MBW 973 User manual

Dew Point Mirror 973
MBW Calibration Ltd.
Seminarstrasse 57
CH-5430 Wettingen / Switzerland
[phone] phone
[phone] fax
0Hwww.mbw.ch
[email protected]
Operation and
Maintenance Manual
Phone: [phone]
Email: [email protected]
Web: www.ima.co.uk
UK Distribution by IMA Ltd:
Parkwell House,
Otley Road,
Guiseley, West Yorkshire,
LS20 8BH, England

Warranty
MBW Calibration Ltd. (MBW) warrants the products it manufactures or distributes to be free of
defects in material and workmanship under normal use and service when operated within the
specified design limitations for a period of 12 months from date of initial shipment. Under this
Warranty, MBW will, at its discretion, repair or replace any component that upon examination
by MBW or its duly authorized representatives proves to be defective during the warranty
period provided the system is returned to the factory for inspection and repair shipping
prepaid. Improper or unauthorized maintenance, storage, repair, or alteration of any kind by
personnel other than MBW or its duly authorized representatives may void all warranties.
Warranty may also be voided for misuse, neglect, accident, corrosion, and improper
installation. This Warranty is exclusive and in lieu of any and all other warranties of
merchantability, fitness for a particular purpose, or any other warranty, expressed or implied,
and all other liabilities and obligations on the part of MBW. MBW will not be liable for any
other claims or damages, either direct, indirect, or consequential arising out of the use of its
products.

i
Table of Contents
Table of Contents ..................................................................................................................... i
Welcome................................................................................................................................... 1
How to Use This Manual ......................................................................................................... 1
For More Information ............................................................................................................. 1
OPERATION.........................................................................................................3
Getting Started......................................................................................................................... 3
Turning the 973 On and Off................................................................................................... 3
What You See........................................................................................................................ 3
The Touch Screen.................................................................................................................. 5
The Measuring Head Assembly............................................................................................. 9
Dew Point Measurement........................................................................................................ 9
System Configuration ........................................................................................................... 12
Menu Options....................................................................................................................... 12
Display Parameters..............................................................................................................13
Graphing Data...................................................................................................................... 13
Control Setup....................................................................................................................... 15
Changing Units..................................................................................................................... 18
Changing Color.................................................................................................................... 19
Analog Outputs .................................................................................................................... 20
Back Panel Connections....................................................................................................... 22
Power Plug........................................................................................................................... 22
Power Switch ....................................................................................................................... 22
RS-232................................................................................................................................. 22
External Temperature.......................................................................................................... 22
Analog Outputs .................................................................................................................... 23
Gas Input and Output........................................................................................................... 23
Barometric Pressure Input................................................................................................... 23
Measurement Tips................................................................................................................. 24
Understand the Measuring Range....................................................................................... 24
Connecting Hoses................................................................................................................24
Cooling Requirements ......................................................................................................... 26
INSTALLATION..................................................................................................27
Facility Requirements ...........................................................................................................27
Environmental...................................................................................................................... 27
Power................................................................................................................................... 27
Preparation for Use ............................................................................................................... 27
Benchtop Use....................................................................................................................... 27
Preparation for Shipping or Transportation ....................................................................... 27

ii
REMOTE COMMUNICATION ............................................................................29
Introduction............................................................................................................................ 29
Hardware Connection & Cabling.......................................................................................... 29
Communications Settings .................................................................................................... 30
Command Syntax ..................................................................................................................30
General Usage..................................................................................................................... 30
Termination Characters ....................................................................................................... 30
Leading and Trailing Spaces ............................................................................................... 31
Case Sensitivity.................................................................................................................... 31
Numeric Values.................................................................................................................... 31
Command Reference............................................................................................................. 32
Commands Listed By Functional Group.............................................................................. 33
MAINTENANCE .................................................................................................37
Mirror Cleaning...................................................................................................................... 37
Exterior Cleaning................................................................................................................... 38
Front Panel........................................................................................................................... 38
Rear Fan Grills..................................................................................................................... 38

