Optidew
Chilled Mirror Hygrometer
User Manual
97551 Issue 4.3
November 2022
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Optidew
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© 2022 Michell Instruments
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otherwise reproduced, communicated in any way to third parties, nor stored in any Data
Processing System without the express written authorization of Michell Instruments Ltd.
Optidew User Manual
Contents
Safety ..............................................................................................................................viii
Warnings ................................................................................................................... viii
Electrical Safety ......................................................................................................... viii
Pressure Safety ......................................................................................................... viii
Hazardous Materials (WEEE, RoHS3 & REACH) ...............................................................ix
Calibration (Factory Validation) ......................................................................................ix
Repair and Maintenance ...............................................................................................ix
Abbreviations ...................................................................................................................... x
1 INTRODUCTION ................................................................................................1
1.1 Optidew Series ................................................................................................... 1
1.2 Optidew Sensor .................................................................................................. 2
1.3 Minimum Measurable Dew Points ......................................................................... 3
1.4 Remote Temperature Probes ............................................................................... 4
2 INSTALLATION ..................................................................................................5
2.1 Unpacking the instruments .................................................................................. 5
2.2 Mounting .......................................................................................................... 5
2.3 Instrument Connections ...................................................................................... 7
2.3.1 Optidew 501 ................................................................................................. 7
2.3.2 Optidew 401 ................................................................................................. 8
2.4 Electrical Connections ......................................................................................... 9
2.4.1 Electrical Supply ............................................................................................ 9
2.4.2 Analog and Digital Communications .............................................................. 10
2.4.2.1 Digital Communications ......................................................................... 10
2.4.2.2 Current Outputs .................................................................................... 11
2.4.2.3 Relay Contacts ...................................................................................... 12
2.5 Sensor Installation ............................................................................................ 13
2.5.1 Environmental monitoring ............................................................................ 13
2.5.2 Monitoring a flowing sample ........................................................................ 13
2.5.3 Environmental Chamber or Glovebox Sensor Mounting ................................. 14
2.6 Temperature Probe Installation .......................................................................... 14
2.6.1 Using Temperature Probes with a chamber port adapter ............................... 15
2.7 Pressure Transmitter Installation ........................................................................ 15
3 USER INTERFACE ............................................................................................16
3.1 Main Display .................................................................................................... 16
3.1.1 Full Screen Mode ........................................................................................ 16
3.1.2 Main Screen ................................................................................................ 17
3.1.3 Customizable Readouts................................................................................ 18
3.1.4 Locking the analyzer ................................................................................... 18
3.1.5 Menu Structure ........................................................................................... 19
3.1.6 Operational Status Display ........................................................................... 20
3.1.7 Sensor Status Display .................................................................................. 21
3.2 Setup Menus .................................................................................................... 22
3.2.1 DCC ........................................................................................................... 22
3.2.2 Logging ..................................................................................................... 23
3.2.3 Outputs .................................................................................................... 24
3.2.4 Alarm ......................................................................................................... 25
3.2.5 Display ....................................................................................................... 26
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Optidew User Manual
3.2.6 Clock ......................................................................................................... 27
3.2.7 Inputs ....................................................................................................... 28
3.2.8 Comms Screen ............................................................................................ 29
3.2.9 Network Settings ........................................................................................ 29
3.3 Optidew 501 Transmitter without display ............................................................ 30
3.3.1 Optics Calibration ....................................................................................... 30
4 OPERATION ....................................................................................................31
4.1 Operating Cycle ................................................................................................ 31
4.2 Operating Guide ............................................................................................... 32
4.2.1 Description ................................................................................................. 32
4.2.2 Operating Practice ....................................................................................... 32
4.3 Good Measurement Practice .............................................................................. 35
4.3.1 Sampling Hints............................................................................................ 35
4.3.2 First-Time Operation .................................................................................... 37
4.4 Operational Functions ....................................................................................... 38
4.4.1 DCC Function .............................................................................................. 38
4.4.2 MAXCOOL – Function .................................................................................. 38
4.4.3 Frost Assurance Technology (FAST) .............................................................. 39
4.4.4 STANDBY Mode........................................................................................... 39
4.4.5 Parameter Conversions & Pressure Compensation ......................................... 39
4.4.6 Data Logging .............................................................................................. 40
5 WARNINGS AND FAULTS ..................................................................................41
6 MAINTENANCE ................................................................................................43
6.1 Mirror Cleaning ................................................................................................. 43
6.2 Exchanging Sensors .......................................................................................... 44
Michell Instruments v
Optidew User Manual
Figures
Figure 1 Optidew 501 (wall mount) and Optidew 401 (bench top) ...............................1
Figure 2 2-stage minimum measureable dew point ....................................................3
Figure 3 General-purpose Probe ...............................................................................4
Figure 4 Labatory/High-temperature Probe ................................................................4
Figure 5 Optidew 501 wall mounting points ...............................................................6
Figure 6 Optidew 501 with touch screen display or DCC control button ........................7
Figure 7 Optidew 501 bottom panel ..........................................................................7
Figure 8 Optidew 401 front and side panels ...............................................................8
Figure 9 Optidew 401 rear panel ..............................................................................8
Figure 10 Power Connector ........................................................................................9
Figure 11 RS458 & Analog output connector .............................................................10
Figure 12 Analog output connector ...........................................................................11
Figure 13 Relay contact connector ............................................................................12
Figure 14 Temperature Probe Adapter ......................................................................15
Figure 15 Main Screen .............................................................................................16
Figure 16 Main Screen layout ...................................................................................17
Figure 17 DCC Menu ...............................................................................................22
Figure 18 Logging Screen ........................................................................................23
Figure 19 Outputs Screen ........................................................................................24
Figure 20 Alarm Screen ...........................................................................................25
Figure 21 Display Screen .........................................................................................26
Figure 22 Clock Screen ............................................................................................27
Figure 23 Inputs Screen...........................................................................................28
Figure 24 Comms Screen .........................................................................................29
Figure 25 Network Settings Screen ...........................................................................29
Figure 26 Typical Operating Cycle .............................................................................31
Figure 27 Room Measurement Example ....................................................................33
Figure 28 Mirror Contaminaton Warning Symbol ........................................................34
Figure 29 Material Permeability Comparison ..............................................................35
Figure 30 Condensation in Sample Tubing .................................................................36
Figure 31 System alarm ...........................................................................................41
Figure 32 Sensor Cleaning .......................................................................................43
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Optidew User Manual
Appendices
Appendix A Technical Specifications .............................................................................. 46
Appendix B Modbus Register Map ................................................................................49
Appendix C Legacy Serial Protocol ............................................................................... 58
C.1 Legacy Mode ...............................................................................58
C.2 Hardware Connection ...................................................................58
C.3 Changing between Modbus and Legacy Mode ................................ 59
C.4 Emulated Legacy Commands ........................................................ 60
C.5 New Commands for Optidew 401-501 ........................................... 62
Appendix D Dimensional Drawings................................................................................64
Appendix E Quality, Recycling, Compliance & Warranty Information ................................ 72
Appendix F Return Document& Decontamination Declaration .........................................74
Michell Instruments vii
Optidew User Manual
!
!
DANGER
Electric
Shock Risk
Safety
The instrument is designed to be completely safe when installed and operated correctly in accordance
with the information provided in this manual.
This manual contains all the required information to install, operate and maintain this product. Prior
to installation and use of this product, this entire manual should be read and understood. Installation
and operation of this product should be carried out by suitably competent personnel only. The
installation and operation of this product must be in accordance with the instructions provided and
according to the terms of any associated safety certicates. Incorrect installation and use of this
product other than those described in this manual and other than its intended purpose will render
all warranties void.
This product meets the essential protection requirements of the relevant EU directives. Further
details of applied directives may be found in the product specication.
Electricity and pressurized gas can be dangerous. This product must be installed and operated only
by suitable trained personnel.
No user serviceable parts inside
Warnings
Where this hazard warning symbol appears in the following sections,
it is used to indicate areas where potentially hazardous operations
need to be carried out and where particular attention to personal and
personnel safety must be observed.
Where this symbol appears in the following sections it is used to
indicate areas of potential risk of electric shock.
Electrical Safety
Ensure electrical safety is complied with by following the directions provided here and observing all
local operation & installation requirements at the intended location of use.
This product is completely safe when using any options and accessories supplied by the manufacturer
of this product for use with it. Refer to Section 2 (Installation) of this manual for further details.
Pressure Safety
For this product to operate satisfactorily, pressurized gas must be connected to it. Observe all the
information contained within this manual and all local operation & installation requirements at the
intended location of use. Refer to Section 2 (Installation) of this manual for further details.
viii 97551 Issue 4.3, November 2022
Optidew User Manual
Hazardous Materials (WEEE, RoHS3 & REACH)
This product does not contain or release any prohibited chemicals listed on the SVHC (Substances
of Very High Concern) Candidate List. During the intended normal operation of this product it is not
possible for the user to come into contact with any hazardous materials. This product is designed to
be recyclable except where indicated.
Calibration (Factory Validation)
Prior to shipment, the instrument undergoes stringent factory calibration that is traceable to national
standards. Due to the inherent stability of the instrument, regular factory calibration is not required,
however recalibration is recommended to maintain measurement traceability.
Michell Instruments can provide a fully traceable factory calibration service for the instrument and it
is recommended that this is considered at intervals of every year of the analyzer's life. Please contact
your local Michell Instruments oce or representative for further details (www.michell.com).
Repair and Maintenance
Apart from user-replaceable components required for routine operational maintenance described
above, the instrument must only be maintained either by the manufacturer or an accredited service
agent. Refer to www.michell.com for details of Michell Instruments’ worldwide oces contact
information.
Michell Instruments ix
Abbreviations
The following abbreviations are used in this manual:
A ampere
AC alternating current
atm pressure unit (atmosphere)
bara pressure unit (=100 kP or 0.987 atm) absolute
barg pressure unit (=100 kP or 0.987 atm) gauge
°C degrees Celsius
°F degrees Fahrenheit
EU European Union
hr hour
Hz Hertz
IEC International Electrotechnical Commission
IP Internet protocol
ml/min milliliters per minute
mg/m3 milligrams per cubic meter
lbs/MMscf pounds per million standard cubic feet
mA milliampere
mins minutes
mmHg millimeter of mercury
Pa pascal
ppmV parts per million (by volume)
ppmW parts per million (by weight)
%Vol percentage volume
psia pound(s) per square inch (absolute)
psig pound(s) per square inch (gauge)
RH relative humidity
RS485/232 standards defining the electrical characteristics of drivers & receivers
RTC real time clock
RTU Remote Terminal Unit
SD storage device card
UART universal asynchronous receiver/transmitter
USB Universal Serial Bus
V Volts
" Inch
Δ delta
% percentage
Ω ohms
Optidew User Manual
x 97551 Issue 4.3, November 2022
Optidew User Manual
1 INTRODUCTION
The Optidew chilled mirror hygrometer is based on the proven, fundamental condensation
temperature dew point principle, giving unmatched long-term drift-free performance.
