This document is a lab report submitted by 7 students for an experiment using the Digiac 1750 Transducer and Instrumentation Trainer. It summarizes the results of 11 experiments measuring the characteristics and output of different transducers, including a servo potentiometer, Wheatstone bridge, RTD, thermistor, photovoltaic cell, phototransistor, photoconductive cell, and strain gauge as the number of coins placed on it increased. Graphs are provided plotting the respective output measurements for each transducer.

1. EEP301 LAB REPORT
TRANSDUCER AND
INSTRUMENTATION TRAINER
(DIGIAC 1750)
SUBMITTED BY:
Vivek Mangal (2010EE50566)
Umang Gupta (2010EE50564)
Mehul Mittal (2010EE50553)
Kumar Sourav (2009EE50796)
Indra Bhushan (2010EE50548)
Aastha Dua (2009EE50052)
Akshay Gupta (2009EE50275)

2. Servo-potentiometer
Aim: To observe the characteristic of the output voltage/dial setting of servo Potentiometer.
Introduction: In a positional Resistance Transducer, the position is observed in terms of resistance.
If the resistive element and a contact is arranged in a rotary manner, the resistance change can be
related to an angular position of the contact. This arrangement can be obtained by using Servo
potentiometer.
Observation: The maximum voltage position is achieved when the dial is at 172O
Angle(o
) Voltage(V)
172 5
150 4.47
120 3.61
90 2.717
60 1.817
30 0.93
0 0.0211
-30 -0.873
-60 -1.769
-90 -2.666
-120 -3.516
-150 -4.37
-180 -5.02
Graph: Voltage as a function of angular position of the dial.
-6
-4
-2
0
2
4
6
-200 -100 0 100 200
Voltage
Voltage

3. Wheatstone Bridge
Aim: To find out the value of unknown Resistance using Wheatstone bridge.
Introduction: A Wheatstone bridge is an electrical circuit used to measure an unknown electrical
resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown
component. Its operation is similar to the original potentiometer.
Wheatstone bridge circuit
When Ig = 0, Rx can be measured as:
Rx = (R2/R1)*R3
Observation:
Zero Setting Dial reading = 202
R3 = 2.02 kOhm
R1 = 10 – R3 kOhm = 7.98 kOhm
R2 = 12 kOhm
10 kOhm Resistor
setting Dial reading R3 = 10*Dial
R1 = (10kOhm -
R3) Rx
10 484 4840 5160 11256
9 476 4760 5240 10901
8 452 4520 5480 9898
7 422 4220 5780 8761
6 386 3860 6140 7544
5 346 3460 6540 6349
4 294 2940 7060 4997
3 250 2500 7500 4000
2 182 1820 8180 2670
1 90 900 9100 1187

4. Graph: Resistance R4 observed as a function of 10kOhm Resistor Setting
Result: Rx comes out to be approximately equal to the resistance applied.
The Platinum RTD (Resistance Temperature Dependent)
Transducer
Aim: To observe the temperature – resistance characteristic in a Platinum RTD Transducer
Introduction: In a Platinum RTD, the increase in resistance is linear, the relationship between
resistance change and temperature rise being 0.385 Ohm/o
C
Rt = Ro + 0.385t, Ro=Rt = 100 Ohm at 0o
C.
Temperature sensor measures the value of temperature in 10mV/o
K
Observation and Calculation:
Platinum RTD voltage recorded = 110 mV
Temperature Sensor INT = 3.056 V
So, temperature = 305.6 o
K = 32.6 o
C
Calculated RTD resistance = 100 + 0.385*(o
C) = 100 + 0.385 * 32.6 = 112.55 Ohm
0
2000
4000
6000
8000
10000
12000
0 2 4 6 8 10 12
Resistance Rx
R4

5. NTC (Negative temperature coefficient) Thermistor
Aim: To observe the temperature-resistance characteristic of a Negative Temperature Coefficient
Thermistor.
Introduction: In an NTC Thermistor, resistance decrease with increase in temperature. Thermistor
differ from RTD as the material used in a Thermistor is generally a ceramic or polymer, while RTD
uses pure metals. RTDs are useful over larger temperature ranges, while thermistors typically achieve
a higher precision within a limited temperature range, typically −90 °C to 130 °C.
Observation:
Thermistor resistance = 10*Dial reading + 1 kOhm
Time(min.)
Temperature
(INT reading)
Temperature
(K)
Temperature
(C) Dial reading
Thermistor
Resistance
(Ohm)
0 3.057 305.7 32.7 258 3580
1 3.089 308.9 35.9 234 3340
2 3.134 313.4 40.4 190 2900
3 3.189 318.9 45.9 152 2520
4 3.23 323 50 118 2180
5 3.267 326.7 53.7 100 2000
6 3.299 329.9 56.9 86 1860
7 3.325 332.5 59.5 74 1740
8 3.344 334.4 61.4 64 1640
9 3.361 336.1 63.1 54 1540
10 3.372 337.2 64.2 50 1500
Graph: Thermistor Resistance plotted as a function of Temperature
0
500
1000
1500
2000
2500
3000
3500
4000
25 35 45 55 65 75
Thermistor Resistance(Ohm)
Thermistor
Resistance(Ohm)

