Baseline Drift Compensation Strategies

Sensor drift is often a very difficult problem to solve. Under ideal conditions, a sensor produces an output signal that is related only to the analyte of interest. When presented with a constant reference state, the so-called baseline signal 

The most common way to deal with the problem of stochastic drift is to modulate the exposure of the analyte to the sensor and to synchronously detect the sensor response. When the analyte is off (i.e., the sensor is zeroed ), the sensor signal can be recorded as the baseline value. Drift-corrected signals can be obtained by subtracting the baseline signal from that recorded when the analyte is on. If the frequency of the on/off modulation is much higher than the frequency of the baseline drift, then this scheme results in dramatically improved stability in the measured data. An implicit requirement in this measurement strategy is that the response kinetics of the sensitive film/analyte combination be sufficiently fast to allow on/off modulation at the desired frequency. 

Baseline drift compensation using this synchronous modulation/detection strategy requires a significant amount of additional hardware to be built around the sensor. Consider, for example, a vapor-measurement instrument. In this case, the modulator could consist of a valve that can alternately expose the sensor to 

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Figure 6.15 Typical baseline-drift compensation strategy a periodic re-zeroing is provided using the air scrubber and three-way valve.

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