Welcome 1
Welcome
Congratulations! With the 973 Dew Point Mirror you will be able to perform precision dew
point and frost point measurements as well as measurements of other parameters such as
relative humidity. The 973 utilizes a full color active matrix liquid crystal display with an
integral touch panel. It has a high contrast ratio and a wide viewing angle for easy readability.
Data is displayed in large easy to read fonts. Using the on screen buttons and menus, you
can easily configure each line of the display for a variety of humidity, temperature, and
pressure parameters that may be viewed in either SI or non-SI units.
How to Use This Manual
If you have the time and inclination, you can read this manual from front to back. Since we
realize your time is valuable and that you may not wish to do that yet, we recommend the
following approach to familiarize yourself with the 973 and start using it right away.
1. With the 973 at hand, go straight to the Getting Started section on page 3. From there,
you can quickly learn to use the 973 to make a dew point measurement.
2. Next, read the System Configuration section beginning on page 12 to learn how to
configure the system to meet your preferences.
3. Finally, read the Back Panel Connections section beginning on page 22. That section
identifies all the electrical and gas connections available on the back panel and explains
how and when to use them.
For More Information
For a more thorough understanding of the 973 and other humidity measurement information,
please read the remaining sections of this manual.
The Installation section covers bench space, environmental, and power requirements.
The Remote Communication section discusses the RS-232 interface both from a hardware
and software perspective. It gives details relating to cabling to connect the 973 to a
computer, and gives the syntax and examples of each of the commands that the 973
recognizes.
The Maintenance section covers topics such as Mirror Cleaning and general maintenance
required to keep your 973 performance at its best.
If the information you seek is not in one of the manual’s included sections, never hesitate to
contact us with your questions. Relevant phone, fax, and email contact information is on the
front page of this manual.

Getting Started 3
Operation
Getting Started
This section allows you to set up and start using the 973 right away. You’ll turn the system on
and quickly familiarize yourself with the layout and features of the display and touch screen.
Next, you’ll learn about the optical mirror assembly for later care and cleaning that may be
required. Finally, you’ll use the 973 to measure the dew point temperature. Set your 973 on the
bench and let’s get started!
Turning the 973 On and Off
The 973 needs a source of normal AC power. Have a look at the label on the back panel of the
instrument for the voltage required. Ensure that the required voltage matches that of your
standard laboratory power receptacles.
1. Using the supplied AC power cord, supply the
proper voltage to the instrument by plugging the
cord into the back of the instrument, then into an
AC receptacle of the proper voltage.
2. The power switch is located on the back panel
next to the power cord input. Turn it ON.
The display should become visible within a few
seconds. If nothing seems to happen, check the
power source. There may also be some fuses
located next to the power switch. You can remove
and replace them with known good ones. Suspect
fuses can be tested for continuity with an ohmmeter.
What You See
When power is applied to the 973, the display will activate within a few seconds. A typical
display configuration is depicted below. If you or someone else previously configured your
system, it may look slightly different. But don’t worry, we’ll show you how to set it up the way
you like.
Data
Lines
Fixed
Function
Keys
Menu
Keys
10.00
25.41
-8.41
14.695
Relative Humidity
%
External Temp
°C
Frost Point
°C
Atm Pressure
psia
Pump Dew/Frost
Control
Mirror
Check Mirror
Cleaning

