www.sensirion.com Sensirion AG, Laubisrütistrasse 50, CH-8712 Stäfa ZH, Switzerland, Phone: +41 44 306 40 00, Fax: +41 44 306 40 30
ASF1400
Bidirectional Mass Flow Meter
_ Unique dynamic range:
0.01 sccm – 400 sccm
_ Outstanding resolution and accuracy
_ Ultra fast response time
_ Hysteresis & offset free
_ Calibrated & temperature compensated
_ RS-232 and
ASF1400 Product Summary
The ASF1400 Mass Flow Meter enables extremely
accurate bidirectional measurement of gas flow over four
orders of magnitude. Its leading performance is based on
SENSIRION’s unsur passed CMOSens ® sensor technology .
With CMOSens®, the on-chip sensor element forms an
integrated whole with the amplification and A/D converter
circuit. This results in superior resolution, fast response
time and large dynamic range at lowest power
consumption.
All measurement data is fully calibrated and temperature
compensated by means of an internal microcontroller.
Mounted in rugged, chemically inert PBT housing the
ASF1400 is suitable for a wide range of applications. Such
include mass flow metering for process control, medical
applications, heating ventilation and air conditioning
(HVAC) solutions, as well as gas flow metrol ogy.
The sensor housing provides two inlets for measuring the
gas flow and withstan ds overpressures of 2 bar (29 psi).
The ASF1400 requires a supply voltage of 7…18Vdc and
provides an RS-232 compliant electrical interface.
Version 2.2 / November
MASS FLOW VOLTAGE
REGULATOR
MICRO
CONTROLLER
RS232 LINE
DRIVER/
RECEIVER
EEPROM
GND
VDD
/CS
MOSI
MISO
SCK
RxD
TxD
MASS FLOW
ASF1400 MASS FLOW METER
SPI
Interface
RS232
Interface
Power
Supply
CMOSens™ SENSOR CHIP
THERMAL
SENSOR
AMPLIFIER
ADC
no longer
supported
Figure 1: Block Diagram ASF1400 M ass Flow Sensor wit h CMOSens® technology.
ASF1400 Bidirectional Mass Flow Meter
Introductory Description
The heart of the ASF1400 mass flow meter is
powered by Sensirion’s unsurpassed CMOSens®
sensor technology. The ASF1400 mass flow meter
therefore provides unbeatable performance at very
attractive system cost. The lowest detectable gas flow
rate is 0.003 sccm, which means a minimum volume
of 3 mm3 gas per minute c an be measured. Covering
at the same time a flow range of more than 4 orders
of magnitude, the ASF1400 sets a new standard
wherever mass flow has to be measured or
controlled.
The ASF1400 device measures true mass flow
independe nt of the am bient temperat ure a nd pressure
changes. You simply connect the gas t o be measur ed
to the ASF1400 device to get an instantaneous gas
flow rate at a sampling rate of up to 7Hz (please
contact us for sampling rates of up to 200 Hz).
A flow range between ±400 sccm can directly be
mea-sured by connecting the ASF1400. To increase
the range, a bypass can be used in conjunction with
the ASF1400 device (see Section 1.4 of this data
sheet).
In addition to mass flow, the ASF1400 device
provides information about the temperature on the
CMOSens® sensor element. Both mass flow and
temperature data are accessed through an RS-232.
The RS-232 interface allows you to directly connect
the ASF1400 device to a PC or PDA using standard
terminal software. If a special interface such as 4-20
mA current output or other is required contact
Sensirion for a customer specific solution.
In general, all gas types can be measured using the
ASF1400 product. However, the standard calibration
gas is nitrogen. Please contact SENSIRION, if you
would like to u se the sensor for applications with other
gases.
To get you started quickly, an evaluation package
including ASF1400 devices, software, cables, rubber
hose and bypass is availabl e from Sensirion AG.
CMOSens® sensor technology
CMOSens® is the base technology for all Sensirion
multi sensor modules and sensor systems. The
unification of semiconductor chip and sensor
technology serves as a platform for highly integrated
system solutions with excellent sensor precision and
reliability. With CMOSens®, the on-chip sensor
element forms an integrated whole with a high-end
amplification and A/D converter circuit. Due to the
compact single-chip design, CMOSens® based
sensors are very resistant to electromagnetic
disturbances (EMC), another important technical
advantage of this state of the art sensor technology.
