Synchronous system to measure µOhm

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< Analog Electronic ~ Synchronous system to measure µOhm

eric

Posted: Sun Sep 10, 2006 9:36 am Post subject: Synchronous system to measure µOhm

Site Admin Joined: 01 Jan 1970 Posts: 311

An Analog Devices application
The circuit in the diagram uses a synchronous-detection scheme
to measure low-level resistances. Other low-resistance-measuring
circuits sometimes inject unacceptably large currents into the system
on test. The present circuit synchronously demodulates the
voltage drop across the system on test and can therefore use very
low currents while measuring the resistance.
The generator, whose output is a 1 kHz signal at a peak level
of 10 V, injects a 1 mA reference current into unknown resistor
RTEST. Instrument amplifier IC1 and precision op amp IC2A amplify
the voltage across RTEST ×105. Synchronous detector IC3 demodulates
this voltage, which is then applied to low-pass filter IC2B.
The low-pass filtering attenuates all uncorrelated

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