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 electronic noise. Reliable measurement of partial pressures with an accuracy of 0.001 mmHg requires special techniques in electronic circuit design. The p02 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, or 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 interfaces these measured voltages properly to an AT-type personal computer, for further software analysis. Another task is design and fabricate the required circuitry for the development of the automated system to make the required measurements.