6. Photovoltaic Cell
Aim: To observe the short circuit current and open circuit voltage characteristic of a photovoltaic cell.
Introduction: A photovoltaic cell can be used either as a current source or a voltage source and is
inherently a linear device. When used as energy source, these photovoltaic cells are known as Solar
Cells.
Observation:
Lamp
filament
Voltage
Short Circuit
Current (uA)
Open Circuit
Voltage (V)
1 0 0
2 0 0.6
3 2.6 2.25
4 20.6 3.56
5 69.9 4.9
6 164.8 6.32
7 324.3 7.78
8 606 9.16
9 802 10.13
10 803 10.16
Graph: Short Circuit Output Current as a Function of Lamp Filament Voltage
The graph is approximately linear after some appropriate voltage is applied.
-100
0
100
200
300
400
500
600
700
800
900
0 2 4 6 8 10 12
Current (uA)
Current (uA)

7. Graph: Open Circuit Voltage as a Function of Lamp Filament Voltage
Result: The open circuit voltage as well as short circuit current is observed to have linear dependence
on the lamp filament voltage.
0
2
4
6
8
10
12
0 2 4 6 8 10 12
Voltage (V)
Voltage (V)

8. Phototransistor
Aim: To observe the output voltage characteristic of a Phototransistor as a function of applied lamp
filament voltage.
Introduction: A phototransistor is in essence a bipolar transistor encased in a transparent case so
that light can reach the base-collector junction. When light falls on the base region, the leakage
current increases, which flows from the base emitter junction, thus functioning as an amplifier.
As the lamp filament voltage increases, current increases, so the voltage drop VCE decreases.
VCE = V – I*R
Lamp filament
voltage Phototransistor output
0 5.01
1 5.01
2 4.95
3 4.52
4 3.315
5 1.226
6 0.842
7 0.816
8 0.8
9 0.788
10 0.781
Graph: Phototransistor Output Voltage as a function of Lamp Filament Voltage
0
1
2
3
4
5
6
0 2 4 6 8 10
Phototransistor output voltage
Phototransistor output

9. Photoconductive Cell
Aim: To observe the output voltage characteristic of a photoconductive cell as a function of applied
lamp filament voltage.
Introduction: The photoconductive cell is a two terminal semiconductor device whose
terminal resistance vary linearly with the intensity of the incident light. It is frequently called a photo-
resistive device. The photoconductive materials most frequently used include cadmium sulphide
(CdS) and cadmium selenide (CdSe). Both materials respond rather slowly to changes in light
intensity.
Observation:
Lamp filament
voltage
Photoconductor output
voltage
0 4.92
1 4.92
2 4.87
3 4.46
4 3.603
5 2.576
6 1.821
7 1.28
8 0.949
9 0.732
10 0.604
Graph: Photoconductor output voltage as a function of applied lamp filament voltage.
0
1
2
3
4
5
6
0 2 4 6 8 10 12
Photoconductor output voltage
Photoconductor
output voltage

10. Strain Gauge Transducer
Aim: To observe the output voltage of a strain gauge transducer as a function of load applied.
Introduction: A strain guage measures the external force applied to a fine wire. A fine wire is usually
arranged in the form of a grid. The pressure change causes a resistance change due to the distortion of
the wire. The value of the pressure can be found by measuring the change in resistance of the wire
grid. Generally this resistance is observed by using a Wheatstone bridge but in this experiment we
observe the output voltage which is linearly dependent on resistance.
Observation:
No. of Coins Output Voltage
0 0
1 0.769
2 1.389
3 2.108
4 2.76
5 3.38
6 3.98
7 4.64
8 5.32
9 6.35
10 7
Graph: Output Voltage as a function of number of Coins placed.
0
1
2
3
4
5
6
7
8
0 2 4 6 8 10 12
Output Voltage
Output Voltage