A sensor system having an analyte modulator, detector and a pump. The concentration of an analyte sample may be modulated at one time constant. The detector may have an output with a drift at another time constant. The one time constant may be shorter than the latter time constant. The latter time constant may be substantially removed from the detector output with a discriminator. A reservoir may receive high concentrations of analyte from the modulator, before analyte is forwarded to the detector and pump via analyte conveyance lines and valving. The modulation or pre-concentration of analyte in the sensor system may entail shorter times and smaller volumes than those needed by the detector. Such mismatches may be alleviated via accumulation of analyte in the reservoir prior to being forwarded to the detector.