The transducer which we are going to use here is called a Thermistor, which is a temperature dependent resistor. Depending on the temperature co-efficient of the thermistor, changes in temperature will either increase or decrease the resistance of the thermistor. This means that the output voltage V OUT is proportional to the temperature.
By calibrating the voltmeter, we can display the temperature in terms of the output voltage. One of the most commonly used applications of Wheatstone Bridge is in the Strain Measurement. Strain Gauge is a device whose electrical resistance varies in proportion to the mechanical factors like Pressure, Force or Strain. For a given strain, the resistance change may be only a fraction of the full range. Therefore, to accurately measure the fractional changes of resistance, a Wheatstone Bridge configuration is used.
The circuit below shows a Wheatstone bridge where the unknown resistor is replaced with a strain gauge. Due to the external force, the resistance of the strain gauge changes and as a result, the bridge becomes unbalanced.
The output voltage can be calibrated to display the changes in strain. In this, the Strain Gauges are carefully mounted as a single unit called as Load Cells, which is a transducer which converts mechanical force to electrical signal. Usually, weight scales consist of four load cells, where two strain gauges expand or stretch tension type when external force is acting and two strain gauges compress compression type when load is placed. If the strain gauge is either tensed or compressed, then the resistance can increase or decrease.
Therefore, this causes unbalancing of the bridge. This produces a voltage indication on voltmeter corresponds to the strain change. If the strain applied on a strain gauge is more, then the voltage difference across the meter terminals is more.
If the strain is zero, then the bridge balances and the meter shows zero reading. This is about the resistance measurement using a Wheatstone bridge for precise measurement. Due to the fractional measurement of resistance, Wheatstone bridges are mostly used in strain gauge and thermometer measurements.
You learned What is a Wheatstone Bridge Circuit, what is the meaning of a Balanced Bridge, how to calculate an unknown resistance using Wheatstone Bridge and also how an Unbalanced Wheatstone Bridge can be used to measure different physical quantities like Temperature and Strain. Your email address will not be published. Wheatstone Bridge Working, Examples, Applications. Among these four resistances, P and Q are known fixed electrical resistances. The potential at terminal D varies when the value of the variable resistor adjusts.
When the resistance value of arm CD varies, then the I2 current will also vary. If we tend to adjust the variable resistance one state of affairs could return once when the voltage drop across the resistor S that is I2.
S becomes specifically capable to the voltage drop across resistor Q i. Then the deflection in the galvanometer is zero when the S2 switch is closed. Now potential of point B with respect to point C is the voltage drop across the Q transistor, then the equation is.
Potential of point D with respect to C is the voltage drop across the resistor S, then the equation is. The electrical resistances of Wheatstone bridge such as P and Q are made of definite ratio, they are ; or known as ratio arms and the rheostat arm S is made always variable from , ohms or from , ohms.
The application of Wheatstone bridge is light detector using Wheatstone bridge circuit. Wheatstone bridge consists of four resistors that are connected in the shape of a diamond. Whetstone bridge can be considered as the simple series-parallel arrangement of resistors and they are connected between a supply voltage and ground Wheatstone bridge circuit consists of two input terminals and two output terminals consisting of four resistors. The bridge is used to find the unknown resistance very precisely by comparing it with a known value of resistance.
In this circuit, the null or balanced condition is used to find the resistance. For the balanced condition voltage at B and D must be equal which is shown in the above figure so no current will flow through the meter and get a balanced condition one of the resistors must be variable. It will change the resistors to adjusting variable resistors to balance the device and the mathematical ratio is used to calculate the fourth resistance. In one mode bridge can measure the unknown resistance value with high accuracy by comparing it with a properly-known resistance, the value of the unknown resistance is measured by varying the resistance of any of the three resistors in the bridge circuit to obtain a balanced condition.
In this condition, the bridge will have a zero output voltage. The bridge is in an unbalanced condition in other mode and the unknown resistance value is determined by the value of the bridge output voltage. This mode of operation is also called an off-null operation. The unbalanced bridge is mostly used for dynamic measurement cases in which the unknown resistance will be a transducer which does the measurement of a physical quantity. AC bridge is similar to the Wheatstone bridge and they are used to measure the capacitance and inductance value.
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