Journal of Applied Physiology, Vol 49, Issue 1 160-166, Copyright © 1980 by American Physiological Society
Programmable gas mixer for controlling concentration as a function of time
J. Jacky
A device for controlling gas concentration as a function of time according
to a predetermined program is described. The apparatus is capable of
producing any arbitrary time-varying gas concentration at frequencies up to
about 4 Hz and can be set to ultra-low frequencies with excellent accuracy
and repeatability. The apparatus consists of a single on/off solenoid valve
for each gas in the mixture, all controlled by a microcomputer. The valve
is rapidly pulsed open and closed, and the concentration of the
corresponding gas in the mixture is proportional to the fraction of the
cycle for which the valve remains open. Prior to an experiment, numerical
values representing the amplitude of the desired concentration wave form at
successive time intervals are entered into the computer memory. When the
program is run, the microcomputer successively translates each of these
values into a pulse-width modulated signal that opens and closes the valves
via optically isolated relays. The processor can also translate an external
control signal into the corresponding pulse train, permitting manual or
automatic control of the mixture. The apparatus can be assembled in several
hours from readily available components costing under $600, including the
microcomputer.
