Functional block diagram of the hand-held photometer.
Photograph showing the measurement system and several one-shot sensors.
Schematic of the instrument analog electronics.
Time drift of the photocurrent generated by a LED stabilized with a constant (dc) current (triangles), a pulsed current bias (1 kHz and 50% of duty cycle) (squares) and with optical feedback (solid line). Data were measured after 160 s of instrument warm-up.
Screen capture of the microcontroller A/D input with a MSO4104 oscilloscope during photometer operation (1 s switched on LED).
Sigmoidal calibration functions of potassium (circles) and nitrate (solid squares). Lines represent the fittings to Eq. (5).
Analytical and technical specifications of the photometer for potassium and nitrate sensors (SD: standard deviation).
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