Michell offers three highly durable sensor options, which are suitable for measuring in
a wide variety of different samples.
1.1 Optidew Series
The Optidew 501 features a compact ABS enclosure with an aluminium base plate and
4 external lugs for easy mounting to a panel or wall. It is available with a 5.7" touch
screen display, or as a "transmitter only" version.
A weatherproof version of the Optidew 501 enclosure is available with a modified
connector panel to improve ingress protection to IP65. Note that the Ethernet and SD
card options are not available in combination with the weatherproof version.
The Optidew 401 is designed to be easy to handle and transport and is ideal for laboratory
or service use. It has a 5.7” touch screen LCD fitted as standard.
INTRODUCTION
Figure 1
Optidew 501 (wall mount) and Optidew 401 (bench top)
Michell Instruments 1
INTRODUCTION
1.2 Optidew Sensor
The new Optidew sensor is available with either a single or dual stage thermoelectric
cooler and with a choice of sensor head materials making it suitable for use in air/inert
gases or in corrosive environments. The following tables show the capabilities of each
sensor type:
Optidew User Manual
Single Stage
Sensor
Approximate maximum
depression at ambient
Maximum operating
temperature
Maximum Recommended
Sensor Temperature for
FAST
Sensor temperature at
23 °C ambient
For more detailed information on the performance of the sensor across its whole
operating temperature range, see below. All versions are rated for use at pressure up
to 2500 kPag (362 psig).
60 °C (140 °F) 70 °C (158 °F) 70 °C (158 °F)
90 °C (194 °F) 90 °C (194 °F) 120 °C (248 °F)
21 °C (70 °F) 30 °C (86 °F) 30 °C (86 °F)
Lowest Measurable Dew Point
-25 °C (-13 °F) -40 °C (-40 °F) -40 °C (-40 °F)
Dual Stage
Sensor
Harsh
Environment
Sensor
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Optidew User Manual
10
1.3 Minimum Measurable Dew Points
The minimum dew point that can be measured is determined by the sensor temperature,
and whether the sensor can be maintained at that temperature. The following chart
assumes operation in a climatic chamber, where the air speed is sufficient to remove
any excess heat generated by the sensor.
0
-10
-20
-30
-40
INTRODUCTION
Minimum measurable dew point °C
-50
-60
10 20 30 40 50 60 70 80 90
Sensor Temperature °C
Figure 2
2-stage minimum measureable dew point
Michell Instruments 3
INTRODUCTION
1.4 Remote Temperature Probes
Two versions of temperature probe are available for the Optidew: a general-purpose
probe rated to +90 °C (+194 °F), and a laboratory/high-temperature probe rated to
+120 °C (+248 °F).
General-purpose Probe
Optidew User Manual
Figure 3
This 75mm (3”) probe is supplied when any of the 'standard' sensor cable options
are selected. it is intended to be installed in its' entirety into the environment to be
measured.
An M12 plug is integrated into the probe itself to connect to the supplied cable.
Laboratory/High-temperature Probe
Figure 4
General-purpose Probe
Labatory/High-temperature Probe
This 50 mm (1.97”) probe is supplied when any of the high temperature cable options
are selected, however it is also designed specifically for compatibility with Michell
Instruments or Rotronic humidity calibration chambers.
The probe is fitted with a 0.5m (1.64 ft) flying lead with an M12 plug to simplify
connection into a calibration chamber. The chosen cable length option is still supplied.
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Optidew User Manual
2 INSTALLATION
2.1 Unpacking the instruments
It is recommended that all packaging is retained, in case products are returned for
service or calibration. Alternatively, if you choose to dispose of the packaging materials,
ensure they are recycled in accordance with local legislation.
Standard contents in the box:
• Calibration Certicate
• 6-Way Alarm Relay Connector
• 8-Way Analog Output / RS485 Connector
• Pt100 Temperature Probe (with separate or integrated M12 cable, depending
on model)
• Chilled Mirror Monitor
• Chilled Mirror Sensor
INSTALLATION
• Chilled Mirror Sensor Cable
• Mains Cable
2.2 Mounting
Optidew 401
The Optidew 401 is designed to be placed on a bench or table during operation.
Alternatively, it can be used inside the optional Transport Case.
Optidew 501
The Optidew can be wall mounted using the four mounting points on each corner (see
Figure 2 for mounting point dimensions). It is possible to install the Optidew 501 outside,
providing it is shielded from direct sunlight and the climate is within the environmental
requirements listed in Appendix A Technical Specifications. It is highly recommended to
choose the weatherproof option if the installation will be outdoors.
Fixings
Secure using 4 off suitable screws or bolts plus washers (M4 x 15 to M6 x 15mm). Unit
must be secured to a solid surface (e.g. brick, concrete, wood minimum 10mm/0.39”
thick) or to a metal chassis plate of minimum 3mm (0.12”) thickness.
Michell Instruments 5
INSTALLATION
Wall Mounting Points
Optidew User Manual
240
(9,4)
145
(5,7)
Figure 5
260
(10,2)
Optidew 501 wall mounting points
180
(7,1)
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Optidew User Manual
2.3 Instrument Connections
2.3.1 Optidew 501
INSTALLATION
1
Figure 6
Number Description
1 DCC Control/ Status indicator
2 Sensor Cable connector
3 Temperature probe cable connector
4 Pressure transmitter cable connector
5 Alarm contacts connector
6 RS485 and analog output connector
7 SD Card slot (optional)
8 Ethernet port (optional)
9 Power Connector
Optidew 501 with touch screen display or DCC control button
5
7
3
2
4
6 8
9
Figure 7
Optidew 501 bottom panel
Michell Instruments 7
INSTALLATION
2.3.2 Optidew 401
1
Optidew User Manual
3
2
Figure 8
Number Description
1 Power Connector
2 Power Switch
3 SD card slot
4 Alarm contacts connector
5 RS485 and analog output connector
6 USB port
7 Ethernet port (optional)
8 Sensor Cable connector
9 Temperature probe cable connector
10 Pressure transmitter cable connector
Optidew 401 front and side panels
6
7
8
Figure 9
9
4
10
5
Optidew 401 rear panel
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Optidew User Manual
2.4 Electrical Connections
2.4.1 Electrical Supply
The Optidew accepts a power supply of the following specification:
Voltage 100...240 V AC
Frequency 50...60 Hz
Power Consumption 30 VA max
See Appendix A, Technical Specification, for full operating parameters.
INSTALLATION
WARNING:
The instrument must be GROUNDED
Optidew 501
The wall mount is supplied with a connector wired to a 2m cable. Only use an appropriately
rated mains supply cord.
This power connector is wired as follows:
Figure 10
NOTE: The Optidew 501 is designed for continuous operation and therefore does not
feature a power on/off switch. As soon as power is applied, the display (or DCC button
on the transmitter version) will illuminate and the transmitter will initiate a DCC cycle.
Power Connector
Replacement power cables are available. Contact your Michell representative.
Optidew 401
The Optidew 401 is supplied with a 2m IEC cable. The IEC socket is on the left-hand
side of the instrument. There is an ON/OFF switch on the front panel. Only use an
appropriately rated detachable mains supply cord.
Michell Instruments 9
INSTALLATION
Fuse
This product is provided with an externally mounted fuse located next to the power
connector. The fuse is rated at 5 x 20 mm medium acting: T 2.5 A H 250V.
Equipment Ratings
This product is designed to be safe at least under the following conditions: between a
temperature range of -40...+60 °C (-40...+148 °F), in maximum 80% relative humidity
for temperatures up to +31 °C (+88 °F) decreasing linearly to 50 %rh at +50 °C (+122
°F). Overvoltage Category II. Pollution Degree 2. Altitudes up to 2000 m (6561.66 ft).
Indoor use only but is IP65 rated.
See Appendix A, Technical Specification, for full operating parameters.
2.4.2 Analog and Digital Communications
NOTE: When using screened cable, the screen should only be connected to a ground
point at either the Optidew installation side, or at the receiving equipment. Failure to
observe this precaution can result in ground loops and equipment malfunction.
Optidew User Manual
2.4.2.1 Digital Communications
From left to right, the first four pins of this connector are used for RS485 communications.
Figure 11
Pin Label Description
GND Ground
RS485 B RS485 Data B
RS485 A RS485 Data A
GND Ground
RS458 & Analog output connector
The Optidew provides Modbus RTU over RS485 or USB (Bench Top only). An Ethernet
module is optionally available for both instruments and provides Modbus TCP
communication.
The Modbus register map can be found in Appendix B.
Application software is available and can be used to communicate with the instrument.
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2.4.2.2 Current Outputs
INSTALLATION
Figure 12
Left to right, the last four pins on this connector are used for mA outputs.
See Section 3.2 for information on configuring the analog outputs.
Pin Label Description
mA2 Channel 2 Current Output
GND Channel 2 Ground
mA1 Channel 1 Current Output
GND Channel 1 Ground
Analog output connector
Michell Instruments 11
INSTALLATION
2.4.2.3 Relay Contacts
There are two sets of relay contacts available via the output connector:
Process Alarm (Relay 1)
This relay changes state to indicate that the process variable has exceeded the alarm
set point value. See Section 3.2 for details on how to configure the process alarm trip
criteria. This alarm can also be used to give an early indication that the Optics require
cleaning.
System Alarm (Relay 2)
This relay changes state to indicate a fault has occurred which requires operator
intervention. See Section 4.6 for detailed information on faults.
Optidew User Manual
Figure 13
Pin Label (from left to
right as shown)
N/C Relay 1 Normally Closed
COM Relay 1 Common
N/O Relay 1 Normally Open
N/C Relay 2 Normally Closed
COM Relay 2 Common
N/O Relay 2 Normally Open
Relay contact connector
Description
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Optidew User Manual
2.5 Sensor Installation
The dew-point sensor contains the optical system and the chilled mirror. It is fitted with
a 12-pin M12 connector to allow easy and secure connection to the instrument using
the supplied sensor cable.
The available options for sensor installation are:
• via a permanently installed sample port into which the remote sensor can
be inserted or
• via a sensor block immediately attached to the sensor around which the
sample circulates or
• in an ambient environment where the sample is diffusing through the
sensor.
NOTE: Ensure that the mirror surface is cleaned before installation. See
Section 6 (Maintenance) for cleaning details.
Connect the remote sensor cable to the sensor and to the instrument via the connector
on the rear panel. The connector is a standard M12. Align the locating pin with the slot
on the socket and press the connector into place. Rotate the outer collar of the cablemounted part in a clockwise direction until finger tight.
INSTALLATION
If exchanging the sensor, refer to Section 6.2.
2.5.1 Environmental monitoring
If the instrument is to monitor the conditions in an environment, the sensor must be
located in a representative position, i.e. not under an air conditioning vent.
A sensor wall mounting bracket is available to conveniently secure the sensor to a wall
or panel.
NOTE: It is recommended that the sensor is fitted with the porous aluminium
guard to baffle it from flowing air currents.
2.5.2 Monitoring a flowing sample
If the sensor is installed within a sealed gas system, it must be fixed securely without
any possibility of leaks. Ensure that the sample flow across the sensor is correctly
regulated.
