Alicat MC Series User manual

1
Precision Gas Mass Flow Controllers
The Fastest Flow Controller Company in the World!
Operating Manual
MC-Series MCS-Series
MCR-Series
WHISPER
MCV-Series

2
Thank you for purchasing an Alicat ow controller.
We know you are going to love your new ow controller. If you have any
questions about operating it, or if something is not working as expected,
please let us know. We are eager to help you in any way possible.
Alicat Scientic, Inc.
[e-mail] • alicat.com
7641 N Business Park Drive, Tucson, AZ 85743 USA
1-888-290-6060
Serial Number: ____________________________
Next Calibration: ___________________________
Recalibrate your ow controller every year.
Your calibration date is labeled on the back of the ow controller. Write that
date in the space above. When it's time for your ow controller's annual
recalibration, contact us by phone, email or live chat to set it up, or ll out the
Service Request Form at alicat.com/service.
07/31/2018 Rev.43 DOC-ALIMAN16C
This Alicat device comes with a NIST traceable calibration
certicate.
This Alicat ow controller conforms to the European
Union’s Restriction of Use of Hazardous Substances in
Electrical and Electronic Equipment (RoHS) Directive
2011/65/EU.
This Alicat ow controller complies with the requirements
of the Low Voltage Directive 2014/35/EU and the
EMC Directive 2014/30/EU and carries the CE Marking
accordingly.
This Alicat ow controller complies with the requirements
of the European Union's Waste Electrical & Electronic
Equipment (WEEE) Directive 2002/96/EC.

3
Welcome to the Alicat way.
You're busy, and the last thing you want to do is waste time wrestling with
your ow controller. We're here to make your life a little easier so you can do
what you do best. It's our pleasure to introduce you to your new Alicat:
• High-accuracy performance for all your gases. Use your ow controller
with any of the 98 or more gases that are part of Gas Select™, page 31.
• Control pressure while monitoring ow rate. Set the closed loop control
algorithm for pressure control, page 26.
• Backlit display with adjustable contrast is easy to read in direct sunlight.
In dimly lit areas, press the Alicat logo to turn on the backlight, page 7.
• Change your STP to match any standard temperature and pressure
reference, page 35.
• Log data to your PC. Talk to the ow controller serially to capture all ow
data for logging and analysis, page 39.
This manual covers the following Alicat Scientic instruments:
• MC and MCR-Series Mass Gas Flow Controllers
• MCD and MCRD-Series Dual Valve Mass Gas Flow Controllers
• MCE-Series Mass Gas Flow Controllers
• MCP-Series Mass Gas Flow Controllers
• MCQ and MCRQ-Series High PressureMass Gas Flow Controllers
• MCS and MCRS-Series Mass Gas Flow Controllers
• MCV-Series Mass Gas Flow Controllers
• MCW (WHISPER) Low Pressure Drop Mass Flow Controllers
This includes Alicat ow controllers labeled as approved for CSA Class 1 Div 2
and ATEX Class 1 Zone 2 hazardous environments. See page 98 for Special
Conditions regarding the use of CSA/ATEX labeled devices.
Please contact Alicat at 1-888-290-6060 or [e-mail] if you have
any questions regarding the use or operation of this device.

4
Table of Contents
Quick-Start Guide ________________________________________6
Getting Started__________________________________________7
Getting to KnowYour Alicat.........................................................................................7
Connectorsand Buttons......................................................................................7
TheFlowControllerDisplay.................................................................................8
Status Messages.................................................................................................8
Mounting.....................................................................................................................9
Plumbing.....................................................................................................................9
Filters ..........................................................................................................................9
ConnectingYour Gas Flow Controller..........................................................................10
MCV ControllerOperatingNotes........................................................................11
MCDDual ValveMass FlowControllerOperatingNotes......................................12
Power and Signal Connections...................................................................................14
RS-232 /RS-485 Digital Input/ Output Signal..................................................15
Analog Signals..................................................................................................16
Option: ColorTFT Display ...........................................................................................17
Navigating and Customizing Your Flow Controller__________________ 18
Flow Controller Menu Map.........................................................................................18
Collecting Live Flow Data...........................................................................................19
Choosing Engineering Units.......................................................................................20
Option: CollectingTotalized Flow Data and Batch Dispensing....................................21
Dispensing Gas inBatches ................................................................................22
Menu.........................................................................................................................24
TaringYour FlowController...............................................................................24
Control Menus............................................................................................................25
Commanding anew setpoint............................................................................26
Changingthesetpoint source............................................................................26
Changingthecontrol loopvariable ...................................................................26
Adjustingthe PID controller ..............................................................................27
About.........................................................................................................................29
Diagnostic Information.....................................................................................29
Basic Conguration Menu..........................................................................................30
ChoosingDeviceEngineeringUnitsfrom the Basic Conguration Menu.............30
Gas Select™................................................................................................................31
Gas Select™ Gas List..........................................................................................32

