Applications of the Wheatstone Bridge
The Wheatstone Bridge is commonly used in conjunction with transducers to precisely measure physical quantities such as strain, temperature and pressure.
A thermistor is a sensor that exhibits a change in its resistance when it is exposed to a change in temperature.
A thermistor is a sensor that exhibits a change in its resistance when it is exposed to a change in temperature.
Modern Wheatstone Bridges are automated, with intelligent interface modules, the output can be conditioned and converted to any desired units for display or processing.
The Wheatstone Bridge has great sensitivity since it can provide a null measurement.
It can be designed to compensate for changes in temperature, a great advantage for many resistive measurements, particularly when the resistance change of the sensor is very small.
Usually the output voltage of the bridge is increased by an amplifier that has a minimum loading effect on the bridge.
Wheatstone Bridge Light Detector
The light dependent resistor (LDR) photocell is connected into the Wheatstone Bridge circuit as shown to produce a light sensitive switch that activates when the light level being sensed goes above or below the pre-set value determined by VR1.
The op-amp is connected as a voltage comparator with the reference voltage VD applied to the inverting pin.
Since both R3 and R4 are of the same 10 kΩ value, the reference voltage set at point D will therefore be equal to half of Vcc. That is Vcc/2.
The potentiometer, VR1 sets the trip point voltage VC, applied to the non-inverting input and is set to the required nominal light level.
The relay turns “ON” when the voltage at point C is less than the voltage at point D.