Datasheet SFM3304-xxx-D
Digital Disposable Mass Flow Meter

Product Summary
Sensirion’s SFM3304-xxx-D is a digital flow meter with particularly small dead space designed for medical applications.
It measures the flow of air and other non-aggressive gases up to 250 slm. The SFM3304-xxx-D is a single-use disposable
sensor, with medical cones for pneumatic connection to standard breathing circuits and an easy-to-use and reliable electricalconnector. The sensor element, signal processing and digital calibration are on a single microchip assuring very fast signal
processing time, best-in-class accuracy and superior robustness to rough handling and adverse conditions.
Based on the SFM3300-250-D, the SFM3304-xxx-D offers similar specifications and additional features due to a newer chip
generation including tunable response time, noise level and sampling rate. The SFM3304-xxx-D is offered in customized
individual packaging, ready for use.
Key characteristics at a glance

Benefits of Sensirion’s CMOSens® Technology▪

Flow range from -250 to 250 slm▪

High reliability and long-term stability▪
▪

I2C interface

▪
▪

▪
▪

Low pressure drop across the sensor
No recalibration neededBest signal-to-noise ratio
Industry-proven technology with a track record ofseveral decades▪

Individual and customized packaging▪
▪

Designed for mass production
High process capability▪

Scalability

Very small dead space

Content
1.

Ordering Information ................................................................ 2

2.

Specifications ........................................................................... 2

3.

Measurement Mode ................................................................. 6

4.

Digital Interface Description ..................................................... 8

5.

Product Dimensions ................................................................. 15

6.

Packaging ................................................................................ 15

7.

Instructions for use ................................................................... 16

8.

Revision History ....................................................................... 16

9.

Important Notices ..................................................................... 17

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1. Ordering Information
The part name and order number are customer specific because the sensor is delivered in an individual package with acustomized label (see Section 6). Please contact your Sensirion representative for more information.
Part name

Description

Order number

SFM3304-xxx-D-250 to 250 slm range, disposable sensor, with integrated heater

TBD

Minimal order quantity is 500 sensors (one box).

2. Specifications
Flow Sensor Specifications1
Parameter
Measurement range

Accuracy 5

Noise Level 5, 7, 10
Span shift due to temperature
variation
Flow step response time (τ63) 9

Conditions

SFM3304-xxx-D

Units-250 to 250

slm 2

Air
Typ. 3

Max.4| flow | < 100 slm±3±5% m.v. 6| flow | > 100 slm

±7

±10

% m.v. 6

offset

±0.1

±0.2

slm2

Typ. 8Max.4| flow | < 25 slm

0.5

2.5

% m.v. 6| flow | > 25 slm

1.5

5% m.v. 6

offset

0.03

0.2

slm 2

0.5

% m.v. per 10°C

default settings 10

3

Resolution (16 bit)Pressure Drop 11

ms
0.01

slm

60 slm

100 / 0.40

230 / 0.93

Pa / inH2O

100 slm

280 / 1.13

550 / 2.21

Pa / inH2O

200 slm

1150 / 4.62

1900 / 7.63

Pa / inH2O

Media compatibility

Air, N2, O2, non-agressive gases, non-condensing

1 Unless otherwise noted, all sensor specifications are valid at T = 25°C with VDD = 3.3 V, absolute pressure = 966 hPa and horizontal flow direction.
2 Mass flow measured in slm: liters per minute at standard conditions (T = 20°C and p = 1013.25 hPa)
3 “Typ”: a CpK of 0.67 is targeted (95% of sensors within the Typ limit)
4 “Max”: no sensor measured outside of these limits will be shipped and a CpK of 1.33 is targeted
5 Total value is the sum of offset and span value
6 % m.v. = % measured value = % of reading
7 Noise Level is defined as standard deviation of individual sensor readings, measured at default settings.
8 “Typ.”: average value
9 The response time can be tuned by adjusting the chip low pass filter, see Section 3.1.
10 Default settings are: flow signal filter set to a response time of 3ms (see Section 3.1), fixed N averaging set to N=2 (see Section 3.2.2).
11 Measured with air in calibration conditions, as described in footnote 1.

