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Chapter: Medical Electronics - Bio-Chemical and Non Electrical Parameter Measurement

Measurement of PHCO3

Blood gas analyzers are used to measure the content of pH, pCO and PO2 from the blood.

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 HCO3calculator 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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