文档介绍：Measure the Resistance via the Wheastone Bridge
purpose:
To understand the principle and characteristics of the Wheatstone bridge.
To understand the concept of sensitivity of bridge.
Learn the “exchange measure method”, with which to eliminate the system error.
apparatus:
Unknown resistances; DC power supply; galvanometer; resistor box; variable resistor; switch and other ponents; electrical bridge.
:
1)The principle and the structure of the Wheatstone bridge
When UC=UD
RX=R1R2RO
2)The sensitivity of the Wheatstone bridge
Because of the sensitivity of the galvanometer is limited, the current through the galvanometer is not truly zero, and the galvanometer cannot efficiently measure it.
The sensitivity of the bridge is defined as the ratio between the deflection of the galvanometer, Dd, and the corresponding relative value of R0.
S=ΔdΔRORO
3)The “exchange measure method”.
Exchange the positions of R1 and R2, or R0 and Rx, and adjusting R0 to R0 ¢, the bridge can get a new balanced state,and RX=R1R2R0'
Combine this equation with RX=R1R2RO, we can get:
RX=RORO'
This equation has nothing to do with R1 and R2. In this way we can make the error only relate to the instrument error of R0, which is the instrument error of resistor box.
procedures:
Use simply constructed bridge to measure the metal film resistor.
Connect the circuit and measure the resistance then exchange R
0 and RX measure the resistance again.
The key points:
Find the balance point.
Measure the sensitivity of the bridge.
Exchange R0 and RX measure the resistance again.
Error analysis:
The uncertainty of R0:
Δapparatus=ΔR0 apparatus=%Ro+(K+1)
The error caused by the sensitivity of the bridge is:
ΔR0*= (S is the sensitivity of the galvanometer)
URo=(ΔR0 apparatus )2+(ΔR0*)2
The relative uncertainty of RX is:
URXRX=(12UR0R0)2+(12UR0'R0')2≈22UR0R0 (N=)
Use box-bridge to measure the resistance.
Make the reading of galvano