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Temperature Sensor Specifications1
Parameter

Value

Measurement range-20 °C to +85 °C

Resolution

16 bitAccuracy±2 °C for -10 < T < 50 °C±3 °C otherwise

Electrical Specifications
Parameter

SymbolSupply Voltage

VDD

Power-up level

VPOR_HPower-down level

VPOR_L

Min.

Typ.

Max

Units

working voltage

3.15

3.3

3.45

V

absolute min andmax ratings

-0.3

5.5

V

1.7

V

1.0

Max Voltage on pins (SDA,
SCL)
Supply current

Condition

absolute min andmax ratings
IDD

V

-0.3

V

6.5

8.6

mA

idle state

0.045

0.6

mA

1.2

uA

sleep mode
51

External heater power
rating

ESD test

VDD+0.3

measuring

External heater resistanceComments

RC parameters:
330 Ohm and 150 pF

Ω
0.5

W

8

kV

Only apply sufficient
power to avoid
condensation or icing.
See section 7.3
Discharge voltage
applied on individual
connector pins while
the device is not
grounded.

1 The measured temperature is the temperature of the bulk silicon in the sensor. This temperature value is not only depending on the gas temperature, butalso on the sensor’s surroundings and self-heating.

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Timing Specifications
Parameter

Symbol

Min.

Typ.

Max.

Power-up time

tPU

Soft reset time

tSR

2

ms

Warm-up time

tw

50

ms

I2C SCL frequency

fI2C

400

1000

kHz

Internal flow sampling rate

fS

4000

4400

Hz

2

3600

Default output rate of the flow
value

fS /2

Internal temperaturesampling rate

fS /26

Units

Comments

ms

Time to sensor readyTime between soft reset commandor exit sleep mode and sensor
ready
To reach accuracy spec after firstmeasurement command

Hz

Adjustable, see Section 3.2.2

Hz

Temperature value is updated every
13 flow values with the default
averaging configuration for the flow
output rate

Conditions of use
Parameter
Calibrated temperature
range
Operating temperature
range1
Extended operating range
Storage temperature
Operating pressure range
Operating overpressure
Rated burst overpressure

Min.

Typ.

Max.

Units

Condition / Comment

+10

+50

°C

dry gas

+5

+50

°C

10-95% rel. hum. (non cond.)

-20
-40
540

+5
70
1140
100
300

°C
°C
hPa
hPa
hPa

0.75

N.m

recommended to use on-sensor heater
10-95% rel. hum. (non cond.), for <48habsolute pressure of gas inside of sensor
gauge
gauge
torsion applied between opposing
pneumatic connectors
based on tests on SFM3300-D

Allowable torsion
Shelf life

3

year

Materials
Parameter
Wetted materials

Si, Si3N4, SiOx, Gold, Epoxy, MABS, silicone

REACH, RoHS

REACH and RoHS compliant

1 For Air and N2. Long term exposure to (high concentrations of) O2 at high temperatures can reduce the product lifetimewww.sensirion.com D1

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Pin Assignment
The pin assignments of the SFM3304-xxx-D can be found in Table 1. The mechanical interface of the SFM3304-xxx-D’s
electrical connector is the same as for the SFM3300-D/AW and SFM3400-D/AW. Please visit sensirion.com for an evaluation
kit cable compatible with our proximal sensor family: SFM3304-D, SFM3300-D/AW and SFM3400-D/AW (available in 2024).

Name
HEATER_GND

Description
Ground for the heater

VDD

VDD Supply

SCL

Serial Clock (I2C Interface)

GND

Connect to ground

SDA

Bidirectional Serial Data (I2C Interface)

HEATER

Supply voltage to the heater

Arrow indicating the positive flow direction

Table 1: SFM3304-xxx-D pin assignment and flow directionwww.sensirion.com D1

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3. Measurement Mode
After the sensor receives a “start continuous measurement” command (for more details see Section 4.3.1) it enters thecorresponding measurement mode and continuously performs a measurement with the update rate of the flow output (seeSection 2.4). A single reading consists of three measurement values: flow, temperature, and one value for a status word (formore details on status word see Section 4.3.2).

