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

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Alarm Reset Wiring
For user connection to reset an
alarm device, see the illustration
above. The 470 ohm resistor is on
the PC board as shipped. Connect
alarm (sonalert, etc.) to terminals 4
and 5. Connect a momentary nor-
mally closed pushbutton switch
across terminals 3 and 4. Retain
the supplied jumper across 1 and 2.
Pressing the pushbutton switch will
reset the system to a pre-alarm
state.
Figure 3

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F/C-DP V-out I-out F/C-DP V-out I-out F/C-DP V-out I-out F/C-DP V-out I-out
-45 0.000 4.000 -11 1.259 8.030 23 2.519 12.059 57 3.778 16.089
-44 0.037 4.119 -10 1.296 8.148 24 2.556 12.178 58 3.815 16.207
-43 0.074 4.237 -91.333 8.267 25 2.593 12.296 59 3.852 16.326
-42 0.111 4.356 -81.370 8.385 26 2.630 12.415 60 3.889 16.444
-41 0.148 4.474 -71.407 8.504 27 2.667 12.533 61 3.926 16.563
-40 0.185 4.593 -61.444 8.622 28 2.704 12.652 62 3.963 16.681
-39 0.222 4.711 -51.481 8.741 29 2.741 12.770 63 4.000 16.800
-38 0.259 4.830 -41.519 8.859 30 2.778 12.889 64 4.037 16.919
-37 0.296 4.948 -31.556 8.978 31 2.815 13.007 65 4.074 17.037
-36 0.333 5.067 -21.593 9.096 32 2.852 13.126 66 4.111 17.156
-35 0.370 5.185 -11.630 9.215 33 2.889 13.244 67 4.148 17.274
-34 0.407 5.304 01.667 9.333 34 2.926 13.363 68 4.185 17.393
-33 0.444 5.422 11.704 9.452 35 2.963 13.481 69 4.222 17.511
-32 0.481 5.541 21.741 9.570 36 3.000 13.600 70 4.259 17.630
-31 0.519 5.659 31.778 9.689 37 3.037 13.719 71 4.296 17.748
-30 0.556 5.778 41.815 9.807 38 3.074 13.837 72 4.333 17.867
-29 0.593 5.896 51.852 9.926 39 3.111 13.956 73 4.370 17.985
-28 0.630 6.015 61.889 10.044 40 3.148 14.074 74 4.407 18.104
-27 0.667 6.133 71.926 10.163 41 3.185 14.193 75 4.444 18.222
-26 0.704 6.252 81.963 10.281 42 3.222 14.311 76 4.481 18.341
-25 0.741 6.370 92.000 10.400 43 3.259 14.430 77 4.519 18.459
-24 0.778 6.489 10 2.037 10.519 44 3.296 14.548 78 4.556 18.578
-23 0.815 6.607 11 2.074 10.637 45 3.333 14.667 79 4.593 18.696
-22 0.852 6.726 12 2.111 10.756 46 3.370 14.785 80 4.630 18.815
-21 0.889 6.844 13 2.148 10.874 47 3.407 14.904 81 4.667 18.933
-20 0.926 6.963 14 2.185 10.993 48 3.444 15.022 82 4.704 19.052
-19 0.963 7.081 15 2.222 11.111 49 3.481 15.141 83 4.741 19.170
-18 1.000 7.200 16 2.259 11.230 50 3.519 15.259 84 4.778 19.289
-17 1.037 7.319 17 2.296 11.348 51 3.556 15.378 85 4.815 19.407
-16 1.074 7.437 18 2.333 11.467 52 3.593 15.496 86 4.852 19.526
-15 1.111 7.556 19 2.370 11.585 53 3.630 15.615 87 4.889 19.644
-14 1.148 7.674 20 2.407 11.704 54 3.667 15.733 88 4.926 19.763
-13 1.185 7.793 21 2.444 11.822 55 3.704 15.852 89 4.963 19.881
-12 1.222 7.911 22 2.481 11.941 56 3.741 15.970 90 5.000 20.000
Table 1—Analog Output Table