As a result, CMOSens® based multi sensor modules
offer excellent sensor precision, fast response time
and a very large dynamic measurement range. In
addition, the digital intelligence of the CMOSens®
sensor technology enables digital interfaces that
permit an easy li nk wit h the s ystem of t he c ustomer, a
real advantage and benefit that results in ready-to-use
problem solutions (“Mount&Sense”).
www.sensirion.com Version 2.2 2/9
ASF1400 Bidirectional Mass Flow Meter
1 Mass Flow Sensor Performance
Table 1: Overview of ASF1 40 0 Gas Sensor Performance1
Parameter Condition Minimum
Typical Maximu
m Units
Flow Sensor
direct measurement -400 400 sccm( )2
using proposed bypass tube(2 )3 -100 100 liter/min( )4
Dynamic Range customized bypas s tube unlimited
unlimited
Resolution 400 sccm flow 0.09 sccm
< 10 sccm flow 0.01 sccm
Lowest Detectable
Flow < 10 sccm flow 0.015(4) sccm
Pressure Drop 400 sccm, pabs. = 1 bar 120 Pa( )5
Repeatability
0.0025 % FS () 6
0.025 % m.v.
0…5 % of full scale 0.05 % FS
() 7
Accuracy 23 C
5…100 % of full scale
1 % m.v.
( ) 7
Offset 23°C < 0.005 < 0.02 % FS
Overpressure
Resistance 2 bar
( )8 depends on resolution setting 142 1280 ms
Response Time ( )9 (see Section 3, Table 2)
Operating
Temperature 0 70 °C
Zero < 0.005 % FS / °C Ambient
Temperature
Coefficient Span < 0.08
% measured value /
°C
Position Sensitivity p =1 bar, small nitrogen flow ±0. 008 % FS
abs
Temperature
Sensor Measures temperature inside the sensor, bu t not of the surrounding air(10 )10
Dynamic Range 0 70 °C
Resolution 0.1 °C
Accuracy 3 2 °C
1 All data apply for calibration conditions (20°C, 1013 mbar) unless otherwise noted.
2 1 sccm = 1 cm3/min at 0°C and 1013mbar pressure (1sccm = 0.001 norm liter)
3 using bypass tube included in Sensirion’s mass flow meter evaluation kit EK-F1
4 1 liter/min = 1000 sccm
5 1 bar = 100 000 Pa = 0.9869 atm = 401.9 inch H2O = 14.5 psi
6 Error = % of full scale (FS) or % of measured value, whichever is bigger.
7 Better calibration available for high volume OEM on request. Allow the Sensor to warm up for best results.
8 For higher overpressure resistance versions please check the EM1 product page.
9 For faster response times please check out the ASF1430 high speed mass flow meter data sheet
The sensor warms up by about 7°C (depending on supply voltage and ventilation).
10
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ASF1400 Bidirectional Mass Flow Meter
1.1 Gas Flow Characteristics
Figure 2 shows the applied gas flow vs. the digital
output of the ASF1400. 1.3 Gas Flow and Pressure Difference
-500
-250
0
250
500
-500 -250 0 250 500
Mass Flow [sccm ]
ASF1400 output [sccm]
The ASF1400 is calibrated for mass flow
measurements. However, there is a well defined
relation between mass flow and pressure drop. This
relation is shown in Figure 4. On request the
ASF1400 can also b e calibrated f or the pressure drop
at its output (for more details refer to the
documentation of the Sensirion Differential Pressure
Sensor ASP1400).
- 400 - 200 0 200 400
Massflow [sccm]
- 150
- 100
-50
0
50
100
150
Differential pressure [Pa]
Figure 2: ASF1400 transfer ch aracteristics.
1.2 Sensor Principle and Gas Types
The ASF1400 device detects mass gas flow by
measuring heat transfer. A heating resistor on a
thermally insulated membrane is kept above ambient
temperature. In the presence of gas flow, the
temperature distribution up- and downstream is
disturbed. This asymmetry is then measured. Due to
the minimal thermal mass of the membrane,
symmetrical arrangement, and accurate temperature
measurement, the revolutionary specifications of the
ASF1400 devices are achieved.
Figure 4: Differential Pressure vs. Mass Flow of
ASF1400 Device.
1.4 Adjusting the Measurement Range
To adjust the measurement range, the ASF1400
device is used in conjunction with a bypass
configuration (see Figure 5). Only a sample of the
total flow actually gets directed through the bypass
channel and the sensor system. A tube with flow
restrictor and all required connection items are
included in the Mass Flow Meter Evaluation Kit EK-
F1, also available from SENSIRION AG.
The above mentioned thermal principle requires
information about the gas type to be measured. The
ASF1400 is available for air and nitrogen. Other gas
types are available on reques t.
In Figure 3 the repeatability of the ASF1400 devices
is compared with the repeatability of a typical Mass
Flow Controller (MFC). It emphasizes the superior
performance of the ASF1400 device.