Flow Signal Filter
The response time and the noise level of the flow signal are both affected by the internal signal processing of the SFM3304. A
central element in this signal processing is a third order low pass filter with a default setting to achieve a τ63 step responsetime of 3 ms.
However, for some applications it might be preferred to have either a faster signal response (at the cost of higher noise level),or oppositely a lower noise level (at the cost of slower signal response).
With the SFM3304 it is possible to reconfigure the low pass filter setting by sending a “start continuous measurement”
command with an additional command argument (see Section 4.2.2). The custom low pass filter setting then stays active foras long as the continuous measurement mode stays active.
The command argument afilter (unsigned 16-bit integer value) defines the low pass filter setting by:
Response Time: τ63

Command argument: afilter

1 ms

33601

3 ms

50961 (default)

5 ms

56105

10 ms

60527

Table 2: Arguments for the command "start continuous measurement" tuning the response time of the flow output.

Figure 1: Model of the flow signal output for a step change of flow with different settings of the low pass filter. Remark: thetime unit 4000/fs approximately corresponds to seconds.

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Averaging of Flow Value
Two modes for on-sensor averaging of the flow signal are available:
1) Average-until-read: in this mode, the sensor averages all measured values prior to read out.
2) Fixed-N averaging: in this mode, every reading is the average of a fixed number (N) of measured flow values. Thisaveraging mode is the default mode selected upon startup and after a reset, with N=2.
Average-Until-Read
If the ‘average till read’ option is chosen, the sensor averages all values xi since the previous read out. This has the benefit
that the user can read out the sensor at his own desired speed, without losing information and thus preventing aliasing.
During the first 𝑡𝐴𝑈𝑅_𝑚𝑎𝑥 = 128/𝑓𝑠 of averaging (typical 𝑡𝐴𝑈𝑅_𝑚𝑎𝑥 = 32 ms), the averaged value is obtained as thearithmetic mean:𝑀𝑥̅ = ∑
𝑖=1

𝑥𝑖
𝑀

for 𝑡 < 𝑡𝐴𝑈𝑅_𝑚𝑎𝑥

If the period between readouts is longer than 𝑡𝐴𝑈𝑅_𝑚𝑎𝑥 , the sensor will continue to average, but using a different algorithm. In
this algorithm, exponential smoothing is used with a smoothing factor 𝛼 = 0.02:
𝑆𝑘 = 𝛼 ∙ 𝑥𝑘 + (1 − 𝛼) ∙ 𝑆𝑘−1,

𝑆0 = 𝑥̅,for 𝑡 > 𝑡𝐴𝑈𝑅_𝑚𝑎𝑥

Where S0 is the arithmetic mean value after the first 𝑡𝐴𝑈𝑅_𝑚𝑎𝑥 and the readout value for flow is Sk.
With an exponential smoothing factor of 𝛼 = 0.02, the value read out by the user is an average value of about the last𝑡𝐴𝑈𝑅_𝑚𝑎𝑥 . In order not to lose information, it is recommended to read out the sensor at least once every 𝑡𝐴𝑈𝑅_𝑚𝑎𝑥 . Pleaserefer to the relevant literature for more information about exponential smoothing.
Average-until-read can be selected by the user by setting N=0 in the argument for the “Configuration of Averaging” command(for more details see Section 4.3.4).
Fixed-N Averaging
Averaging may also be set to a fixed number 1N128 of measurements to be averaged (c.f. Section 4.3.4). This type of
averaging is especially suited to avoid any averaging (N=1). If fixed-N averaging is chosen, the update time for new readings
is 𝑁 × 1/𝑓𝑆 accordingly. Averaging has the benefit that the user can read out the sensor at his own desired speed, without
losing information and thus preventing aliasing. In this case, the averaged value 𝑥̅ is the arithmetic mean of the individual
measurements xi:

If no averaging is desired, set N to 1. The default mode selected upon startup and after a reset is this fixed-N averaging with
N=2.

