Perma Pure Baldwin-Series M225 - Manual (Page 5)

Section C: Principle of Operation 5
C: P
RINCIPLE OF
O
PERATION
Thank you for purchasing the Perma Pure Baldwin™ Classic Series Thermo-Electric
Cooler. Our Classic Model M225 features a unique slim design leaving additional
space to install or access other sample conditioning system components. A unique
drop-down door on the M225 provides easy access to electronic boards and the
power supply. The electronic control board is mounted on the door for easy access.
The process of sampling combustion product stack gas or exhaust from internal
combustion engines requires a method to remove the moisture from the sample,
without removing the gas components of interest. The Baldwin-Series Classic
Thermo-Electric Cooler is an ideal way to decrease the dew point of combustion
gases to a repeatable, stable, constant low dewpoint. This cooler prevents water
condensation in sample pre-filters, sample pumps, and gas analyzers. For gas
analyzers where water vapor is an interferent, a stable, repeatable dewpoint
becomes a part of the gas analyzer performance specification. Perma Pure coolers
provide this constant low water concentration, resulting in an accurate component
gas measurement.
All Baldwin-Series coolers use thermo-electric elements (Peltiers) to cool the
sample gas to the desired dew point temperature. A Classic Thermo-Electric Cooler
is best illustrated as a small
heat pump with no moving
parts. The Peltiers operate on
direct current and may be used
for heating or cooling by
reversing the direction of
current flow. This is achieved
by moving heat from one side
of the module to the other with
current flow and the laws of
thermodynamics. A typical
single stage Peltier (Figure 1)
consists of two ceramic plates
with p- and n-type
semiconductor material
(bismuth telluride) between the
plates. The elements of
semiconductor material are
connected electrically in series and thermally in parallel.
When a positive DC voltage is applied to the n-type thermo-electric element,
electrons pass from the p- to the n-type thermo-electric element and the cold side
temperature will decrease as heat is absorbed. The heat absorption (cooling) is
proportional to the current and the number of thermo-electric elements. This heat is
Figure 1: Thermo-electric element (Peltier)