Discussion of the experiment

Weifeng Su04/10/2009

Wheatstone bridgePrinciple: RA & RB are connected in series.

RX & RS are connected in series.

RA & RX are connected in parallel.  

RB & RS are connected in parallel.

When bridge is balanced,

1) IG=0, I1=I3 and I2=I4

2) potential of point ‘2’ = potential of

point ‘4’,

               U2=U4So, I1RA=I2Rx (1)

I3RB=I4Rs (2)

(1)/(2),

Fig. 1The circuit diagram of a Wheatsone bridge

I1

I2

IG

I3

I4

SB

AX

S

B

X

A RR

RR

R

R

R

R

Wheatstone bridge

Set up the circuit

)()()( 22

21 ABABA RuRuRu

G

S2

E S1

• Balancing the bridge

coarse adjustment & finer adjustment

How can we get the largest sensitivity?

Determine the measurement uncertainty of RX

when the sensitivity M is the largest.2222 )

)(()

)(()

)(()

)((

S

S

B

BA

x

X

B

SAX R

Ru

R

Ru

R

Ru

R

Ru

R

RRR

A

10/)(;0)()( 111 SSBBBAB RRuRuRu

3)(2

aRu AB

Oscilloscope

Principle:

Oscilloscope Principle:

http://chem.ch.huji.ac.il/instruments/test/oscilloscope_principle_animated.html

Oscilloscope

Lissajous figure Lissajous Figures are a special case of parametric equations, where x a

nd y are in the following form: x = A sin(at + δ)

y = B sin(bt + γ) Lissajous curves can be seen on oscilloscopes and are the result of combi

ning 2 trigonometric curves at right angles.

http://pagesperso-orange.fr/olivier.granier/meca/simul/lisajou/simul.html

Oscilloscope How to measure a signal by oscilloscope?

To measure aDC signal

0.5V/DIV

2.68DIV×0.5V/DIV=1.34V

Oscilloscope How to measure a signal by oscilloscope?

To measure anAC signal

0.5V/DIV2ms/DIV

Peak-peak amplitude:3.56DIV×0.5V/DIV=1.78V

Period: T=3.16DIV×2ms/DIV=6.32ms;Frequency:f=1/T=158Hz

The property of diodeto allow an electric current in one direction

half wave rectification full-wave rectification

Input signal

Output signal

Input signal

Output signal