Sensor Start-Up and Warm-Up Behavior
The typical time for system power-up (until the sensor responds to communication requests) is 2 ms. The typical time from asoft reset until the sensor responds to communication requests is also 2 ms.
After reset or start-up of the sensor, the sensor’s internal heater is off and is automatically turned on by performing a Start
Continuous Measurement command (see Section 4.3.1). The very first measurement after Start Continuous Measurement isready after approximately 4 ms.

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Due to the thermal measurement principle, a total warm-up time of typically 50 ms1 is necessary for an accurate
measurement. This includes the 4 ms needed for measurement initialization.

Sensor Check at Start-Up
The gas flow sensor checks the integrity of its entire memory content at start-up automatically using a CRC check sum. In
case the CRC check fails, the I2C-interface is deactivated.
The following command provides a further possibility for an integrity check: Read Product Identifier (command code 0xE102,
see Section 4.3.8). Ideally suited to test if the sensor is connected correctly.

4. Digital Interface Description
The sensor’s digital interface is compatible with the I2C protocol. This chapter describes the available command set. For
detailed information about the I2C protocol, please consult the document "NXP I2C-bus specification and user manual" (I2Cbus specification and user manual (nxp.com)).
The physical interface consists of two bus lines: a data line (SDA) and a clock line (SCL) which need to be connected via pullup resistors to the bus voltage of the system.

I2C Address
The I2C address for the SFM3304-xxx-D is:
Product Version

I2C address (hex)

I2C address (binary)

SFM3304-xxx-D

0x2E

0b010’1110

Table 3: I2C addresses of the SFM3304-xxx-D
In the I2C protocol, a read or write bit follows the I2C address.

I2C Sequences
An I2C sequence typically consists of a command sent by the master to the slave (the sensor) and a subsequent readout ofdata by the master from the slave. It depends on the specific command if an argument to the command is needed and if data
can be read out from the slave following the command. I2C read sequences can be aborted with a NACK and STOP
condition. The following sections provide I2C sequences for the specific tasks. Dark areas with white text indicate that thesensor controls the SDA (Data) line:
Write Command without Argument
The commands have a length of 16 bits:
I2C master sends the write header and writes a 16-bit command:

Figure 2: I2C sequences to send a command without an argument to the sensor.

1 Warm-up time under default settings.

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Write Command with Argument
Commands have a length of 16 bits and are followed by a 16-bit argument plus an 8-bit checksum:
I2C master sends the write header and writes a 16-bit command, followed by a 16-bit argument plus a CRC byte:

Figure 3: I2C sequences to send a command with an argument to the sensor.
Read data from the Slave
After that, data is read from the sensor in multiples of 16-bit words, each followed by an 8-bit checksum to ensurecommunication reliability. I2C sequences can be aborted with a NACK and STOP condition as indicated below.
I2C master sends the read header and receives multiple 16-bit words followed by a CRC byte:

Figure 4: I2C sequences to read results from the sensor. Dark areas with white text indicate that the sensor controls the SDA(Data) line

I2C Commands
The command set consists of a set of various commands, which are described in the following sections:
•
•
•
•
•
•
•

Start Continuous Measurement
Stop Continuous Measurement
Configuration of Averaging
Read Scale Factor, Offset, and Flow Unit
Soft ResetEntering and Exiting Sleep Mode
Read Product Identifier

Start Continuous Measurement and Read Results
The sensor measures both flow and temperature and provides in a third data buffer a status word. All three measurement
results can be read out through one single I2C read header when the continuous measurement is running.
The command code for starting the continuous measurement is 0x3603. If sent without an argument (see Figure 2) the
measurement starts in default mode. For custom filter settings the command can be sent with an argument (see Figure 3),
where the argument configures the flow signal filter as described in section 3.1.
Command code (Hex)Gas

Command argument

Response Time

0x3603

Gas 0: Air

NA (call without argument)

3 ms

0x3603

Gas 0: Air

Flow signal filter setting (call withargument)

