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PRINCIPLES OF OPERATION
The MARK V uses an electrochemical fuel cell containing two platinum electrodes to
detect and measure the concentration of alcohol vapor in expired breath. When breath
is drawn into the fuel cell by the sampling system, a small voltage is generated
proportionate to the breath alcohol concentration. This voltage is then fed to an
electronic amplifier and displayed on screen.
The instrument is simple to operate and may be used as often as required provided that
a suitable delay is allowed between successive tests. This time delay allows the fuel
cell to clear itself of alcohol and prevents the possibility of additive readings. If no
alcohol is present in a test, a second test may be analyzed immediately, since the fuel
cell voltage is already at zero. Unless the breath alcohol level of the subject is very
high, the instrument will generally be clear enough to receive and analyze a second
sample in less than two minutes.
