APPENDIX
C
Theory of Operation
PROGRAM STEP 2, COOLING
An electrical current is passed through the thermocouple, cooling it
by means of the Peltier Effect to a temperature below the dew point.
Water condenses from the air in the chamber to form microscopic
droplets upon the surface of the thermocouple.
PROGRAM STEP 3, DEW POINT CONVERGENCE
Electronic circuitry “pumps” thermal energy from the thermocouple
via Peltier cooling in such a way as to cancel out heat influx to the
thermocouple by conduction, convection, and radiation. Given this,
the temperature of the thermocouple is controlled exclusively by the
water condensing upon its surface. Thermocouple temperature,
depressed below the dew point in Step 2, rises asymptotically
toward the dew point as water continues to condense. When the
temperature of the thermocouple reaches the dew point, condensa-
tion ceases, causing the thermocouple temperature to stabilize.
PROGRAM STEP 4, END OF SEQUENCE AND
READOUT
The reading on the display is proportional to the vapor pressure of
the solution. When this final reading is reached, a chime sounds
and the “In Process” changes to “Osmolality.”
The result is displayed in Sl units of osmolality—mmol/kg.
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