Flow restrictor
ASF
1400
0 100 200 300 400
Massflow [sccm]
0
0.1
0.2
0.3
0.4
0.5
Repeatability [% of measured value]
200
Specs of typical MFC
Repeatability ASF 1400
Figure 5: Extending the measurement range of the
ASF1400 device usin g a bypass configurati on. Only a
sample of the total flow actually gets directed through
the bypass channel and the sensor. Shown tube with
flow restrictor is included in the EK-F1 evaluation kit.
Figure 3: Comparison of the repeatability of the
CMOSens® ASF1400 device compared to a typical
Mass Flow Controller (MFC).
www.sensirion.com Version 2.2 4/9
ASF1400 Bidirectional Mass Flow Meter
2 Pins and Digital Interface The measurement values are provided as a signed
floating point number together with the corresponding
unit (sccm for mass flow, C f or temperature). In ca se
of an overflow, the o utp ut shows oF.
A S F 1 4 0 0
G N D
V D D
/ C S
M O S I
M I S O
S C K
R x D
T x D
2.3 Serial Peripheral Interface (SPI)
The in earlier versions available SPI interface is due
to changes in electronic components no longer
supported.
Figure 6: ASF1400 pin out. 3 Configuration and Commands
GND and VDD (Power Supply) The ASF1400 device accepts a set of commands
through its RS-232 interface (see table 3 for valid
commands; for correct settings of the RS-232 refer to
Section 2.1).This allows the user to configure the
ASF1400 device. Since the configuration is stored in
the internal EEPROM, it is maintained after power
breaks.
The ASF1400 requir es a v oltage supply of between 7
V and 18 V. Since this voltage is internally regulated,
there are no stringent requirements as far as ripple
and stability are co ncerned.
2.1 Connector With the exception of the stop s command, all
commands have to be terminated by the return key
(↵, ASCII #10 or #13). After completion of a
command, the ASF1400 returns ok and is ready to
take a new inst ruction. Before enteri ng a command, it
may be necessary to clear the buffer by means of
using ↵.
You need an EDAC 395-010-520-102 connector to
connect the sensor. Please check the EDAC
homepage for details (www.edac.net).
Alternatively the AVX 00 6338 020 000 04 0 or AVX
00 6338 020 000 04 2 connectors can be used to
connect the ASP1400 as well. (See www.farnell.com,
order codes 635789 or 635730). There is a trade-off between resolution and
measurement time. Possible settings are listed in
Table 2. Choosing 12 bit results in a measurement
interval of 142 ms. With the max resolution of 15.2 bit,
a new measurement is provided every 1280 ms. For
faster sampling rates refer to the ASF1430 high
speed mass flow meter device data sheet.
2.2 RS-232 Interface
All configurations (see also Section 3) for the
ASF1400 can be set using its RS-232 interface). To
communicate with the ASF1400 via RS-232 the
following pins are required:
RxD (Receiving Data Line) Table 2: Resolution settings using the res=value
command and corresponding response times
TxD (Transmitting Da ta Line)
GND (Ground)
The RS-232 of the ASF1400 is config ured as follows:
Baudrate 9600
Data Bits 8
Stop Bits 1
Parity none
Protocol none
With these settings, the ASF1400 device can be
connected to any PC or PDA equipped with terminal
software.
res= Resolution [bit] data interval [ms]
1 12.0 142
2 13.0 284
3 13.5 427
4 14.0 569
5 14.3 711
6 14.6 853
7 14.8 995
8 15.0 1138
9 15.2 1280
Table 3: Commands of the ASF1400 device.
Command Output Description
help↵ commands Lists all available commands
www.sensirion.com Version 2.2 5/9
ASF1400 Bidirectional Mass Flow Meter
ver↵ version Provides type of sensor, software, hardware and customer version
get↵ Start single measurement
go↵ Starts series of measurements
s stop Stops series of measurements
reset↵ Resets ASF1400 device
res=1..9↵ resolution Sets resolution: 1 -> 12 bits; 9 -> 15 bits, see Table 2
res? resolution Shows actual setting
mod=F | T↵ mode Selects Flow- (F) or Temperature mode (T)
mod? mode Shows actual setting
Disp=s,d display mode Shows Flow (s) or Flow+Temperature (d) *no effect in the Temerature mode
Disp? display mode Shows actual setting
defspi=P | G↵ define spi Sets SPI in Push- (P) or Get mode (G), see also Section 4.3
Notes:
• Default settings are marked in bold letters
• The commands are not case sensitive.
