Model2000 Series DewPrime
Dew
Point Hygrometers
Introduction
------------
easy
access
to the mirror for cleaning without
discon-
necting sample lines and connections (S2); (2) the
logic
level front panel
Automatic
Balance Control
(ABC)
LED
is "ON"
steady
when the instrument is
standardiz-
ing, and
"
ON"
fla
s
hing when the
standardization
cycle
is
completed
and the instrument is
depressing
(cooling)
to the dew point; (3) Alarm set points
that
are
program-
mable over the entire Sensor range; and
(
4)
a
"CON-
TAMJNATED"
LED
and
logic level olllput that
signals
when and
if
the Sensor miJror needs cleaning.
1.3 AUTOMATIC BALANCE CONTROL
(ABq
-ABC
Cycle.
Thi
s
cycle can be
programmed
to start
at
any specified time and repeated at
programmed
inter-
val
s
.
Thi
s
feature allows the user to program the
ABC
cycle to occur at off-hours such as late at night or
early
morning when the
restandardization
will
cause
the
least
interruption of the sampling
process.
--8erial
Port
.
The
serial
port is RS-232C compatJ.'ble
and can be used to remotely
program
setup
paxameters,
initiate an ABC cycle, or output data to a
terminal,
printer, or
computer.
-The
Setup
Parameters
include time plus date,
units
The
Model2000
Series
incorporates
an
all-electronic,
(°F
or
0
C),
ABC
start
time
,
ABC
interval, alarm limits,
timed,
Automatic
Balance Control (ABC) circuit
To
correct for
changing
"dry mirror' reflectance as
a
fimction of
contamination,
the mirror is heated
periodi-
cally to a
temperature
in excess of the
dew
point,
and
the
optical bridge output is balanced electronically
for
the present
reflectance
.
This heating is accomplished
by
reversal of the voltage across the th.mnoelectric
cooler
inside the
Sensor.
The ABC cycle in the
Model2000
Series can be
pro-
grammed to start at a specific time
and
at any
interval
thereafter
.
The cycle can also be initiated manually by
a
pushbutton
on the front panel or via the serialport
This
feature
increases
the time interval between sensor
and
sample-line
cleanings
without adversely
affecting
overall
performance.
Sensitivity
to
particularly
troublesome
impurities,
such
a
s
salts and other soluble contaminants,is
negligible
with
EdgeTech hygrometers
because the
compensation
circuit and the low thermal mass of the Sensor
design
permit use of a heavy condensate layer on the
mirror
surface
without need for a coalescence precool cycle
or
other
gimmickry
to offset the servo instability, drift,
and
loss of
accuracy
often
enco1.mtered
in other
chilled
mirror
hygrometer
s
.
1.4
PROGRAMM.ABn.JTY
The Model 2000 Series' fimctions can be
programmed
via the front panel keypad or the RS-232
serial
port.
analog outputs, baud rate, automatic
data
output
interval,
and digital averaging interval
(0-16).
-The
Data Output Function
sends
the
date,
time,
dew
point, and a1mn status to any
serial
device
such
as
a
computer,
printer, or
dat
a
logger
equipped
with an
RS-
232C input. The
data
can be sent either on
command from
the external device or
automatically
at
programmed
intervals.
-The
Control Function allows the user to start
an
ABC
cycle, initiate xoaximmn cool/heat, and send
the
status such as alarm condition, ABC cycle, or
maximmn
heat/cool.
All
commands are listed on a Help menu
that
can be
printed
or displayed on a
terminal.
-Aualog
Outputs.
Two
outputs
,
0-5
VDC and
4-20
ma, are available
simultaneously
at the rear
terminal
connectors.
They can be scaled
electronically
to corre-
spond to any
dewpointnmge.For
instance,
0
V/4
ma
can be set to -40°C
and
5 V
/2
0 ma can be set to
+
1
0°C.
Any combination of
dew
points within the
measuring
range can be used This feature allows the user
to
customize the range for a particular
strip
chart
recorder
or to
expand
the
scale
for greater
precision.
Scaling
can
be programmed easily via the front panel keypad or
the
remote
serial
port
-Alar
m
Relays. Two programmable Form C relays
are
provided to control valves,
anmmciators,
etc.Each
alarm
relay can be set independently for high or low,
latching
or unlatching,
and
at any dew
point
1-3
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