Design, calibration and tests of versatile low frequency impedance analyser based on ARM microcontroller

Abstract

Numerous simple impedance analysers based on the microcontroller (μC) and dedicated impedance converter integrated circuits (IC) were reported recently. In many applications sophisticated analogue circuitry has to be appended to enhance the measurement possibilities or to circumvent the limitations. In this paper the impedance analyser IMP-STM32 based solely on the μC and general purpose operational and instrumentation amplifiers is presented. It uses the internal DAC and ADCs in the μC to generate the excitation and to measure the response of the measured object. It also uses the external analogue circuits to condition the excitation signal and measure voltage and current. The magnitudes and phase shifts of voltage and current are evaluated using the three parameter sine fitting algorithm allowing for fast low-frequency impedance measurements. The calibration procedure of completed device is presented as well as the tests of its accuracy. The device allowed for measurements at frequency range between 1mHz and 100kHz in 1Ω to 1GΩ impedance range with 1% accuracy. IMP-STM32 was also compared to the Agilent 4294A precision impedance analyser. In the middle of the impedance ranges (1Ω to 300kΩ) the discrepancies between the two were less than 0.2%.