MCE 311 Lab 5

MCE 311 Engineering Measurements

MCE 311 Engineering MeasurementsSummer 2015

Experiment No:5

Title:Rotational Speed and Position Measurements

Date:5 / 7 / 2015

Group number:

Student NameID

ItemMaxGrade

Title and Format5

Abstract5

Introduction5

Theory10

Experimental Procedure10

Data and Results15

Discussion and Analysis25

Error/Sensitivity Analysis10

Overall impression5

Figures, Tables, and References5

Appendix: Raw Data Summaries5

Total100

Table of Contents

Table of Contents2Table of Figures3Abstract4Introduction5Theory6Experimental Procedure7Data and Results9Discussion and Analysis11Error/Sensitivity Analysis12Overall impression13Figures, Tables, and References14Appendix: Raw Data Summaries15

Table of Figures

Figure 1: Reflective Opto Transducer Disk6Figure 27Figure 38Figure 49

Table 19Table 210Table 310

AbstractThis lab report explains what Slotted Opto & Reflective Opto Transducers are, and how they operate. An experiment was carried out in order to understand how the devices worked when applied practically. The results of the experiment will be discussed further in this report.

Introduction

Simple stand-alone electronic circuits can be made to frequently flash a light or play a musical memo, but in order for an electronic circuit or system to perform any useful task or function it needs to be able to communicate with the "real world" whether this is by reading an input signal from an "ON/OFF" switch or by activating some form of output device to illuminate a single light. The type of input or output device used really depends upon the type of signal or process being sensed. Transducers can be used to sense a wide range of different energy forms such as movement, electrical signals, radiant energy, and there are many different types of both Analogue and Digital input and output devices. The slotted opto transducer is used to measure the speed of AC and DC motors and stepper motor break. The reflective opto transducer is used to measure the position of motor solenoid and panel meters. It mainly consists of an infra-red LED and a phototransistor. This is similar to the slotted opto device, however; the elements are arranged here such that the beam is either reflected back or broken.

Theory

The Slotted Opto Transducer operates by emitting a light signal from an infra-red LED onto a disk with a slot. On the other side of the disc a silicon phototransistor is mounted. Whenever the signal passes through the gap it emits a voltage, and whenever the signal is blocked by the disk the voltage is drastically reduced. In order to measure the rpm the frequency of the voltage peaks with respect to time can be calculated.Figure 1: Reflective Opto Transducer Disk

The Reflective Opto Transducer operates under the same principle of the Slotted Opto Transducer however instead of utilizing a gap it operates under the principle of reflection of the signal. As seen in the figure above the disk above has different areas with different shades. The light areas represent the reflective areas that the signal bounces of and in turn emits a voltage. While the shaded areas represent the areas that cut the signals. Different combinations of these areas emit different voltages and in turn we can tell the position to the nearest 45 degree (8 different combinations).

Experimental Procedure

Part A: Slotted Opto TransducerTo begin this experiment first of all the circuit was connected as shown in figure 1 and assure that the variable resistor knob is turned fully counter clockwise to give zero voltage. Figure 2Switch on the power supply and rotate the shaft was rotated by hand until the light was broken by the rod and the LED was off. At that instant the value of the voltage was recorded. Then the slotted rod was rotated until the LED was on and the value of the voltage was recorded. After the initial readings were taken, the Time/counter was set to COUNT and FREE RUN. Now the 10k wire wound resistor was varied until the reading of the voltmeter gave 2 volts by that time the shaft started to rotate. Each time the voltage was increased by 1 v the value of the frequency was recorded from the multimeter. 9 readings were recorded in the table and plotted on the graph.

Part B: Reflective Opto TransducerFirst of all the circuit shown in figure 2 was connected.

Figure 3The power supply was switched on and the drive shaft was rotated by hand until all of the three LEDs were off. The voltage of each LED was measured while they are off. Then all of the LEDS were turned on and the voltage of each LED was measured while they are on. The values of the voltage output were recorded in Table 2. With the shaft initially in the position were all LEDs are off, the shaft was rotated counter clockwise and recording the each change in the LEDs state as 1 and 0. These values were recorded in Table 3.

Data and Results

Part A: Slotted Opto TransducerTable 1 shows the values of the frequency recorded from varying the voltage. Table 1voltage (v)speed (rev/min) speed( rev/s)

2.00405.006.75

3.00654.0010.90

4.00864.0014.40

5.001104.0018.40

6.001362.0022.70

7.001662.0026.70

8.001860.0031.00

9.002112.0035.20

10.002376.0039.60

Figure 4

Part B: Reflective Opto Transducer.Table 2 shows the measured voltage when LEDs were switched on and off Table 2output Output voltage (v)

LED offLED on

A0.5334.84

B0.6524.86

C0.6224.86

Table 3 shows the position of the shaft at each turn Table 3positionABC

0000

1100

2110

3010

4011

5111

6101

7001

Discussion and Analysis

Part A: Slotted Opto TransducerThis type of transducer is manly used to measure the speed of a rotating object. As the results shows, when the slot in the rotating disc allows the light to pass through it, it gave a voltage of 4.90 v. also when the disc has broken the light it gave a value of 18mV. Hence, this explains the principle behind this sensor. The sensor detects the variation on voltage and each time it does that it counts. Dividing the number of counts over a period of time it gives us the frequency and from it the speed can be calculated. The graph plotted of voltage supplied to motor verses the speed shows that the speed of the disc is directly proportional to voltage supplied to the motor. This is expected, since as the voltage increase it supplies more energy to the shaft which will convert it to kinetic energy and as a results we will have a higher speed.Part B: Reflective Opto TransducerThis type transducer is more likely for locating positions. The results in table 3 shows that there are 8 different positions. Each combination of 1 and 0 represents a position on the reflective disc.

Error/Sensitivity Analysis

Difficulty in reading the number of revolutions per second because the number kept flickering and changing and did not settle on one value. The LED of the timer which showed the number of revolutions was off making it impossible to know the number of revolutions that have been completed. Calibration Error: This error occurs when the device reads a value when it is in an ideal or unloaded state. This error is also known as zero or offset error. There was some difficulty adjusting the rotating disc as well as adjusting the LEDs to be all off because every slight movement/rotation affects the reading. The connecting wires have some internal resistance that cause the wires to overheat. There was some difficulty in reading the number of revolutions per second because the number kept flickering and changing and did not settle on one value.

Overall impression

This lab was the most enjoyable session so far. First, we measured the rotational speed in rev/sec of a Slotted Opto-Transducer at different voltages. Then, we measured the output voltages of a Reflective Opto-Transducer when the Gray Code Disc was at different positions. Last, we plotted a graph to verify and check the linearity of our results.

Figures, Tables, and References

Previously provided

Appendix: Raw Data Summaries

15