The gas connections for the remote sensor are either via a permanently installed sample
port into which the remote sensor can be inserted or via a sensor block immediately
attached to the sensor around which the sample circulates. Gas sample entry into the
sensor block is via couplings that can be installed into the provided ⅛” NPT female
threads. A bonded seal is provided to fill the connection between the sensor and the
block.
Ensure that all connections to and from the sensor block are made with appropriate
materials and fittings for moisture measurement. For guidance on suitable apparatus,
see Section 4.3.
Michell Instruments 13
INSTALLATION
2.5.3 Environmental Chamber or Glovebox Sensor Mounting
If the sensor is to be positioned into a sealed but open environment (glove box,
environmental chamber or area to be monitored) a female thread of M36 x 1.5-6 H is
required to suitably thread onto the sensors male M36 x 1.5-6 g thread. The bonded
seal provided will require a good surface finish (0.8 Ra) across a minimum sealing face
of DIA 46.0 mm (1.81“) to ensure leak-free operation up to the max operating pressure
of the sensor (25 barg / 363 psig). The bonded seal will also require a strong hand
tightening to ensure leak-free sealing of the two mating faces.
Always ensure you have tightened up with adequate torque to ensure leak-free sealing.
Care should be taken when fitting the sensor to ensure the bonded seal remains
centralized whilst threading the two mating M36 x 1.5 parts together. Also ensure that
the sensor is suitably located in a position that will see a representative flow of the
sample to be measured.
Optidew User Manual
2.6 Temperature Probe Installation
The temperature probe is supplied pre-wired and simply requires fitting to the connector
on the Optidew control unit prior to use.
Take into consideration how you will use the readings from your temperature probe
before installing it. If the measurement will be used in combination with the dew point
measurement to calculate %rh, then the temperature probe should be installed in a
location which is most representative of the temperature of your environment or sample.
Be aware that when depressing the mirror temperature by more than 40 °C (104 °F),
the Optidew dew-point sensor will generate a small amount of heat in the surrounding
area. Try to situate the temperature probe upstream of the dew-point sensor and at
least 150 mm (5.91”) away.
Refer to Section 4.4.5 for more information on calculated parameters and which
measured inputs are used to derive them.
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Optidew User Manual
2.6.1 Using Temperature Probes with a chamber port adapter
The following Michell Instruments and Rotronic products are available to order with a
port adaptor which fits the Laboratory/High Temperature Probe only:
• HygroCal100
• S904
• Optical
• Hygrogen 2
INSTALLATION
Figure 14
Temperature Probe Adapter
2.7 Pressure Transmitter Installation
Pressure transmitters are available for the Optidew in several ranges. Any 4...20 mA
pressure transmitter can be wired into the Optidew control unit via the 4-pin M12
connector. Michell can supply a pressure transmitter with the Optidew, which is installed
via a 1/8” NPT male thread.
The pressure source should be installed with consideration to the calculated values
which will be used. For example, if the dew-point sensor is installed at process pressure,
then the pressure sensor should be installed into the sample block. However, if the if
the dew-point sensor is installed at a different pressure to the process, the pressure
sensor should be installed in a different location which is at full process pressure. For
information on the pressure compensation feature refer to Section 4.4.5.
Michell Instruments 15
USER INTERFACE
3 USER INTERFACE
There are two different local user interfaces available. The analyzer features a 5.7” color
touch screen display and the transmitter has a button with multicolor LED indicator.
The application software gives the user access to all functionality available through the
local user interface. The Optidew offers three interfaces to connect to a PC or network:
• RS485
• USB (only available on Optidew 401)
• Ethernet (Optional)
3.1 Main Display
When the instrument is switched on, an ‘initialising’ overlay will be shown while the
menu system loads.
After the menu system has loaded, the Main Screen will show.
Optidew User Manual
Figure 15
3.1.1 Full Screen Mode
Any of the readouts can be shown in full screen mode by touching and holding the
readout.
Main Screen
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Optidew User Manual
3.1.2 Main Screen
USER INTERFACE
1
1
1
2
5 6 87
Figure 16
No. Name Description
1 Customizable Readouts
Display measured and calculated parameters. See
Section 3.1.3 for additional information
3
4
Main Screen layout
2 Sensor Status Display
3 Trend Graph
Operational Status
4
Display
5 DCC On/Off
6 Max Cool On/Off
7 Standby/Operate
8 Setup
Displays both thermo-electric cooler (TEC) drive
and optical signal condition. Also indicates whether
TEC is 1 or 2 stage. See Section 3.1.7 for additional
information
Plots measured dew point over time. Time base can
be changed in display settings. Touch the readout
once to enter full screen mode.
See Section 3.1.6 for a detailed description of this
area.
Initiates or cancels a DCC. See Section 4.4.1 for an
explanation of the DCC function.
See Section 3.2 for DCC setup parameters.
Initiates or cancels a Max Cool. See Section 4.4.2 for
an explanation of the Max Cool function.
Toggles between Measure and Standby modes.
When switching to Measure mode a DCC cycle will be
initiated.
Access the Setup menu. See Section 3.1.5 for
information on the menu structure and options.
Michell Instruments 17
USER INTERFACE
3.1.3 Customizable Readouts
The three readouts on the Main Screen can be configured by the User to show any of
the following parameters:
• Dew Point
• Temperature
• Pressure
• % Relative Humidity
Optidew User Manual
• g/m
3
• g/kg
• ppm
V
• %Vol
• Twb
• wvp (water vapor pressure)
• Dew Point (pressure corrected)
To change a parameter:
1. Touch the readout once to enable parameter selection
2. Touch the left or right arrows to select the parameter to be displayed
3. Touch the center of the readout to conrm selection
3.1.4 Locking the analyzer
From firmware version 1.0.1 onwards it is possible to lock the analyzer so unauthorized
users cannot change any settings. Go to the SETUP page and in the bottom lefthand corner there is a padlock icon on that is greyed out. Pressing it will bring up the
passcode entry screen where you will need to enter 5491. The padlock icon will become
solid to show it is now activated.
After five minutes, this function will lock the analyzer (you will need to return to the
main screen). To unlock the screen, you must enter 5491.
It is possible to deactivate the function before it is triggered or after activation by simply
pressing the solid padlock item in the Settings Menu.
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3.1.5 Menu Structure
DCC Logging Output Alarm
USER INTERFACE
Setup
Setpoint
Mode
Interval
Period
Output Hold
FAST
FAST SetP
Interval
Filename Output Type Parameter
Status
Output Select
Parameter Setpoint A
Minimum
Maximum
Alarm
Type
Setpoint B
Hysteresis Display Hold
Contamination
warning
Calibrate
Optics
Display Clock Inputs CommsType
Resolution Date
Stability Compensation
Primary Unit Direction
Pressure Unit
Language
Timebase
Brightness
Time
Source
Ambient
temp sensor
Setpoint
Pressure Unit
Setpoint
Range Low
Range High
Modbus
Address
Setup
IP
Address
Subnet
mask
Default
Gateway
Michell Instruments 19
USER INTERFACE
3.1.6 Operational Status Display
Optidew User Manual
ΔDP
Mode Shows current operation mode:
Next Mode Measure, Standby, DCC, Max Cool, Data Hold
Process
Sensor
Shows total change in measured dew point over the time base of
the trend graph
Status of process alarms
Alarm is active
Alarm is inactive
For further information on alarm configuration see Sections 3.2
and 5.
Indicates whether the sensor has established a condensate
formation, or if the system is in a transient condition:
Heating, Cooling, Control.
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3.1.7 Sensor Status Display
TEC Drive
USER INTERFACE
Indicates whether the sensor is heating or cooling
the mirror:
Also indicates the power level applied as a
percentage of total possible.
Indicates the reflectivity of the mirror, and
whether this is clean or has a condensate
formation.
Optical Signal
Connected
sensor
Logging
The target is 100% signal level, which indicates
the optimal film thickness has been achieved. 0%
indicates that the mirror is free of condensate.
For further information see Section 4.2.1.
Shows the sensor type that the control unit is
configured for.
To connect a 1-Stage sensor to a control unit
configured for 2-Stage or vice-versa, you must
first use the PC application software to enter
the sensor configuration code found on the
calibration certificate.
Refer to Section 6.2 (Exchanging Sensors).
When shown, the Optidew is currently logging
data to SD. See Section 4.4.6 for further
information.
Pressure
Compensation
Displayed when pressure compensation is active.
See Section 4.4.5 for further information.
Michell Instruments 21
USER INTERFACE
3.2 Setup Menus
3.2.1 DCC
Optidew User Manual
Type
Setpoint
Mode
Interval
Period
Output
hold
Figure 17
DCC heating temperature can either be relative to last measured dew
point or an absolute temperature. Actual temperature or Δ is defined by
‘Setpoint’.
Available input: Relative, Absolute
Mirror heating temperature during DCC, either absolute or relative to last
measured dew point. See ‘Type’ option above.
Available input: 1...120 °C
DCCs can either be triggered automatically at every Interval, or they can
be manually triggered only.
Available input: Manual, Auto
Time between automatic DCCs
Input format: hh:mm
Limits: 01:00...99:00
Duration of a DCC
Input format: hh:mm
Limits: 00:01...00:59
Minimum time to hold analog outputs after finishing a DCC
Input format: hh:mm
Limits: 00:04...00:59
DCC Menu
FAST
FAST SetP
Turns frost assurance on or off. See Section 4.4.3 for further information
Available input: On, Off
Passing this mirror temperature will trigger the frost assurance function
without a DCC
Available input: -28...-2 °C
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3.2.2 Logging
USER INTERFACE
Interval
SD status
indicator:
Figure 18
Changes the interval at which data is recorded
Input format: mm:ss –
Limits: 00:05...10:00
Indicates status of inserted SD card:
Logging Screen
No SD Card inserted
Ready to log
Initialising card
Error occurred
SD Card is write protected
Logging
Start/Stop
Begins a new log (file name is generated automatically) or ends
a log in progress.
Michell Instruments 23
USER INTERFACE
3.2.3 Outputs
Optidew User Manual
Output selector
arrows
Output Type
Parameter
Alarm
Minimum
Maximum
Figure 19
Selects the output to be adjusted
Determines the mA output range
Available input: 0...20 mA, 4...20 mA
Assigns the chosen calculated or measured parameter to this
output channel
Available input: DP, Temperature, Pressure, %rh, wvp, g/m3,
g/kg, ppmV, Wet Bulb
If the selected alarm is tripped, then this output will be forced
to Namur alarm level (20.6 mA).
