Kelvin Bridge

Brand: CL

Model: QJ67P

Pictures are for reference only.

Kelvin bridge: In 1862, when W. Thomson of the United Kingdom encountered difficulties in measuring small resistance using a single-arm bridge, he found that the cause of the large measurement error was the lead resistance and the contact resistance at the connection point. These resistance values ​​may be much larger than the resistance being measured. Therefore, he proposed a bridge circuit, which was called the Thomson bridge. Later, because he was promoted to Lord Kelvin, it was also called the Kelvin bridge.

This adds an arm, and finally it becomes the electrical schematic diagram of the double-arm bridge in Figure 10. It is easy to see from the schematic diagram that in order to further consider the influence of lead resistance and contact resistance, resistors R3 and R4 are connected, and their values ​​must be greater than 10Ω. In addition, in order to consider the influence of the difference between R4/R2 and R3/R1 on the measurement results when the bridge is balanced, and to make the shunt current I3 smaller, we use a thick wire R of less than 0.001Ω to connect resistors Rn and Rx. In order to increase sensitivity, an amplifier circuit is added so that the unbalanced current I0 is amplified and then indicated by the galvanometer.