EKT 314/4 WEEK 9 : CHAPTER 4 DATA ACQUISITION AND CONVERSION ELECTRONIC INSTRUMENTATION

Chapter 4 Problem Statement Do not know the overall figure of Data Acquisition System Do not know how ADC work Do not know how DAC work To figure out how complex system works To know what is Sample and Hold

Chapter 4 Objectives To figure out the DAS To investigate how ADC work To investigate how DAC work To know the function of Multiplexer To know how Sample & Hold concept work

Chapter 4 Content Introduction Single Channel Data Acquisition Systems Multi Channel Data Acquisition Systems Data Conversion Multiplexers Sample and Hold

Chapter 4 Content Introduction DAS Parts General Block Diagram Objectives Single Channel DAS.

Introduction: Parts Typical DAS consist of: Sensors Signal Conditioning Data Conversion Data Processing Multiplexing Data Handling and Associated Transmission Storage System Display System

Introduction: General Block Diagram

Introduction: Objectives Objective of DAS To acquire necessary data at correct speed & time. To inform operator all data efficiently To monitor complete system operation To provide effective human communication system and identify problem areas To enable data collection, analyse and storing To enable unit performance indices computation.

Chapter 4 Content Introduction Single Channel DAS Parts Block Diagram Characteristic Multi Channel DAS.

Single Channel DAS: Parts Consist of: Signal Conditioner Analog to Digital Converter Buffer Display / Record Devices

Single Channel DAS: Block Diagram

Single Channel DAS: Characteristic Perform repetitive conversion at free running, internally determined rate Outputs are in digital code words: Data Over Range Indication Polarity Information Output Validity Status

Chapter 4 Content. Single Channel DAS Multi Channel DAS Parts Block Diagram Characteristics Comparison with Single Channel Data Conversion.

Multi Channel DAS: Parts Consist of: Signal Conditioner Multiplexer Sample-Hold Circuit Analog to Digital Converter Logic Circuit Buffer Processor/Controller

Multi Channel DAS: Block Diagram

Multi Channel DAS: Characteristics Input from Multiple Data Source Work based on Input Sampling Multiple Input Multiplexed (TDM) before processed Can be divided into two different system type based on location of A/D-Multiplexer: Multiple Input – A/D(s) – Multiplexer – Processor Multiple Input – Multiplexer – A/D - Processor

Multi Channel DAS: Characteristics

DAS Comparison Single ChannelMultiple channel Simple Low parts count Slower since coding need to be change (BCD to Digital) Data availability time cannot be controlled Accurate Complex and need to be designed wisely to avoid high cost Faster since data to be read already in digital form Data always available Less accurate but acceptable if sampling condition acceptable

Chapter 4 Content. Multiple Channel DAS Data Conversion Digital to Analog Converter (DAC) Analog to Digital Converter (ADC) Multiplexer.

Data Conversion Important aspect of digital data processing ADC used to encode analog signal to equivalent digital values (signals) DAC used to decode digital values (signals) to produce equivalent analog signal. Both conversion have condition: Upper bound Lower bound

Chapter 4 Content. Multiple Channel DAS Data Conversion Digital to Analog Converter (DAC) Analog to Digital Converter (ADC) Multiplexer.

DAC: Working Principle Input is Digital, Output is Analog Digital Value converted to Equivalent Analog Value Can Use: Variable Resistor Network Opamp (Summing Circuit)

DAC: Variable Resistor Network Bit 2 (MSB) Bit 1Bit 0 (LSB) /72/71/7 Binary Equivalent Weight (LSB) n – number of bit

DAC: Variable Resistor Network Bit 3 (4/7) Bit 2 (2/7) Bit 0 (1/7) Analog ValueVref = +7V Vref = +14V 000Vref(0)00 001Vref(1/7)12 010Vref(2/7)24 011Vref(1/7 + 2/7)36 100Vref(4/7)48 101Vref(4/7 + 1/7) Vref(4/7 + 2/7) Vref(4/7 + 2/7 + 1/7) 714

DAC: VRN Equiv. Circuit

DAC: VRN – Millman’s theorem Voltage appearing at any node in a resistive network is equal to the summation of the current entering the node divided by the summation of the conductances connected to the node.

DAC: VRN – Millman’s Theorem Suppose we have digital value of 001 to be converted into analog voltage Value 0 = 0 Volt Value 1 = +7Volt

DAC: VRN – Millman’s Theorem Applying Millman’s Theorem:

DAC: Ladder Type Network R-2R LADDERBinary ladder

DAC: Ladder Type Network Assignment 1: R-2R Ladder Assignment 2: Binary Ladder *Submit in Monday Lab Session

Chapter 4 Content. Multiple Channel DAS Data Conversion Digital to Analog Converter (DAC) Analog to Digital Converter (ADC) Multiplexer.

ADC: Working Principle Based on Successive Approximation Method Compare bit by bit (from highest bit to lowest bit) Start Signal Stop Signal

ADC: Block Diagram

ADC Operation Start=1, SAR= b, RingCounter = 0, Vref=5V, Vin=1V OperD7D7 D6D6 D5D5 D4D4 D3D3 D2D2 D1D1 D0D0 VoutCmp D 7 Set Vin< D 6 Set1Vin< D 5 Set1Vin> D 4 Set1Vin> D 3 Set1Vin< D 2 Set1Vin< D 1 Set1Vin> D 0 Set1Vin>

ADC Operation: 1V in, 5V ref

EKT 314/4 WEEK 9 : CHAPTER 4 END ELECTRONIC INSTRUMENTATION