Unbalanced Bridge Circuit:
Two kinds of bridge circuits (unbalanced and balanced) are utilized in resistance thermometer temperature detection circuits. An unbalanced bridge circuit shows in the figure uses a millivoltmeter which is calibrated in units of temperature which correspond to the RTD resistance.
Figure: Unbalanced Bridge Circuit
The battery is linked to two opposite points of the bridge circuit. The millivoltmeter is linked to the two remaining points. A rheostat regulates bridge current. The regulated current is separated between the branch along with the fixed resistor and range resistor R1 and the branch along with the RTD and range resistor R2. Since the electrical resistance of the RTD changes after that the voltage at points X and Y changes. A millivoltmeter detects the change in voltage caused by unequal division of current in the two branches. A meter could be calibrated in units of temperature because the only changing resistance value is that of the RTD.