Isolation amplifier

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3 different types of isolation amplifiers are explained...

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Isolation amplifier

  1. 1.  Isolation amplifiers provide electrical isolation and an electrical safety barrier.  They protect the patients from leakage currents.  They break the ohmic continuity of electrical signals between input and output.  Isolated power supplies are provided for both the input and output stages.  Used to amplify low level signals.
  2. 2. Three types of methods are used to design isolation amplifier    Transformer isolation Optical isolation Capacitive isolation
  3. 3. It uses either frequency modulated or a pulse width modulated carrier signal.  Internally it has 20KHz oscillator, transformer, rectifier and filter to provide supplies for each isolated stages.  Rectifier- input to primary OPAMP.  Transformer- couples the supply.  Oscillator – input to secondary OPAMP.  A low pass filter is used to remove the other frequency components. 
  4. 4.    High common mode rejection ratio High linearity High accuracy
  5. 5.  MEDICAL Patient Monitoring and Diagnostic Instrumentation  INDUSTRIAL Ground Loop Elimination and Off-ground Signal Measurement  NUCLEAR Input/output/Power Isolation
  6. 6.  The biological signal is converted into a light signal by LED for further process.  It has patient circuit which is the input circuit and a phototransistor which forms the output circuit.  Each circuit is battery driven.  The input circuit converts the signal to light and the output circuit converts the light back to signal.
  7. 7. Original frequency and amplitude is obtained.  High linearity.  No modulator or demodulator is needed as it couples optically.  Improves patient safety 
  8. 8.  INDUSTRIAL PROCESS CONTROL  DATA ACQUISITION  INTERFACE ELEMENT  BIOMEDICAL MEASUREMENTS  PATIENT MONITORING  TEST EQUIPMENT  CURRENT SHUNT MEASUREMENT  GROUND-LOOP ELIMINATION  SCR CONTROLS
  9. 9. It uses digital encoding of the input voltage and frequency modulation.  The input voltage is converted to proportional charge on the switched capacitor.  It has modulator and demodulator circuits.  The signals are sent across a differential capacitive barrier.  Separate supplies are given for both sides. 
  10. 10. Ripple noises are removed.  It avoids device noise, radiated noise and conducted noise.  High immunity to magnetic noises.  Useful for analog systems.  Has high gain stability and linearity. 
  11. 11.      DATA ACQUISITION INTERFACE ELEMENT PATIENT MONITORING ECG EEG
  12. 12.    Commonly used Transformer isolation amplifier Cost Optical- low cost due to less components Transformer Capacitor coupled- high cost Isolation voltage Optical- low (800V) Transformer- medium (1200V) Capacitance- high (2200V)
  13. 13.   Isolation resistance Optical- 10^12 Transformer- 10^10 Capacitance- 10^12 Gain stability and Linearity Optical- 0.02% Transformer- between 0.005% and 0.02% Capacitance- 0.005% (best)

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