Available input: None, System, Process, Both
The minimum output range for the selected parameter
Available input: Dependent on parameter
The maximum output range for the selected parameter
Available input: Dependent on parameter
Outputs Screen
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3.2.4 Alarm
USER INTERFACE
Type
Parameter
Setpoint
Low Setpoint
High Setpoint
Hysteresis
Contamination
Warning
Calibrate Optics
Figure 20
Sets the trip criteria for the process alarm
Available input: Over, Under, In. Band, Out. Band, Off
Sets the parameter associated with the process alarm
Available input: DP, Temperature, Pressure, %rh, wvp, g/m3,
g/kg, ppmV, ppmW, Wet Bulb
Sets the trip point for Over or Under alarm types
Available input: Dependent on parameter
Sets the low trip point for Band alarm types
Available input: Dependent on parameter
Sets the high trip point for Band alarm types
Available input: Dependent on parameter
Sets the deviation from trip point before the alarm deactivates
Available input: Dependent on parameter
Sets whether an Optics Warning trips the process alarm.
Refer to Section 5 for information about the optics warning.
Available input: On, Off
It is necessary to run this function whenever the mirror is
cleaned, or if a different dew-point sensor is installed. Following
this, a DCC will begin.
Alarm Screen
Michell Instruments 25
USER INTERFACE
3.2.5 Display
Optidew User Manual
Resolution
Temperature Unit
Pressure Unit
Timebase
Stability
Display Hold
Language
Figure 21
Changes the number of decimal places for all displayed
parameters
Available input: 1 DP, 2 DP
Measurement unit for temperature values
Available input: °C, °F
Measurement unit for pressure values
Available input: kPa, psig, psia, barg, bara
X axis span for trend graph on main screen
Input format: hh:mm
Limits: 00:01...10:00
Determines a stable measurement following DCC, which is
conditional to release Data Hold. Entered value is ΔDP over 30s.
Available input: 0.2...20
When enabled, values on display are also held during Data Hold
Available input: Off, On
Sets User Interface language
Available input: English, Deutsch, Español, Français, Italiano,
Português, USA, Russian, Chinese, Japanese
Display Screen
Brightness
Display backlight control
Available input: 0...100%
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3.2.6 Clock
USER INTERFACE
Figure 22
Date Current date
Time Current time
Clock Screen
Michell Instruments 27
USER INTERFACE
3.2.7 Inputs
Optidew User Manual
Source (Pressure
Input)
Pressure Unit
Value (If ‘Fixed’
selected)
Range Low (If
‘External’ selected)
Range High (If
‘External’ selected)
Compensation
Direction
(If ‘Compensation’ On)
Figure 23
Changes between pressure input from external 4...20 mA
transmitter or a fixed value
Available input: Fixed, External
Measurement unit for pressure inputs
Available input: kPa, psig, psia, barg, bara
Sets pressure used for internal calculations
Sets the low range of the connected pressure transmitter
Sets the high range of the connected pressure transmitter.
Recalculate dew point based on pressure input
Available input: Off, On
Select ‘From Atmos’ if dew-point sensor is at atmospheric
pressure.
Select ‘To Atmos’ if dew-point sensor is at entered fixed
pressure or pressure measured by transducer.
Inputs Screen
Source (Temperature
Input)
Value (If ‘Fixed’
selected)
Changes between temperature input from external PT100
or a fixed value. Available input: Fixed, External
Sets temperature used for internal calculations
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3.2.8 Comms Screen
USER INTERFACE
Modbus-Adresse Sets the Modbus slave address for this Optidew
Setup Access the TCP/IP Network Settings page
3.2.9 Network Settings
Figure 24
Comms Screen
Figure 25
IP Address IP address of the instrument (default 10.0.50.100)
Subnet Mask Determines network subnet address (default 255.255.255.0)
Default Gateway Default gateway address (default 10.0.50.254)
Network Settings Screen
Michell Instruments 29
USER INTERFACE
3.3 Optidew 501 Transmitter without display
The Optidew 501 can also be ordered as a blind transmitter without display. This variant
instead comes with a single multi-function button with integrated colored LED status
indicator.
The indicator changes color and pulse rate depending on the instrument status.
Meaning LED Color
Initialisation White
DCC Blue
DCC Plus Flashing Blue (Fast)
Optics balance Flashing Blue
Searching for dew point Flashing Green
Optidew User Manual
Searching for dew point – Optics
contaminated
Optics contaminated & Process alarm off Magenta
Optics contaminated & Process alarm on Flashing Red/Magenta
Measuring Green
Measuring & Process alarm on Flashing Red
MaxCool Blue
Standby Flashing Yellow
Standby – Optics contaminated Flashing Yellow/Magenta
System Fault Red Red
Pressing the button has two different effects, depending on the mode that the instrument
is in:
In DCC or DCC Plus mode – pressing the button returns to standby
In all other modes – pressing the button initiates manual DCC
Flashing Magenta
3.3.1 Optics Calibration
After power is applied the LED indicator on the front of the instrument will turn white
for the first 5 seconds. Pressing the button during this phase will initiate an optics
calibration. The indicator will flash indicating the button-press has been registered.
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4 OPERATION
4.1 Operating Cycle
OPERATION
Figure 26
At initial switch-on, the instrument enters a DCC cycle for 2 minutes. During this time
the mirror is heated above the prevailing dew point to ensure that all condensate
is driven off the surface of the mirror. The degree of heating is determined by the
configuration of the ‘Type’ and ‘Setpoint’ parameters in the DCC menu (see Section 3.2
for further information).
The mirror is maintained at this temperature for the DCC period (default 4 minutes) or
2 minutes on switch-on. During the DCC process, Data Hold fixes the analog outputs
at the same value(s) as before DCC commenced. Data Hold typically lasts 4 minutes
from the end of a DCC cycle, or until the instrument has reached the dew point. This
procedure is in place to prevent any system which is connected to the outputs from
receiving a 'false' reading.
After the DCC period has finished, the measurement period commences, during which
the control system decreases the mirror temperature until it reaches the dew point.
The sensor will take a short amount of time to form a film of condensate and control
on the dew point. The length of this stabilization time depends upon the dew-point
temperature. When the measurement is stable or tracking very slow changes in dew
point, the Sensor indicator in the Operational Status display will indicate ‘Control’. Note
that at dry dew points (below around -20 °C/-4 °F) the sensor may display ‘Control’
when the mirror temperature is still slowly oscillating, always use the trend graph on
the display as a secondary indication
Typical Operating Cycle
The end of a DCC cycle re-sets the interval counter, meaning that another DCC will start
(by default) after 4 hours have elapsed. Once the measurement is stable, Data Hold will
release, and the analog outputs will resume their normal operation. At this point the
Status area of the Operational Status display will change to ‘Measure’.
Michell Instruments 31
OPERATION
4.2 Operating Guide
4.2.1 Description
Once the Optidew has been powered on and has carried out its’ initial DCC, it will
attempt to find the dew point. In order to measure the dew point, a Chilled Mirror
hygrometer must control a thin film of condensed water or ice on the mirror.
To initially form the condensate layer the mirror must be cooled past the actual dew
or frost point. The control system will then gradually heat the mirror to reduce the
thickness of this condensate layer. It typically takes several heating/cooling cycles
until the instrument has achieved the optimal film thickness where evaporation and
condensation are occurring in equilibrium. This is the true dew/frost point of the sample.
After finding the true dew point, the control system will continue to maintain the film
thickness at a constant level. Any decrease in actual sample dew point will cause
evaporation from the condensate film to increase – reducing its thickness and causing
the control system to cool the mirror to compensate. Likewise, if the dew point increases
then condensation on the mirror will increase, and the control system will heat to
compensate.
Optidew User Manual
In extreme cases where the dew point decreases very abruptly, then the condensate will
be completely evaporated from the mirror. In these scenarios the system will ‘search’
for the dew point again by cooling, resulting in cooing past the dew point as described
above. A similar situation occurs when the dew point increases abruptly, however the
condensate film can be lost here by the control system heating to compensate and
exceeding the new dew point.
4.2.2 Operating Practice
There are two basic methods of measuring with the Optidew:
In-situ measurements are made by placing the sensor(s) inside the environment to be
measured.
Extractive measurements are made by installing the sensor into a block within a sample
handling system, and flowing the sample outside of the environment to be measured
through this system
Extractive measurements are recommended when the conditions in the environment
to be measured are not conducive to making reliable measurements with the product.
Examples of such conditional limitations are:
• Excessive flow rate
• Presence of particulates matter
• Presence of entrained liquids
• Excessive sample temperature
• Dew point is beyond depression capability at sample temperature
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The basic considerations for each measurement type are as follows:
In Situ:
1. Dew-Point Sensor position Will the sensor see an area of the
environment that is representative of what you want to measure? For
example; you are looking to measure the Relative Humidity of a room
which is controlled by an HVAC vent at either end (see Figure 27) you will
get very dierent readings depending on whether the sensor is positioned
at point A, point B or point C. Point C provides the most representative
sampling point given that it won’t be disturbed by the vent or the door.
1
OPERATION
2
A
3
B
C
4
1. Door
2. HVAC Duct, air into room
3, 4. Ceiling Vents
Figure 27
2. Gas speed If you are planning on installing the sensor in a duct, consider
how fast the sample gas is moving through it. Excessive ow speed will
cause displacement of the condensate layer on the mirror, leading to
unstable measurement.
Room Measurement Example
If this is the case, then a guard tted over the sensor can mitigate the
eects of excessive gas speed by dissipating the sample throughout
its surface area. An appropriate guard can be purchased from Michell
Instruments, contact your local representative.
Michell Instruments 33
OPERATION
3. Particulates Particulates passing over the sensor can build up on the
Optidew User Manual
mirror over time. This can cause a loss of mirror reectivity. DCC will
compensate for this by taking into account anything on the surface of
the mirror when resetting the optical condition, however if the problem
becomes too severe, the ‘mirror contamination warning’ symbol will be
displayed in the Sensor Status display.
Figure 28
4. Sample temperature Consider the dierence between the sample
temperature and the dew-point temperature. Make sure that the sensor
you are using has the cooling capability to make the measurement (see
Section 4.5 for further information). If the sensor does not have the
necessary cooling capability, then you should consider an extractive
system so the sample can be cooled prior to measurement.
5. Sample pressure If you are interested in readings in terms of ppmV or
g/kg, ensure that the sensor is positioned in an environment of known
pressure. You can then either enter this pressure into the Optidew via the
‘Inputs’ screen (see Section 3.2) or connect a pressure sensor directly to
the point of measurement (see Section 2.6).
Extractive
If the sensor will be mounted into a sample conditioning system, then the above points
are still of relevance, but the following should also be considered:
1. Extraction point Make sure that the chosen extraction point is
representative of the process, i.e. that the sample of interest is owing
past the extraction point, and it is not being pulled from a dead volume.
Mirror Contaminaton Warning Symbol
2. Enclosure and sample line heating If the sample has a dew point
greater than ambient temperature, then all components upstream of the
sensor will need to be heated to at least 10 °C (18 °F) above the sample
dew point to ensure the water remains in vapor phase.
3. Sample block ow path The sensor block must be congured with gas
inlet and outlets installed in the side ports. The top is either blanked or
used to install a pressure transmitter.
If replacing an old Optidew installation then be aware that using
the old sensor block will result in poor response speed at low
dew points, as it does not allow enough ow across the mirror.
