Omega CMDP Series User manual

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User’s Guide
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Series CMDP
A chilled mirror
hygrometer
TM

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omega.com [email protected]m
Servicing North America:
U.S.A. Omega Engineering, Inc.
Headquarters: 800 Connecticut Ave. Suite 5N01, Norwalk, CT 06854
Toll-Free: 1-800-826-6342 (USA & Canada only)
Customer Service: 1-800-622-2378 (USA & Canada only)
Engineering Service: 1-800-872-9436 (USA & Canada only)
Tel: [phone] Fax: [phone]
e-mail: [email protected]

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The information contained in this document is believed to be correct, but OMEGA accepts no liability for any errors it contains, and
reserves the right to alter specifications without notice.

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Ordering Configuration
CMDP-D Duct mounted chilled mirror hygrometer (dew point only)
CMDP- W Wall mounted chilled mirror hygrometer (dew point only)
CMDPT-W Wall mount chilled mirror hygrometer (dew point/air temperature)
CMDP-P Pipe mounted chilled mirror hygrometer (dew point only)
The CMDP overviews
The CMDP series is a family of low-cost dew point chilled mirror transmitter that can be
configured as a duct, wall, pipe, or an OEM unit. The unit offers stable, accurate and
repeatable measurements that are traceable to NIST. Available air temperature option for wall
and OEM configurations. Settable service cycles for balancing and cleaning the mirror. The
CMDP is a primary measurement using a fundamental principle to measure the dew point very
accurately. Simple maintenance to cleaning the mirror requires using a wetted cotton swab to
restore the transmitter to normal operation. Because of its construction, the customer can enjoy
a long life of excellent performance.
FEATURES
1. Precision accuracy.
2. Two 4-20mA outputs (configurable).
3. Durable and fast responding
4. Automatic balance function for the
mirror, optical circuitry.
4. RS232 communication
5. Simple maintenance-mirror cleaning
SPECIFICATIONS
OPERATING LIMITATIONS:
Temperature: -40°C to +70°C. High temperatures will damage the electronics.
Accuracy: ± 0.5C of reading for both dew point and temperature
Repeatability: ± 0.05C
Calibration: NIST Traceable
Measurement Range: Dew Point -20C (@ 25C) to 60C (non-condensing)
Dew Point -40C (@)0C)
Temperature probe: (optional) -40C to 120C
Output: (2) 4 to 20mA output at 24Vdc (configurable). Default settings: -20C to 60C (unless
specified on purchase order.
Supply Voltage: 24Vdc +/-3V @1.0A
Weight: 2lbs
Wetted material: nickel, ultem and anodized aluminum

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Pressure rating: 5 ATM. Thread size 1.25”-12 UNF
WARNING: Pressure more than allowable rating may cause the housing to
burstand cause serious personal injury.
Air Velocity: 50 to 900m/min
Optional:
Air Temperature probe dimensions: length 5”, O.D. 0.1875 (3/16”)
Air temperature connection: 4 wire (flying leads)
CMDP Instructional Guide
The CMDP is a single stage chilled mirror hygrometer configured for duct mount, wall mount and OEM application. For
Pipe Mount applications please consult factory. The CMDP requires 24VDC @1 A for power. It is has two 4-20mA
outputs factory scaled for -40C to 60C. The unit also has a RS232 communication connection that can be accessed using
either the Hyper terminal or TeraTerm program which is available on most computers.
Notes: Even though the unit is scaled from -40C to 60C, the unit can only measure to -20C dew point at ambient
temperature conditions (25C). If the dew point is lower than -20C, the user will have to cool the body of the sensor to a
lower temperature. The unit has depression capability of 45C (meaning if at ambient (25C), subtract 45 from 25C and
that will be your lowest dew point (-20C). So, lowering the temperature of the sensor will get you to lower measurable
dew points.
Wiring instructions for the CMDP series
Terminal Block
All wiring is done to the 12-pin terminal block located on the PCB
Pin 1 Tx (RS232)
Pin 2 Rx (RS232)

