Analog  Digital Conversion Properties: Resolution/ precision aantal bits Conversion time Max. sample frequency Prijs

Precision

Sample frequency

Aliasing

Analoog  Digitaal Conversie Principes Successive Approximation Flash ADC Sigma Delta ADC

Successive Approximation

Flash ADC

Sigma-Delta ADC

SigmA Delta Converter type HI7190 Sample frequency: 10MHz, , 24 - Bit, High Precision, 22 - Bits Resolution

Resolution and Bandwith

Digitaal  Analoog (DAC) DAC met R – 2R weerstanden Pulsbreedte modulatie (PWM)

Operational Amplifier

Optelschakeling OpAmp 1 V 2 k Bereken Vo

LSB = onderste of bovenste weerstand? DAC Ropamp = 1 k V0 = ? LSB = onderste of bovenste weerstand? 1 4 V

DAC met R-2R netwerk

Pulse Width Modulation Digital Analog Converter Toepassing: servomotorregeling Modulation frequency Duty Cycle = verhouding hoog/laag

Pulse Width Modulation Digital Analog Converter Toepassing: servomotorregeling Volt Volt Volt Modulation frequency > 600 Hz (hangt van de traagheid van de motoras) Duty Cycle = verhouding hoog/laag

Sensors & Data Acquisition Systems Amplifiers & Analog Filters Sample & Hold ADC

Transducers Sensors Small Signals Signal Conditioning Wiring/Grounding Phenomena  ADC Transducers Sensors Small Signals Signal Conditioning Wiring/Grounding

Voorbeeld van een sensor: rekstrookje R = weerstand = soortelijke weerstand L = lengte A = doorsende

Strain Gauge / Rekstrookje Dummy Gauge:Temperature compensation

Strain Gauge

Applications Force sensors Spirometers Truck weigh stations Position sensors

Force to Voltage: Weatstone Bridge Circuit R1= R2= RG1= RG2 = 1000 ; RG MAX= 10 ; VEX = 5 V

Intermezzo on Cascaded Resistors Vin Vout R1 R2

Intermezzo on Cascaded Resistors Vin Vout R1 R2

Force to Voltage: Weatstone Bridge Circuit In rust: R1= R2= RG1= RG2 = 1000 ; RG MAX= 10 ; VEX = 5 V

Assignment: Calculate the differential input voltage for the ADC In rust: R1= R2= RG1= RG2 = 1000 ; RG MAX= 10 ; VEX =Vin= 5 V

Sensor, Amplifier & ADC Amplifier Weatstone bridge + A ADC - mV/bit?

Assignment: Specify the gain of the amplifier Input range of the ADC = 5 V The ADC = 12 bit

Opamp

The ideal Amplifier 2. Input impedance--infinite 1. Gain--infinite 2. Input impedance--infinite 3. Output impedance--zero 4. Bandwidth--infinite

Closed Loop Inverted Amplifier

Assignment: Design the amplifier Voor Weatstone bridge: welke versterker? R1 = ? R2 = ?

Beter algemeen systeem Sensor-output- & ADC-input impedance Rsensor Vsensor VADC RADC

Measurement errors - t.g.v. mismatch sensor-output-/ADCinput- impedance t.g.v. aardlussen t.g.v. te lage “CMRR”

Sensor output impedance Strain Gauge Vs = 50 mV; Rs = 1000  Thermocouple Rs < 20  pH Electrode Rs = 100 M

Rsensor RADC Error (%) 10 k 1 M 1 1 k 100 k 2 100  3 50 k 4 Assignment: Determine the measurement error as a result of the mismatch sensor-resistance and the ADC input-resistance Rsensor RADC Error (%) 10 k 1 M 1 1 k 100 k 2 100  3 50 k Sevo motor potmeter ADC PIC’s 16F876 4

Measurement error t.g.v. mismatch sensor-output-/ADC input- impedance Stel: 10 bits ADC; Bij welke van de 4 systemen is de fout > 1 bit? Zijn de berekende errors absoluut of relatief? Hoe kunnen deze fouten opgelost worden? Hardwarematig ….? Softwarematig …..?

Measurement errors - t.g.v. mismatch sensor-output-/ADCinput- impedance t.g.v. aardlussen t.g.v. te lage “CMRR”

Ground-Referenced / Floating Signal Source

Grounded Measurement System

Floating / Differential Input Measurement System

Grounded Signal source/ Grounded Measurement System  aardlus

Grounded Signal Source/ Floating Measurement System

Floating Source/ Floating Measurement System R1 = R2 (10k < R < 100k)

Instrumentation Amp.

Common mode & Differential mode narekenen Plaatje aanpassewn 2.525 V 2.475 V 5.0 V Common mode = 2.5 V Differential mode = 25 mV

Common Mode Rejection Ratio (CMRR)Beter 20 log ingangsbereik ADC = 0 – 5 Volt; Versterkingsfactor 200; 12 bits ADC Eis: fout mag max. 1 bit zijn. 12 bits ADC  1 : 4096; 1 LSB = 5000 mV/4096 =  1,25 mV. Bij ingang versterker is dit 1,25/200 = 6,25 V CMRR (dB) = 20 log (Differential mode/ Common Mode) = 20 log ( 6,25 V / 10V)  100 dB. (factor 10000) 20 dB = factor 10

Toepassing Unshielded Twisted Pair EMS