4 Getting Started
Data Lines
The first four lines of the display are for numeric or graphic representation of the measured data.
We refer to those first four lines as data lines.
10.00
Relative Humidity
%
If numeric, a data line contains the value to the
left, with the parameter description and units to
the right.
-9.65
Time Span 20.16.30
-10.2
Time Span 00:30:00
-9.8
If graphic, a data line shows a simple graph of
the data over time.
The choice of which parameter is shown on which data line, as well as whether a data line is
viewed as numeric or graphic, is easily selectable. You’ll see how to make these selections
shortly.
Status Bar
Flow Rate 60
30
0
STABLE
Balance
Indicator
+
-
Frost
Density Hi
0
Mirror
Residue Hi
0
The status bar contains balance, density,
contamination, and flow rate indicators. The
configuration of the status line is fixed and
never changes.
Fixed Function Keys
Pump Dew/Frost
Control
Mirror
Check Mirror
Cleaning
The bottom line of the display contains a row of
fixed function keys. You’ll use these keys to
start and stop the pump, enable and disable
measurement of dew point, and other things.
The function of each of these keys never
changes, and they are always available for
use.
Menu Keys
To the right side of the display is a column of
menu keys. Each of these keys changes
function as needed.
Notice that the bottom key in this column is
different from the rest. The bottom key is used
to cycle the upper keys through the various
menu options. The text on the bottom key
changes to indicate the currently selected
menu option. The text of the upper keys
change based on the functions available in the
menu.
Use this key to change menus

Getting Started 5
The Touch Screen
The 973 utilizes a touch screen for user interaction. To activate a menu option or toggle a
function on or off, simply touch the screen directly over the key or object desired.
Calibrate the Touch Screen
Before using the 973 for the first time, you may need to calibrate the touch screen to your finger
positioning preference. Here’s how –
1. Press and hold the enter key on the numeric
keypad for 3 or 4 seconds. If you’ve done it
correctly, you’ll hear two loud short beeps.
If not, release the key and try again.
2. With the tip of your finger, press the center
of the yellow key in the upper right corner of
the touch screen. It is labeled ‘Touch This
Key’. Once you touch it, the yellow color
goes away and another key turns yellow.
3. Now, touch the yellow key that’s in the lower
left corner of the touch screen. Once you
touch it, the yellow color goes away and you
have successfully calibrated the touch
screen.
4. Test your new touch screen calibration by pressing each of the six blank menu keys on the
right side of the touch screen several times. If they seem not to work well, just repeat the
calibration steps again from the beginning.
You may recalibrate the touch screen as often as needed, however, it is rarely required.

6 Getting Started
Navigating the Menus
The various menus of the right column of keys are navigated by using the key in the lower right
corner of the touch screen. Each time you press the lower right key, a new menu appears on
the keys directly above it. The menu is circular, meaning that once you go past the last menu,
the first one appears again and the process starts over. You can use the +/- key on the keypad
to move backward through the menus. Use the enter key to clear the menu.
Selecting Parameters to Display
Selecting which parameters to display on the data lines is easy. It is done with the Parameter
menu.
1. Use the lower right menu key to select the
Parameter menu. ‘Parameter’ appears on
the key, and the keys above get left pointing
arrows. Notice that each key corresponds
to the data line it points toward.
2. Press the arrow key corresponding to the
data line you wish to change. Notice that
each time you press the arrow key, the
parameter of the data line changes. The
parameter selection is circular, meaning that
once you reach beyond the last available
parameter the first one is again displayed
and the cycle starts over.
3. Change the parameters on any of the other
data lines with the same method.
4. If you like, you may clear the menu keys
when finished by cycling through all the
menus using the lower right key on the
touch screen, or by pressing the enter key
once. Note that this is not required and
nothing is wrong with leaving the Parameter
menu (or any other menu) on the screen.

Getting Started 7
Selecting Graph vs. Numeric Data
Any data line may be viewed either as numeric or as a graph. The Numeric/Graphic menu is
used to toggle any data line between numeric and graph mode.
1. Use the lower right menu key to select the
Numeric/Graphic menu. ‘Numeric/Graphic’
appears on the key, and the keys above
contain left pointing arrows. Notice that
each key corresponds to the data line it
points toward.
2. Press the arrow key corresponding to the
data line you wish to change. Notice that
the data line toggles between numeric or
graph mode each time you press the key.
3. Select numeric or graph mode on any of the
other data lines with the same method.
[Notice that if a line is currently displaying the Status
Bar, no arrow appears on the adjacent menu key. The
Status Bar is not changeable in the Numeric/Graphic
menu.]
4. If you like, you may clear the menu keys
when finished by cycling through all the
menus using the lower right key on the
touch screen, or by pressing the enter key
once. Note that this is not required and
nothing is wrong with leaving the
Numeric/Graphic menu (or any other menu)
on the screen.

