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Princess Sumaya Univ. Electronic Engineering Dept. 3441 Industrial Instruments 1 Chapter 3 Digital Signal Conditioning. Dr. Bassam Kahhaleh. Digital Signal Conditioning. Objective Introduce the basic technique of digital signal conditioning, especially interfacing, in process control.

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digital signal conditioning
3441 - Industrial Instruments 1Digital Signal Conditioning

Objective

Introduce the basic technique of digital signal conditioning, especially interfacing, in process control.

digital signal conditioning1
3441 - Industrial Instruments 1Digital Signal Conditioning

Digital Signals

Pressure

Level

Temperature

digital signal conditioning2
3441 - Industrial Instruments 1Digital Signal Conditioning

Digital Signals

TTL Output

  • Totem-pole
  • Tri-state
  • Open-collector

I H = 0.04 mA

I H = 0.4 mA

I L = 1.6 mA

I L = 16 mA

digital signal conditioning3
3441 - Industrial Instruments 1Digital Signal Conditioning

TTL Interfacing

  • Never leave inputs unconnected
  • Never short-circuit outputs to ground or Vcc
  • Never short-circuit outputs together unless they are tri-state or open-collector outputs
  • Never use pull-down resistors
  • Be careful when using different power supplies (VCC1 = +5, VCC2 = +12).
digital signal conditioning4
3441 - Industrial Instruments 1Digital Signal Conditioning

TTL Interfacing

What is the minimum resistance value?

When the tri-state output is floating:

V should be max 0.8, IR = 1.6 mA

 R = 0.8 / 1.6 = 0.5 KΩ

V

IR

Now what happens when the tri-state output goes high?

V should be min 2.4 V, therefore IR = 2.4 / 0.5 K = 4.8 mA !!

digital signal conditioning5
3441 - Industrial Instruments 1Digital Signal Conditioning

TTL Interfacing

+VCC

+VCC

Typically, R = 10 KΩ

 IR max = (5 – 0.2) / 10 = 0.48 mA

IR

V

Now what is the value of V when the tri-state outputs goes floating?

IR = 0.04 mA  V = 5 – 0.04 x 10 = 4.6 Volts

digital signal conditioning6
3441 - Industrial Instruments 1Digital Signal Conditioning

TTL Interfacing

+VCC

LED:

V = 1.5 ~ 1.6 V

I = 10 ~ 15 mA

IR

R

Vo

Standard TTL gates should not source such current to a LED, but it can sink it.

What is the minimum value of R?

VO max = 0.8 V, IR = 15 mA

 R = (5 – 1.5 – 0.8) / 15 = 0.18 KΩ

Typically, VO max = 0.2 V, IR = 15 mA, R = 220 Ω

digital signal conditioning7
3441 - Industrial Instruments 1Digital Signal Conditioning

TTL Interfacing

+VCC2

+VCC1

VCC2 > VCC1

IR

R

Vo

digital signal conditioning8
3441 - Industrial Instruments 1Digital Signal Conditioning

TTL Interfacing

Relay current = 40 mA

β = 100

 IB = 0.4 mA

R = (2.4 – 0.7) / 0.4

= 4.25 KΩ

R

digital signal conditioning9

+

+

3441 - Industrial Instruments 1

Digital Signal Conditioning

Converters

Comparators

2.2 mV/°C

T

0.352 V

Alarm

0.2 V / kPa

P

2.0 V

Comparators’ Power Supply?

digital signal conditioning10

+

3441 - Industrial Instruments 1

Digital Signal Conditioning

Converters

Hysteresis Comparators

Vout

R f

VO

R

Vin

Vout

Vref

0

Vin

VL

VH

digital signal conditioning11
3441 - Industrial Instruments 1Digital Signal Conditioning

Converters

Digital-to-Analog Converters (DAC)

Bipolar DAC

Conversion Resolution?

digital signal conditioning12

+

3441 - Industrial Instruments 1

Digital Signal Conditioning

R

Converters

R-2R ladder

DAC

R

R

R

V out

2R

2R

2R

2R

2R

b0

b1

b2

b3

VR

digital signal conditioning13

RTH = R

+

VTH

= ½ VR

3441 - Industrial Instruments 1

Digital Signal Conditioning

R

Converters

R-2R ladder

DAC

R

R

R

V out

2R

2R

2R

2R

2R

VR

digital signal conditioning14

RTH = R

+

VTH

= ¼ VR

3441 - Industrial Instruments 1

Digital Signal Conditioning

R

Converters

R-2R ladder

DAC

R

R

R

R

V out

½ VR

2R

2R

2R

digital signal conditioning15
3441 - Industrial Instruments 1Digital Signal Conditioning

Converters

Analog-to-Digital Converters (ADC)

Bipolar ADC

Conversion Resolution?

digital signal conditioning16
3441 - Industrial Instruments 1Digital Signal Conditioning

Converters

Parallel Feedback ADC

SC

VX

Logic CountingNetwork

EOC

bn-1

bn-2

b1

b0

Comparator

...

DAC

digital signal conditioning17

C

bn-1

bn-2

b1

b0

Digital

Counter

R

−VX

+

+VR

Comparator

Logic Control

EOC

SC

3441 - Industrial Instruments 1

Digital Signal Conditioning

Converters

Ramp ADC (Dual-Slope)

VO

V1

t

0

T1

t x

VO

digital signal conditioning18
3441 - Industrial Instruments 1Digital Signal Conditioning

Converters

Conversion-Time Consequences

Vi

VN+1

VN

t

C

digital signal conditioning19

+

3441 - Industrial Instruments 1

Digital Signal Conditioning

Converters

Sample-and-Hold (S/H)

Vc(t)

Vin(t)

ADC

C

S/H