Ohmic instruments DPSC-35XR User manual

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DPSC-35XR(L) MANUAL
DEW POINT SIGNAL
CONDITIONER KIT
SF-SLS-553 (A)
Phone [phone]
Toll Free(800) 626-7713
Fax [phone]
www.ohmicinstruments.com
Sales: [email protected]
Service: [e-mail]
Ohmic Instruments
3081 Elm Point Industrial Drive
St. Charles, MO 63301 USA

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© Ohmic Instruments
2014

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Contents
Introduction ............................................................................................... 4
Features .................................................................................................... 4
Installation ................................................................................................. 5
Operation .................................................................................................. 6
RS-232 Interface....................................................................................... 6
Recalibration ............................................................................................. 7
Special Order ............................................................................................ 8
Mounting Template ................................................................................... 9
Wiring Diagram ....................................................................................... 10
Alarm Reset Wiring ................................................................................. 11
Analog Output Table ............................................................................... 12
Sensor Precautions................................................................................. 13
Specifications .......................................................................................... 13
Logging Commands (logging version only) ............................................ 14
Warranty.................................................................................................. 15

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INTRODUCTION
Ohmic’s Dew Point Signal Condi-
tioner Kit, Model DPSC-35XR (and
DPSC-35XRL, the time-stamp log-
ging version) is used to measure
the water vapor content of com-
pressed and process air. The kit
may be used to install dew point
measurement capability in electrical
panels and enclosures. The kit’s
components consist of a micropro-
cessor-based printed circuit card,
remote probe (PDPS-610TH), LCD
display and bezel. The probe con-
sists of a thin film polymer IC hu-
midity sensor and NTC thermistor
assembled in a stainless steel ½”
NPT fitting supplied with either a
protective screen or manifold and a
6 ft. cable. The printed circuit board
uses an EEPROM memory which
stores calibration data for the indi-
vidual sensor. *The probes are
not interchangeable as
each probe has calibration
data stored in an EEPROM
on the circuit board.
The circuit card converts the volt-
age output of the IC humidity sen-
sor and the resistance of the ther-
mistor to dew or frost point (frost
point is displayed below 32F) by
utilizing an embedded proprietary
program developed by OHMIC In-
struments. The program utilizes
psychrometric equations published
by ASHRAE (American Society of
Heating, Ventilation and Air Condi-
tioning Engineers) and referenced
to the Hyland-Wexler equations
used by NIST. The DPSC-35XR
provides rapid response to changes
in the amount of water vapor with a
high degree of repeatability and
accuracy. Once installed with suita-
ble filtration in compression and
process air or gases, the unit will
provide many years of dependable
service. Each unit is calibrated to
NIST traceable dew point stand-
ards.
FEATURES
The DPSC-35XR provides a direct
digital display in either F or C
dew/frost point temperature, linear
analog outputs (0-5 VDC & 4-
20mA) outputs, an alarm output
(0.5A SPST relay) and an RS-232
computer interface which enables
the measurements to be transmit-
ted to a personal computer. Options
include a 32 Kbyte data logger and
time clock which enables dew/frost
point and dry bulb temperature data
to be field recorded at time
stamped intervals and later upload-
ed to a PC. Information on this op-
tion is on Page 14. The unit has a
range of -40 to +80F dew/frost
point.
The DPSC-35XR and DPSC-
35XRL are identical, except for the
inclusion of the aforementioned
time-stamp logging function on the
latter.

