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Issue #214 May 2008
Where Analog And Digital Collide
An Easy-To-Use LCR Meter
Third Place Microchip 2007 Design Contest
by Miguel Rusch
Start | LCR Meter | Back to Basics | The Big Picture | Creating a Wave | Analog Stages | Signal Conditioning | User Interface | Firmware | Take a Measurement | System Performance | Further Development | What's Next? | Sources & PDF
FURTHER DEVELOPMENT
To correctly measure the impedance, or more importantly the equivalent series resistance (ESR) of electrolytic capacitors, a DC-bias voltage must be applied. I’ll add this to the next prototype as a fixed (e.g., 2 V) bias that is isolated from the measurement equipment by small-value DC-blocking capacitors.
Input overload protection is another feature that is especially important for large electrolytic capacitors. It is easy to add to the design. When the DUT is connected, stored energy in the device will discharge into the measurement circuit. Effective protection can be provided by varistors or Zeners coupled with forward-biased diodes.
The final version of this project will be incorporated into a multimeter-style enclosure. It will include battery power for portable use.
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