Calibration of a system for the computer-assisted operation of a small animal inhalation facility

The initialization of chambers in the computer-assisted inhalation facility at the National Institute of Environmental Health Sciences (1) includes a series of operations that we call "characterization." Characterization consists of two parts, the first of which is one of the topics of this report. In the first part of the characterization the mathematical relationship between the concentration of the chemical of interest and the output of the analyzer is approximated. This amounts to establishing a standard against which subsequent, daily calibrations can be compared. The second part of the characterization represents a wholly automatic operation in which certain dynamic characteristics of the system are quantified. A daily calibration is performed at the beginning of each day of chamber operation after the system has been characterized. The daily calibration data are checked against the characterization standard. The conversion equation for the daily operation of the chamber is derived from the daily calibration data combined with the characterization data. An equation that converts the output of the analyzer to units of concentration of the chemical of interest is at the heart of the computer-assisted monitoring and control system for our inhalation facility. The equation is derived from a calibration procedure that is conducted prior to starting each day's chamber operation. Quality control requires that, in addition to having a daily calibration of the system, a standard of reference be available against which each day's calibration data can be checked. This practice provides protection against the introduction of spurious calibration data on a daily basis, as well as providing a means for the detection of longer term drift.(ABSTRACT TRUNCATED AT 250 WORDS)