5
UsingCOMPOSER™ toPersonalize MixedGas Compositions...............................33
Addinga new mixedgas compositiontoCOMPOSER.........................................34
Dening STP/NTP ReferenceValues...........................................................................35
Advanced Setup.........................................................................................................36
Display Setup.............................................................................................................36
Sensor Setup..............................................................................................................37
ConguringYour Flow Controller for Serial Communications.....................................38
Serial Communications____________________________________39
Establishing Serial Communications..........................................................................39
Serial Streaming vs Polling ........................................................................................40
Taring Serially............................................................................................................41
Collecting Flow Data Serially......................................................................................41
Commanding a New Setpoint Serially........................................................................42
Quick Serial Command Guide.....................................................................................43
Using Gas Select and COMPOSER Serially...................................................................44
Troubleshooting Your Flow Controller __________________________45
Maintenance and Recalibration______________________________48
Gas Properties Data ______________________________________49
Numerical List of Gases____________________________________57
Device Units ___________________________________________60
Accessories____________________________________________62
Accessories.................................................................................................................63
Specication Sheets______________________________________64
Optional Pinouts ________________________________________ 94
Additional Information for Alicat CSA and ATEX Approved Devices _______98
Limited LifetimeWarranty ________________________________ 101

6
Quick-Start Guide
Setup
• Tare your ow controller. After you connect the ow controller, ensure
that no air is owing through the device, power it on and ensure it has a zero
setpoint. After a few seconds, it will auto-tare.
• Choose your engineering units. Press the button above or below any
parameter to enlarge it in the middle of the display. If you select that same
item a second time, you can change the engineering unit for that parameter.
You can chosse units for all of the parameters at once by selecting MENU >
BASIC CONFIG > DEVICE UNITS.
• Connect your ow controller. Ensure that ow through your device will be
in the same direction as the arrow on the ow body (usually left to right).
Operation: Flow Control
• Choose your setpoint. Select SETPT from the Main Display to select your ow
rate. Press SET, and the controller immediately adjusts to the new setpoint.
• Monitor live ow readings. You can monitor live readings of ow, pressure
and temperature by viewing the screen. Readings are updated in real time.
• (Optional) Capture a totalized reading. The totalizer option displays the
total ow that has passed through the device since the last time the totalizer
was reset. Press TOTAL/MENU to access the totalizer.
Operation: Pressure Control with Flow Monitoring
• Switch the closed loop control to pressure. Select MENU > CONTROL > ADV
CONTROL > LOOP SETUP > LOOP VAR, and then choose Absolute Pressure. Your Alicat
will now control absolute pressure while monitoring ow rate.
• Choose your setpoint. Select SETPT from the Main Display to select a pressure
setpoint. Press SET, and the controller immediately adjusts to the new setpoint.
Maintenance and Care
• If your gas is clean, your ow controller will require no periodic cleaning.
• Calibrate your ow controller annually. Request an Alicat factory
calibration at alicat.com/service or by calling Alicat at 1-888-290-6060.

7
Getting to KnowYour Alicat
Getting Started
Connectors and Buttons
The drawings below represent the default conguration of a standard Alicat
mass ow controller (MC series) with an upstream valve. Your ow controller's
appearance and connections may dier, especially if it has been ordered with
a large Rolamite valve or a downstream valve.
DATE
0
MC-20SLPM-D NO DIM
6/7/2018
REV.
DATE
0
MC-20SLPM-D NO DIM
6/7/2018
REV.
DATE
0
MC-20SLPM-D NO DIM
6/7/2018
REV.
Process ports
LCD display
Softkey buttons
Communications/Power
Power Jack
Backlight on/o button
Mounting holes