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SENSOR PRECAUTIONS
The following is a list of limits of operation. Exceeding these limits can
cause sensor failure and voids all warranties.
I. Humidity: 1 to 99% RH - NON CONDENSING
II. Temperature: 0 to 185°F
III. Max. Pressure: 175 psi
IV. Electrical: Never connect the sensor probe to any other device; the
signal conditioning circuitry in the DPSC-35XR is specific to the sensor.
Connecting the sensor to other circuitry or meters (including multi-
meters) can cause damage to the sensor.
V. Particulate Contamination: The sensors should be shielded from par-
ticulate contaminants. The protective screen should always be in place,
especially when the quality of the air is in question. Never sample air of
gases with oil mist or separated water.
VI. Chemical Contamination: Exposure to corrosive or reactive chemicals
should be avoided. Chemicals, such as sulfides, acids, and mercury will
cause permanent damage.
SPECIFICATIONS
Water Vapor Sensor……………….HC-610 (Integrated Thin Film Polymer)
Temperature Sensor………………………….………...10K NTC Thermistor
Dew/ Frost Point Range………………………………………...-40 to +80 °F
Dry Bulb Temperature Range…………………………………….0 to 185 °F
Dew/ Frost Point Accuracy……………………….+4°F from -40°F to +20°F
+2°F from +20°F to +80°F
Maximum Temperature…………………………………..…….Probe: 185°F
Electronics: 120°F
Sensor Response Time…..……………..10 seconds for 63% Step Change
Display Type………………………..………………….….3-½ Digit LCD; 0.5"
Analog Outputs…………………..………………………..0-5 VDC & 4-20mA
Power……………………………………….……………...120 VAC, 50-60 Hz
Fuse…………………………………….………………………..½ Amp, 250 V
Computer Interface…….…...Bi-directional RS-232. Data in ASCII Comma
Delimited Format. 9600 Baud, 8 Data Bits, 1
Stop Bit, No Parity, Flow Control Xon/Xoff
Dimensions…….………………Circuit Board: 4¼” x 6” x 1.88” (H x W x D)

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LOGGING COMMANDS FOR LOG-
GER VERSION ONLY (DPSC-35XRL)
1. When the unit is powered up, the
computer’s screen will display the
following:
(Date) (Time) (RH) (Temp) (Dew Point) (Set Point)
To reset the time stamp using your
computer, type:
TMM DD YY hh mm ss
where:
MM = month (01--12)
DD = day (01--31)
YY = year (00--99)
hh = hours (00--23)
mm = minutes (00--59)
ss = seconds (00--59)
then press “Enter”.
2. A maximum of 2383 readings can be
stored; however, once the memory
logging space has been filled, a
wrap feature of the memory storing
will cause the oldest data to be over-
written. Thus, when the memory is
full, the logger will hold a “sliding
window” spanning 2383 readings.
Uploading the logged data can be
done at any point. The stored read-
ings are transmitted chronologically,
each line of the display correspond-
ing to one scan of the sensors. For a
full logger memory of 2383 readings,
uploading takes approximately three
minutes. Note, however, that a slow
scrolling speed of the terminal
screen might stretch this interval to
about four and a half minutes.
Uploading will not clear the logger
memory; this makes repeated up-
loading of the same data possible.
Data will be stored in the nonvolatile
memory incorporated into the logger,
without having power applied to the
unit, for as long as ten years.
3. The following commands apply to the
logger version (DPSC-35XRL) only:
S<Enter> Transmits current settings
of parameters: C#, L#, N#
(C is autotransmit data in
seconds, L is logging rate
in seconds, N is number of
readings logged, 0 to
2383)
Ln<Enter> Set logging rate to “n”
seconds (“n” is 3 to
32767). For n=0, 1, 2,
logging is off.
E9090<Enter> Clear stored data.
U<Enter> Upload stored data. Read-
ings, including a time
stamp, are transmitted in
chronological order, one
line corresponding to one
scan of the sensors.
H<Enter> Halt the uploading of data.
This command will work
only when uploading is in
progress.
When halted, only two commands
are accepted:
Q<Enter> Terminate the uploading
in progress and resume
the measurement and
logging functions. This
command will work only
following the “halt” com-
mand (H).
U<Enter> Resume loading. This
command will work only
follow-ing the “halt” com-
mand (H).
4. The unit will not log when power is
turned off.

