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ASF1400

P1-P3P4-P6P7-P9
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 be calibrated for 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 characteristics.
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 request.
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
Specs of typical MFC
Repeatability ASF 1400
Figure 5: Extending the measurement range of the
ASF1400 device using a bypass configuration. 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 for temperature). In case
of an overflow, the output 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 requires a voltage 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 concerned.
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 instruction. Before entering 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 Data Line)
GND (Ground)
The RS-232 of the ASF1400 is configured 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 the ASF1400 make sure the ASF1400 is not in measurement mode. Issue therefore a stop command
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 resistance 2.0 bar
4.2 Electrical Specifications
Table 3: ASF1400 DC 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 loaded
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
P1-P3P4-P6P7-P9

ASF1400

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Buy ASF1400
Manufacturer:
Sensirion
Description:
Flow Sensors Sensor device
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