According to Sec. 3.1

Table 4: I2C commands to start continuous measurement

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After the command has been sent, the chip continuously measures and updates the measurement results. New results (flow,
temperature, and status word) can be read continuously with a single I2C read header for each measurement.
Further commands must not be sent until the stop measurement command has been sent. Consult section 4.3.3 formore details.
After the start measurement command is sent:-

the first measurement result will be available after 4 ms
accuracy deviations can occur during the first 50 ms (including the 4 ms)

If an I2C read header (I2C address + read bit) is sent to the sensor when no measurement data is available, the sensor will
respond with a NACK condition. Otherwise, the sensor will respond with the following output:
Preceding command

Consecutive read

Description

Continuous measurement

Byte1: Flow 8msb
Byte2: Flow 8lsb
Byte3: CRC
Byte4: Temp 8msb
Byte5: Temp 8lsb
Byte6: CRC
Byte7: Status Word 8msb
Byte8: Status Word 8lsb
Byte9: CRC

After a start continuous measurement command, themeasurement results can be read out.
The temperature and the consecutive bytes do not need tobe read out (every time). The read sequence can be aborted
by a NACK and a STOP condition.

Table 5: Consecutive reads after I²C command to start continuous measurement (see Section 4.2.3). The flow andtemperature values are 16bit signed integers. For conversion into physical units refer to Section 4.5.

Status Word
The status word is returned along with every flow and temperature measurement. It contains an identifier representing themeasurement command that is currently running, information on the currently selected averaging mode and the filter setting
configuration. The table below lists the values returned by the status word.
Measurement
Mode
Command
Code ofrunningmeasurement
command

Status Word (bits 15:0)
Bits <15:12>:
identifier for thecurrently
runningmeasurement
command

Bit <11>: status ofexponential
smoothing

0: Exponential
smoothing is
not active
0x36030b0000

1: Averaging mode
has switched toexponential
smoothing

Bit <10>: averaging
mode

Bit <9>: command argument
reception

0: Average-UntilRead is active

0: No command argument
received; default filter settings
applied

1: Fixed-N
averaging is active

1: command argument has
been received; signal filter isconfigured accordingly

Bits <8:0>:
configured number of
averages

Configured numberof averages. (0 for
average until readmode)

Table 6: Values returned by the status word.

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Stop Continuous Measurement
CommandCommand code (Hex)Description

Stop continuous
measurement

0x3FF9This command stops the continuous measurement and puts thesensor in idle mode. After it receives the stop command, the sensor
needs up to 0.5ms to power down the heater, enter idle mode andbe receptive for a new command.

Table 7: I²C command to stop continuous measurement.
When the sensor is in continuous measurement mode, the sensor must be stopped before it can accept anothercommand. The only exception is the soft reset command (see Section 4.3.6). In idle mode the sensor will consume lesspower but consider the sleep mode for most effective energy saving results.
Configuration of Averaging
Command

Configure averaging

Command code (Hex)0x366A

Command argument

Description

N

This command configures the sensor’s averaging mode:
1) N=0: average-until-read mode (c.f. Section 3.2)
2) 1≤N≤128 (default N=2): fixed-N averaging mode. N is thenumber of internal measurements that are averaged for one
returned measurement value (i.e. the average over N flow
samples, where N = CmdArgument, c.f. Section 3.2).
The configured averaging mode will be used for flow measurements
until a reset or re-execution of this command is performed. After areset, averaging is set to fixed-N averaging mode with N = 2. The
highest averaging number allowed is 128. If a higher number is usedin the command argument, it will be overruled by the maximal valueof 128 samples to average.
If no averaging is desired, set N to 1.

Table 8: I²C command to configure averaging.

