Omega CMDP Series User manual

1
User’s Guide
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Series CMDP
A chilled mirror
hygrometer
TM

2
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]

3
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

2
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:
NAME
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
<INSERT COMPANY NAME HERE> IS
NEXT ASSY USED ON
MATERIAL
FINISH
SIZE
A
DWG. NO. REV
PROHIBITED. APPLICATION
2
DO NOT SCALE DRAWING
SCALE: 1:4
1
WEIGHT: SHEET 1 OF 1

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Chilled mirror hygrometers (CMH) use a primary fundamental principal measurement which is a change in resistance.
This principle works when a sample of process gas flows across a special polished coated mirror.
The mirror
temperature is lowered by thermal electric coolers (located beneath the mirror block/mirror) until the water vapor of gas
condenses out on to the mirror in the form of either dew or frost. There is an optical circuit which constantly monitors
the mirror surface and looks for equilibrium between the optical LED detectors (a reference and the dew detector). The
temperature of the mirror surface is measure by a highly accurate Platinum Resistance Thermometer (PRT) which is
embedded and sealed in the mirror block which is thermally connected to the mirror. The PRT resistance measurement is
what makes this a fundamental dew point measurement.
In more detail, a fundamental measurement is such that the parameter being measured, is the same as the
Standard International definition of that parameter. In the case of the Chilled Mirror Hygrometer, that measurement is
the temperature of the mirror surface covered by a water layer that is in equilibrium between the liquid and gaseous
phases of water. If that temperature measurement is accomplished by a platinum resistance thermometer, the
measurement is equivalent to the definition of dew point. Tables constructed by NIST, notably by Wexler and
Greenspan, establish the equivalence of dew point and the vapor pressure of water. Using this equivalence and a second,
fundamental, temperature measurement, realizes the definition of Relative humidity: Vapor pressure of water/saturation
vapor pressure (temperature) of the gas being measured, X100(%) i.e. %RH =100*PH2Ov/PSAT. Addition of a 3rd
measurement, the pressure of the gas being sampled, allows measurement of almost every other humidity parameter.
Some further unit examples: absolute Humidity (gH2Ov/m3), mixing ratio (gH2Ov /kgDRY), Parts per million (PH2Ov/(PTot-
PH20)), enthalpy(h), to name a few.
Chilled mirrors hygrometers are used where accuracy, typically +-0.2°C or better, repeatability, stability and no
drift are paramount. CMH are the preferred reference standard in most calibration labs. Also, CMH work well due to
their ruggedness, their inertness, their simple maintenance and ability to accurately measure sample gasses remotely
from process, i.e. ovens, dryers, furnaces, etc. Dew points above ambient can be measured by heating the chilled mirror
and associated components. Chilled mirrors can be, and are, constructed as an insertion probe, provided the temperature
of the process is < ~95 °C.
In closing, the upside of the chilled mirror hygrometer is that it uses a fundamental principal, it can be designed to be
inert to many corrosive gases, it is a repeatable in its measurement, there is no measurable hysteresis, it is very accurate
and has a very long operating life. The downside is that it is expensive and is typically slower in response time when
compared to other secondary principal humidity measurements.

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WARRANTY / DISCLAIMER
OMEGA ENGINEERING, INC. warrants this unit to be free of defects in materials and workmanship
for a period of
13 months from date of purchase. OMEGA’s WARRANTY adds an additional one (1)
month grace period to the normal
one (1) year product warranty to cover handling and shipping
time. This ensures that OMEGA’s customers receive maximum coverage on each product.
If the unit malfunctions, it must be returned to the factory for evaluation. OMEGA’s Customer Service
Department will issue an Authorized Return (AR) number immediately upon phone or written request.
Upon examination by OMEGA, if the unit is found to be defective, it will be repaired or replaced at no
charge. OMEGA’s WARRANTY does not apply to defects resulting from any action of the purchaser,
including but not limited to mishandling, improper interfacing, operation outside of design limits,
improper repair, or unauthorized modification. This WARRANTY is VOID if the unit shows evidence of
having been tampered with or shows evidence of having
been damaged as a result
of excessive corrosion; or current, heat, moisture or vibration; improper specification;
misapplication; misuse or other operating conditions outside of OMEGA’s control.
Components in which wear is not warranted, include but are not limited to contact points,
fuses, and triacs.
OMEGA is pleased to offer suggestions on the use of its various products. However, OMEGA
neither assumes responsibility for any omissions or errors nor assumes liability
for any damages that result from the use of its products in accordance with
information provided by OMEGA,
either verbal or written. OMEGA warrants
only that the parts manufactured by it will be as specified and free of defects.
OMEGA MAKES NO OTHER WARRANTIES OR REPRESENTATIONS OF ANY KIND
WHATSOEVER, EXPRESS OR IMPLIED, EXCEPT THAT OF TITLE, AND ALL IMPLIED
WARRANTIES INCLUDING ANY WARRANTY OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE HEREBY
DISCLAIMED. LIMITATION OF LIABILITY: The remedies of purchaser set forth herein are
exclusive, and the total liability of OMEGA with respect to this order, whether based
on contract, warranty, negligence, indemnification, strict liability or otherwise, shall not
exceed
the purchase price of the component upon which liability is based. In
no event shall OMEGA be liable for consequential, incidental or special damages.
CONDITIONS: Equipment sold by OMEGA is not intended to be used, nor shall it be used: (1) as a
“Basic Component” under 10 CFR 21 (NRC), used in or with any nuclear installation or activity; or (2)
in medical applications or used on humans. Should any Product(s) be used in or with any nuclear
installation or activity, medical application, used on humans, or misused in any way, OMEGA assumes
no responsibility as set forth in our basic WARRANTY / DISCLAIMER language, and, additionally,
purchaser will indemnify OMEGA and hold OMEGA harmless from any liability or damage whatsoever
arising out of the use of the Product(s) in such a manner.
RETURN REQUESTS/INQUIRIES
Direct all warranty and repair requests/inquiries to the OMEGA Customer Service Department. BEFORE
RETURNING ANY PRODUCT(S) TO OMEGA, PURCHASER MUST OBTAIN AN AUTHORIZED RETURN (AR)
NUMBER FROM OMEGA’S CUSTOMER SERVICE DEPARTMENT (IN ORDER TO AVOID
PROCESSING DELAYS). The assigned AR number should then be marked on the outside of the return
package and on any correspondence.
The purchaser is responsible for shipping charges, freight, insurance and proper packaging to prevent
breakage in transit.
FOR WARRANTY RETURNS, please have the
following information available BEFORE
contacting OMEGA:
1. Purchase Order number under which the
product was PURCHASED,
2.
Model and serial number of the product under
warranty, and
3.
Repair instructions and/or specific problems
relative to the product.
FOR NON-WARRANTY REPAIRS, consult OMEGA
for current repair charges. Have the following
information available BEFORE contacting OMEGA:
1.
Purchase Order number to cover the COST
of the repair,
2.
Model and serial number of the product, and
3.
Repair instructions and/or specific problems
relative to the product.
OMEGA’s policy is to make running changes, not model changes, whenever an improvement is possible. This affords
our customers the latest in technology and engineering.
OMEGA is a trademark of OMEGA ENGINEERING, INC.
© Copyright 2019 OMEGA ENGINEERING, INC. All rights reserved. This document may not be copied, photocopied,
reproduced, translated, or reduced to any electronic medium or machine-readable form, in whole or in part, without the
prior written consent of OMEGA ENGINEERING, INC.

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