• In order to send a new command to t he ASF1400 mak e sure the ASF14 00 is not in meas urement mod e. Issue therefore a stop comm and
s first. After this, any instruction can be given to the ASF1400 and a new series of measurement can be started by go↵.
• Due to the limited write cycles allowed for the EEPROM, excessive configuration modifications should be avoided.
4 Specifications ASF1400
4.1 Absolute Maximum Ratings
Ambient storage temperature -65°C to 150°C
Ambient operating temperature 0°C to 70°C
Overpressure r esistance 2.0 b ar
4.2 Electrical Specifications
Table 3: ASF1400 D C Characteristics.
Parameter Conditions Min. Typ. Max. Units
Power Supply DC DC 7 9 18 V
VDD = 9 V, no load 20 mA
Operating Current 27 mA
VDD = 9 V, 3kΩ at RS232 output
Power Dissipation VDD = 9 V, no load 180 mW
Table 4: ASF1400 RS-232 Characteristics.
Parameter Conditions Min. Typ. Max. Units
RS232 Output
Transmitter output l oaded
with 3kΩ ±5 ±9 V
Output Voltage Swing
Power-Off Output Resistance 300 Ω
Output Short Circuit Current ±18 mA
RS-232 Input
Voltage Range -15 15 V
Voltage Threshold
Low 0.8 1.2 V
High 1.7 2.4 V
Hysteresis 0.2 0.5 1.0 V
Resistance 3 5 7
kΩ
www.sensirion.com Version 2.2 6/9
ASF1400 Bidirectional Mass Flow Meter
5 Physical Dimensions and Mounting Information
The ASF1400 is mounted in chemically inert PBT housing.
The rugged package has been designed to withstand
overpressures of up to 2 bars. Higher pressure packages of
up to 10 bars are available on request.
Physical dimensions and mounting information are
provided in Figure 11 and Table 6.
1
8
!
" #
holes for
∅
3 mm screws
nozzles for ∅ 6 mm
rubber hose.
h
Table 6: Physical Dimensions of the ASF1400 device.
Length L 45.0 mm
Width W 40.0 mm
Height h 15.5 mm
Distance D 25.2 mm
Diameter d 5.0 mm
Pitch s 2.54 mm
Pitch H 20.6 mm
Pitch G 29.1 mm
Pitch N 10.0 mm
Figure 11: Physical dimensions and mounting information of the ASF1400.
Holes for
® screws
PT
(∅ 2.2 mm, screw in
not more than 4.4 mm
)
6 Ordering Information
For small ordering quantities the ASF1400 sensor can be ordered directly at Farnell on http://www.farnell.com. Farnell is a
worldwide distributor of electrical, electronic and industrial component products.
When ordering ASF1400 series devices at SENSIRION please refer to the following part numbers. For the latest product information
access SENSIRION’s website on http://www.sensirion.com
Calibrated for Gas Type Range Packaging Type
Air ± 400 sccm 2 bar ASF1400
Notes:
Packages to sustain common mode pressures of 10 bars are available on request.
Special electrical interfaces such as 4-20 mA output or others are available on request.
For faster response times refer to the ASF1430 data sheet.
A evaluation kit including ASF1400 devices, evaluation software and other accessories such a b ypass, rubber hose and cable s
can be ordered. For detailed information check out the description of the Mass Flow Meter Evaluation Kit EK-F1 on
http://www.sensirion.com
www.sensirion.com Version 2.2 7/9
ASF1400 Bidirectional Mass Flow Meter
Important Notices
• the defective product shall be returned to
SENSIRION’s factory at the Buyer’s
expense; and
Warning, personal injury
Do not use this product as safety or
emergency stop devices or in any other
application where failure of the product could
result in personal injury. Do not use this
product for applications other than its
intended and authorized use. Before
installing, handling, using or servicing this
product, please consult the data sheet and
application notes. Failure to comply with
these instructions could result in death or
serious injury.
• the warranty period for any repaired or
replaced product shall be limited to the
unexpired port i on of the origin al perio d.
This warranty does not appl y to any equipment which
has not been installed and used within the
specifications recommended by SENSIRION for the
intended and proper use of the equipment. EXCEPT
FOR THE WARRANTIES EXPRESSLY SET FORTH
HEREIN, SENSIRION MAKES NO WARRANTIES,
EITHER EXPRESS OR IMPLIED, WITH RESPECT
TO THE PRODUCT. ANY AND ALL WARRANTIES,
INCLUDING WITHOUT LIMITATION, WARRANTIES
OF MERCHANTABILITY OR FITNESS FOR A
PARTICULAR PURPOSE, ARE EXPRESSLY
EXCLUDED AND DECLINED.
