well as R3 and Rx. Between the bridge arms there is a cross connection, the bridge branch, to which the metrological signal is applied.

Bridge circuit, shown as H-circuit and as bridge circuit

If the voltage dividers consisting of R1, R2, R3 and Rx have the same impedance values, then the voltage drops in the series circuits are identical and no voltage is applied to the bridge arm. If the impedances differ slightly, then the smallest unbalances cause different voltage drops, which can be measured as a voltage difference in the bridge branch. It is not the impedance values that are important, but the ratio of the impedances in the two voltage dividers. This must be the same. If the impedances and the impedance to be measured are in the correct ratio, then such a bridge circuit reacts extremely sensitively to small and smallest impedance differences.

With measuring bridges, this effect is exploited and a series resistor is replaced by the resistor Rx to be measured. The resistor R3 is then changed until the ratio of R3 to Rx corresponds to that of R1 to R2, and the measuring bridge is in symmetry. The R3 resistance value is used to determine the resistance value of Rx after adjustment.

Applications of bridge circuits

There are various bridge circuits, which differ according to their design and application in that their series circuits consist of different two poles, of ohmic resistors as in the Wheatstone bridge and the Thomson bridge, or of impedances as in the Maxwell bridge and the Wien bridge, or with diodes as in the Graetz bridge.

Informations:
 Englisch: bridge circuit Updated at: 26.05.2012 #Words: 317 Links: measurement, bridge, voltage, receiver (Rx), connection Translations: DE Sharing: