Model2000 Series
DewPrime
Dew
Point
Hygrometers
----------
Maintenance and
Calibration----------
These adjustments are
made
at the
factory
and
nonnally
do not have to be changed. However,
changes
in
cable
lengths
used
to mount the dew point
Sensor remotely
may
require readjustment (there is
approximately
a
0
.
1
oc
change
in output for
a
50-foot
change
in
cable
length).Factory adjustments are
made
based on
cable
lengths specified at time of
purchase.
If
it
becomes
necessary to check the operation of the PRT
amplifier,
or
if
the
remote cable length is changed
significantly
after
shipment
fro
m
EdgeTech,
then the
procedures
descdbed
in
subsection
5.5 should be followed. A
precision
cah'brated resistance decade box with a ±().01%
accuracy
is required for
making
these
adjustments
.
·
55
CALIBRATION OF THE
PRT
AMPLIFIER
When
recalibration
is attempted for the
reasons
dis-
cussed above, the following procedure is
recommended:
1. Remove the Sensor from the end of the cable
(either
long or short) and prepare a
precision resistance
decade box to be used to
simulate
the PRT
in
the
Sensor
.
2.
Tum on power to the Model 2000 Series
and
wait
1
/
2 hour to ensure
that
all
electronic
s
have reached
an
equilibrium
condition.
3. Remove the top cover by removing the six
retaining
screws.
4.
SettheresiSWice
decade box to
100
.
00
ohms.
5
.
Use three
equal
length and gauge wires
to
connect pins 4 and 10 of the
connector
removed
from
the Sensor to
each
other and to one terminal
of
the decade box. Connect the other
terminal
of
the
decade box to pin 9 of the Sensor cable
connector.
6
.
The
front
panel digital meter should be reading
00
.
0°C
at this time. Adjust the ZERO
potentiometer,
R76, on the
Main
Board
um:il
this
readmg
is
attained.
7. Set the
resiSWice
decade box to 119.40 ohms
and
adjust the SPAN
potentiometer,
R69, on the
Main
Board for a display of
+50.0°C
.
8
.
Set the
resistance
decade
box to
13.4
.
70
ohms
and
adjust the LIN
(Linearity) potentiometer,
R83,
on
the Main Board for a display of
+90
.
0°C.
9
.
Repeat steps 6,7,
and
8 as often as
required
to
bring
each temperature reading to within
::!;().1
oc
of
the
values given. Each
adjustment
interacts slightly
with
the others so it may be necessary to repeat
these
steps
several
times.
10. By setting the resi.stmce decade box to 88.22 ohms,
a lower value of -30°C can be
checked.
11
.
Once calibration
has
been
completed,
remove
the
resistance
decade
box and
reattach
the Sensor to
the
end of the
cable
.
After
the Sensor is
reconnected,
press the MABC key and
reattach
tbe
Coo1rol
Unit
cover to the chassis. The
resistor
values to be used
for cahlmltion
purposes
(listed
in
the
above proce-
dure) are nominal values that serve for most Model
2000 Series
Sensors
.
This
allows
for
interchange-
ability of Sensors without
recalibration.
However,
if
the
cah'bration
values for
a
particular
Sensor
are
different from those listed here, the
COirect
values
will
be included on a
separate
docmnent shipped
with the
Sensor
and
the
certificate
of cah"'bration.
5.6 OPERATING
ADJUSTMENTS
The
Model2000
Series is
designed
to operate without
operator
control.
Although
there are several
potentiom-
eters on the PC
boards,
all are &.ctory set, and
nonnally
it is not necessary to
adjust
them.
Ho er,
certain
adjustments
may be
made
by the user after a
knowledge
of the instrument and its
capabilities
bas been achieved,
and whenfamiliarity with the
instrument
bas
been
gained. These adjustments are
BALANCE,
TmCK-
NESS, GAIN, and
COMPENSATION.The
BALANCE
adjustment
affects the static setup of the instrument,
and
the other three affect the
dynamic
response
of the
instrument to changes
in
the
dew point temperature
of
the
gas sample
in
the Sensor.
5.6.1 Balance for S2
Sensor
Move the selector switch on the main board to the
"660"
position. The BALANCE
control,
potentiometer
R52,
is
used
to make the
CONfROL
LED (10-LED bargraph)
·
5-2
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