Discussion of the experiment Weifeng Su 04/10/2009

Wheatstone bridge Principle: When bridge is balanced, 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=U4 So, I1RA=I2Rx (1) I3RB=I4Rs (2) (1)/(2), I1 I2 IG I3 I4 Fig. 1The circuit diagram of a Wheatsone bridge

Wheatstone bridge Set up the circuit Balancing the bridge coarse adjustment & finer adjustment How can we get the largest sensitivity? E S1 Determine the measurement uncertainty of RX when the sensitivity M is the largest. Since the accuracy of the measurement crucially depends on the smallness of the current through the ammeter, a galvanometer with high sensitivity is used. The galvanometer is therefore very delicate and can be easily damaged if excessive current is let to pass it. To prevent this, the galvanometer is first bypassed with a shunt resistor for a coarse adjustment so that the bridge is roughly balanced. When the bridge is balanced at the low sensitivity, the finer adjustment can be achieved by reducing the shunt resistor gradually.

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 and 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 combining 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 a DC signal 0.5V/DIV 2.68DIV×0.5V/DIV=1.34V

Oscilloscope How to measure a signal by oscilloscope? To measure an AC signal 0.5V/DIV 2ms/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 diode to allow an electric current in one direction Input signal Input signal Diodes have two active electrodes between which the signal of interest may flow, and most are used for their unidirectional electric current property. The unidirectionality most diodes exhibit is sometimes generically called the rectifying property. The most common function of a diode is to allow an electric current in one direction (called the forward biased condition) and to block the current in the opposite direction (the reverse biased condition). Thus, the diode can be thought of as an electronic version of a check valve. Output signal Output signal half wave rectification full-wave rectification