8
Getting Started
The Flow Controller Display
The gure below identies the various features of the ow controller display.
Press the large button with the Alicat logo to toggle the backlight on and o.
For more details, see the Menu Map on page 18 and the menu-by-menu
descriptions that follow it.
Main Display
Flow Temp
+24.38
#C
SLPM
Air
MassFlow
+15.44
TOTAL/
MENU
+15.44
SLPM
+16.67
LPM
SETPT
0.000
#C
+24.38
PSIA
+13.60
TOTAL Accesses the optional
ow totalizer (page 21).
MENU Enters the Menu system
(page 24).
SETPT Sets the ow or pressure
control setpoint (page 26).
Engineering unit for the
highlighted parameter.
Status messages will display
here (below).
Selected gas calibration
(page 31).
Mass Flow
+15.44
SLPM
Highlights mass ow rate
in the center:
Volu Flow
+16.67
LPM
Highlights volumetric (actual)
ow rate in the center:
Highlights temperature in
the center:
Highlights pressure in
the center. Push a second
time to choose pressure
parameter:
Abs Press
+13.60
PSIA
Internal absolute pressure:
Gage Press
-0.12
PSIG
Internal gauge pressure:
(optional):
Baro Press
+13.72
PSIA
Barometric pressure
(optional):
Status Messages
Analog-digital converter error: ADC
Valve exhaust is active: EXH
Valve hold is active: HLD
Front display is locked: LCK
Mass ow over range of device: MOV
Overpressure limit exceeded (optional): OPL
Totalizer rolled over to 0: OVR
Pressure over range of device: POV
Totalizer missed out of range ow: TMF
Temperature over range of device: TOV
Volumetric ow over range of device: VOV

9
Getting Started
Mounting
No straight runs of pipe are required upstream or downstream of the ow
controller. Most Alicat ow controllers can be mounted in any position,
including upside-down. (MCS/MCRS series ow controllers use media-isolated
sensors that must be tared after changing orientation.)
Caution: Flow controllers that use large Rolamite valves (MCR/MCRW/
MCRQ/MCRS) should be mounted with their valve oriented vertically
(right-side up). If another orientation is desired, please contact Alicat.
Plumbing
Your controller has been shipped with plastic plugs tted into its ports. To
lessen the chance of contaminating the ow stream, do not remove these
plugs until you are ready to install the device.
Standard Alicat Gas Flow controllers have female inlet and outlet ports.
Welded VCR and other specialty ttings may have male connections.
» If you are using a tting that does not have a face seal, use thread-sealing
Teon tape to prevent leakage around the port threads, but do not wrap
the rst two threads. This will minimize the possibility of getting tape into
the ow stream and clogging the laminar ow elements (LFE).
» If you are using a tting that has a face seal, there is no need to apply
Teon tape to the threads.
Warning: Do not use pipe dopes or sealants on the process connections
as these compounds can cause permanent damage to the controller
should they get into the ow stream.
Filters
When pressure drop is not an issue, use in-line sintered lters to prevent
large particulates from entering the ow controller. Suggested maximum
particulate sizes are as follows:
» 5 microns for units with ow ranges of 1 sccm or less.
» 20 microns for units with ow ranges between 2 sccm and 1 slpm.
» 50 microns for units with ow ranges of 1 slpm or more.

10
Getting Started
Connecting Your Gas Flow Controller
Inlet Connection Port
Outlet Connection Port
Flow Direction Arrow
Control Valve
(upstream valve shown)
Warning: Using the ow controller above the maximum specied
internal line pressure, or above the maximum recommended
dierential pressure between the inlet and outlet, will result in
permanent damage to the internal pressure sensors.
A common cause of this problem is the instantaneous application
of high-pressure gas, as from a snap-acting solenoid valve either
upstream or downstream of the ow controller. If you suspect that
your pressure sensor is damaged, please discontinue use of the device
and contact Alicat.
See the chart below for pressure limits.
Model Max Pressure at Sensor Max Dierential Pressure
MC//MCR/MCS 145 psig 75 psid
MCW/MCRW 45 psig 15 psid
MCQ/MCRQ 305 psig 100 psid
Your Alicat ow controller can measure and control ow generated by
positive pressure and/or suction. Connect the controller so that the ow
travels in the same direction as the ow arrow, usually from left to right as you
look at the front of the device.