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INSTALLATION
CAUTION: The DPSC-35XR is
powered by 120 VAC. When pow-
ered, the unit has several live ter-
minals exposed. The printed cir-
cuit card should be installed in a
suitable electrical enclosure. All
wiring should be performed with
the power supply disconnected.
Installation should be performed
by qualified personnel.
Cut an opening in the electrical en-
closure for the LCD display and
bezel (see Fig. 1 on Page 9). Mount
the printed circuit card in the enclo-
sure using insulated standoffs to
assure the printed circuit card does
not contact metal or conductive sur-
faces. Connect power inputs to the
screw terminals and the appropriate
alarm, analog output and computer
interfaces per Fig. 2 (Page 10). The
probe is connected to polarized
connectors J4 and J5. Install the
sensor fitting prior to connecting the
probe’s cable to the circuit card so
as not to twist the cable. It is highly
recommended that the main power
to the unit be fused or wired to a
circuit breaker, and the unit should
have a chassis or earth ground con-
nection.
The analog outputs are powered by
the printed circuit card and do not
require an additional power supply.
They provide linear 0-5 VDC and 4-
20mA outputs for chart recorders or
other instrumentation. A table for
the analog outputs is on Page 12.
The analog signal wires and RS-
232 interface cable should be rout-
ed away from and in a separate
conduit from the power cable. The
relay is normally open “dry” contact
which closes when the dew point
exceeds the set point.
Place selector switch S2 in the de-
sired position (see Figure 2) for ei-
ther C or F operation. Whenever
S2 is changed, the setting will not
be implemented until the unit is re-
set by shutting off the power and
reenergizing the circuit.
The 4 position DIP switch deter-
mines what the LCD module dis-
plays, as labeled on the micropro-
cessor. Do not remove the push-on
jumper located near the micro-
processor. This may cause the
embedded program to be altered
or erased, rendering the unit in-
operable.
The probe is equipped with a ½”
male NPT stainless steel fitting. The
½” fitting may be installed directly in
vessels, pipelines, or tees. An op-
tional manifold that accommodates
tubing may be ordered. Always use
Teflon tape to form an air tight seal.
Do not remove the protective
screen from the fitting. The probe
may be installed to pressures of 175
PSIG. For sampling air or gas that
exceeds 185F, the air should be
sampled through at least 3 to 4 feet
of uninsulated heat sink tubing
(such as copper refrigeration tub-
ing). A nominal flow rate of 5 SCFH
through ¼” OD tubing is recom-
mended. For air at atmospheric or
low pressure a vacuum pump may
be utilized. If you are sampling com-
pressed air and venting to atmos-
pheric pressure, the dew point of
the air will decrease proportional to
the pressure therefore a back pres-

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sure regulator or orifice should be
used for “pressure dew point” read-
ings.
While the sensor recovers from ex-
posure to saturated water vapor, it
is recommended that a coalescing
5µm filter be used as filters to re-
move liquid water, oil mist, and par-
ticulate. Oil mist forms a vapor barri-
er over the sensor which slows re-
sponse time. (When used on a des-
iccant dryer, a filter should be used
to prevent fines from accumulating
on the probe.)
To adjust the set point, potentiome-
ter PR1 (J1), shown in Figure 2
(Page 10), must be adjusted. The
set point is viewed via the RS-232
interface (see below) on a PC or on
the display by setting the DIP
switch. The alarm indicates when
the dew point exceeds the set point
value and automatically resets when
the dew point is below the set point.
The DPSC-35XR also has built in
circuitry to latch the alarm requiring
a momentary switch to reset; con-
tact OHMIC for information on wir-
ing for this feature.
OPERATION
Prior to operation recheck all wiring
and make sure all pneumatic con-
nections are leak free. When dry air
is introduced to the sensor keep in
mind that in order to register low
readings such as -40F, all moisture
must be purged out of sampling
lines. If a sensor has been stored in
ambient humidity it may take longer
to “dryout”, therefore sufficient time
is required for stabilization. For most
air drying systems 5 to 15 minute
stabilization time is typical. Most
probes exhibit negligible drift; how-
ever, as contaminates accumulate
on the surface, the response time
generally becomes slower.
RS-232 INTERFACE– Connecting
the DPSC-35XR to your Computer
Connecting to a serial port The
DPSC-35XR can be plugged into any
9-pin PC serial (COM) port using a 9-
pin serial cable, available from most
computer stores. If your computer
has a 25-pin COM port, 25-pin to 9-
pin serial adapters are also available
from most computer stores and can
be used with the cable [Serial data is
transmitted using Pin 5 (ground), Pin
3 (transmit), and Pin 2 (receive)].
Some computer COM ports and seri-
al adapters are not fully implemented
(not all pins are used). If the DPSC-
35XR is connected to a partially im-
plemented serial port, functions may
be erratic or the unit may fail to com-
municate. Please consult the owner’s
manual for your computer if this oc-
curs. Set up your communications
program as described on the next
page.
Connecting to a USB port If your
computer has USB ports you can get
an optional RS-232 to USB adapter
from Ohmic. Ohmic recommends
using an RS-232 to USB adapter
only with Windows XP© and Win-
dows Vista©. Connect the DPSC-
35XR using the RS-232 to USB
adapter. Turn on your computer.
When your computer recognizes the
device click OK and follow the in-
structions for installing the driver soft-
ware. Set up your communications
program as described next.