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4.3 Good Measurement Practice
4.3.1 Sampling Hints
Ensuring reliable and accurate moisture measurements requires the correct sampling
techniques, and a basic understanding of how water vapor behaves. This section aims
to explain the common mistakes and how to avoid them.
Sampling Materials – Permeation and Diffusion
All materials are permeable to water vapor since water molecules are extremely small
compared to the structure of solids, even including the crystalline structure of metals.
The graph below demonstrates this effect by showing the increase in dew point
temperature seen when passing very dry gas through tubing of different materials,
where the exterior of the tubing is in the ambient environment.
OPERATION
Figure 29
What this demonstrates is the dramatic effect that different tubing materials have on
the humidity levels of a gas passed through them. Many materials contain moisture
as part of their structure and when these are used as tubing for a dry gas the gas
will absorb some of the moisture. Always avoid using organic materials (e.g. rubber),
materials containing salts and anything which has small pores which can easily trap
moisture (e.g. nylon).
As well as trapping moisture, porous sampling materials will also allow moisture vapor
to ingress into the sample line from outside. This effect is called diffusion and occurs
when the partial water vapor pressure exerted on the outside of a sample tube is
higher than on the inside. Remember that water molecules are very small so in this
case the term ‘porous’ applies to materials that would be considered impermeable in
an everyday sense – such as polyethylene or PTFE. Stainless steel and other metals
can be considered as practically impermeable and it is surface finish of pipework that
becomes the dominant factor. Electropolished stainless steel gives the best results over
the shortest time period.
Take into consideration the gas you are measuring, and then choose materials appropriate
to the results you need. The effects of diffusion or moisture trapped in materials are
more significant when measuring very dry gases than when measuring a sample with a
high level of humidity.
Material Permeability Comparison
Temperature and Pressure effects
As the temperature or pressure of the environment fluctuates, water molecules are
Michell Instruments 35
OPERATION
adsorbed and desorbed from the internal surfaces of the sample tubing, causing small
fluctuations in the measured dew point.
Optidew User Manual
Adsorption
solid to the surface of a material, creating a film. The rate of adsorption is increased at
higher pressures and lower temperatures.
Desorption
constant environmental conditions, an adsorbed substance will remain on a surface
almost indefinitely. However, as the temperature rises so does the likelihood of desorption
occurring.
Ensuring the temperature of the sampling components is kept at consistent levels is
important to prevent temperature fluctuation (i.e. through diurnal changes) continually
varying the rates of adsorption and desorption. This effect will manifest through a
measured value which increases during the day (as desorption peaks), then decreasing
at night as more moisture is adsorbed into the sampling equipment.
is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved
is the release of a substance from or through the surface of a material. In
Dew Point > T
Dew Point < T
Figure 30
Condensation in Sample Tubing
If temperatures drop below the sample dew point, water may condense in
sample tubing and affect the accuracy of measurements.
Maintaining the temperature of the sample system tubing above the dew point of the
sample is vital to prevent condensation. Any condensation invalidates the sampling
process as it reduces the water vapor content of the gas being measured. Condensed
liquid can also alter the humidity elsewhere by dripping or running to other locations
where it may re-evaporate.
Although ambient pressure does not change drastically in a single location, the gas
sample pressure does need to be kept constant to avoid inconsistencies introduced
by adsorption or desorption. The integrity of all connections is also an important
consideration, especially when sampling low dew points at an elevated pressure. If
a small leak occurs in a high-pressure line, gas will leak out, however, vortices at the
leak point and a negative vapor pressure differential will also allow water vapor to
contaminate the flow.
Theoretically flow rate has no direct effect on the measured moisture content, but
in practice it can have unanticipated effects on response speed and accuracy. An
inadequate flow rate may:
• Accentuate adsorption and desorption eects on the gas passing through
the sampling system.
• Allow pockets of wet gas to remain undisturbed in a complex sampling
system, which will then gradually be released into the sample ow.
• Increase the chance of contamination from back diusion. Ambient air
that is wetter than the sample can ow from the exhaust back into the
system. A longer exhaust tube can help alleviate this problem.
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• Slow the response of the sensor to changes in moisture content.
An excessively high flow rate can:
• Introduce back pressure, causing slower response times and unpredictable
changes in dew point
• Result in a reduction in depression capabilities in chilled mirror instruments
by having a cooling eect on the mirror. This is most apparent with gases
that have a high thermal conductivity such as hydrogen and helium.
System design for fastest response times
The more complicated the sample system, the more areas there are for trapped moisture
to hide. The key pitfalls to look out for here are the length of the sample tubing and
dead volumes.
The sample point should always be as close as possible to the critical measurement
point to obtain a truly representative measurement. The length of the sample line to the
sensor or instrument should be as short as possible. Interconnection points and valves
trap moisture, so using the simplest sampling arrangement possible will reduce the time
it takes for the sample system to dry out when purged with dry gas.
OPERATION
Over a long tubing run, water will inevitably migrate into any line, and the effects of
adsorption and desorption will become more apparent.
Dead volumes (areas which are not in a direct flow path) in sample lines, hold onto
water molecules which are slowly released into the passing gas. This results in increased
purge and response times, and wetter than expected readings. Hygroscopic materials
in filters, valves (e.g. rubber from pressure regulators) or any other parts of the system
can also trap moisture. Plan your sampling system to ensure that the sample tap point
and the measurement point are as close as possible to avoid long runs of tubing and
dead volumes.
Filtration
All trace moisture measurement instruments and sensors are by their nature sensitive
devices. Many processes contain dust, dirt or liquid droplets. Particulate filters are used
for removing dirt, rust, scale and any other solids that may be in a sample stream.
For protection against liquids, a coalescing or membrane filter should be used. The
membrane provides protection from liquid droplets and can even stop flow to the
analyzer completely when a large slug of liquid is encountered, saving the sensor from
potentially irreparable damage.
4.3.2 First-Time Operation
Before using the instrument, please read through the Installation, Operation and
Maintenance sections of this manual. This instruction assumes that all recommendations
within these sections have been followed, and that the control unit and sensors are
physically installed and all electrical connections complete.
• Ensure that all sample connections are in good condition, of
appropriate materials and are leak tight
• Clean the mirror according to the instructions in Section 6.1
• Control the ow rate to within 0.1…2 Nl/min (1 l/min optimal)
• Power on the instrument
NOTE: If the dew-point sensor has been swapped, refer to Section 5.2
Michell Instruments 37
OPERATION
4.4 Operational Functions
4.4.1 DCC Function
Dynamic Contamination Control (DCC) is a system designed to compensate for the loss
of measurement accuracy which results from mirror surface contamination.
During the DCC process the mirror is heated to a default temperature of 20 °C (36 °F)
above the dew point to remove the condensation which has formed during measurement.
The surface finish of this mirror, with the contamination which remains, is used by
the optics as a reference point for further measurements. This removes the effect of
contamination on accuracy.
After switch-on, the mirror is assumed to be clean, therefore the instrument will only
run a DCC for 2 minutes to quickly establish a clean mirror reference point. By default,
every subsequent DCC is 4 minutes in duration and will automatically occur every 4
hours.
At certain times it may be desirable to disable the DCC function in order to prevent it
from interrupting a measurement cycle, e.g. during a calibration run. This is achieved
by setting ‘Mode’ to ‘Manual’ in the DCC menu. See Section 3.2 for further details.
Optidew User Manual
A manual DCC can be initiated or cancelled by touching the DCC button on the Main
Screen. The DCC button is context sensitive, i.e. if DCC is on, the Main Screen shows
DCC OFF as being selectable. Similarly, if DCC is off, DCC ON is shown.
It is possible to change the parameters relating to the DCC cycle on the DCC Setup
Screen, refer to Section 3.2.
DCC Plus
DCC Plus is a feature designed to further control the build-up of contaminants on the
mirror surface without physical intervention from the operator. The function operates
immediately prior to either a scheduled automatic DCC or a manual DCC, by cooling the
mirror for a few seconds before heating it.
This cooling causes additional condensation on the mirror, which dissolves water-soluble
matter, and dislodges non water-soluble matter. When the surface is then heated and the
water evaporated, the contamination will cluster together leaving areas of clean mirror
between, which has less overall impact on the optics.
4.4.2 MAXCOOL – Function
The MAXCOOL function overrides the dew point control loop and applies maximum
cooling drive to the Peltier heat pump. It can be used to determine:
• What temperature the mirror can be driven down to with reference to the
sensor body.
• Whether or not the instrument is controlling at the dew point and
whether it is able to reach it. This situation could, for instance, arise
when attempting to measure very low dew points where, possibly due to
a high ambient temperature, the Peltier heat pump is unable to depress
the temperature far enough to reach the dew point.
• Whether the instrument is controlling by switching MAXCOOL on for a
short period and then switching back to MEASURE. This will depress the
mirror temperature briey and when it is switched back to MEASURE the
38 97551 Issue 4.3, November 2022
Optidew User Manual
control loop should be able to stabilize the mirror temperature at the dew
point again.
The MAXCOOL function can be turned on by touching the MAXCOOL button on the Main
Screen.
4.4.3 Frost Assurance Technology (FAST)
In carefully controlled laboratory conditions, super-cooled water can exist in temperatures
as low as -48 °C (-54.4 °F). However, when using a chilled mirror instrument it only
occurs on the mirror at temperatures down to around -30 °C (-22 °F).
A gas in equilibrium with ice is capable of supporting a greater quantity of water vapor
at a given temperature than a gas in equilibrium with liquid water. This means that a
measurement below 0 °C (+32 °F) taken over water will read approximately 10% lower
than the same measurement taken over ice.
There are two modes of FAST operation, enabling and disabling FAST acts on both
modes:
Following DCC: the Optidew makes an initial dew point measurement. If the initial
measurement is between -3 °C and -30 °C (+26.6 °F and -22 °F), then the mirror is
driven down to below
OPERATION
-35 °C (-31 °F) to ensure the formation of ice on the mirror surface. The instrument
then continues operation as normal.
Dynamic: whenever the measured dew point drops below the value set as ‘FAST SetP’,
the mirror is driven down to below -35 °C (-31 °F) to ensure the formation of ice on the
mirror surface. The instrument then continues operation as normal.
Note that Data Hold is active whenever FAST is active.
NOTE: Maximum recommended sensor temperatures to enable FAST to reach its
required cooling set-point are:
1 Stage Sensor: 21 °C (70 °F)
2 Stage Sensor: 30 °C (86 °F)
For further information, see Section 3.2.
4.4.4 STANDBY Mode
In STANDBY mode, drive to the Peltier heat pump is disabled.
The main use for this feature is during set up (when measurements are not required),
i.e. when flow rates are being adjusted and the analog outputs are being configured.
4.4.5 Parameter Conversions & Pressure Compensation
Many parameters which are calculated by the Optidew require a temperature or pressure
reading in addition to dew point to ensure the calculated value is correct.
These additional readings can either come from a sensor connected to the Optidew, or
from a fixed (manual) input. See Section 3.2 for details on external inputs.
Michell Instruments 39
OPERATION
Optidew User Manual
Calculated Parameter
Wetbulb
If external sensors are used to generate the inputs, then the sensors should be positioned
with so that they are making a measurement representative of the environment seen by
the dew-point sensor.