Read Scale Factor, Offset, and Flow Unit
This command provides the scale factor and offset to convert flow readings into physical units (see Section 4.5). The scale
factor and offset are specific to the calibrated gas and its corresponding lookup table used for the flow measurement.
Therefore, the gas needs to be specified in the command argument by the command code of the corresponding start
continuous measurement (see Section 4.3.1).
For the SFM3304-xxx-D, the flow unit is a fixed value 0x0148 and corresponds to slm: standard liter per minute at 20°C and1013.25 hPa pressure.
Command

Read Scale Factor, Offset, and Flow Unit

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Command code (Hex)Command argument (Hex)0x3661

Command code of desired gas for scale factor, offset and flow unit
(Section 4.3.1). The command argument needs to be followed by
the correct CRC (Section 4.2). For the SFM3304-xxx-D the only
calibrated gas is air, according to Table 4 the command argument
is 0x3603 with the corresponding CRC 0x3A.

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Preceding command

Consecutive read

Description

Read Scale Factor,
Offset, and Flow Unit

Byte1: Scale factor 8msb
Byte2: Scale factor 8lsb
Byte3: CRC
Byte4: Offset 8msb
Byte5: Offset 8lsb
Byte6: CRC
Byte7: Flow Unit 8msb
Byte8: Flow Unit 8lsb
Byte9: CRC

After a “Read Scale Factor, Offset, and Flow Unit” command, thecorresponding results can be read out. The scale factor and offset
are a 16-bit signed integer number represented by a two’s
complement (ranging from -32’768 to 32’767).
The flow unit is a 16-bit identifier.

Table 9: I2C command to read the scale factor, offset, and flow unit. Result of this command.

Soft ResetCommandI2C address + W bit + Consecutive read Descriptioncommand code (Hex)General call reset

0x0006This sequence resets the sensor with a separate reset block, which is as
much as possible detached from the rest of the system on chip.
Note that the I2C address is 0x00, which is the general call address, andthat the command is 8 bits long. The reset is implemented according to
the I2C specification.

NA

Table 10: Reset command
After the reset command the sensor will typically take 2ms to reset. During this time, the sensor will not acknowledge its
address nor accept commands.
Entering and Exiting Sleep ModeIn sleep mode the sensor uses a minimum amount of power. The mode can only be entered from idle mode, i.e. when thesensor is not performing measurements.
This mode is particularly useful for battery operated devices. To minimize the current in this mode, the complexity of the sleep
mode circuit has been reduced as much as possible, which is mainly reflected by the way the sensor exits the sleep mode. In
sleep mode the sensor cannot be soft reset.
CommandCommand code
(Hex)

Consecutive read

Description

Enter Sleep mode

0x3677NA

The sleep command can be sent after a stop continuous measurement
command has been issued and the sensor is in idle mode.

Exit Sleep mode

0x00

NA

The sensor exits the sleep mode and enters the idle mode when it
receives an I2C write header (i.e. the valid I2C address and a write bit(‘0’)) plus one byte of data (i.e. the command is only 8 bits).
The sensor should wake up within 2ms. Note that the I2C address is not
acknowledged. It is necessary to poll the sensor to see whether thesensor has received the command sequence to exit the sleep mode andhas woken up. Polling with a write header (I2C address and a write bit)can be used to check whether the sensor has woken up.

Table 11: Sleep mode commands

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Read Product Identifier
The product identifier and the serial number can be read out by sending the command below. The command can only be
issued in idle mode, i.e. when the sensor is not performing measurements
CommandCommand code (Hex)

Read productidentifier

0xE102

Consecutive read
Byte1: Product number [31:24]
Byte2: Product number [23:16]
Byte3: CRC
Byte4: Product number [15:8]
Byte5: Product number [7:0]
Byte6: CRC
Byte7: Serial number [63:56]
Byte8: Serial number [55:48]
Byte9: CRC
Byte10: Serial number [47:40]
Byte11: Serial number [39:32]
Byte12: CRC
Byte13: Serial number [31:24]
Byte14: Serial number [23:16]
Byte15: CRC
Byte16: Serial number [15:8]
Byte17: Serial number [7:0]
Byte18: CRC

Description

The command returns:
32-bit unique product and revision number. The
number is listed in Table 13 below.
Note that the last 8 bits are the revision number andare subject to change as long as the datasheet ispreliminary.
64-bit unique serial number in the format of an
unsigned long integer.
The serial number can be converted from binary into decimal,
whereby in decimal it has the following format:
yywwxxxxxx, where: yy: last 2 digits of calibration year, ww:calibration week, xxxxxx: unique 6-digit sequential number
within the calibration week.