If the Buyer shall purchase or use SENSIRION
products for any unintended or unauthorized
application, Buyer shall defend, indemnify and hold
harmless SENSIRION and its officers, employees,
subsidiaries, affiliates and distributors against all
claims, costs, damages and expenses, and
reasonable attorney fees arising out of, directly or
indirectly, any claim of personal injury or death
associated with such unintended or unauthorized use,
even if SENSIRION shall be allegedly negligent with
respect to the design or the manufacture of the
product.
SENSIRION is only liable for defects of this product
arising under the conditions of operation provided for
in the data sheet and proper use of the goods.
SENSIRION explicitly disclaims all warranties,
express or implied, for any period during which the
goods are operated or stored not in accordance with
the technical specifications.
SENSIRION does not assume any liability arising out
of any application or use of any product or circuit and
specifically disclaims any and all liability, including
without limitation consequential or incidental
damages. All operating parameters, including without
limitation recommended parameters, must be
validated for each customer’s applications by
customer’s technical experts. Recommended
parameters ca n and do vary in different applications.
ESD Precautions
The inherent d esign of thi s compo nent caus es it to be
sensitive to electrostatic discharge (ESD). To prevent
ESD-induced damage and/or degradation, take
customary and statutory ESD precautions when
handling t his product.
See application note “ESD, Latchup and EMC” for
more information. SENSIRION reserves the r ight, without further notice,
(i) to change the product specifications and/or the
information in this document and (ii) to improve
reliability, functions and design of this product.
Warranty
SENSIRION warrants solely to the original purchaser
of this product for a period of 12 months (one year)
from the date of delivery that this product shall be of
the quality, material and workmanship defined in
SENSIRION’s pu blished specificat ions of the product.
Within such period, if proven to be defective,
SENSIRION shall repair and/or replace this product,
in SENSIRION’s discretion, free of charge to the
Buyer, provided that:
Copyright 2001-2008, SENSIRION.
©
CMOSens is a trademark of Sensirion
®
All rights reser ved
RoHS and WEEE Statement
The SDP6x0 family compl ies with requirements of th e
following directives:
• notice in writing describing the defects shall
be given to SENSIRION within fourteen (14)
days after their appearance;
• EU Directive 2002/96/EC on waste electrical
and electronic equipment (WEEE),
OJ13.02.2003; esp. its Article 6 (1) with
Annex II.
• such defects shall be found, to
SENSIRION’s reasonable satisfaction, to
have arisen from SENSIRION’s faulty
design, material, or workmanshi p;
• EU Directive 2002/95/EC on the restriction of
the use of certain hazardous substances in
electricaland electronic equipment (RoHS),
OJ 13.02.2003 ; esp. its Article 4.
www.sensirion.com Version 2.2 8/9
ASF1400 Bidirectional Mass Flow Meter
Revision history
Table 1: Revision history
Date Version Page(s) Changes
Dec. 2001 Preliminary all First public release
May 2005 V2.1 all Specifications, typos, various small modifications
November 2008 V2.2 all SPI interface no longer supported ,overpressure resistance changed,
new ISO-Logo, sales Office Information, introduction of revision history,
new disclaimer, RoHS compliance
Headquarters and Sales Office
Sensirion AG Phone: + 41 44 306 40 00
Laubisruetistrasse 50 Fax: + 41 44 3 06 40 30
CH-8712 Staefa ZH e-mail: info@sensirion.com
Switzerland Web: www.sensirion.com
Sales Office USA (for North American customers only)
SENSIRION Inc Phone: +1 805-409 4900
Westlake Pl. Ctr. I, suite 204 Fax: +1 805-435 0467
2801 Townsgate Road e-mail: michael.karst@sensirion.com
Westlake Village, CA 91361 Web: www.sensirion.com
USA
Sales Office Korea (for Korean customers only)
Sensirion Korea Co. Ltd. Phone: +82 31-440-9925~27
#1414, Anyang Construction Twr B/D Fax: +82 31-440-9927
1112-1, Bisan-dong, Anyang-city e-mail: info@sensirion.co.kr
Gyeonggi-Province, Web: www.sensirion.co.kr
South Korea
Sales Office Japan (for Japanese customers only)
Sensirion Japan Co. Ltd Tel : +81 3-3444-4940
Representative Director: Keiichi Hasegawa Fax: +81 3-3444-4939
Shinagawa Station Bldg. 7F, 4-23-5, Takanawa, e-mail: info@sensirion.co.jp
Minato-ku, Tokyo, Japan Web: www.sensirion.co.jp
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