4.4.6 Data Logging
The data logging function allows all of the measured parameters to be logged at a
user specified interval on the supplied SD card via the SD card slot on the base or side
of the instrument. The filename for each log file is generated automatically from the
instrument date and time.
%rh
wvp
g/m
g/kg
ppm
ppm
%Vol
Temperature input
required
Pressure input
required
3
V
W
Log files are saved in CSV (comma separated value) format. This allows them to be
imported easily into Excel or other programs for charting and trend analysis. To set up
data logging refer to Section 3.2.
40 97551 Issue 4.3, November 2022
Optidew User Manual
5 WARNINGS AND FAULTS
The Optidew contains a comprehensive self-diagnosis system to alert the user whenever
there is an issue which could affect the measurement. These alerts are divided into two
categories:
Warnings – A problem which is not currently affecting the measurement but requires
attention.
Faults – A problem which requires immediate attention. Whenever a fault is triggered, the
Optidew will switch to ‘Standby’ and remain in this mode until the operator intervenes.
When a Fault is present, the System Alarm symbol will appear over the sensor status
display on the main screen. Pressing the System Alarm symbol will display all current
faults and warnings. At any other time, active warnings can be viewed by pressing the
right-hand side of the sensor status display. A system fault will usually be accompanied
by one or more warnings, which describe the problem in more detail.
Once a fault has been resolved, it is necessary to run a DCC cycle to return the
instrument to normal operation.
WARNINGS AND FAULTS
Figure 31
For more information on fault codes, please see the next page.
System alarm
Michell Instruments 41
WARNINGS AND FAULTS
Possible Fault Codes
No. Name Description
06 Mirror Overheat Mirror Temperature above 130 °C (266 °F)
02 Optics Fault (Search Fail) Unable to establish clean mirror condition
03 Optics Fault (< Min Limit) Signal below allowable limit
04 Optics Fault (> Max Limit) Signal above allowable limit
Optidew User Manual
08 Heating Saturation
09 Cooling Saturation
01 Mirror Pt1000 Fault Chilled Mirror sensor internal Pt1000 fault
04 Temp. Probe Fault External temperature probe fault
07 Pressure Tx. Fault External pressure transmitter fault
17 Mirror Contaminated
11 Mirror Pt1000 Fault (Open) Chilled Mirror sensor Pt1000 open circuit
12 Mirror Pt1000 Fault (Low)
13 Mirror Pt1000 Fault (High) Chilled Mirror sensor Pt1000 above upper limit
08 Temp. Probe Fault (Open) External temperature probe open circuit
09 Temp. Probe Fault (Low)
10 Temp. Probe Fault (High) External temperature probe above upper limit
14 Pressure Tx. Fault (Open) Pressure transmitter signal < 0.2 mA (open circuit)
TEC drive saturated in heating mode beyond
allowable time limit
TEC drive saturated in cooling mode beyond
allowable time limit
Mirror requires cleaning followed by Optics
Calibration
Chilled Mirror sensor Pt1000 short circuit/below
lower limit
External temperature probe short circuit/below
lower limit
15 Pressure Tx. Fault (Alarm)
16 Pressure Tx. Fault (Fail) Pressure transmitter signal > 21 mA, or < 3.6 mA
Pressure transmitter signal 3.6…3.8 mA, or
20.5…21 mA
42 97551 Issue 4.3, November 2022
Optidew User Manual
!
6 MAINTENANCE
6.1 Mirror Cleaning
Throughout the life of the instrument, periodic cleaning of the mirror surface and optics
window may be required. The frequency of this depends upon operating conditions and
the potential in the application for contaminants to be deposited on the mirror.
The Optidew will notify the user on the state of mirror contamination. The instrument will
initially give a warning in the sensor status display (or as a Magenta/flashing Magenta
indication on the transmitter version) when contamination is detected but will continue
to operate. Cleaning the mirror, then running a DCC is necessary when this warning is
displayed. If the contamination reaches levels which will drastically affect performance,
a fault alarm will trip, causing the instrument to switch to standby mode until action is
taken.
For remote indication of an optics warning, the process alarm contact can be set to trip
whenever the optics warning is active. See Sections 3.2 and 5 for further information.
The cleaning procedure is as follows:
1. Set the instrument to Standby
MAINTENANCE
2. If mounted in a sample block, disconnect the sensor cable and remove
the sensor from the block.
3. Clean the mirror surface and optics window rstly with a cotton bud/QTip soaked in distilled water, then with one of the following solvents:
methanol, ethanol, or isopropyl alcohol. To avoid damage to the mirror
surface do not press too rmly on the cotton bud/Q-Tip when cleaning.
Allow the cleaning solvent to fully evaporate.
4. Finally, clean the mirror again using a fresh cotton bud moistened with
distilled water. This last step is necessary to remove any dry residue left
by the alcohol and is an important part of the cleaning process.
5. Press the ‘Calibrate Optics’ button in the ‘Alarms’ screen. For the Optidew
501 Transmitter without display, refer to Section 3.3.1 (Optics Calibration).
Figure 32
WARNING: Do not attempt to remove the sensor potting from the mirror
during cleaning (as shown in Figure 32, right-hand picture)
Sensor Cleaning
Michell Instruments 43
MAINTENANCE
6.2 Exchanging Sensors
It is recommended to keep the dew-point sensor with the control unit that it was
originally ordered with. However, if it is necessary to replace the sensor or exchange it
for a spare, there are two steps which need to be taken.
1. Connect to the control unit via the application software and click the
'Enter Sensor Conguration' button at the Main Options window and enter
the password 7316Sens.
2. Enter the 12 character conguration code found on the calibration
certicate for the sensor you are connecting. Connect the new sensor,
then navigate to the 'Alarms' screen, and press the 'Calibrate Optics'
button. A DCC will follow, which cannot be cancelled. Do not disconnect
the sensor during this time.
Optidew User Manual
44 97551 Issue 4.3, November 2022
Optidew User Manual
APPENDIX A
Appendix A
Technical Specifications
Michell Instruments 45
APPENDIX A
Appendix A Technical Specications
Performance
Optidew User Manual
Dew Point Measurement
Accuracy
Repeatability ±0.05 °C (±0.09 °F)
Sensitivity ±0.01 °C (±0.02 °F)
Response Stable measurement at +10 °C (+50 °F) dp within 1 minute
Sensor Single Stage Dual Stage
Dew Point Range (°C) -25...+90 -40...+90 -40...+120
Temperature Range (°C) -40...+90 -40...+90 -40...+120
%rh Range @ 23 °C 2,25...100 0,45...100 0,45...100
Material
Corrosion & Saturation
Protection
Mirror Temperature
Measurement
±0.15 °C (±2.7 °F)
Dew-Point Sensor
POM (Head)
Aluminium (Body)
Active Component Isolation System
Pt1000, Class A
POM (Head)
Aluminium (Body)
Harsh
Environment
PEEK (Head)
Aluminium (Body)
Recommended Sample Flow
Pressure 2500 kPag max
Process connection M36 x 1.5...6 g
Temperature Measurement
Accuracy
Temperature Measurement Pt100, Class A
Cable length
Sensor cable
Pressure Measurement
Accuracy
Pressure Measurement
Range
Ambient (environmental measurements)
to 2 Nl/min (flowing sample)
Remote PRT
±0.1 °C (±0.18 °F)
0.3, 3, 5, 10 & 20m (0.98, 9.84, 16.4, 32.81 & 65.62ft) lengths
available (cables can be combined)
Standard: 90 °C (194 °F) max temperature
High temperature: 120 °C (248 °F) max temperature
Remote Pressure Sensor (Optional)
±0.25% FS
0...160 KPa or 0...2500 KPa
Cables
Process Connection 1/8” NPT-M
46 97551 Issue 4.3, November 2022
Optidew User Manual
Control Unit
Resolution 1 or 2 decimal places selectable
°Cdp or °Fdp
Relative humidity – %
Absolute humidity – g/m3, ppmV, %Vol
Mixing Ratio – g/kg
Measurement Units
Enclosure Wall Mount Bench Top
Material ABS ABS
Wet Bulb Temperature (Twb) – °C, °F
Water Vapor Pressure (wvp) – Pa
Ambient Temperature – °C, °F
pressure converted DP – °C, °F
pressure – KPa, Bara, Barg, Psia, Psig
APPENDIX A
Two mA outputs, selectable
Analog Outputs
Digital Communications
Alarms
Inputs 4...20 mA for pressure sensor 4...20 mA for pressure sensor
Data Logging SD card slot (optional) SD card slot
Ingress Protection
Dimensions
Weight
Display
0...20, 4...20 (maximum load
500Ω)
Modbus RTU over RS485
Modbus TCP over Ethernet
(optional)
1x Process Relay,
1x Alarm Relay,
Both Form C, 1 A, 30 V DC
IP54
IP65 (optional)
220 x 175 x 75 mm
(8.66 x 6.89 x 3”)
Control unit: 1.5 kg (3.3 lb)
Sensor: 200 g (7.05 oz)
Analyzer 5.7” color touch screen
Transmitter Status LED
Two mA outputs, selectable
0...20, 4...20 (maximum load
500Ω)
Modbus RTU over USB & RS485
Modbus TCP over Ethernet
(optional)
1x Process Relay,
1x Alarm Relay,
Both Form C, 1 A, 30 V DC
IP54
220 x 175 x 118 mm
(8.66 x 6.89 x 4.65”)
Control unit: 1.5 kg (3.3 lb)
Sensor: 200 g (7.05 oz)
5.7” color touch screen
Environmental Conditions
Supply Voltage 100...240 V AC, 50...60 Hz
Power consumption 30 VA max
-20...+50 °C (-4 °F…+122 °F), up to 100 %rh non-condensing or
100 %rh condensing with IP65 version
Michell Instruments 47
APPENDIX B
Optidew User Manual
Appendix B
Modbus Register Map
48 97551 Issue 4.3, November 2022
Optidew User Manual
Appendix B Modbus Register Map
All the data values relating to the Optidew are stored in 16-bit wide holding registers.
Registers can contain either measured or calculated values (dew-point, temperature,
relative humidity etc.), or configuration data (analog output or alarm settings).
Modbus RTU Implementation
This is a partial implementation of the Modbus RTU Standard with the following codes
implemented:
Function Code Description
3 Read Holding Register
6 Write Holding Register
16 Write Multiple Holding Registers
Register Types
APPENDIX B
Data Type Description
float
uint16
int16 16-bit signed integer.
boolean
Communications
In order to communicate with the instrument over a USB connection, first install the
Michell application software which contains a USB->UART bridge driver. The Optidew
will then appear in Device Manager as a virtual serial port.
Serial Port Settings (USB/RS485)
9600 Baud Rate, 8 Data Bits, No Parity, 1 Stop Bit, No Flow Control
Modbus TCP
If using the Ethernet connection, the instrument uses the Modbus TCP protocol instead
of Modbus RTU. Refer to resources online for the key differences.
