DC Motors and Generators

1
DC Motors and Generators
2
A Cutaway DC Motor Generator
3
Typical DC M-G Diagram
4
Some general definitions for m-g

• Stator Non moving (think stationary) part of an
  electric rotating machine. In a motor it
  generally contains the primary winding of wires.
• Rotor the rotating part of an electric machine
  connected to and turns the drive shaft.

5
Some general definitions for m-g

• armature sometimes referred to as just the
  rotor, but also infers the reaction of the
  magnetic field produced by the current on the
  magnetic lines of force produced by a field coil
  of an electric
• motor/generator (m-g).

6
Some general definitions for m-g

• Shunt field a particular type of field coil for
  a DC motor that is connected with the armature in
  parallel.
• Series field a field coil that is wired in
  series with the armature.
• Compound- a combination of the
• above 2

7
Some general definitions for m-g

• Commutator bars of metal grouped around the
  shaft of a motor to provide an electrical
  connection between the armature coils and
  brushes. They maintain current flow in one
  direction by reversing the magnetic polarity of
  the rotor each revolution cycle.

8
The typical circuit
9
Saturation or Magnetization Curves
10
Saturation or Magnetization Curves
11
Saturation or Magnetization Curves
12
Saturation or Magnetization Curves
13
DAC Specifications

• Accuracy -
• A comparison of the actual output with the
  expected output. Generally specified as a
  percentage of the full scale output.

10 Vfs , 0.2 accuracy 20 mV
14
DAC Specifications
Vref The full scale (or maximum) output
voltage Vref- The minimum output voltage
15
DAC Specifications

• Speed -
• Output settling time. Time required for
  output to settle after an input word change.

16
DAC Example

• Given a 2-bit DAC with an 8 V full scale_at_ 0.2
  accuracy, find resolution andaccuracy in terms
  of voltage.

17
DAC Example
8 V
6 V
4 V
2 V
00
01
10
11
18
Analog-to-Digital Conversion
19
Definition

• Analog-to-Digital Converter -
• Circuit that converts an analog voltage into a
  digital value.

20
Analog to Digital Conversion Basics
21
(No Transcript)
22
Digital Ramp ADC
23
(No Transcript)
24
Successive Approximation ADC (SAC)
25
(No Transcript)
26
(No Transcript)
27
Flash ADC
8 V
Vin
5 V
Encoding
Q1
Q0
28
ADC Specifications

• Resolution -
• Also referred to as quantizing error. Error
  between actual analog value and its digital
  representation.

29
ADC Specifications

• Accuracy -
• A comparison of the actual output with the
  expected output. Same as for DAC.

30
ADC Specifications

• Conversion Time -
• Time required to digitize each sample.
  Function of conversion method and number of bits.

31
ADC Techniques

• Parallel Comparator (Flash) - Very
  high-speed conversion
• Dual Slope - Slow Speed, High Resolution
• Successive Approximation - High Speed, Medium
  Resolution

32
Sample and Hold

• Used when input signal is quicklyChanging
  (high frequency applications).

33
Sampling Rate

• Frequency of samples.(e.g. 44 kHz or every
  22.7 ms)

Each sample is quantizedinto a digital
number.(e.g. 12 bits)
34
ADC and DAC Conversion