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PCB blue connector:
Pin 3 (+) 4-20mA output
Pin 4 Ground
Pin 5 (+) 4-20mA output
Pin 6 (-) common for 4-20mA outputs
Pin 7 (-) Air temperature probe
Pin 8 (-) Air temperature probe
Pin 9 (+) Air temperature probe
Pin 10 (+) Air temperature probe
Pin 11 Return
Pin 12 24Vdc (@1A)
Protocol setup to run or program the CMDP.
No special software is needed. User can use either the TeraTerm program or the HyperTerminal program on their PC.
Connect the RS232 connection from the Dew Tran and using a USB converter connect to your PC.
Protocol configuration: Baud rate 19.2K, 8 Bits, 1 stop Bit, No parity
To access the menu, hit the “esc”
The Cap lock key must be on when selecting commands.
Calibrating Current Outputs
There are 2 methods for calibrating the 4-20 mA. outputs. Method 1 uses a digital ammeter, capable of 1 uA.
Resolution. The second method uses high precision (.005%) Resistor(s), In range of 10 – 750 ohms. The
factory Calibration is done using 100.00 ohm resistors.
for output 1, connect Ammeter across BLACK Wire and RETURN. From normal operation, enter following
keystrokes:
<ESC> <C>hange <O>utputs <C>alibrate <C>urrent.
at the “Sense Resistor Value (Y/N) OHMS?” Prompt, enter <N>
Enter<1> for Current output 1. The prompt “4 mA. = ?, enter the value displayed on Ammeter, as mA’s
Continue for the next 2 prompts (12 mA. and 20 mA.)
the prompt “4 mA. = 1XXXX” is displayed, check Ammeter for 4.00 mA. reading. Press <CR> to sequence (8,
12, 16 ,20 mA.) Values, with corresponding Ammeter Readings. If calibrated values good, at “Save Calibration
(Y/N)?, enter<Y>.

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Operations
There are two ways to determine if the sensor is operating/properly functioning.
Reminder: When the unit is first powered on, the unit will take 3-5 minutes to control. Typically, the unit goes
through what we call an ARC condition. Which is a balancing cycle, the unit initial heats up, then goes into an
acquiring mode (hunting for the dew point) and then the control mode.
1) If you are using the RS232, output you can view the data via your computer to see if the unit is in control.
The data will be streamlined on your PCs and you will see the word “control” at the end of each line.
2) Another method is by viewing the red light on the PCB. If the red light is in a steady state (always on), the
unit is in control.
3) If the red light is blinking, the unit is most likely in one of these three states.
a. The unit was just powered on and is going through its ARC cycle for 3-5minutes.
b. The mirror is dirty (has contaminants on it) and it needs to be cleaned. Refer to the clean mirror
procedure.
c. If the above 2 steps do not remove the blinking red light condition, the unit could be out of range to
measure that dew point/frost point. (Ex: if your ambient condition is 25C and your dew points is
below -20C, the unit can not measure that dew point (red light will blink). A way to correct that is to
lower the body temperature of the sensor to a point where the dew point is measurable with this unit.
Clean Mirror
mirror
1) Power down
2) Gain access to the mirror
3) Clean mirror with a wetted (using isopropyl alcohol) cotton swab.
4) Dry the mirror surface with a dry cotton swab.
5) Reinstall sensor shield if applicable.
6) Power the CMDP on
7) Also, the mirror can be cleaned during the ARC (when red light is blinking) by following the above steps 2- 5
Control light

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Airflow adjustments
There are air 6 holes in the middle of the outer shell. 2 large holes, 2 medium, and 2 small. The holes allow the airflow
to the mirror (where the measurement is made).
To adjust the airflow to the mirror, the Phillip set screw must be removed. Once removed, twist the outer shell to the
correct hole for airflow and then re-install the set screw to hold the outer shell in place.
For example: if the larger airflow hole has been selected and your signal is constantly oscillating after the red light is in a
steady state. You might want to select a smaller hole to slow down the airflow to the mirror. If that doesn’t work, try to
clean the mirror.
Set screw
Outer shell
Airflow holes

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For Pipe Mount configurations;
Roscid supplies a Hex Bushing: Red Brass, 1 1/2 in x 1 in Fitting Pipe Size, Male NPT x Female NPT, Class 125.
The sensor head (black flow rate cap) should be installed at least 1” into the process gas.
If the reading is oscillating, you might need to adjust the black flow rate cap, slowing the flow rate down.
Chilled Mirror Hygrometer, a fundamental first principal measurement for dew point:
Black flow rate cap

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R 22.35
50.55
1
174.5
B69.85
R 11.18
91.95
R. 9.14
136.4 B
147.32
44.45
A
PROPRIETARY AND CONFIDENTIAL
UNLESS OTHERWISE SPECIFIED:
DIMENSIONS ARE IN mm
TOLERANCES: FRACTIONAL
ANGULAR: MACH BEND
TWO PLACE DECIMAL
THREE PLACE DECIMAL
INTERPRET GEOMETRIC
TOLERANCING PER:
DRAWN
CHECKED
ENG APPR.
MFG APPR.
Q.A.
COMMENTS:
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DATE
TITLE: A
CM-10-D
THE INFORMATION CONTAINED IN THIS
DRAWING IS THE SOLE PROPERTY OF
<INSERT COMPANY NAME HERE>. ANY
REPRODUCTION IN PART OR AS A WHOLE
WITHOUT THE WRITTEN PERMISSION OF
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NEXT ASSY USED ON
MATERIAL
FINISH
SIZE
A
DWG. NO. REV
PROHIBITED. APPLICATION
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DO NOT SCALE DRAWING
SCALE: 1:4
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WEIGHT: SHEET 1 OF 1