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The circuit shown in the schematic features zero drift operational amplifiers (LTC1250 and LTC1050) and a precision instrumentation switched capacitor block (LTC1043). This design will maintain excellent DC accuracy down to microvolt levels. This method was chosen over the use of a true RMS-to-DC or log converter because of the expense and temperature sensitivity of these parts. Only a
single 5V power supply is required. Integrated circuit U1,
an LTC1046, converts the 5V supply to – 5V to supply power to U2, U3 and U4. U2A, part of an LTC1043 switched capacitor building block, provides the excitation for the sensor, switching between 5V and – 5V at a rate of approximately 2.2kHz. This rate can be varied, but we recommended that it be kept below approximately 2.4kHz, which is one-half the auto zero rate of U3.