8 Getting Started
Selecting Units
The data may be viewed in any of the many available units. There are two Units menus used to
change the units of displayed data.
1. Use the lower right menu key to select the
Units menu. ‘Units’ appears on the key, and
the keys above contain current units
indications such as ‘Temp °C’. Notice that
each of the keys contain different types of
units. In this case, the keys do not correspond
to the adjacent data lines, but rather to
different units types.
2. To change temperature units, press the key
labeled ‘Temp’. Notice that the corresponding
units change each time the key is pressed.
Also notice that any data line that is currently
indicating temperature data also changes to
reflect the newly selected units.
3. Change other units (such as pressure, flow
rate, etc.) with the same method.
4. Note that there are two Units menus since
there are so many types of units that may be
changed. The second Units menu is obtained
by pressing the lower right menu key again.
5. If you like, you may clear the Units keys when
finished by cycling through all the menus using
the lower right key on the touch screen, or by
pressing the enter key once. Note that this is
not required and nothing is wrong with leaving
the Units menu (or any other menu) on the
screen.

Getting Started 9
The Measuring Head Assembly
The heart of the 973 Dew Point Mirror instrument is
the measuring head assembly. It is designed to be
highly sensitive and accurate, yet rugged and easily
accessible for periodic mirror cleaning. Although not
required prior to initial operation, you may wish to
familiarize yourself with the location and accessibility
of the mirror and the other optical components within
this assembly.
For further discussion of the measuring head, and
the mirror cleaning procedure, refer to Mirror
Cleaning on page 37.
Dew Point Measurement
When you power the 973 on, it begins in an idle state. In this state, it measures and displays
temperature, pressure, and flow transducers, but does not yet provide any meaningful humidity
related data. In order to provide humidity data (dew point, frost point, %RH, etc.), the Dew/Frost
Control mode must be enabled and gas must be flowing across the mirror. If %RH is desired,
note also that an external temperature probe must be connected. For external temperature
probe use, see External Temperature on page 22.
Starting / Stopping the Pump
Some gas flow is required over the mirror when measuring the dew or frost point temperature.
The nominal gas flow desired is approximately 20 to 60 liters/hour (0.2 to 1.0 liters/minute). If
your 973 is equipped with an internal gas pump, you can use it to provide the necessary gas
flow. If not, then you may need to provide for gas flow in some manner.
Use the Pump key on the bottom row of the touch screen to toggle the pump on/off. The Flow
Rate indicator on the status line should indicate that gas is flowing. The actual rate of flow is not
critical, but is best when within the limits previously mentioned. The gas flow may be adjusted
with an external valve, or by changing the pump control parameters. See Pump Control on
page 17.
Measuring the Room Ambient Dew Point Temperature
Enable Control
Lets use the 973 to measure the dew point temperature of the room by enabling the portion of
the system responsible for cooling and maintaining the mirror at the dew or frost point
temperature. Do so by pressing the Dew/Frost Control key. When enabled, a green bar on
the key illuminates and any dew or frost point temperature indication begins to drop as the
mirror cools toward the dew or frost point temperature. See Selecting Parameters to Display on
page 6 to select one of those parameters for display.
What You’ll See
When the Dew/Frost Control is enabled, have a look at the Status Bar (if you have your screen
set up to show it). The Status Bar has visual bar graphs that represent Balance, Density, Mirror
Residue, and Flow Rate.
Pump
Dew/Frost
Control
Flow Rate 60
30
0