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Communications Program
The DPSC-35XR transmits data via
its RS-232 output as soon as it is
powered up. In order to receive the
data, a communications (or terminal)
program must be running on your
computer. We recommend Tera
Term; it is easy to use, free, and
available for download from
www.download.cnet.com. When you
reach that page, type “Tera Term” in
the Search box; you will then be able
to download the installation program.
Then:
1. Install the program and run it.
2. A New Connection window will
open. Click the “Serial” button,
then select the COM port you will
be using, and click OK.
3. Tera Term should now be ready
to receive data from the DPSC-
35XR. Make sure they are con-
nected and power up the DPSC-
35XR.
4. Text will be displayed indicating
the version of the embedded pro-
gram. The computer will then
display four numbers: Relative
Humidity, Dry Bulb Temperature,
Dew Point, and Set Point. New
readings will be displayed every
few seconds and are in a comma
delimited format that can be cop-
ied and pasted into a spread-
sheet program, if desired.
Communications Commands
All commands are in upper-case
characters (set your CAPS LOCK
on). n indicates where a number
must be entered:
Cn<Enter> Set auto data transmit
interval for displayed
readings to n seconds
(n is an integer from 3
to 32767). For n=0, 1,
and 2, automatic trans-
mission is turned off.
Default value is n=3
seconds.
D<Enter> Transmits the latest set
of readings.
S<Enter> Transmit current settings
of parameters.
Note: To enable the screen to dis-
play what you are typing, go to the
menu bar in Tera Term, click on Set-
up, select Terminal, and checkmark
the “Local Echo” box.
RECALIBRATION
The DPSC-35XR is a microproces-
sor-based instrument. It has no user
calibration adjustments. The unit can
be recertified to NIST traceable
standards by returning it to Ohmic
Instruments. Certification is valid for
one year and is recommended on a
yearly basis. Calibration consists of a
computer based system to program a
9-point calibration curve which is
stored in the unit’s EEPROM. The
calibration is referenced to a NIST
traceable chilled mirror.

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The DPSC-35XR and its accom-
panying sensor probe are cali-
brated as a system, due to
slight variances between sen-
sors. For this reason, the unit
and its probe bear matching
serial numbers and should be
kept together if you have more
than one set, to insure accura-
cy. When returning DPSC-
35XR’s for service and recali-
bration, be sure to include the
corresponding probes.
SPECIAL ORDER
For a nominal fee, the DPSC-35XR
can be retrofitted by Ohmic with ei-
ther or both of these options:
24 Volt: The DPSC-35XR can be
modified so it will operate from a 24
volt DC source instead of AC.
Time Stamp Datalogging: Adds time
stamp and logging functions to the
unit’s communication with your com-
puter. This is standard on the DPSC-
35XRL.

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Figure 1
DPSC-35XR Mounting Template
(Template drawing is to be used on installation side of enclosure)

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Figure 2
Card Wiring Diagram