Precision Variable Frequency Drive

Group May07-13

Jason Kilzer

Nick Nation

Dave Reinhardt

Matt Shriver

Client: Jim Walker

Faculty Advisor: Professor Ajjarapu

Precision Variable Frequency Drive

• Nick – Uses and Constraints

• Jason – Technology and Overall Design

• Matt – Detailed Design

• Dave – Requirements, Schedules, Conclusions

Problem Statement

The problem is the ability of a record player to keep a specific speed. The synchronous motor used on a record player is supposed to play the record at a specific speed. However, the motor does not always run at the specified speed which causes the record to sound out of pitch. A precision variable frequency drive will provide a constant frequency to the synchronous motor which in turn will maintain a constant speed of the record table.

Executive Summary

Synchronous motors are motors that run at a specific speed. A customer may want to run the motor at different speeds, like for a record player that needs to operate at 45 and 33 1/3 rpm. A precision variable frequency drive is a way to speed up or slow down the motor by changing the frequency of the input voltage.

 

This product will be designed to adjust the frequency between 58 to 62 hertz by the turning of a dial. The digital display will be accurate up to the thousandth of a hertz. In addition, a strobe light will allow the user to observe the rpm of the motor. The precision variable frequency drive will have a long term drift that requires a gradual decrease/increase of speed that allows for more accurate tuning.

Operating Environment

• Indoors• No extreme dust• No extreme temperatures

Intended Users and Uses

• Users– Avid music listener– Lay person

• Uses– Adjust the frequency of the turn-table– With other synchronous motors

Assumptions

• Constant linkage – the belt connecting the motor to the turntable is constant over a short time period. Basically, an increase in motor speed by a certain factor will result in an increase in the speed of the turntable by the same factor.

• Plug – the plug from the record player can plug into a standard three pronged outlet.

Limitations

• Precision – the precision variable frequency drive will be accurate to .1 Hertz.

• Price – the total end product cost must be less than $1,000.

• Frequency Range – 58 to 62 Hertz with step of 0.1 Hertz.

• Nominal Voltage – 120 VAC.

• Stability – the precision variable frequency drive must be stable. Short term stability of less that +/- 0.01%. It shall not be affected by fluctuations in incoming voltage or frequency.

• Power Output – 75 W minimum.

• Input Voltage – the input voltage will be a standard household outlet of 120 V at 60 Hz. single phase

Design Considerations

• Maximum weight and size• Minimum power output• Minimum operating frequency

Functional Requirements

• Synchronous motor frequency controller• Knob controller to adjust frequency• Digital read-out of frequency• Portable strobe system

Technology Considerations

• Pulse Width Modulation

• Crystal Oscillator

Technology Approach Considerations

1.  An AC/DC converter was needed to change the input of AC voltage to DC voltage.

2.  The pulse width modulator will allow the user to change the frequency of the voltage.

3.  A low pass filter would change the DC signal back into an AC signal at the desired frequency.

4. A amplifier would be needed to step the voltage up to an appropriate level to feed the turn-table.

5. A frequency counter would be used to display the frequency output of the low pass filter.

6. A strobe light system would be used to measure the RPM of the motor.

Testing Considerations

• Pulse-width modulator

• Strobe system

• Complete system

Product Design

Power Source

• 110-120 VAC• 60 Hz nominal frequency• Standard wall outlet

AC to DC Converter

The AC to DC converter will take in 120 VAC and produce 25 Volt DC. The project team will purchase this component. The group is going to purchase a converter of the same type that a cell phone charger would use. The converter is around $20 to purchase. After the power has been changed into DC pulse width modulation can take place.

Circuit Simulation via Simulink

Pulse Width Modulator (PWM)

Circuit Design of PWM

Triangle Waveform Generator Circuit

U2

uA741

3

2

74

6

1

5+

-

V+

V-

OUT

OS1

OS2

U1

uA741

3

2

74

6

1

5+

-

V+

V-

OUT

OS1

OS2

R3

10k

-VCC+VCC

00

R5

12.5k

0

V110Vdc

V2-10Vdc

-VCC

0

R4

1k

R2

20k

0

Z4

Zener_diode

+VCC

V30Vdc

-VCC

C1

1n

+VCC

V

Z3

Zener_diode

Triangle Waveform

Comparator Circuit+VCC

V2-10Vdc

V110Vdc

Q1

Q2N3904

VTRI0 -VCC

-VCC0

R4

20+VCC

R5

20

+VCC

V

0

V410Vac

Q2

Q2N3904

+VCC

00

0

U1uA741

3

2

74

6

1

5+

-

V+

V-

OUT

OS1

OS2

Waveform after PWM

Low Pass Filter

Waveform After Low-Pass Filter

Transformer

Waveform After Transformer

Frequency Counter

A frequency counter will connect to the circuit after the low pass filter and measure the frequency of the AC signal being outputted to the voltage amplifier. This device will display the frequency of the power it is sampling on a LCD screen. Figure 8 shows a picture of the frequency counter that will

be purchased.

Product Design

Strobe Light System

Figure 10: Strobe Light Schematic (Vinyl Engine)Figure 11: The strobe light shinning on the special disc. (Vinyl Engine)

The strobe system will be used to measure the the RPM of the turn-table. As the picture shows, there are three different circles for the three rates, 33 1/3, 45, and 78.

Personal Requirements

Name Task 1 Task 2 Task 3 Task 4 Task 5 Task 6 Task 7 Task 8 Totals

Reinhardt, Dave 1 7 40 6 5 4 5 24 92

Kilzer, Jason 1 10 42 3 5 2 5 18 86

Nation, Nick 1 7 40 3 5 6 5 18 85

Shriver, Matt 1.5 6 40 3 5 6 5 20 86.5

Total (hours) 4.5 30 162 15 20 18 20 80 349.5

Other Resource Requirements

Item Team Hours Other Hours Cost

Miscellaneous Parts & Materials  0  0 $20.00 

Device Components 2 0 $65.94

Project/Poster Printing 5 0 $0.00

Total 7 0 $85.94

Financial Requirements

Item   W/O Labor With Labor

Miscellaneous Parts & Materials    $20.00  $20.00

Device Components   $65.94 $65.94

Project/Poster Printing   $0.00 $40.00

  Subtotal $85.94 $125.94

Labor at $15.00 per hour:    

Reinhardt, Dave     $1,380.00

Kilzer, Jason     $1,290.00

Nation, Nick     $1,275.00

Shriver, Matt     $1,297.50

  Subtotal   $5,242.50

  Total $85.94 $5,368.44

Schedule

Deadline Chart

Design Evaluation

FunctionalityRelative

ImportanceEvaluation

ScoreResultant

ScoreStablility of frequency 15% 80% 12.00%Adjustable frequency between 58-62 Hz 25% 100% 25.00%Accurate strobe light system 5% 60% 3.00%Safety 15% 100% 15.00%Precision of .1 Hz 20% 100% 20.00%User friendly 5% 90% 4.50%LED display of output frequency 5% 70% 3.50%Output at least 75W 10% 50% 5.00%

Score 88.00%

Summary

Upon review of the detailed project design, it has been decided to continue the project as planned. It will be continued as scheduled because the detailed design has meet the functional requirements of the precision variable frequency drive.

Questions?