10 Getting Started
The Balance Indicator
Although it is directly obtained from the intensity of the mirror’s reflected light signal, the Balance
Indicator is effectively the first derivative of the dew thickness. In other words, it indicates the
rate of growth or decay of the condensed layer on the mirror. While the dew or frost layer is
growing in thickness due to an increase in condensation on the mirror surface, the indicator is
above center. The faster the layer grows the higher the indication. Conversely, if the layer is
evaporating from the mirror surface thereby becoming thinner, the indicator is below center.
The faster it decays the lower the indication. When the indicator is in the center, it indicates that
the thickness of the dew or frost layer is neither growing nor decaying and that the layer on the
mirror surface is in equilibrium with the gas. In this center-balanced indication, there is no net
exchange of water vapor between the gas and the mirror surface. If the humidity of the gas
sample is homogeneous and of low enough variability for the control system to sense a steady
value, the Balance Indicator will illuminate a green ‘Stable’ message, and the system will emit a
few short audible beeps.
The Density Indicator
The Density Indicator graphically depicts the approximate relative thickness of the dew or frost
layer currently on the mirror surface. Since the 973 has the ability to differentiate between dew
and frost layers, it will also indicate which state the mirror’s layer is in. The label within the
density indicator will change from Layer Density (when it the state of the layer is uncertain) to
either Dew Density or Frost Density (when either dew or frost is assumed). For more
information regarding Dew/Frost point determination see Dew / Frost Control on page 15.
Disable Control
To disable the control system, press the Dew/Frost Control key again. The green bar on the key
disappears indicating that the control is no longer enabled. Any dew or frost point temperature
indications will begin to rise toward the temperature of the measuring head, often within several
degrees of the ambient room temperature. Also, the density indication drops off and the
balance indication moves downward but eventually returns toward center.
External Temperature Connection
The 973 is equipped with an external
temperature sensor. This sensor, along with the
dew point and pressure measurement, allows
the 973 to accurately determine and display
relative humidity. The external temperature
probe connection is made at the back panel.
Gas Inlet Connection
While the previous example did not rely on any external gas connections, the 973 is equipped
with fittings for connection of gas inlet and outlet tubing. This allows the 973 to measure the
dew or frost point of chambers and other devices that can be connected to it via tubing. If you
have a gas source you wish to measure, such as a humidity generator or chamber, connect a
tube between it and the 973 gas inlet on the back of the unit.
STABLE
Balance
Indicator
+
-
Frost
Density Hi
0
Dew/Frost
Control

Getting Started 11
The input and output connectors are clearly
labeled on the Sample Gas section of the back
panel. Depending on the specific model and
ordered options, the stainless steel gas input
and output connections may be 6 mm
Swagelok, ¼ inch Swagelok, or ¼ inch Cajon
VCR.
Note that you should never attempt to measure
any gas with a dew point temperature that is at
or above the temperature of the room. If you
do, condensation will form inside the tubing. [For
high dew point measurements, a Model 373H or 373HX with
heated internal components and heated hoses is required.]
Swagelok®Tube Fittings
Swagelok®brand tube fittings are generally used to connect the gas inlet and outlet tubes to the
973 system. Depending on the configuration of your specific 973, the back panel fittings are
either ¼” or 6 mm. When ordering tube fittings from your local Swagelok®supplier, be sure to
specify the correct size for your instrument. Swagelok®tube fittings come to you completely
assembled, finger-tight and ready for immediate use. Disassembly before use is unnecessary and
can result in dirt or foreign material getting into the fitting and causing leaks.
SWAGELOK®Tube Fittings are installed in three (3) easy steps:
Simply insert the tubing into the SWAGELOK®Tube Fitting.
Make sure that the tubing rests firmly on the shoulder of
the fitting and that the nut is finger-tight.
Before tightening the SWAGELOK®nut, scribe the nut at the 6
o’clock position.
Hold the fitting body steady with a backup wrench and tighten
the nut 1-1/4 turns.cWatch the scribe mark, make one
complete revolution and continue to the 9 o’clock position.
By scribing the nut at the 6 o’clock position as it appears to you,
there will be no doubt as to the starting position. When the nut is
tightened 1-1/4 turns to the 9 o’clock position, you can easily
see that the fitting has been properly tightened.
Use of a Swagelok®Gap Inspection Gage (1-1/4 turns from
finger-tight) ensures sufficient pull-up.
cFor 1/16“, 1/8“, 2 mm, 3 mm and 4 mm size tube fittings, only ¾ turn from finger-tight is necessary.