IEE754 32-bit single precision floating point, spans 2 16-bit
holding registers. First register contains the most significant bits.
16-bit unsigned integer, can contain options list e.g. 0 = Dew
Point, 1 = Temperature.
Can be treated like a uint16, where 0 = false/disabled, and 1 is
true/enabled.
Michell Instruments 49
APPENDIX B
Register Address
Dec Hex Access Data Type Description Comment
Instrument Information
0 0000 R|W uint16 Instrument Modbus Address
2 0002 R uint32 Instrument Serial MS
3 0003 Instrument Serial LS
4 0004 R uint16 Instrument Firmware Version
5 0005 R uint16 Register Map Version
Measured and Calculated Values
6 0006 R float Dew/Frost point MS Units = Temperature
7 0007 R Dew/Frost point LS
8 0008 R float Ambient Temp MS Units = Temperature
9 0009 R Ambient Temp LS
10 000A R float Pressure MS Units = Pressure Unit
11 000B R Pressure LS
12 000C R float Relative Humidity MS
13 000D R Relative Humidity LS
14 000E R float ppm (vol) MS Default = Dry Basis,
15 000F R ppm (vol) LS
16 0010 R float ppm (wt.) MS Mol weight of carrier set
17 0011 R ppm (wt.) LS
18 0012 R float Absolute Humidity MS Units = g/m
19 0013 R Absolute Humidity LS
20 0014 R float Mixing Ratio MS Units = g/kg
21 0015 R Mixing Ratio LS
22 0016 R float Wet Bulb MS Units = Temperature
23 0017 R Wet Bulb LS
24 0018 R float Water Vapor Pressure MS Units = Pascal
25 0019 R Water Vapor Pressure LS
30 001E R uint16 Temperature Unit Set using register 100
0=°C
1=°F
31 001F R uint16 Pressure Unit Set using register 101
0=psig
1=psia
2=barg
3=bara
4=kPa
Instrument Status
33 0021 R uint16 Operating Mode
Optidew User Manual
Unit
Unit
register 105 for wet
basis
in register 108
3
Unit
50 97551 Issue 4.3, November 2022
Optidew User Manual
5=MaxCool
6=DCC
7=Hold
8=Messung
9=Standby
10=FAST
13=System Failure
34 0022 R uint16 Mode Hrs Left
35 0023 R uint16 Mode Mins Left
36 0024 R uint16 Mode Secs Left
37 0025 R uint16 Sensor Status
1=Cooling
2=Heating
3=In-Control
4=Idle
38 0026 R uint16 Fault Status 1
bit0=Optics Search Fail
bit1=Optics Min Limit
bit2=Optics Max Limit
bit3=Ambient Pt100 Fail
bit4=Mirror Pt100 Fail
bit5=Mirror Overheat
bit6=Loop Fail (Pressure Tx)
bit7=Heating Saturation
bit8=Cooling Saturation
39 0027 R uint16 Fault Status 2
bit0=Ambient Pt100 Open
bit1=Ambient Pt100 Low
bit2=Ambient Pt100 High
bit3=Mirror Pt100 Open
bit4=Mirror Pt100 Low
bit5=Mirror Pt100 High
bit6=Loop Open (Pressure Tx)
bit7=Loop Alarm (Pressure Tx)
bit8=Loop Fail (Pressure Tx)
bit9=Contaminated
40 0028 R uint16 Alarms Status
bit0=System
bit1=Process
41 0029 R uint16 Logging Status
0=Not Fitted
1=No Card
2=Ready
3=Logging
4=Writing
5=Mount Error
6=Write Error
7=Mounting
8=Write Protected
9=Unknown
42 002A R boolean Data Hold Active
APPENDIX B
Michell Instruments 51
APPENDIX B
43 002B R boolean Display Hold Active
50 0032 R int16 Peltier Drive %
51 0033 R uint16 Optics Signal %
Calculation Parameters
100 0064 R|W uint16 Set Temp Unit
0=°C
1=°F
101 0065 R|W uint16 Set Pressure Unit
0=psig
1=psia
2=barÜ
3=bara
4=kPa
103 0067 R|W boolean %rh - Force Over Water WVP wvp calculated over
104 0068 R|W boolean %rh - Force Over Water SWVP
(WMO standard)
105 0069 R|W boolean ppm(vol) Wet Basis Use wet basis calculation
106 006A R|W float Atmospheric Pressure MS Atmospheric pressure
107 006B R|W Atmospheric Pressure LS
108 006C R|W float Mol Weight MS Carrier gas molecular
109 006D R|W Mol Weight LS
110 006E R|W boolean Pressure Correction Enabled
111 006F R|W uint16 Pressure Correction Direction
0=To atmospheric
1=From atmospheric
Pressure Sensor Configuration
112 0070 R|W uint16 Pressure Sensor Source
0=External
1=Fixed
113 0071 R|W uint16 Pressure Sensor Unit
0=psig
1=psia
2=barg
3=bara
4=kPa
114 0072 R|W float Manual Pressure MS
115 0073 R|W Manual Pressure LS
116 0074 R|W float Pressure Range Low Ma MS 4 mA
117 0075 R|W Pressure Range Low Ma LS
118 0076 R|W float Pressure Range High Ma MS 20 mA
Optidew User Manual
water in %rh calculation
(not recommended)
swvp calculated over
water in %rh calculation
as per WMO standard
method
used for pressure
conversion
weight for Mixing Ratio /
ppm(wt.), default air
52 97551 Issue 4.3, November 2022
Optidew User Manual
119 0077 R|W Pressure Range High Ma LS
120 0078 R|W float Pressure Range Low MS Pressure Sensor Zero
121 0079 R|W Pressure Range Low LS
122 007A R|W float Pressure Range High MS Pressure Sensor Span
123 007B R|W Pressure Range High LS
Temperature Sensor Configuration
124 007C R|W uint16 Temperature Sensor Source
0=External
1=Fixed
125 007D R|W float Manual Temperature MS
126 007E R|W Manual Temperature LS
Instrument Configuration
127 007F R|W uint16 DCC Setpoint Mode
0=Absolute
1=Relative
128 0080 R|W int16 DCC Temperature Setpoint (Degrees * 100)
129 0081 R|W uint16 DCC Interval Mode
0= Manual
1= Auto (Recommended)
130 0082 R|W uint16 DCC Interval Mins
131 0083 R|W uint16 DCC Duration Mins
132 0084 R|W boolean FAST Enable
134 0086 R|W float FAST Setpoint MS
135 0087 R|W FAST Setpoint LS
136 0088 R|W uint16 Peltier Stages
1=1 Stage
2=2 stage
137 0089 R|W uint16 Stability Band (Degrees * 1000) .
Threshold to end Data
Hold
140 008C W uint16 Set Mode
1=Standby
2=DCC
4=MaxCool
8=Cancel MaxCool
16=Calibrate Optics
Display Parameters
145 0091 R|W uint16 Language
0=English
1=German
2=Spanish
3=French
4=Italian
5=Portuguese
6=USA
7=Russian
8=Japanese
9=Chinese
APPENDIX B
Michell Instruments 53
APPENDIX B
146 0092 R|W uint16 Decimal Places
147 0093 R|W uint16 Displayed Parameter 1
0=Dew/Frost point
1=Temperature
2=Pressure
3=Relative Humidity
4=ppm(vol)
5=ppm(wt.)
6=Mixing Ratio
7=Absolute Humidity
8=Wet bulb
9=WVP
10=%vol
148 0094 R|W uint16 Displayed Parameter 2
149 0095 R|W uint16 Displayed Parameter 3
150 0096 R|W boolean Enable Display Hold
Analog Output Settings
155 009B R|W uint16 Analog 1 Type
0=0…20 mA
1=4…20 mA
156 009C R|W uint16 Analog 1 Parameter
0=Dew/Frost point
1=Temperature
2=Pressure
3=Relative Humidity
4=ppm(vol)
5=ppm(wt.)
6=Mixing Ratio
7=Absolute Humidity
8=Wet bulb
9=WVP
10=%vol
157 009D R|W float Analog 1 Range Low MS
158 009E R|W Analog 1 Range Low LS
159 009E R|W float Analog 1 Range High MS
160 00A0 R|W Analog 1 Range High LS
161 00A1 R|W uint16 Analog 2 Type
162 00A2 R|W uint16 Analog 2 Parameter
163 00A3 R|W float Analog 2 Range Low MS
164 00A4 R|W Analog 2 Range Low LS
165 00A5 R|W float Analog 2 Range High MS
166 00A6 R|W Analog 2 Range High LS
167 00A7 R|W uint16 Analog 1 Alarm Type
R|W 0=None
1=System Only
2=Process Only
3=Both
168 00A8 R|W uint16 Analog 2 Alarm Type
171 00AB R|W uint16 Process Alarm Parameter
Optidew User Manual
54 97551 Issue 4.3, November 2022
Optidew User Manual
0=Dew/Frost point
1=Temperature
2=Pressure
3=Relative Humidity
4=ppm(vol)
5=ppm(wt.)
6=Mixing Ratio
7=Absolute Humidity
8=Wet bulb
9=WVP
10=%vol
172 00AC R|W uint16 Process Alarm Type
181 00B5 R|W uint16 Data Hold Mins
Ethernet Settings
201 C9 R|W uint16 IP Address 1 Default IP is 10.0.50.100
Reading this register
causes all IP address,
subnet and gateway
registers to be updated
from Ethernet add-on
board
202 CA R|W uint16 IP Address 2 10.0.50.100
203 CB R|W uint16 IP Address 3 10.0.50.100
204 CC R|W uint16 IP Address 4 10.0.50.100
205 CD R|W uint16 Subnet Mask 1 255.255.255.0
206 CE R|W uint16 Subnet Mask 2 255.255.255.0
207 CF R|W uint16 Subnet Mask 3 255.255.255.0
208 D0 R|W uint16 Subnet Mask 4 255.255.255.0
209 D1 R|W uint16 Gateway 1 10.0.50.254
210 D2 R|W uint16 Gateway 2 10.0.50.254
211 D3 R|W uint16 Gateway 3 10.0.50.254
212 D4 R|W uint16 Gateway 4 10.0.50.254
Writing this register
causes all IP address,
subnet and gateway
registers to be written to
Ethernet add-on board.
APPENDIX C
Michell Instruments 55
APPENDIX B
Further Reading
Optidew User Manual
http://www.simplymodbus.ca/FAQ.htm is an excellent resource
covering the basics of the Modbus protocol. Full descriptions
of the function codes (FC03/FC06/FC16) can be found in the
sidebar.
https://www.scadacore.com/tools/programming-calculators/
online-hex-converter/ is an excellent resource for determining
register types/byte order issues in raw received Modbus data.
56 97551 Issue 4.3, November 2022
Optidew User Manual
APPENDIX C
Appendix C
Legacy Serial Protocol
Michell Instruments 57
APPENDIX C
Appendix C Legacy Serial Protocol
C.1 Legacy Mode
Legacy serial mode enables backward compatibility with Dewmet TDH and Optidew 1
serial protocols using either RS485 or USB.
