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ELECTRONIC INSTRUMENTATION EKT 314/4 WEEK 5 : CHAPTER 3 SIGNAL CONDITIONING Chapter 3 Problem Statement Don’t know why signal conditioning needed. Don’t know where should the signal conditioning part to be located. Don’t know what actually the content of signal conditioning part. Don’t know what the function of signal conditioning parts. Chapter 3 Objectives To understand why signal conditioning is important To know where exactly signal conditioning circuit exist To implement amplifier, modulator and filter circuit in system To suit each circuit to system implementation Chapter 3 Content Introduction Signal Conditioning Circuit (SCC) Function Preliminary Requirement Signal Conditioning (SC) System Type Amplifier Modulator Filter Chapter 3 Content Introduction Signal Conditioning Circuit (SCC) Function Preliminary Requirement Signal Conditioning (SC) System Type Amplifier Modulator Filter Introduction SCC Function Perform Linear Task/Process 2. Perform Non-Linear Task/Process 1. Chapter 3 Content Introduction Signal Conditioning Circuit (SCC) Function Preliminary Requirement Signal Conditioning (SC) System Type Amplifier Modulator Filter SCC Function Perform Linear Task/Process 1. › › › › › › 2. Amplification Attenuation Integration Differentiation Addition Substraction Perform Non-Linear Task/Process SCC Function Perform Linear Task/Process 2. Perform Non-Linear Task/Process 1. › › › › › › › Modulation Demodulation Sampling Filtering Clipping & Clamping Squaring & Linearizing Multiplication Chapter 3 Content Introduction Signal Conditioning Circuit (SCC) Function Preliminary Requirement Signal Conditioning (SC) System Type Amplifier Modulator Filter Preliminary Requirement Passive Transducer Require excitation Require amplification Active Transducer Require amplification Signal Excitation Only needed by passive transducer since they cannot generate their own voltage or current Excitation come from external source External source can be ac or dc Chapter 3 Content Introduction Signal Conditioning Circuit (SCC) Function Preliminary Requirement Signal Conditioning (SC) System Type Amplifier Modulator Filter SC System Type DC Signal Conditioning System 2. AC Signal Conditioning System 1. SC System Type 1. DC Signal Conditioning System 2. Generally used for common resistance transducers (e.g. potentiometer and straing gauges) AC Signal Conditioning System Used for variable reactance transducers For systems where signal have to be transmitted via long cables to connect the transducers to signal conditioning equipment. DC Signal Conditioning System AC Signal Conditioning System Signal Conditioning (SC) System Type DC SC System AC SC System Chapter 3 Content Introduction Signal Conditioning Circuit (SCC) Function Preliminary Requirement Signal Conditioning (SC) System Type Amplifier Modulator Filter Amplifier Two types Operational Amplifier (OpAmp) Instrumentation Amplifier Amplifier Normal Amplifier Block Diagram OPAMPs Non-Inverting / Inverting Integrator / Differentiator Sum/Scale/Average Substractor Comparator Instrumentation Amplifier Amplifier: Block Diagram Input Stage • Dual input balanced output differential amplifer • Double-ended high gain amplifier • Gain = 60 Intermediate Stage • Single-ended differential amplifier • Dual input unbalanced output differential amplifier • Gain = 30 Level Shifter • Level translator circuit • To bring dc output voltage to ground potential Output Stage • Push-pull complementary amplifier • Gain = 5 to 10 OPAMPs Vo = AVid = A(V+ - V-) A – Large signal voltage gain Vid – differential input voltage V+ - noninverting terminal voltage V- - inverting terminal voltage OpAmp Operation Non-Inverting Scaling Amplifer Inverting Averaging Amplifier Integrator Substractor Differentiator Comparator Summing Amplifier