12 System Configuration
System Configuration
You may configure many aspects of the 973 based on your preferences at the time. For
instance, you may easily select which humidity, temperature, and pressure values to indicate on
the screen, the order in which they should appear, their units, and whether each will be shown
as a number or as a graph. In addition to display configuration, you can also change how the
973 performs its control functions such as Dew/Frost determination, ORIS control, tube heating,
mirror pre-cooling, etc. Most configuration settings that you change remain valid until the next
time you change them, even if you shut the 973 off.
Menu Options
The 973 has several menus available which are used to configure the system to your
requirements. To activate each of the menus, press the lower right menu key. Notice that it is a
slightly different color than all the other keys on the touch screen.
Each time you press this menu key, the 973 advances to the next menu and the key’s label
changes to indicate which menu is currently active. Once you’ve reached the last menu item,
and press the menu key again, the menu options just start over again at the beginning.
Pressing +/- on the keypad steps backward through the menus. Pressing enter on the keypad
clears all menus from the screen. Note however, that there is no requirement to clear the
menus from the screen for any reason other than cosmetic, or for fear of accidentally changing a
configured option.
Simplified descriptions of each menu follows.
Parameter The Parameter menu is used to select which parameter to display on each of the four
data lines. Each menu item key contains an arrow and directly corresponds with its
adjacent data line.
Numeric /
Graphic The Numeric/Graphic menu is used to toggle a data line between displaying the data
as numbers or as a graph. Each menu item key contains an arrow and directly
corresponds with its adjacent data line.
Control Setup The Control Setup menu is used to configure such things as dew/frost control, pump
control, internal and external heater control, cooling water control, etc.
Units The Units menu is used to change units used for displaying data. Unit changes are
system global, meaning that if the temperature units are changed, then all temperature
values displayed (including dew and frost point temperatures) will appear in the new
units. Since there are so many units that may be configured, there are two units
menus.
Fore Color The Fore Color menu is used to temporarily change the color of the lines drawn on
graphs and the color of text (number and letters). Each data line may be changed
individually. Unlike other selections, changing colors is only temporary and cycling the
power causes the 973 to return to standard color settings.
Back Color The Back Color menu is used to temporarily change the color of the background drawn
on graphs and numeric data lines. Each data line may be changed individually. Unlike
other selections, changing colors is only temporary and cycling the power causes the
973 to return to standard color settings.
Analog
Outputs The Analog Outputs menu is used to configure the calibration, scaling, and parameter
selection for output of data to the Analog Output connectors on the back panel if your
unit is so equipped. Both analog output ports are separately configurable.

System Configuration 13
Display Parameters
Use the Parameters menu to select which parameters to display on the data lines. When you
select parameters for display on any of the four data lines, those selections remain valid until
you change them again, even if you turn the 973 off. See Selecting Parameters to Display on
page 6 to select which values to display. A list of the available parameters follows. Note that
not all parameters are available on all systems since some systems may not contain the
associated hardware components.
Dew Point
Frost Point
%RH
%RH WMO
Volume Ratio
Weight Ratio
Absolute Humidity
Specific Humidity
Vapor Pressure
Head Pressure
Atmospheric Pressure
Flow Rate
External Temperature
Head Temperature
Graphing Data
Any value that you can view numerically can also be viewed as a graph at any time. The 973
automatically maintains a short history of each and every selectable parameter so that a graph
may be seen instantly whenever a data line is toggled from a numeric mode to a graph mode.
Selecting Between Numeric Data and Graph
Selecting between numeric and graph modes is done with the Numeric / Graphic menu. See
Selecting Graph vs. Numeric Data on page 7.
Changing Graph Attributes
To change the graph attributes, you need to
bring up the graph dialog. Do this by pressing
the touch screen directly on the graph whose
attributes you’d like to change.

