CHARARCTERISTICS OF ELECTROMECHANICAL TRANSDUCERS1. Aim of the experiment Here the purpuse of the experiment is to measure the position using Reflective Opto Transducers , Gray Coded Disc , and Servo Potentiometer and also we will use Inductive Transducers , and Tacho-Generator for speed measurement.2.1.1. Experiment

This is the known values upward and here the experimental resultsPosition CBA

0000

1001

2011

3010

4110

5111

6101

7100

As you see here the experimental values are all same with the known value.We found the experimental values with rotating the shaft of the motor .We can easily understand that light emitted led means 1 and the dark one 0.So we filled the table according to this information.Table 2.2OutputOutput Voltage

LED OFFLED ON

A0,64,85

B1,34,88

C0,654,85

Here in table 2.2 as you see ,we found output voltages of leds.We turned the shaft until we saw the maximum and minimum voltage values.

Question 1.1The electrical circuit arrangement for the reflective opto transducer is like that ;

The digiac 1750 (D1750) unit is a comprehensive transducer and instrumentation trainer with examples of a full range of input and output transducers, signal conditioning circuits and display devices. The unit is self contained and enables the characteristics of individual devices to be studied and also their interconnection to form complete closed loop systems. The only additional items recommended are an electronic voltmeter and an oscilloscope.

Question 1.2The reflective opto sensor is a device employing an infrared L.E.D. and photo transistor.The components are arranged so that the beam is returned if a reflective surface is placed at the correct distance.The reflective surface is a gray coded adhesive overlay on a aluminum disk which revolves with the drive shaft.

Gray code is a sequence of binary numbers where only one bit changes at a time. Marching through the integer sequence then only requires flipping one bit at a time which in certain applications drastically reduces any errors. With Gray code only one bit is changing from OFF to ON and therefore there is no error. In automation it's particularly good for position transducers used to measure the angle of a shaft. This application benefits from the cyclic nature of Gray codes, because the first and last values of the sequence are different by only one bit. That is, if you feel like going round and round in circles.In an optical absolute encoder there is a disk with a Gray code pattern like so... Black areas produce a low voltage output from the associated reflective opto sensor while white areas reflect infa-red produce a high voltage.A beam of light, LED or laser, is shot through the disk and the light is picked up on the other side by a gang of phototransistors. This light is converted into electrical signals which can be read as Gray code or converted to BCD. As the shaft (and therefore the disk) rotate the light coming through the holes changes but only slightly based on the Gray code. Thus the controller reading the phototransistors knows the exact position of the shaft.

Question 1.3

If the signals in all parts of a control system are continuous functions of time, the system is Classified as continuous time feedback control system. Typically all control signals are of low frequency and if these signals are unmodulated, the system is known as a d.c.control system.These systems use potentiometers as error detectors, d.c amplifiers to amplify the error signal, d.c. servo motor asactuating device and d.c tachometers or potentiometers as feedback elements.If the control signal is modulated by an a.c carrier wave, the resulting system is usually referred to as an a.c control system.These systems frequently use synchros as error detectors and modulators of error signal, a.c amplifiers to amplify the error signal and a.c servo motors as actuators. These motors also serve as demodulators and produce an unmodulated output signal.

2.2.1. Experiment: Characteristics of a Servo Potentiometer

Output Voltage(v)Dial Setting(degree)

5.00163

4.67150

3.78120

2.890

1.960

0.9430

0.050

-0.84-30

-1.68-60

-2.56-90

-3.44-120

-4.26-150

-5.00185

Table 4: output voltage servo potentiometer

Here we changed the values of the degrees on the servo potentiometer clockwise and also counterclockwise to find the maximum negative and maximum positive value of the voltage.Then other samples of voltages were recorded according to the control dial setting.

Question 2.1

-As we know from the experiment input voltages of it changes between 5 and 5 volt.So we should observe that maximum values should be 5 and 5.-Error-sensingnegative feedbackto correct the performance of a mechanism.-It applies only to systems where thefeedbackor error-correction signals help control mechanical position, speed or other parameters.

Question 2.2

The charateristic of servo potentiometer around 0 degree is ; output voltage is too small nearly zero and the value will not be measured with perfect accuracy.

Question 2.3

The output voltage is approximately 5 volt.And this output is the max voltage value.After 180 degree ; voltage decreasing with time.

2.3.1.Experiment: Characteristics of an Inductive Transducer

The maximum output voltage when the slot is immediately above the inductive sensor = 6.5VOutput voltage with the slot over the inductor = 6.73 voltMaximum value of output voltage = 7.14 volt

Counting or speed measurement :

Speed of shaft recorded with the inductive sensor = 6 rev/secThe speed of the shaft recorded without Low Pass Filter = 195 rev/sec

Table 2.6 The shaft speed for comparison

Motor VoltageShaft Speed (rev/sec)2V4V7V10V

Inductive Transducer6142831

Slotted Opto Transducer5142740

2.4.1 experiment : Characteristics of a DC Permanent Magnet Tacho-Generator

Table 2.8 The output voltage against shaft speed

Output Voltage(Moving Coil Meter) , VShatft Speed(rev/sec) , n

25

2.510

5.020

7.030

9.540

Question 4.1The output voltages versus to shaft speed graph explains that chacteristic of tacho-genearator is nearly linear because voltage is doubled and speed of shaft is nearly doubled and voltage is four times to first voltage and then speed of the shaft is approximately eight times greater than first speed. When the values are getting bigger , the linearity gets worse.Calibration of the moving coil meter to indicate speed directly :

Table 9: The motor speed

Shaft Speed (rev/min)600100012001600

Calculated Shaft Speed (rev/sec)10172026

Shaft Speed from Counter (rev/sec)11172228

Question 4.2

Using counter is easier than using calibrated Moving Coil Meter for setting the motor speed, because you don't need to calibrate the counter.

CONCLUSONGenerally ; in this experiment we measured position and speed using various components of DIGIAC 1750 and also using them we construct the circuit which is needed.We learned the properties of the most of the components of DIGIAC 1750 as expressed in the answers of the questions.