Chapter: Medical Electronics : Bio-Chemical and Non Electrical Parameter Measurement
Measurement of PHCO3
MEASUREMENT OF PHCO3
·
Blood gas analyzers are used to measure the content
of pH, pCO and PO2 from the blood.
·
Two gases of accurately known O2 and CO2
percentages are required for calibrating the analyzer in pO2 and pCO2
modes. These gases are used with precision regulators for flow and pressure
control.
·
Two standard buffers of known pH are required for
calibration of the analyzer in the pH mode.
·
Input signal to the calculator is obtained from the
outputs of the pH and pCO2 amplifiers
·
The outputs are adjusted by multiplying with a
constant and are given to an adder circuit
·
The output of adder is passed to antilog generators
circuit. Then it is passed to A/D converter for display. Resistance R is used
to adjust zero at the output.
·
Total CO2 is calculated by summing the
output signals of the calculators and the output of the pCO2
amplifier
The base excess calculator consists of three
stages.
In the
first stage, the output of pH amplifier is inverted in an operational
amplifier, whose gain is controlled by a potentiometer.
The
output of HCO3—calculator is inverted in the second
stage.
The third
stage is a summing amplifier A3 whose output is given to A/D converter,
that gives a digital read out.
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