14 System Configuration
Scaling
Each graph can have its own scaling (or y-axis)
values. There are three distinctly different
scaling modes to choose from:
Autoscale
Fixed Range
Maximum / Minimum
You may also change the Time Span of the
graph from this dialog.
•Autoscale
Autoscale mode determines the scaling automatically so that all of the stored data will be visible
on the graph at the best possible resolution. As the range of the data changes, so does the
range of the graph. In autoscale mode, you can select a minimum that you want the graph to
scale to. This is very useful for data that is very stable with little variation. This prevents the
973 from setting the scaling to such a small range that even the highly stable data appears
visibly as wildly variable. For viewing dew or frost point graphs, setting this Autoscale Minimum
to a value of at least 0.2 or more is generally preferable. This allows the graph range to close in
on the data as it stabilizes at a point without becoming too narrow. You can experiment with this
value to determine your personal preferences with different parameters. Autoscale mode is the
power up default.
•Fixed Range
Fixed Range scaling allows you to select a fixed graph range, but automatically centered on the
current data point. In other words, as the current data varies so does the graph center point, but
the overall range remains fixed. This fixed range auto centering is mostly used to monitor data
for stability.
•Maximum / Minimum
You can specify the maximum and minimum values used for the graph. This is completely fixed
scaling. If the data falls outside the maximum and minimum values you specify, you will not see
them on the graph. If you wish to see the data that is outside the values you specified, you’ll
need to specify maximum and minimum values with a larger spread.
You can change the graph scaling at any time, and freely switch between the three scaling
modes as well. Try it.
1. Using the touch screen, press directly on the graph you which to change. A graph scaling
dialog box will appear. One of the buttons in the Description column will have a green
indicator. That shows you the currently selected mode. Note that there are three buttons –
one for each mode.
2. Press the button of the mode you’d like to change to. Note that for the MinMax option, only
the Maximum button need be pressed (as Minimum is then automatically assumed).
3. Press the corresponding button in the Change To column for the range you selected.
4. Using the numeric keypad, enter the value needed. If the number shown in the Value
column is already correct, no entry is needed here. If you make a mistake while entering
the value, use the touch screen and press on the number in error. Each time you press the
touch screen there, the number will backspace one, erasing the flawed digits.

System Configuration 15
5. Once the value is shown is what you want press the Ok button (or the enter key) to accept
the new value, or press the Cancel button to abort all changes made to the mode and to any
values.
The only values that get accepted by the system are those that correspond with the selected
mode. In other words, if you change the value of the Autoscale Minimum, but Fixed Range is
the selected mode, the Autoscale Minimum value remains unchanged.
Time Span
Changing the time span allows you to see a longer or shorter history period for the data. The
973 stores a fixed number of data points independent of the selected time span. Changing the
time span changes the interval used for data storage. With a 15 minute time span, the graph
data is sampled and stored every few seconds. However, with a 2 hour time span, the graph
data is only sampled, stored, and updated about once a minute.
When you change the time span, the old data previously sampled and stored at the old interval
will be incrementally replaced by new data sampled at the new interval. The Time Span as
indicated on the graph will always reflect the actual time span of the currently stored data, and
will eventually agree with the time span you select. Regardless of the graph selected, the
selected time span is common to all graphs so that they all have the same time relationship to
one another.
The result of a time span change might not be seen instantaneously. It will take some time for
the old data at the old time interval to be replaced by data at the new time interval as
determined by your selected time span.
Viewing Data both as Numeric and as a Graph
Since all displayable data may be viewed either numerically or as a graph, it does not matter
which parameters are selected on which lines of the display. Often times you may even want to
select the same parameter on two different data lines. That way you can have one of them set
for numeric mode and the other one showing you a graph of that same data.
Control Setup
With the Control Setup, you can control the manner in which the 973 operates. The control
setup capabilities are accessible through the Control Setup menu. See Navigating the Menus
on page 6.
Dew / Frost Control
The 973 can control on either dew point or frost point, and has the ability to distinguish the
difference through a function known as Force Frost. The Dew / Frost Control setup menu is
used to control the Force Frost function and also allows for setup of the ORIS (Optimal
Response Injection System) operation.
Force Frost Below
For mirror temperatures above 0°C, water vapor condenses on the mirror as liquid water (dew).
A condensation layer resulting from a mirror temperature above 0°C is considered a dew point.
For mirror temperatures far below 0°C (generally mirror temperatures below –40°C), water
vapor condenses on the mirror as solid ice (frost). A condensation layer resulting from a mirror
far below 0°C is considered a frost point.