11
MCV Controller Operating Notes
Alicat’s MCV mass ow controller is equipped with an integrated Swagelok®
positive shuto valve. The normally closed valve is actuated by a gas (typically
air) and opens when supplied with 60-120 psig of pressure. The shut-o valve
closes again when this pressure is removed.
A common method for actuating the shuto valve incorporates a three-way
solenoid valve (below). Pressure is applied to one side of the solenoid valve
while the other side of the solenoid is left open to atmosphere. When the
solenoid is energized, pressure is delivered to the shuto valve, causing it
to open. When the solenoid is returned to a relaxed state, the gas vents to
atmosphere, allowing the shut-o valve to close.
All standard MC-Series device features and functions are available on
the MCV-Series and operate in accordance with the standard MC-
Series operating instructions.
Three-way Solenoid Valve
MCV Mass Flow
Controller
Vent
Positive
Pressure
MCV mass ow controller and three-way solenoid valve.
Getting Started

12
MCD Dual Valve Mass Flow Controller Operating Notes
The MCD is a versatile Dual-Valve Mass Flow and Pressure Controller. It can be
used to:
• Measure mass ow and volumetric ow in both directions, plus absolute
pressure and temperature.
• Control mass or volumetric ow from a pressurized source or to vacuum.
• Control absolute pressure or back-pressure in a owing process.
• Control absolute pressure in a closed volume with automatic venting.
Application examples are shown below and on the following page. Please
contact Alicat if you have any questions regarding MCD use.
Process Connecon
Inlet Valve
Outlet Valve
MCD front view
Process Connecon
Inlet Valve
Outlet Valve
MCD rear view
Getting Started

13
ProcessGas Source
Vacuum Source or Vent
Flowing Absolute Pressure Control
Back-Pressure Control
Posive Pressure Control
FLOW
ProcessGas Source
Vacuum Source or Vent
Bidirectional Mass orVolumetric Flow Control
FLOW
FLOW
Closed Process
Gas Source
Vacuum Source or Vent
Dead-Ended Absolute Pressure Control
FLOW
Getting Started

14
Power and Signal Connections
Power can be supplied to your controller through either the power jack or the
multi-pin connector on top of your device.
Small valve controller power jacks require a 12-30 Vdc power supply
with a 2.1 mm female positive center plug capable of supplying at
least 250 mA. 4-20 mA analog signal outputs require at least 15 Vdc, ,
and 0-10 Vdc outputs require at least 10 Vdc..
Large valve controllers require a 24-30 Vdc power supply with a 2.1
mm female positive center plug capable of supplying at least 750 mA.
Standard 8-Pin Mini-DIN Pinout
Pin Function Mini-DIN
cable color
1Not Connected (or optional 4-20 mA Primary Output Signal) Black
2Static 5.12 Vdc (or optional Secondary Analog Output [4-20 mA, 0-5 Vdc,
1-5V dc, 0-10 Vdc] or Basic Alarm) Brown
3Serial RS-232RX / RS-485(–) Input Signal (receive) Red
4Analog Setpoint Input Orange
5Serial RS-232TX / RS-485(+) Output Signal (send) Yellow
60-5 Vdc (or optional 1-5 Vdc or 0-10 Vdc) Output Signal Green
7Power In (as described above) Blue
8Ground (common for power, digital communications, analog signals and
alarms) Purple
Note: The above pinout is applicable to all the ow controllers and controllers with the Mini-DIN
connector. The availability of dierent output signals depends on the options ordered. Optional
congurations are noted on the unit’s calibration sheet.







1 2
3 4 5
6 7 8
Getting Started
Caution: Do not connect power to pins 1 through 6, as permanent
damage can occur.
It is common to mistake Pin 2 (labeled 5.12 Vdc Output) as the
standard 0-5 Vdc analog output signal. Pin 2 is normally a constant
5.12 Vdc that reects the system bus voltage.
For 6-pin locking industrial connector, DB9 and DB15 pinouts, see
page 92 to page 95 or visit alicat.com/pinout.

