The Wheatstone bridge circuit
This circuit was described in 1833 by Samuel Hunter Christie (1784-1865).
However, It was Mr. Charles Wheatstone who gave many uses to the Wheatstone bridge circuit when he discovered it in 1843. As a result, this circuit bears his name. It is the most sensitive circuit to measure a resistance
The Wheatstone bridge circuit is a very interesting circuit and it is used (as we know) to measure the value of passive components such as resistors. The circuit can be connected to any direct current voltage (VDC), but it is not recommended to use it over 12 volts.
 When the bridge is in balance:
R1 = R2 y Rx = R3 then....
R1 / Rx = R2 / R3
In this case, the potential difference (the voltage) between points A and B, where we placed an ammeter, is 0 volts. This shows us that there is no current flowing between these two points (0 amps)
When Rx = Ra, VAB = 0 and there is no current
If you do not know the value of Rx, the bridge should be balanced modifing the value of R3. When you have achieved the balance, R3 will be equal to Rx (Rx = R3). R3 must be a variable resistor with a particular feature that allows us to read very precise values.
For example:
If R1 and R2 = 1K (Kilohm) and R3 = 5K, Rx must be 5K to ensure that the voltage between A and B (VAB) is zero (no current)
Thus, in order to know the value of a resistor Rx, you have to connect the unknown resistor (Rx) and begin to change the value of R3 until the current between points A and B is zero. When this happens, the value of Rx will be equal to the value of R3
There are many interesting applications of the Wheatstone bridge in the industry field like a temperature sensor, pressure sensor, etc..
These sensors change the value of their resistances according to the variation of temperature, pressure, etc.)
It is in the ammeter where we can see the level or degree of imbalance or difference between the actual value and the real one.
It is also used in the electric power distribution systems where it is used to detect cracks or faults in the distribution lines.
Related Links
- Resistors in series and parallel
- Wire wound resistor
- Photoresistor - LDR
- Resistors in series and parallel
- Energy dissipation in resistors (Joule's Law)
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