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WARRANTY
Not withstanding any provision of any agreement the
following warranty is exclusive.
Ohmic Instruments warrants each instrument it
manufactures to be free from defects in material and
workmanship under normal use and service for the
period of 1-year from date of purchase. This warranty
extends only to the original purchaser. This warranty
shall not apply to fuses or any product or parts which
have been subjected to misuse, neglect, accident, or
abnormal conditions of operation.
In the event of failure of a product covered by this
warranty, Ohmic Instruments will repair and recali-
brate an instrument returned within 1 year of the
original purchase: provided the warrantor's examina-
tion discloses to its satisfaction that the product was
defective. The warrantor may, at its option, replace
the product in lieu of repair. With regard to any instru-
ment returned within 1 year of the original purchase,
said repairs or replacement will be made without
charge. If the failure has been caused by misuse,
neglect, accident, or abnormal conditions of opera-
tions, repairs will be billed at a nominal cost. In such
case, an estimate will be submitted before work is
started, if requested.
THE FOREGOING WARRANTY IS IN LIEU OF ALL
OTHER WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY IMPLIED
WARRANTY OF MERCHANTABILITY, FITNESS,
OR ADEQUACY FOR ANY PARTICULAR PUR-
POSE OR USE. OHMIC INSTRUMENTS SHALL
NOT BE LIABLE FOR ANY SPECIAL, INCIDENTAL,
OR CONSEQUENTIAL DAMAGES, WHETHER IN
CONTRACT, TORT, OR OTHERWISE.
If any failure occurs, the following steps should
be taken:
1. Notify Ohmic Instruments giving full details of the
difficulty, and include the model, type, and serial
numbers (where applicable). On receipt of this
information, service data, or shipping instructions
will be forwarded to you.
2. On receipt of shipping instructions, forward the
instrument, transportation prepaid. Repairs will be
made and the instrument returned, transportation
prepaid.
SHIPPING TO MANUFACTURER FOR REPAIR
OR ADJUSTMENT
All shipments of Ohmic Instruments products should
be made via United Parcel Service or "Best Way"
prepaid. The instrument should be shipped in the
original packing carton, or if it is not available, use
any suitable container that is rigid and of adequate
size. If a substitute container is used, the instrument
should be wrapped in paper and surrounded with at
least four inches of excelsior or similar shock absorb-
ing material.
CLAIM FOR DAMAGE IN SHIPMENT TO
ORIGINAL PURCHASER
The instrument should be thoroughly inspected
immediately upon delivery to purchaser. All material
in the shipping container should be checked against
the enclosed packing list. The manufacturer will not
be responsible for shortages against the packing
sheet unless notified immediately. If the instrument is
damaged in any way, a claim should be filed with the
carrier immediately. (To obtain a quotation to repair
shipment damage, contact Ohmic Instruments.) Final
claim and negotiations with the carrier must be com-
pleted by the customer.
Ohmic Instruments will be pleased to answer all
application or use questions, which will enhance your
use of this instrument. Please address your requests
or correspondence to:
Ohmic Instruments
3081 Elm Point Industrial Drive
St. Charles, MO 63301 USA
ATTN: Technical Support
Or call Ohmic Technical Support at 410-820-5111.
All rights reserved. This manual may not be repro-
duced in full or in part without written permission of
Ohmic Instruments. Information contained within this
manual is believed to be accurate and reliable.
However, Ohmic Instruments assumes no liability for
its use. Ohmic Instruments reserves the right to
supply its instruments with design changes and/or
component substitutions that may not be document-
ed in this manual. Contact our engineering depart-
ment for information on equipment revisions not
covered in this manual.
Phone [phone]
Toll Free(800) 626-7713
Fax [phone]
www.ohmicinstruments.com
Sales: [e-mail]
Service: [e-mail]

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