15







9876

9876
15 3 24 1 532 4
Serial Cable End Serial Port
















1
876
5
4
3
2
8 Pin Mini-DIN Cable End 8 Pin Mini-DIN Connector
RS-232 / RS-485 Digital Input / Output Signal
To use the RS-232 or RS-485 digital signal, connect the RS-232 / RS-485 Output
Signal (Pin 5), the RS-232 / RS-485 Input Signal (Pin 3) and Ground (Pin 8) to
your serial port as shown below. (See "Serial Communications" on page 39
for details)
9 Pin Serial Connection 8 Pin Mini-DIN Connection
Pin Function Function Pin
5 Ground Ground 8
3 Transmit Receive 3
2 Receive Transmit 5
DB9 to 8-Pin Mini-DIN Connection for RS-232 / RS-485 Signals
Getting Started

16
Analog Signals
Primary Analog Output Signal
Most Alicat instruments include a primary analog output signal, which is
linear over its entire range. For both standard 0-5 Vdc and optional 0-10 Vdc
output signals, a zero ow condition is usually in the range of 0.010 Vdc. Zero
ow for the optional 1-5 Vdc and 4-20 mA output signals is 1 Vdc and 4 mA,
respectively. Full-scale ow is 5 Vdc for 0-5 Vdc and 1-5 Vdc signals, 10 Vdc for
0-10 Vdc signals and 20 mA for 4-20 mA signals.
Alicat's default 8-pin mini-DIN connector places the primary analog output
on Pin 6 for voltage signals and Pin 1 for 4-20 mA current signals. Ground for
these signals is common on Pin 8.
Option: Second Analog Output Signal
Alicat's default 8-pin mini-DIN connector places the secondary analog output
on Pin 2 for both voltage and current signals. Your device's secondary analog
signal may dier from its primary output signal.
See the Calibration Sheet that shipped with your meter to determine
which output signals were ordered.
Option: 4-20 mA Current Output Signal
If your meter has a 4-20 mA current primary or secondary output signal, your
ow meter will require 15-30 Vdc power.
Caution: Do not connect 4-20 mA devices to “loop powered’” systems,
as this will destroy portions of the circuitry and void the warranty. If
you must interface with existing loop powered systems, always use a
signal isolator and a separate power supply.
Setpoint Analog Input Signal
Your mass ow controller may be a congured with a dierent analog inout
signal than its output signal(s). One method for providing a remote setpoint
to controllers with a 0-5 Vdc or 0-10 Vdc analog signal is shown below.
Note: Devices with 4-20 mA input signalsare current sinking devices.
The receiving circuit is essentially a 250 ohm resistor to ground.
Getting Started
5.12 Vdc
50 KOhm
Potentiometer
0-5 Vdc
1
2
3
4
5
6
7
8

17
Option: Color TFT Display
Instruments ordered with a color display function the same as standard backlit
monochrome instruments, but color is used to provide additional on-screen
information.
Multi-Color Display Indicators
» GREEN: Parameter labels and adjustments associated with the button
directly above or below the label are presented in green.
» WHITE: The color of each parameter is displayed in white while operating
under normal conditions.
» RED: The color of a parameter is displayed in red when its value exceeds
128% of the device’s specications.
» YELLOW: Menu items that are ready to be selected appear in yellow. This
color replaces the symbol (>) in selections on monochrome display.
Press the Alicat logo button to turn o the color display backlight. The
ow meter remains in operation while the backlight is o.
LCD Contrast
LCD contrast is ranged from 0 to 11 on color displays, with 11 indicating the
greatest contrast. See "Display Setup" on page 36.
Specications for Instruments with Color Displays
The following specications replace the standard power specications when
the instrument is equipped with a color display. All other specications from
your device's specication sheet remain in eect.
Specication Small Valve
Controller LargeValve Controller
Supply Voltage 12 to 30 Vdc 24 to 30 Vdc
Supply Current 290 mA @ 12Vdc
200 mA @ 24Vdc 780 mA @ 24Vdc
Getting Started

