Download characteristics of passive circuit elements (r,l,c)

Esc 102 Introduction to Electronics, 2004-2005/I
EXPERIMENT 2
CHARACTERISTICS OF PASSIVE CIRCUIT ELEMENTS (R,L,C)
Part A: ADDITIONAL OPERATIONS ON CRO
Note: Please refer to the CRO and FG Front Panel diagrams of Expt.1. You need to identify the
inputs/switches, etc of CRO and FG using the pin numbers indicated below.
1. EXTERNAL TRIGGER
(a) Set up the CRO for normal operation. Display on CH-1 the calibration voltage available on
the CRO front panel. Make the waveform stationary by LEVEL CONTROL. Measure the
peak-to-peak value of the voltage and its frequency. Sketch the waveform.
(b) Change the TRIGGER source to EXTERNAL (‘10’ of CRO) and verify that the display is
stable only when the same signal is also connected to the EXTERNAL TRIGGER input
terminal (‘14’ of CRO).
2. ASSYMETRIC PULSE WAVEFORM
(a) Try to set the controls of the Function Generator (FG) to produce a pulse train of 500Hz
with 0.5msec high level, and 1.5msec low level. Set the voltage level using DC OFFSET
(‘15’ of FG) such that low level of the Pulse is 0 volts and the high level is 5 volts. Observe
and sketch the pulse waveform seen on the CRO.
(b) Return DC OFFSET controls to locked position (off position).
Part B: FAMILIARIZATION WITH PASSIVE CIRCUIT ELEMENTS
1.
RESISTORS:
Resistors are usually classified according to the following three properties.
(a)
Composition (e. g. carbon granule, carbon film, metal film, wire wound etc.)
(b)
Power rating (e. g. 1/8w, 1/4w, ½ watt, 1 watt etc)
(c)
Tolerance (e. g. 20%. 10%,. 5%, 1 %, etc)
The first two have to be found out from the manufacturer's specification sheet. Tolerance is
usually indicated on the body of the resistor itself along with the value of the resistance. The
value and the tolerance, are either printed on the resistor, or are indicated by a colour bands.
Resistor Colour Code: The resistance values are colour-coded on the resistors using 3 bands.
The 1 st and the 2nd bands give the significance digits of the resistor value, while the 3rd band
gives the number of zeros to the right of the two significant digits. The ten colours and the
corresponding digits, 0-9 are as follows.
Black(0),
Green (5),
Brown (1),
Blue (6),
Red (2),
Violet (7),
Orange (3),
Grey(8),
1
Yellow(4),
White (9).
The 4th band indicates the to1erance; a golden band indicates a tolerance of 5 %, while a silver
band indicates 10 %. Absence of the 4th band implies a tolerance of 20 %. A brown band
indicates 1 % tolerance.
Experiment: Using the colour code, note down the values and tolerances of the different
resistors given to you.
2. CAPACITORS
Capacitors are classified according to the dielectric material used in their fabrication. The ranges of
values available vary from type to type. Some of the commonly encountered types are: Electrolytic
(above 1 F), Polyester (0.001-10 F), Paper (0.001-10 F), Mica (0.001-0.1 F) and Ceramic (less
than 1 F). Capacitors used most commonly in the laboratory have the values printed on them. The
tolerance is 20 % unless indicated otherwise.
Experiment: Identify the different types of capacitors from their approximate distinguishing features as
listed below, and note down their values as well as voltage ratings. It must be emphasized that features
given below should be used as rough guidelines.
(i) Electrolytic: Polarity indicated by + and - signs and/or a red mark
(ii) Polyester and Paper: Cylindrical or oblong moulded body (no obvious distinction between
polyester and paper)
(iii) Mica: Flat rectangular body with colour dots giving the specifications.
(iv) Ceramic: Tabular or disc shaped.
Caution: When used in experiments, the voltage rating of capacitors (as well as their polarity in the
case
of electrolytic) must be strictly adhered to, failing which the capacitors may explode.
..
3. INDUCTORS
An inductor generally consists of a coil of a good conductor, (usually copper) wound on an insulating
cylindrical former, which may or may not have a ferromagnetic core. The winding may be singlelayer, multilayer or honeycomb. Note the construction of the different inductors given to you and write
down the type of the inductor.
Part C: DISPLAY OF V-I CHARACTERISTICS OF R, L, C ELEMENTS
For a two terminal device, the circuit of Fig. 2.1 can be used to obtain its V-I characteristics. Note
that the resistance RM is used to measure current through the device. Also, note that while actual
voltage drop across the device should be measured to obtain its V-I characteristics, here what is
measured is the voltage drop across the series combination of the device and the current
measuring resistance RM. For this voltage to be a good approximation to the voltage drop across
the device, the value of RM, should be chosen such that the voltage drop across it is negligible
compared to the drop across the device. In other words, Vo > > VM.
1.
2.
3.
Resistor:
Set up the circuit shown in Fig. 2.1.The corresponding Rs and RM values to be used are given in
Table 2.1. First choose a 10K resistor as the device under test.
Set the FG to give a signal of 5 sin t (freq=100Hz). You will have to use the CRO for doing this.
Observe the voltage applied to the two channels CH-1 and CH-2 simultaneously by putting the
MODE switch to DUAL position. Verify that the voltage drop across RM (i.e. VM) is much
2
4.
5.
6.
7.
8.
smaller than the drop across the device. Note down the two waveforms and their relative position
in time. Observe carefully whether the two waveforms are in phase or not.
Put the CRO MODE to XY display mode. Observe the V-I characteristics of the device. Note
down the characteristics. Explain the graph.
Repeat steps 3 and 4 for frequencies of 1 KHz and 10KHz, choosing the values indicated in Table
2.1. Use CRO to set the frequency.
Comment on the results obtained.
Capacitor: Repeat steps 2 to 6 using the given 0.1F ceramic capacitor as the device under test.
Observe and note the variations in the amplitude of VM.for 100Hz, 1KHz and 10KHz.
Inductor: Repeat steps 2 to 6 for the given Inductor of 1.0 mH. However, keep Rs =100ohms,
RM=10ohms and do measurements at f= 100KHz only. Choose f=20 KHz and f=50 KHz and note
carefully the variations in the amplitude of VM.
VO
VM
RM
Fig. 2.1 Test Circuit for Part C
For these measurements
Keep Rs = 1 KΩ
Device under test
Resister 10 KΩ
Capacitor 0.1 μF
Test Frequencies
1 KHz
RM
100
100
100 Hz
RM
100
100
Table 2.1
3
10 KHz
RM
100
10