Table 12: Read product identifier command

Product

Product number

SFM3304-xxx-D

0x0405010x

Table 13: Product number for SFM3304-xxx-D

Checksum Calculation
The 8-bit CRC checksum transmitted after each data word is generated by a CRC algorithm. Its properties are listed in Table
14. The CRC covers the contents of the two previously transmitted data bytes. To calculate the checksum, only these two
previously transmitted data bytes are used.
Property
Value
Name
CRC-8
Protected dataread data
Width
8 bit
Polynomial
0x31 (x8 + x5 + x4 + 1)
Initialization
0xFF
Reflect input
False
Reflect output
False
Final XOR
0x00
ExampleCRC (0xBEEF) = 0x92
Table 14: Checksum definitionwww.sensirion.com D1

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Number Format and Conversion to Physical Values
The number format of the flow and temperature signals and the conversion to a physical value with a scale factor and an
offset where applicable is explained below:
Scale Factors and Offsets
SFM3304-xxx-D

SignalComment

Scale Factor

Offset120 LSB16 / slm

0 LSB16

Temperature
200 LSB16 / °C
Table 15: Scale factors and offsets

0 LSB16

Gas 0: Air

Can be read out using an I2C-command(c.f. Sec. 4.3.5)

Flow
The digital calibrated gas flow signal read from the sensor is a 16-bit signed integer number represented by a two’s
complement (ranging from -32’768 to 32’767). The integer value can be converted to the physical value by subtracting theoffset and dividing it by the scale factor (gas flow in 𝑠𝑙𝑚 =𝑠𝑒𝑛𝑠𝑜𝑟 𝑜𝑢𝑡𝑝𝑢𝑡−𝑜𝑓𝑓𝑠𝑒𝑡). The scale factor and offset are specific to𝑠𝑐𝑎𝑙𝑒 𝑓𝑎𝑐𝑡𝑜𝑟

every calibrated gas.
The flow unit slm signifies standard liters per minute with reference temperature equal to 20°C and reference pressure equal
to 1013.25 hPa.
Temperature
The digital calibrated temperature signal read from the sensor is a 16-bit signed integer number represented by a two’s
complement (ranging from -32’768 to 32’767). The integer value can be converted to the physical value by subtracting theoffset and dividing it by the scale factor (temperature in ℃ =𝑆𝑒𝑛𝑠𝑜𝑟 𝑂𝑢𝑡𝑝𝑢𝑡−𝑜𝑓𝑓𝑠𝑒𝑡).
𝑆𝑐𝑎𝑙𝑒 𝑓𝑎𝑐𝑡𝑜𝑟

Flow Unit
The flow unit is specific to every calibrated gas and is specified in Section 4.5.1. It can further be read out using an I2Ccommand (Section4.3.5). The flow unit is given by a 16-bit unsigned word, where the information about the unit is encoded in
the first 13 bits as follows:
1. Bits <3:0>: unit prefix (multiplier)
2. Bits <7:4>: time base (e.g. per minute)
3. Bits <12:8>: unit (e.g. standard liter)
The allowed values for the 3 unit constituents are given in the table below:
Bits<12:8>

Signification:
Unit

Bits
<7:4>

Signification:
Time Base

Bits
<3:0>

Signification:
Unit Prefix

overall code (16 bits)

Signification: flow
unit

0b00001=1

standard liter(T0=20°C,
p0=1013.25
hPa)

0b0100=4

per minute

0b1000=8

10-0 = 1

0b 0000 0001 0100
1000
= 0x0148= 328

standard liter per
minute (slm) withreference temperature=20°C and reference
pressure=1013.25 hPa

Table 16: Possible result(s) for the flow unit

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5. Product Dimensions
All dimensions are in millimeters.

