Detailed introduction of the Wheatstone Bridge formula

The Wheatstone Bridge (also known as the Single Arm Bridge) is an instrument that accurately measures resistance. The universal Wheatstone bridge resistors R1, R2, R3, and R4 are called the four arms of the bridge, and G is a galvanometer to check the current of the branch in which it is located.

When there is no current flowing through G, the bridge is said to reach equilibrium. When balancing, the resistance of the four arms satisfies a simple relationship, and the relationship can be used to measure the resistance.

The Wheatstone bridge is a bridge circuit composed of four resistors. These four resistors are called the bridge arms of the bridge. The Wheatstone bridge uses the change of the resistance to measure the change of the physical quantity. The MCU collects the voltage across the variable resistor and then Processing, you can calculate the corresponding physical quantity changes, is a highly accurate measurement method.

Unbalanced bridges are generally used to measure small changes in resistance values. For example, a strain gauge (made of a grid of wires attached between two layers of thin paper or plastic film) is attached to an object to deform the object. When the strain gauge is deformed, the resistance of the strain gauge is changed from Rx to Rx+ΔR when the bridge is balanced. At this time, the current Ig passed by the galvanometer will also change, and then according to the relationship between Ig and ΔR. ΔR is measured, and then the shape variable of the object is calculated from the relationship between ΔR and solid deformation.

In this way, strain, tension, torque, vibration frequency, etc. can be measured.

The Wheatstone Bridge was not invented by Wheatstone. In measuring electrical resistance and other electrical experiments, the circuit called Wheatstone Bridge is often used. Many people think that this bridge was invented by Wheatstone. In fact, this is A misunderstanding, this bridge was invented by British inventor Christie in 1833, but since Wheatstone first used it to measure resistance, people used to call this bridge the Wheatstone bridge. .

The Wheatstone bridge is a bridge circuit composed of four resistors. These four resistors are called the bridge arms of the bridge. The Wheatstone bridge uses the change of the resistance to measure the change of the physical quantity. The MCU collects the voltage across the variable resistor and then Processing, you can calculate the corresponding physical quantity changes, is a highly accurate measurement method. The circuit form is shown below.

In the bridge, there are three resistors whose fixed resistance values ​​are R1, R2, and R3, and the fourth resistor is variable to Rx. When Rx changes, the voltage between the two points B and D changes. By measuring the change in voltage, it is possible to know the change in the physical quantity in the environment, and to achieve the purpose of measurement. The following example shows the calculation method of the bridge circuit.

Assume that R1 flows through R1, the current of R2 bridge arm is I1, flows through R3, the current of Rx bridge arm is I2, and the bridge supply voltage is VCC, as shown in the figure below.

The voltage across each resistor can be calculated by Ohm's law. On the two arms R1 and R2, R1 and R2 divide the VCC voltage, and the voltage obtained across the R2 resistor is V1. On the R3 and Rx bridge arms, R3 and Rx divide the VCC voltage, R3. The voltage obtained across the resistor is V2. V1 and V2 are calculated using Ohm's law, respectively.

Current I1 flowing through resistors R1 and R2:

Voltage V1 across R2:

Current I2 flowing through resistors R3 and Rx:

Voltage across R3:

Voltage difference between V1 and V2:

This shows that:

If all four resistors are equal, that is, R1=R2=R3=Rx, then ΔV=0, that is, the bridge is in an equilibrium state;

A change in Rx causes a change in ΔV;

The Wheatstone bridge is a detection circuit. Although its structure is simple, its accuracy and sensitivity are relatively high, and it is widely used in medical diagnosis and detection instruments.

The measurement sensitivity of the Wheatstone bridge is of great significance in scientific research and production applications. The Wheatstone Bridge is widely used in contemporary scientific measurement and is also widely used in automatic control.

Wheatstone bridges are also widely used in weighing detection components.

1600 Puffs

Shenzhen Xcool Vapor Technology Co.,Ltd , http://www.xcoolvapor.com