Digital Measurement

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????????????????????
Digital Measurement
303251 EE Instruments Measurements , EECPE ,
NU Piyadanai Pachanapan
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Analog v.s. Digital
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???????????????????? Digital Measurement

• ?????????????????????????????????????
  ???????????????????

• ?????????????????????????? (Human reading
  Interpolation errors)

• ??????????????????????? (increases reading speed)

• ???????????????????????????? (Processing)
  ,?????? (Controlling) ???? ??????? (Recording)
  ????????

• ?????????????????????????? (Noise)

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Analog Measurement
Digital Measurement
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??????????????????????????????????????

• Input Range /- 1.0 V to /- 1,000.0 V, with
  automatic range selection and overload indication

• Absolute Accuracy as high as /- 0.005 of
  the reading

• Resolution 1 part in 106 ( 1 can be
  read on the 1-V input range)

• Input Characteristic Input Resistance
  typically 10

• Output Signal BCD (binary coded decimal)
  output for digital processing or recording

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?????????????????????????????????? Analog to
Digital Converter (ADC)

• ??????????????? Analog ??????? Digital ???? 4
  ???? ??????

1. Counting Converter

2. Successive Approximate
3. Dual Slope Converter
4. Flash Converter
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?????????????? ADC
Digital to Analog Converter

• ?????????? DAC ??? Comparator

• ?????? Logic ??????????????????????????

• ???????????????? DAC ??????????????????????
  input (?????????)

• ???????????????????? DAC ??????? ?????? input

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1. Counting Converter

• ????????????????????? ????????? Analog -gt Digital

• ????????????????????????????? ???????????????????
  ???????????????????????? (?????? input,
  ????????????)

• ?????????? ??????????

• Digital to Analog Converter (DAC)

• Comparator

• Counter

• Logic gate

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Counting Converter
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And Gate
Look Up Table
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AND

• ????? D/A ????????????????????? 1 ?????????
  (Counter) ??????????????????? analog
  ?????????????????? ?????

• Comparator ?????????????????????? input ???
  ??????????????????

• ????????????? 2 ??????? ?????? output ???
  comparator ????????? 0 (logic 0)
  ????????????????????????????? 0 (logic 1)

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• ?????? output ??? comparator ????????? logic
  gate ??? clock (????????????)

• logic 1 ? clock ???????? ? ??????????????????

• logic 0 ? clock ????????? ? ????????????????? ?
  ???????????????? ????????????????

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• ?????????????????????????????

1. DAC setting time, tda

2. Comparator setting time, ts
3. Logic Reaction setting time, tl
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??????? ??? Counting Converter

• ????????????????? 0 ???? ??????????????????
  ????????

• ?????????????? ? Output ???? delay
  (???????????????)

• ?????????????????????????

• ????????????????????????? ???????????????????????
  ?????? ???????????????????? 0 ????

• ????????????????? input ???? ????????????????????
  ????? ?????????????????????

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??? ???? / ??
Check ? ???? counter

• Count Up ? ?????? ()

• Count Down ? ????? (-)

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Digital Voltmeter ?????? Counting Converter
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2. Successive Approximate

• ????????????? Binary Search ????????????

• ??????????????????????????????????????????????
  ??????????????????????? ??????? ???? ????????

• ??????????????????????????????
  ??????????????????????????????????????????????????
  ?? ??????????????????????

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3 bit, 0-7
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Flow Chart
Vsp mid point of the current space
being tested
Vest the current estimate of the voltage with
zeros in the bit position which have not yet been
tested
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??????? Successive Approximate
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????? ??????? Successive Approximate

• ??????????????????? Counting Algoritm

• ???????????????????????????? (n ???) ?????? n
  bit converter ?????????????? 2n ????? ??? ?????
  Vin ?????

??????? ??????? Successive Approximate

• ??? Vin ????????????????? ????? binary search gt
  ?????????????????? ???? Vin ?????????? 5 V ???? 2
  V

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• Successive Approximate ?????? 9 bit , 0 - 511

• ????? 499

• ????? 320

???????????????????????? ????? 9 ????? ( n)
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(No Transcript)
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??????????????????????????? input
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Digital Voltmeter ?????? Successive Approximate
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3. Dual Slope ADC

• ?????????????? Integrator ???????????? Comparator

????????????? C
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???????? SW1 ????? Vin
????? Vo ????
(??????????? ???)
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???????? SW1 ????? Vref
????? Vo ????
(??????????? ??)
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?????????????????? Dual Slope Converter

1. ????? SW1 ????? Vin ???????? M.t (?????????????)
   ????? Vin Vx

2. ???????? M.t ????? SW1 ????? Vref
????????????????????? ?????? Vo 0
(?????????????? N.t)
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3. ????????????? ????????????????? ??????
??.?????? counter
?????
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• ???????????????????????? ?????????????

- ?????????? input, Vin
- ??? R, C ??????? Integrator

• ?????????????? ADC ??????? ???

• ??? comparator?????????????? ?
  ?????????????????? ???????????????????????????????
  ?????

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• ??????????? Comparator ??????????????

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• ?????????????????????????? (???????????????
  )

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Digital Voltmeter ?????? Successive Approximate
Vin
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4. Flash Converter

• ???????????????????????????????? (Voltage
  Divider) ?????????????????????????????? comparator

• ??????????? Vin ??? Comparator ???????? ????????

• ?????????????????????????? ??????? logic ?????
  ??????

Logic 1 ????? ????????????????? Vin
Logic 0 ????? ????????????????? Vin
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3 bit flash converter
0 7 V
????????????????????????????????????????
???????????? bit ???????
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???????? IC ??????? ADC
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End Of Unit