Model2000
Serie
s
DewPrime
Dew
Point
Hygrometers
----------
Maintenance and
Calibration----------
5.1 ROUTINE MAINTENANCE
T.
o ensure the
maximum
in
accurate
and
reliable
•
. operation
ofthe Model2000
Series
,
a
periodic
m.al:D.tenance
program
should
be
established.
The
first
area of interest is to avoid
impeding
the normal flow
of
air by natural
convection around
the
instrument by
ensuring
that items do not get
placed
near or
mder the
Model2000 Series Control Unit.
5.2 MIRROR CLEANING SCHEDULE
Contrazy to what might be
expected,
the mirror sur:filce
in the Sensor need not be
spotless
for proper
operatio
n
.
I
n
fact, mirror
surface contnninants
act as nuclei for
the
condensate
,
thus
hastening formation.
The buildup of
contamination
on the mirror
surface
normally
occurs very
slowly.
Dust
and other
matter
borne by the
sample
gas
adhere
to the mirror surface
as
they are
collected
by the dew layer present on
the
mirro
r
.
Also,
particulate
matter that may be
passed
by
system line filters can also be
deposited
on the
mirror's
surface.
The net
result
of the
buildup
of
contaminants
on
the mirror
surface
is
reduced
reflectivity.
This
is
the
same effect
caused
by the
presence
of dew on the
mirror.
Therefore,
it
is
necessary
to
compensate
the
circuitry
occasionally to account
for the
change
in
reflectivity
of
the
mmor
sur:filce
due to
coiJtaminants.
This
compensation
for
change
in miiror
reflectivity
is
accomplished automatically
in the Model 2000
Series
with each
Automatic
Balance
Control
(ABC)
cycle.
This
patented
feature
adjusts the
circuitry automatically
for
any
reduction
in mirror
surface reflectivity
that
occurs
when the mirror is dry, and
ensures
that normal
opera-
tion of the Model 2000
Series
will be proper, even
after
long periods of
continuous tmattended operation.
Eventually
,
however,
buildup of
contaminants
on
the
Sensor mirror su:rbce may
become
so
great
that
it
is
necessary
to clean the
mirror
surface.
Normally
,
inter-
vals of 90 days
between routine mirror cleanings
can
be
easily achieved.
However,
i
f
gas
sample operating
conditions
are
particularly
severe
,
more frequent
mirror
cleaning
s
will be
required.
Whenever
the
instrument
cannot
electronically
adjust for conrnm inarion,
the
ABC
cycle cannot be
completed.
This is
indicated
by
the
illumination
of the
CONTAMINATED LED
.
When
this
occurs, clean the mirror
surface
and optical
parts.
Then
depress the MABC
key
on the
Model2000
Series
front
panel to allow the
circuitry
to
readjust
for the
clean
mirror
surface before
retuming
to
normal operation.
5.3 MIRROR CLEANING
To clean the
mirror surface
in the S2 Sensor, remove
the
spin-off cover from the
Sensor to expose
the
mirror.
For
the
S1,
remove tbree
hex
head
screws.
When operatmg with a
pressurized
sampliDg
system,
be
sure
to
remove
pressure from the
Seusor prior
to
removing the Sensor
cover.
When the cover
has
been
removed, lightly
dampen a
Q-
tip with
isopropyl
alcohol.
Q-tips and
cleaner
are
provided in the
Cleaning
Kit shipped with the
Model
2000
Series.
Do
not use
an excessive
amount of
cleaner
on the Q-tip. Shake the Q-tip
to remove
all
excess
fluid
prior to
cleaning
tlie mirror
surfuce.
After
cleaning
the
mirror surface, remove
all traces
of
the
cleaning
fluid with the dry end of the
Q-tip
.
To
remove
particulate
matter
present
around the
mirror
surface, use a clean, dry
Q-tip,not isopropyl alcohol.
For those
applications where
the
isopropyl
alcohol
is
ineffective
in
removing
hard
deposits
or
varnishes,
a
polishing
paste-Simichrome
Polish
(
Competition
Chemicals,
Iowa
Falls,
Iowa
50125)--may
be used
sparingly.To prevent excessive
ero<Ii:ng
of the
mirror
surface, avoid using this
material unless necessary.
5.4 CALIBRATION OF
PRT
A
Platinum Resistance Thennometer
(PRT) is used
in
the dew point
Sensor
.
To
measure
the
temperature
,
the
PRTresistance
is
converted
to
a voltage
by
aPRT
amplifier
.
This
amplifier contains control
s
for ZERO,
SPAN,
and
LINEARITY.
By
adjustin
g
these
controls,
the PRT
amplifier produces
a
linear output voltage
proportional to
the
temperature sensed
by the
PRT.
5-1
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