Impedance measurement with microcntroller

Generally impendance is measured through LCR Meters in lab. LCR Meters are very costly (I have seen only agilant products). For amateurs and for low cost product which involve impendance measurement needs an alternative method. What the commercial products contain is of two types fixed frequency and variable frequency type. Both uses a sine wave as excitation to the circuit and the input/output gain and phase relations give the impendance of the load.

For our purpose we can do the same things with some microcontrollers, ANALOG-DEVICE has a number of products for this, the most useful one is AD5933:  1 MSPS, 12 Bit Impedance Converter Network Analyzer

If you choose AD5933 then you have to do nothing just read the impendance data through a I2C protocol on any microcontroller.

  • Otherwise do all the job sinewave generation
  • Reading the output wave (sine wave but it is phase shifted and attenuated by the load impendance)
  • Save the sinewave data or export to PC through serial port
  • Process the data to get the impendance data.

For all the above jobs there are FPGA chips available from ANALOG DEVICES

For sinewave generation upto 50MHz with I KHz steps: AD9835

Phase Detector/Frequency Synthesizer
ADF4002

Phase Detector/Frequency Synthesizer : ADF4002

For Phase detection, gain detection: AD8302

please read the application note AN691(low frequency phase detection) from analog devices

A similar device, also available from Analog Devices, Inc., is the AD5934, a 2.7 V to 5.5 V, 250 kSPS, 12-bit impedance converter, with an internal temperature sensor and is packaged in a 16-lead SSOP.

Applications

  • Electrochemical analysis
  • Bioelectrical impedance analysis
  • Impedance spectroscopy
  • Complex impedance measurement
  • Corrosion monitoring and protection equipment
  • Biomedical and automotive sensors
  • Proximity sensing
  • Nondestructive testing
  • Material property analysis
  • Fuel/battery cell condition monitoring

References:

springerlink.com/content/t1x8135413p1354v/

analog.com/en/rfif-components/direct-digital-synthesis-dds/ad5933/products/product.html

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