1. 3441 Industrial Instruments 1 Chapter 3 Digital Signal Conditioning
Princess Sumaya University
Industrial Instruments 1
Princess Sumaya Univ. Electronic Engineering Dept.
3441 Industrial Instruments 1 Chapter 3 Digital Signal Conditioning
Dr. Bassam Kahhaleh
Dr. Bassam Kahhaleh

2. Digital Signal Conditioning
Princess Sumaya University
Industrial Instruments 1
Digital Signal Conditioning
Objective
Introduce the basic technique of digital signal conditioning, especially interfacing, in process control.

3. Digital Signal Conditioning
Princess Sumaya University
Industrial Instruments 1
Digital Signal Conditioning
Digital Signals
Pressure
Level
Temperature

4. Digital Signal Conditioning
Princess Sumaya University
Industrial Instruments 1
Digital 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

5. Digital Signal Conditioning
Princess Sumaya University
Industrial Instruments 1
Digital 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).

6. Digital Signal Conditioning
Princess Sumaya University
Industrial Instruments 1
Digital 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 !!

7. Digital Signal Conditioning
Princess Sumaya University
Industrial Instruments 1
Digital 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

8. Digital Signal Conditioning
Princess Sumaya University
Industrial Instruments 1
Digital 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

9. Digital Signal Conditioning
Princess Sumaya University
Industrial Instruments 1
Digital Signal Conditioning
TTL Interfacing
+VCC2
+VCC1
VCC2 > VCC1 IR R Vo

10. Digital Signal Conditioning
Princess Sumaya University
Industrial Instruments 1
Digital 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

11. Digital Signal Conditioning
Princess Sumaya University
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?

12. Digital Signal Conditioning
Princess Sumaya University
Industrial Instruments 1
Digital Signal Conditioning
Converters
Hysteresis Comparators
Vout
R f VO R
Vin + −
Vout
Vref
Vin VL VH

13. Digital Signal Conditioning
Princess Sumaya University
Industrial Instruments 1
Digital Signal Conditioning
Converters
Digital-to-Analog Converters (DAC)
Bipolar DAC
Conversion Resolution?

14. Digital Signal Conditioning
Princess Sumaya University
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

15. Digital Signal Conditioning
Princess Sumaya University
Industrial Instruments 1
Digital Signal Conditioning R
Converters
R-2R ladder
DAC R R R − +
V out 2R 2R 2R 2R 2R VR
VTH
RTH = R
= ½ VR

16. Digital Signal Conditioning
Princess Sumaya University
Industrial Instruments 1
Digital Signal Conditioning R
Converters
R-2R ladder
DAC R R R R − +
V out
½ VR 2R 2R 2R
VTH
RTH = R
= ¼ VR

17. Digital Signal Conditioning
Princess Sumaya University
Industrial Instruments 1
Digital Signal Conditioning
Converters
Analog-to-Digital Converters (ADC)
Bipolar ADC
Conversion Resolution?

18. Digital Signal Conditioning
Princess Sumaya University
Industrial Instruments 1
Digital Signal Conditioning
Converters
Parallel Feedback ADC SC VX
Logic Counting Network
EOC
bn-1
bn-2 b1 b0
Comparator
...
DAC

19. Digital Signal Conditioning
Princess Sumaya University
Industrial Instruments 1
Digital Signal Conditioning
Converters
Ramp ADC (Dual-Slope) VO V1 t T1
t x
Digital
Counter
Logic Control
Comparator
−VX
bn-1
bn-2 b1 b0 SC
EOC − +
+VR R C VO

20. Digital Signal Conditioning
Princess Sumaya University
Industrial Instruments 1
Digital Signal Conditioning
Converters
Conversion-Time Consequences Vi
VN+1 VN t
 C

21. Digital Signal Conditioning
Princess Sumaya University
Industrial Instruments 1
Digital Signal Conditioning
Converters
Sample-and-Hold (S/H)
Vc(t)
Vin(t) + −
ADC C
S/H

22. Digital Signal Conditioning
Princess Sumaya University
Industrial Instruments 1
Digital Signal Conditioning
End of Chapter 3