16 System Configuration
However, for mirror temperatures between 0 and approximately –30°C, the state of the
condensed layer is generally indeterminate since dew can, and does, exist on the mirror in a
meta-stable state at temperatures well below 0°C. In reality, the condensed layer on the mirror
could be dew, frost, or some combination of the two. Significant errors can result if wrongful
assumptions are made and can be in excess of 2°C.
To eliminate this problem, the 973 can automatically force all sub-zero condensation to a known
state of frost using the Force Frost function. Force Frost works by rapidly cooling the mirror
below –40°C forcing the condensate to solidify to a layer of ice or frost. The mirror will then re-
stabilize at the frost point temperature. Once the condensed layer is in a state of frost, it will
remain frost for all sub-zero mirror temperatures.
You can enable or disable the Force Frost function, and also decide at which temperature it
begins to work. From the Control Setup menu, press Dew/Frost Control (the top menu key).
Change the value of the Force Frost Below field. Mirror temperatures below this value will be
forced to frost.
Now enable or disable the Force Frost function by pressing the Force Frost Below button. A
green indicator light on the button means that the function is enabled. If the light is not
illuminated, then the Force Function is disabled, and no Force Frost will be performed.
Complete your preference by pressing Ok or the keypad’s enter key.
Enable ORIS Below
If the option is installed, the Optimal Response Injection System is used to speed system
response for very low frost point measurements typically when the gas is drier than
approximately –60°C. ORIS works by momentarily injecting a small amount of water vapor into
the dry gas stream to rapidly seed the initial formation of frost on the mirror. This process allows
the required layer to build within a matter of minutes rather than hours. ORIS is typically used
for frost point measurements below about –60°C, but allows you to set it to any reasonable
value.
You can enable or disable the ORIS function, and also decide at which temperature it begins to
work. From the Control Setup menu, press Dew/Frost Control (the top menu key). Change the
value of the Enable ORIS Below field. Mirror temperatures below this value, when there is not
yet any frost formation on the mirror, will use ORIS to more rapidly form the initial frost layer.
Now enable or disable the ORIS function by pressing the Enable ORIS Below button. A green
indicator light on the button means that the function is enabled. If the light is not illuminated,
then ORIS is disabled, and no rapid layer formation will be performed. Complete your
preference by pressing Ok or the keypad’s enter key.
Mirror Cleaning Control
When the fixed Mirror Cleaning key at the bottom of the screen is pressed, the mirror
immediately warms to a pre-specified temperature, readying the measuring head for removal of
the cover and optical assembly. If the mirror and other internal measuring head components
become exposed to normal atmospheric air while cold, the possibility of undesired condensation
exists. By warming the mirror and other internal components to a safe head removal
temperature prior to accessing the mirror, this adverse condensation is avoided.
The safe temperature to which the mirror and internal components will be warmed during a
Mirror Cleaning procedure is selectable from the Mirror Cleaning key of the Control Setup menu.
Enter a value between 20 and 50°C for the Min Head Removal Temp.