Pneumatic connectors of the SFM3304-xxx-D are ISO5356-1:2015 compatible medical cones. Details about this type of
connection can be found in the description of the standard.
Dimension
LengthProximal large pneumatic connector
Proximal small pneumatic connector
Distal large pneumatic connector
Distal small pneumatic connector
Dead space
WeightConditioncone
socketsocket
cone

Value
69.3
22
15
22
15
<10
<20

Unit
mm
mm
mm
mm
mm
ml
g

6. Packaging
Individual Packaging
Each sensor is placed in a blister-type single unit packaging, composed of printable paper (permeable to ethylene oxide) andthermoformed plastic sealed together.
Individual packaging
Physical dimensions

105 x 53 x 30 mm

Printable area

79 x 37 mm

Printable paper (bottom of packaging)

Wipak Gas Paper 60

Thermoformable plastic (top of packaging)

Wipak Fitform 150

Label artwork
The label is defined in collaboration with the customer. Once the label is approved by the customer, the part name and the ordernumber of the SFM3304-xxx-D are also defined in an addendum of the datasheet.

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Higher level of packaging
The individually packaged sensors are shipped in a box containing 500 sensors, which is the minimal order quantity. Optional
service of smaller boxing (10 sensors per box) can be agreed upon, please reach out to your Sensirion contact for further
information.
Shipping box

Number of sensors in a box

100 perforated bands of 5 single packaged sensors = 500 sensors

Box dimensions

59 x 39 x 33 cm

Box weight

9 to 10 kg

7. Instructions for use
Flow direction
Positive flow direction is from the distal to proximal side, so that inspiratory flows are positive and expiratory flows negative. The
flow direction is also indicated by an arrow on the sensor PCB.

Inlet flow conditions
The SFM3304 is sensitive to jetting inlet conditions. To prevent large signal noise and measurement errors do not directly
connect adapters with inner diameter less than 10 mm to the SFM3304. In case small inner diameter cannot be avoided,
inserting a filter or an angle piece between the jet and the SFM3304 will improve the inlet conditions. Early testing of thecustomer specific inlet conditions is recommended.

Heater operation
The sensor has an external heater for cases where the gas flowing through the sensor contains high humidity and is warmer
than the ambient temperature, and therefore than the sensor housing. In such cases, heating the sensor can help to avoid
condensation or icing. Sufficient power should be provided for this purpose, but excessive power must be avoided for two
reasons:
1) to stay within the operating temperature range,2) to maintain the best accuracy.
Reading out the chip temperature can be used as feedback on the current sensor temperature.

8. Revision History
Date

AuthorVersionChanges

10.2023

PSIM

v1.0

first released datasheet

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9. Important Notices
Do not use this product as safety or emergency stop devices or in any other application where failure of the product could resultin 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.
If the Buyer shall purchase or use SENSIRION products for any unintended or unauthorized application, Buyer shall defend, indemnify andhold harmless SENSIRION and its officers, employees, subsidiaries, affiliates and distributors against all claims, costs, damages andexpenses, 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.
ESD Precautions
The inherent design of this component causes it to be sensitive to electrostatic discharge (ESD). To prevent ESD-induced damage and/or
degradation, take customary and statutory ESD precautions when handling this product. See application note “ESD, Latchup and EMC” formore information.
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 thisproduct shall be of the quality, material and workmanship defined in SENSIRION’s published specifications 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:•
notice in writing describing the defects shall be given to SENSIRION within fourteen (14) days after their appearance;•such defects shall be found, to SENSIRION’s reasonable satisfaction, to have arisen from SENSIRION’s faulty design,material, or workmanship;•
the defective product shall be returned to SENSIRION’s factory at the Buyer’s expense; and•the warranty period for any repaired or replaced product shall be limited to the unexpired portion of the original period.
This warranty does not apply 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.
SENSIRION is only liable for defects of this product arising under the conditions of operation provided for in the data sheet and proper useof 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 can and dovary in different applications.
SENSIRION reserves the right, 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.
Copyright © 2022, by SENSIRION. CMOSens® is a trademark of Sensirion. All rights reserved

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