Real-time calibration schemes for field-portable instrumentation

Field instruments that can measure environmental levels of contaminants and provide real-time, calibrated analyses can reduce the cost of sample collection and analysis. The analytical data provided by such field instrumentation must provide analytical results statistically equal to or better than standard laboratory analyses.; Microcontroller-based interfacing provides a dedicated computer for each instrument, making it possible to have a self-contained computer-controlled instrument. Their real-time processing of the information makes real-time calibration possible in portable field instruments. The research presented here describes development of prototypes of several MC68HC11-based portable instruments and the calibration schemes associated with them.; A portable gamma ray spectrometer based on a CsI(Tl) scintillator (1.8 cm x 1.8 cm x 4 cm) with an integral PIN diode (1.8 cm x 4 cm) was designed, constructed, and evaluated. This low cost field gamma ray spectrometer operated with minimum power requirements when compared to the more common PMT-based devices. This microcontroller-based spectrometer demonstrated reliability and accuracy in measuring gamma emitters while unattended for up to one week. Also, in its self-contained memory it stored up to seven spectra automatically on a daily basis. Special software was designed to monitor the long term stability and reliability of the spectrometer. Gamma ray spectra were collected from calibrated standards and local soils.; Also, another prototype field instrument, a portable fiber optic spectrometer with a built-in real time calibration scheme was assembled. It contained a microcontroller interface, a fiber optic spectrometer module, and a multi-color LED source. Again, special software referencing a built-in LED provided calibration to compensate for wavelength shift and intensity drift. This device measured pH remotely.; Finally, a computer-controlled interface communicating with a SPEX 1403 monochromator and digital photometer was constructed and evaluated. It controls the SPEX system remotely and records the data for laser Raman spectrometry. The primary function of the interface was to accurately maintain wavenumber precision of the collected spectrum. Representative spectra and new wavelength calibration schemes are presented.