Non-Inverting Amplifier Key: Input signal is applied to the non-inverting input terminal. Vo V V 0 RF R1 V Vin Vo Vin Vin RF RF R1 1 Vo 1 Vin RF R1 RF R Vo AF 1 F Vin R1 Inverting Amplifier Key: The input signal is applied to the inverting terminal. Vin V V Vo R1 RF V V 0 Vin Vo R1 RF Vo RF AF Vin R1 OpAmp as Integrator OpAmp as Integrator Key: Use CF instead of RF I in I f Vin V dV CF C R1 dt Vin V d (V Vo ) CF R1 dt V V 0 Vin dV C F o R1 dt t t Vin dVo C F 0 R1 dt 0 t 1 Vo Vin dt C F R1 0 Practical Integrator Circuit At low freq and dc signal, CF acts like an open circuit Close loop gain = open loop gain Produce too much output offset voltage. Practical Integrator Circuit At zero freq (DC) and without negative feedback, the circuit treats the input offsets as a valid input signal charges the capacitor. This drive the output into +ve or –ve saturation. Practical Integrator Circuit Insert RF in parallel with CF Resistor, RF used must be at least 10 times the input resistance, R1 Integrator Application To use constant input voltage to produce a ramp voltage Analog Computer A/D Conversion Signal Wave Shaping OpAmp as Differentiator OpAmp as Differentiator Key: Input resistor replaced by capacitor Ic I f C1 dVc V Vo dt RF C1 d (Vin V ) V Vo dt RF V V 0 because A C1 dVin V o dt RF Vo C1 RF dVin dt Practical Differentiator Circuit This differentiator has tendency to undesirably oscillate The gain RF/XC1 increases at a rate of 20dB/decade with increases in frequency become unstable Practical Differentiator Circuit As the freq increases, input impedance XC decreases, making the circuit more susceptible to high frequency noise. This noise is superimposed after amplification, on the differential output signal. Practical Differentiator Circuit Introduce R1 and CF 0.01RF < R1 < 0.1RF so close loop gain reduced to between -10 to -100. Practical Differentiator Circuit Consideration: 1. fa is the highest freq range to be differentiated fa = 1/(2RFC1) Practical Differentiator Circuit Consideration: 2. fb is the gain limiting frequency at which the gain begins to decrease at a rate of 20db/decade. fb = 1/(2R1C1) R1C1=RFCF fb=20fa Differentiator Application Detection of the leading and trailing edges of rectangular pulse Wave shaping circuit to detect high frequency components in an input signal. Rate of change detector in FM modulators. Triggering the time base generator in an oscilloscope. OpAmp as Summing Key: Depends on relation of Ra, Rb, Rc, RF, circuit can be summing, scaling or average amplifier. I a Ib Ic I f I I 0 Va V Vb V Vc V V Vo Ra Rb Rc RF V V 0 Va Vb Vc Vo Ra Rb Rc RF Sum, Scale, Average Amplifier Function Condition 1 Sum Ra=Rb=Rc=RF 2 Scale Ra≠Rb ≠ Rc 3 Average Ra=Rb=Rc Scale : Va Vb Vc V o Ra Rb Rc RF Ra Rb Rc RF RF RF Vo Va Vb Vc Rb Rc Ra Sum : Va Vb Vc V o Ra Rb Rc RF Ra Rb Rc RF Vo (Va Vb Vc ) Average : RF 1 R n R Vo (Va Vb Vc ) F R V V V Vo a b c 3 Ra Rb Rc R; OpAmp as Substractor Key: All R value are same. at node V : Va V V Vo R R Vo Va 2V at node V : Vb V V 0 R R V V b 2 V V , Substitute into Vo : Vo Va Vb OpAmp as Comparator Key: Opamp used without feedback. Amplifier goes either to saturation limit +Vcc or – VEE One terminal considered as reference terminal. When V+ > V-, Vo When V+ < V-, Vo OpAmp as Comparator If V- = GND, slight V+++ result in Vo = +Vsat = +VCC If V- = GND, V+ goes slightly below 0, Vo = -Vsat = -VEE Diodes used to protect opamp from damage due to excessive Vin. OpAmp as Comparator If Vin feed to V+ then it is called non-inverting comparator. If Vin fed to V- then it is called inverting comparator. Comparator Application Discriminator Voltage level detector Oscillator Digital interfacing Schmitt trigger Amplifier Normal Amplifier Instrumentation Amplifier Important Features Difference with Normal Opamp ELECTRONIC INSTRUMENTATION EKT 314/4 WEEK 5 : CHAPTER 3 END