Neither of these is a full RS232 compatible port so legacy mode emulates the protocol
but has some missing features:
• No RS232 control lines.
• No echoing of characters.
• Packets are handled half-duplex, so sending a command to the instrument
while it is transmitting will result in the instrument ignoring the command
and the PC side receiving corrupt data.
Only a small subset of commands are implemented for reading data, many of the setup
commands used on legacy instruments are not meaningful in the context of Optidew
401-501.
Optidew User Manual
Where a read value is not available on the Optidew 401-501 a replacement value is
formatted to appear identical; see Section C.4 (Emulated Legacy Commands) for more
details.
RS485 and USB share the same buffer in legacy mode and should not be used
at the same time.
1.1 Serial Settings
Baud Rate 9600
Data Bits 8
Stop Bits 1
Parity None
Flow Control None
C.2 Hardware Connection
2.1 RS232
An RS485 to RS232 converter can be used to make the Optidew 401-501 backwards
compatible with an existing RS232 connection, the converter has to handle transmit/
receive switching automatically and in a timeframe suitable for normal Modbus operation.
2.2 USB
The Optidew 401-501 USB expansion port can be used with a PC, this appears as
a virtual serial port and should work with any software written to use a serial port
providing it does not send and receive data at the same time as the instrument still
processes this as if it was a half-duplex connection.
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Optidew User Manual
C.3 Changing between Modbus and Legacy Mode
3.1 Entering Service Codes on the HMI
From the main menu, navigate to the ABOUT screen. Press three times on the A in the
title About in the top left corner of the screen; a numerical keypad will appear, where
you can enter the service codes listed below.
3.2 Changing to Legacy mode
3.2.1 Using Modbus
Write the value “737” to Modbus register address “450”.
3.2.2 Using the display
The service code “53161” can be entered into the display to switch to legacy mode.
NOTE: After either of these methods Modbus will cease to function, the display or a
legacy serial command must be used to re-enable Modbus.
APPENDIX C
3.3 Changing to Modbus mode
3.3.1 Using legacy commands
Enter the command “modbus=1<CR>” (<CR> being carriage return).
3.3.2 Using the display
The service code “53160” can be entered into the display to switch to Modbus mode.
NOTE: After either of these methods Legacy mode will cease to function, the display or
Modbus commands must be used to re-enable legacy mode.
Michell Instruments 59
APPENDIX C
C.4 Emulated Legacy Commands
4.1 Optidew 1
“Y” or “y”
Returns a single status report with the following format.
“:050714980344012405892116160897201<cr><lf>”
Position Example Description
1 : Fixed start character
2–5 0507 Dew Point * 10, 0507 = 50.7 degrees
Negative values have +8000 added, 7999 = -0.1 degrees
6–9 1498 Ambient Temperature * 10, 1498 = 148.9 degrees
Negative values have +8000 added, 7999 = -0.1 degrees
10–13 0344 Relative Humidity * 10, 0344 = 34.3%
14–17 0124 [DIFFERS FROM ORIGINAL PROTOCOL DUE TO OPTICS
BALANCE]
Signal Level – now film thickness
0000 = 000% = No film
0100 = 100% = Correct level of film for control
0200 = 200% = double film or higher
18–21 0589 Heat pump drive
0 = heating mirror at 100% drive
450 = 0% drive, not heating or cooling mirror
1023 = cooling mirror at 100% drive
22 2 Instrument Status
0 = DCC, 1 = Output is held, 2 = measure, 3 = system
alarm, 4 = process alarm
New status values
5 = Standby, 6 = FAST, 7 = System Failure, 8 = Max Cool
23–27 11616 G/M3 * 100, 11616 = 116.16
28–32 08972 G/Kg * 100, 08972 = 89.72
33 0 Temperature unit, 0=°C, 1=°F
34 1 Sensor status, 0 = cooling, 1 = control, 2 = heating
35 <cr><lf> Carriage return and line feed
Optidew User Manual
4.1.2 “X” or “x”
Begins sending status reports (see command “Y” above) every second until a stop
command is received (see “ST” below).
4.1.3 “ST” or “st”
Stops the automatic sending of status reports (see command “X” above).
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APPENDIX C
4.1.4 “
Initiates a DCC, Optidew 401-501 features that occur as part of a DCC cycle, such as
DCC Plus and FAST operate as normal.
4.1.5 “
Returns a single report of Dew Point in the following format:
“101.2<CR><LF>“
4.1.6 “
Returns a single report of temperature in the following format:
“23.4<CR><LF>“
4.1.7 “
Returns a single report of relative humidity in the following format:
“42.5<CR><LF>”
ABC
GDP
GTP
GRH
” or “
” or “
” or “
” or “
abc
gdp
gtp
grh
”
”
”
”
4.2 Dewmet TDH
4.2.1
“TDH
” or
“tdh
”
Returns a single status report with the following format:
“12.3_Cdp__45.6_%RH__78.9_degC<CR><LF>”
“_“ in the example above are space characters that have been replaced to make it easy
to see the formatting.
Value Description
12.3 Dew Point to 1 decimal place
C Temperature unit, °C or °F
45.6 Relative Humidity to 1 decimal place
78.9 Ambient temperature to 1 decimal place
C Temperature unit, °C or °F
<CR><LF> Carriage return and line feed
NOTE: The values output by this command are only updated when the
instrument is not in output hold.
On boot up the values are set to:
Dew Point = 0.0
%rh = 100.0
Temperature = -100.0
As the instrument boots in output hold, these values will not change until
after the first output hold period ends.
Michell Instruments 61
APPENDIX C
C.5 New Commands for Optidew 401-501
5.1 “RST” or “rst”
Initiates an optics reset, features that normally operate as part of an optics reset such
as DCC, FAST etc will operate as normal.
Returns “OK<CR><LF>”.
5.2 “Modbus=1”
Changes the instrument serial mode to Modbus, this is saved in non-volatile storage and
persists after the instrument is switched off.
NOTE: Legacy commands will cease working immediately after this command,
a Modbus command or the display must be used to re-enable legacy mode.
5.3 “DCC” or “dcc”
Initiates a DCC, features that occur as part of a DCC cycle, such as DCC Plus and FAST
operate as normal.
Optidew User Manual
Returns “OK<CR><LF>.
5.4 “IDD” or “idd”
Returns the instrument model ID in the format “ID=42241<CR><LF>”.
The “Optidew 401-501” always returns “42241”.
5.5 “VER” or “ver”
Returns the firmware version in the format “V1.010<CR><LF>” for version 1.01.
5.6 “SER” or “ser”
Returns the instruments serial number in the format “#0000123<CR><LF>”.
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APPENDIX D
Appendix D
Dimensional Drawings
Michell Instruments 63
APPENDIX D
Appendix D Dimensional Drawings
Optidew 401 Bench Top analyzer
Optidew User Manual
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Optidew User Manual
DIMENSIONS IN mm
(INCHES IN BRACKETS)
240.0mm 9.449"
Optidew 501 Wall Mount Analyzer – IP54
APPENDIX D
145.0mm 5.709"
180.0mm 7.087"
260.0mm 10.236"
220.0mm 8.661"
69.5mm 2.736"
Michell Instruments 65
APPENDIX D
260.0mm 10.236"
Optidew 501 Wall Mount Transmitter – IP65
90.0mm 3.543"
Optidew User Manual
240.0mm 9.449"
180.0mm 7.087"
214.0mm 8.425"
40.0mm 1.575"
145.0mm 5.709"
61.5mm 2.421" 126.0mm 4.961"
220.0mm 8.661"
73.7mm 2.903"
69.5mm 2.736"
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Optidew User Manual
44.8mm 1.764"
101.8mm 4.008"
30.8mm 1.213"
32.0mm 1.260"
Single Stage Dew-Point Sensor
O
46.0mm 1.811"
APPENDIX D
101.8mm 4.008"
44.8mm 1.764"
30.8mm 1.213"
32.0mm 1.260"
M36 x 1.5
28.0mm 1.102"
M30 x 1.5
O
Michell Instruments 67
APPENDIX D
Dual Stage Dew-Point Sensor
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Optidew User Manual
Sample Block
APPENDIX D
Michell Instruments 69
APPENDIX D
Standard Temperature Probe
Optidew User Manual
Ø10.5mm [0.413”]
Ø3.7mm [0.146”]*
1mm [0.039”]
5.6mm [0.22”]
* Weld burr may extend from 1 mm (0.04”) from colar to towards tip of probe.
Probe and connector rated 90 °C (194 °F).
High Temperature Probe
Maximum temperature measurement 120 °C (248 °F)
Connector rated 120 °C (248 °F )
Probe and cable rated 250 °C (482 °F)
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APPENDIX E
Appendix E
Quality, Recycling & Warranty
Information
Michell Instruments 71
APPENDIX E
Optidew User Manual
Appendix E Quality, Recycling, Compliance & Warranty Information
Michell Instruments is dedicated to complying to all relevant legislation and directives. Full information
can be found on our website at:
www.michell.com/compliance
This page contains information on the following directives:
• Anti-Facilitation of Tax Evasion Policy
• ATEX Directive
• Calibration Facilities
• Conflict Minerals
• FCC Statement
• Manufacturing Quality
• Modern Slavery Statement
• Pressure Equipment Directive
• REACH
• RoHS3
• WEEE2
• Recycling Policy
• Warranty and Returns
This information is also available in PDF format.
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Optidew User Manual
APPENDIX F
Appendix F
Return Document &
Decontamination Declaration
Michell Instruments 73
APPENDIX F
Optidew User Manual
Appendix F Return Document& Decontamination Declaration
Decontamination Certicate
IMPORTANT NOTE: Please complete this form prior to this instrument, or any components, leaving your
site and being returned to us, or, where applicable, prior to any work being carried out by a Michell
engineer at your site.
Instrument Serial Number
Warranty Repair? YES NO Original PO #
Company Name Contact Name
Address
Telephone # E-mail address
Reason for Return /Description of Fault:
Has this equipment been exposed (internally or externally) to any of the following?
Please circle (YES/NO) as applicable and provide details below
Biohazards YES NO
Biological agents YES NO
Hazardous chemicals YES NO
Radioactive substances YES NO
Other hazards YES NO
Please provide details of any hazardous materials used with this equipment as indicated above (use continuation sheet
if necessary)
Your method of cleaning/decontamination
Has the equipment been cleaned and decontaminated? YES NOT NECESSARY
Michell Instruments will not accept instruments that have been exposed to toxins, radio-activity or bio-hazardous
materials. For most applications involving solvents, acidic, basic, ammable or toxic gases a simple purge with dry
gas (dew point <-30°C) over 24 hours should be sufcient to decontaminate the unit prior to return.
Work will not be carried out on any unit that does not have a completed decontamination declaration.
Decontamination Declaration
I declare that the information above is true and complete to the best of my knowledge, and it is safe for Michell
personnel to service or repair the returned instrument.
Name (Print) Position
Signature Date
F0121, Issue 2, December 2011
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Optidew User Manual
NOTES
Michell Instruments 75
www.ProcessSensing.com
http://www.michell.com
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