This paper presents a low-cost and accurate interface for four-electrode conductivity sensors. The interface mainly consists of an analog front-end, a multiplexer, and a voltage-to-time converter. The analog front-end is used to provide a controlled excitation voltage for the sensor and to convert the sensor signal (conductance) into a voltage signal. The voltage-to-time period converter acts as an asynchronous converter for the sensor signals (voltage), which employs a relaxation oscillator and outputs a period-modulated signal. Experimental results over a conductance range of 0.1 /spl mu/S to 20 mS show a random error of 1.6/spl times/10/sup -5/ and a systematic error of 6.6/spl times/10/sup -5/ for a measurement time of 110 ms.
['Xiujun Li', 'G.C.M. Meijer']
A low-cost and accurate interface for four-electrode conductivity sensors