1. EKT 314/4 WEEK 6 : CHAPTER 3 SIGNAL CONDITIONING EKT 314 Electronic instrumentation

2. Chapter 3 Content Introduction Signal Conditioning Circuit (SCC) Function Preliminary Requirement Signal Conditioning (SC) System Type Amplifier Modulator Filter

3. Amplifier Two types Operational Amplifier (OpAmp) Instrumentation Amplifier

4. Difference with ordinary opamp Often a package consisting of numbers of opamps (wired up with accurate and stable resistive feedback to give a desired gain). Can be used directly. Often yield a high CMRR.

5. Instrumentation Amplifier

7. Derivation

8. Conclusion From derived equation: The output of operational amplifier depends on R 1 and R 2. If R 2 is fixed, R 1 (potentiometer) will become the gain selector terminal.

9. Commercial Instrumentation Amplifier Example AD612/4

11. Step 1: Eliminate Casing

12. Step 2: Reposition Guard Res.

13. Step 3: Reposition O/p Opamp

14. Step 4: Rearrange 40k & 16.8k

15. Step 5: Arrange Res @ p3 – 12

16. Step 6: Labelling R2-R7

17. Step 7: Forming R1 Resistor

18. Controlling Instrumentation Amplifier Example

20. Gain Programming Steps #CS=0, #WR=0 IC3.1=1, D[3:0] Latch into IC1 #RD=1, IC3.10=0, IC3.4=1 IC2 control = 0, IC2 output = Hi-Z D[3:0] not conflict

21. Gain Programming Steps Programming data available at A,B,C,D 7442 only have one ‘1’ output at pin 1-8 Only one Pin from IC5 will active

22. Gain Programming Steps So, Gain Prog pin will be connect only to one pin X2 X4 X8 X16. X256

23. Gain Reading Steps #CS=0, #WR=1 IC3.1=0 #RD=0, IC3.10=1, IC3.4=0 IC2 control = 1 D[3:0] now have data from IC1 (previously set)

24. Additional – Isolation Amplifier Isolation amplifiers provide electrical isolation and an electrical safety barrier. They protect data acquisition components from common mode voltages, which are potential differences between instrument ground and signal ground. Instruments without an isolation barrier that are applied in the presence of a common mode voltage allow ground currents to circulate, leading in the best case to a noisy representation of the signal under investigation.

25. Additional – Isolation Amplifier In the worst case, assuming that the magnitude of common mode voltage and/or current is sufficient, instrument destruction is likely. Amplifiers with an isolation barrier allow the front-end of the amplifier to float with respect to common mode voltage to the limit of the barrier's breakdown voltage, which is often 1,000 VDC, peak AC, or more. This action serves to protect the amplifier and the instrument connected to it, while still allowing a reasonably accurate measurement.

26. Additional – Isolation Amplifier These amplifiers are also useful when you need to amplify low-level signals in multi-channel applications. They can also eliminate measurement errors caused by ground loops. Amplifiers with internal transformers reduce circuit costs by eliminating the need for additional isolated power supply. We usually use them as analogue interfaces between systems with separated grounds.

27. Additional – Isolation Amplifier 2 Types of Isolation Amplifier: Two ports: When the DC-DC is not integrated. When there are two isolated parts. Three ports: When the DC-DC is integrated. The parts are isolated between them.

28. Additional – Isolation Amplifier In most applications, an output voltage is obtained by passing the output current through a resistor. Other possible applications: Floating pulse amplifier output voltage and current interface. Instrumentation in high-noise environments. Analogue front-end processing. Medical instrumentation.

29. Chapter 3 Content Introduction Signal Conditioning Circuit (SCC) Function Preliminary Requirement Signal Conditioning (SC) System Type Amplifier Modulator Filter

30. Chapter 3 Content Introduction Signal Conditioning Circuit (SCC) Function Preliminary Requirement Signal Conditioning (SC) System Type Amplifier Modulator Function Chopper Examples Filter

31. Modulator Function To enable dc signal to be used in ac system Used to change direct current, or very slow varying signals into square waves (or pulses). Circuit consist of additional circuit component known as chopper. Many type of Choppers: Electromechanical Chopper, Transistor Chopper, Balanced Transistor Chopper, Photo Optical Chopper, etc.

32. Chapter 3 Content Introduction Signal Conditioning Circuit (SCC) Function Preliminary Requirement Signal Conditioning (SC) System Type Amplifier Modulator Function Chopper Examples Filter

33. Electromechanical Chopper

34. Transistor Chopper

35. Balanced Transistor Chopper

36. Chapter 3 Content Introduction Signal Conditioning Circuit (SCC) Function Preliminary Requirement Signal Conditioning (SC) System Type Amplifier Modulator Function Chopper Examples Filter

37. Magnetic Modulator

38. Diode Bridge Type Modulator

39. Capacitance Modulator

40. Solid State Modulator-Demodulator

41. EKT 314/4 WEEK 6 : CHAPTER 3 END ELECTRONIC INSTRUMENTATION