Investigation of errors in microcontroller interface circuit for mutual inductance sensor

Abstract

This paper proposes direct microcontroller interface circuit on Arduino platform, which is realized using the inductive sensors. The circuit is composed of two external resistors and two reference inductors resulting in four RL circuits. The microcontroller independently excites the two RL circuit on the primary side in order to measure the discharging time of voltage across each inductor. The discharging time of voltage across the inductors on the secondary side is measured similarly which is excited due to mutual inductance from the primary side. The technique of time-to-digital conversion from the built-in timer of microcontroller enables estimation of inductance value, which is compared with the actual value for self-inductance and mutual inductance circuits. Error analysis on the discharge time measurement are performed viz, parasitic resistance, parasitic capacitance on input–output ports along with ringing effects and relative quantization error. The resistance and inductance estimation with regards to varying time period of oscillation of crystal is performed to analyze the effect of oscillation frequency on estimation. The parasitic resistance and quantization effects both contribute to the non-linearity errors (NLE) which is investigated further experimentally. The optimum value of the resistance was observed to be 120Ω and 60Ω for the primary and secondary side respectively. For primary side, the current and power consumption is 29 mA and 145 mW respectively, while for the secondary side, the current and power consumption is 27.5 mA and 137.5 mW respectively. The maximum NLE of −0.18 %FSS and −0.24 %FSS has been observed for an inductance range of 1 mH–10 mH along both primary and secondary sides respectively, whereas for an inductance range of 10 mH–100 mH, the NLE achieved was 0.29 %FSS and −0.34 %FSS for the primary and secondary sides respectively. The future scope of the linear position displacement of the inductive sensor concludes the paper. Keywords: Microcontroller, Arduino UNO, Mutual inductance sensor, RL circuit