A LOW-NOISE ELECTROMETER FOR AN AUTOMATED OEC MEASUREMENT SYSTEM

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Measurement of the hemoglobin oxygen equilibrium curve (OEC) in an automated system is hampered by noise. To obtain reliable results in reading partial pressures in the range of 0.01 mmHg requires special techniques in electronic circuit design. The P02, pH, and the pC02 electrodes have very high internal resistance with very low output signal levels. When these devices are used in an environment contaminated by radiofrequency interference (RFI) from a computer, the magnetic fields of stepping motors, as well as power line transients generated by a high current water bath, the electrode output leads must be kept short and shielded. The electrode signals must be kept scaled and offset by a computer- controlled signal processor that properly interfaces these measured voltages to an AT-type personal computer, for further software analysis. Another task to be performed is the designing and fabrication of the required circuitry for the development of the automated system to perform the required measurements.