18
Navigating and CustomizingYour Flow Controller
Flow Controller Menu Map
SETPT
+15.44
MENU/
MAIN
SLPM
+15.44
TOTAL/
TIMER
+14.71
REMAIN RESET
2:56 h:m:s
+45.29
M AVG +15.44 SL
SLPM
Air
Mass Flow
+15.44
TOTAL/
MENU
+15.44
SLPM
+16.67
LPM
SETPT
+15.44
#C
+24.38
PSIA
+13.60
Main Display
*
Optional
Flow
Totalizer
Basic Cong (p. 30)
MAIN
BACK
STP/
NTP
DEVICE
UNITS
GAS
Air
Adv Setup (p.25)
MAIN
BACK
DISP
SETUP
COMM
SETUP
SENSOR
SETUP
About (p. 29)
MAIN
BACK
MFG
INFO
DEVICE
STATE
DEVICE
INFO
Main Menu (p. 24)
MAIN
ADV
SETUP
BASIC
CONFIG
TARESABOUTCONTROL
Tares (p. 24)
MAIN
BACK
TARE
FLOW
AUTO
TARE
-ON-
TARE
PRESS
*
*
*
*
*
*Press MAIN to return
to the Main Display.
Start Here
Control (p. 25)
MAIN
ADV
CONTROLBACK
SETPT
+15.44
*
Without
Flow
Totalizer

19
Navigating and CustomizingYour Flow Controller
Collecting Live Flow Data
The Main Display has three primary functions:
• Collecting live temperature, pressure and ow data (see below)
• Changing engineering units for temperature, pressure and ow (page 20)
• Changing the ow or pressure control setpoint (page 26)
This screen displays live data for all ow parameters simultaneously. Live
data is measured 1000 times every second but refreshed more slowly on the
display. Press the button above or below any of the four ow parameters once
to highlight its value in the center of the screen. Press the same button again
to enter the engineering unit selection menu for that parameter (page 20).
Main Display
Flow Temp
+24.38
#C
SLPM
Air
Mass Flow
+15.44
TOTAL/
MENU
+15.44
SLPM
+16.7
LPM
SETPT
+15.44
#C
+24.38
PSIA
+13.60
TOTAL Accesses the optional
ow totalizer (page 21).
MENU Enters the Menu system
(page 24).
SETPT Sets the ow or pressure
control setpoint (page 26).
Engineering unit for the
highlighted parameter.
Status messages will display
here (see page 8).
Selected gas calibration
(page 31).
Mass Flow
+15.44
SLPM
Highlights mass ow rate
in the center:
Volu Flow
+16.67
LPM
Highlights volumetric (actual)
ow rate in the center:
Highlights temperature in
the center:
Highlights pressure in
the center. Push a second
time to choose pressure
parameter:
Abs Press
+13.60
PSIA
Internal absolute pressure:
Gage Press
-0.12
PSIG
Internal gauge pressure:
(not available on all devices):
Baro Press
+13.72
PSIA
Barometric pressure
(not available on all devices):

20
Choosing Engineering Units
Press the button above or below any of the four
ow parameters twice to enter its unit selection
menu. You can change units in two ways:
Button engineering units alter the display only,
not the serial data frame:
• Select Set button eng units and press SELECT to
change the engineering unit on the display only.
This does not alter the controller data frame.
Device engineering units alter both the display
and the ow controller data frame:
• Select Set device eng units and then choose
the engineering unit as above. An additional
conrmation screen asks you to conrm the
serial change.
• If the button engineering unit is dierent than
the device engineering unit, Set device eng units
will not appear. First select Show device eng units to
revert the button to the current device unit for
that parameter. Enter the unit selection menu
again to change the device engineering unit.
Examples of changing device engineering units:
SETCANCEL
PRESSING SET WILL
AFFECT DISPLAY
AND SERIAL VALUES.
VERIFY CONNECTED
SERIAL DEVICES
EXPECT THE CHANGE.
SELECTCANCEL
Show baro pressure
DOWN
UP
Set button eng units
Set device eng units
Show gauge pressure
Show abs pressure
>
Navigating and CustomizingYour Flow Controller
SELECTCANCEL
DOWNUP
Set device eng units
Set button eng units
>
SELECTCANCEL
DOWNUP
Show device eng units
Set button eng units
>
#C
Air
Flow Temp
+24.38
SETPT
+15.44
#C
+24.38
PSIA
+13.60
#F
Air
Flow Temp
+75.88
SETPT
+15.44
#F
+75.88
PSIA
+13.60
Changing device units:
°C is the existing device
engineering unit, so the unit
selection menu displays
Set device eng units. Select this to
choose a new unit.
Changing device units:
°F is not the existing device
engineering unit, so the unit
selection menu displays
Show device eng units. Select this
to revert the button unit to the
device unit for this parameter.
The example above shows the unit
selection menu for a device that has
the internal barometer option.