Cleaning Methods
Applicable to following sensors
SFM3x00-AW
Key content▪
Details on performed cleaning tests▪
Cleaning instructions▪
Post cleaning recommendations

Summary
The SFM3x00-AW sensors are designed to withstand cleaning and autoclaving procedures. Sensirion SFM3x00AW sensors show a performance within specifications for up to 30 cycles and more, depending on the cleaningprocedure. Qualifications tests and results are described in this application note.
Cleaning conditions, in particular autoclaving, are harsh. Therefore care should be used at all times andaccording to the handling instructions described in the present document.

1 Introduction
This application note describes the qualification tests applied at Sensirion together with handling instructions forthe cleaning procedure. These instructions should be followed in order to avoid damage to the sensor.
Caution: Never attempt to remove the mesh or to remove dirt behind the mesh using a sharp tip. Any mechanicaldamage of the mesh or the housing may lead to a reduced sensor performance.
Caution: Medical device manufacturers are recommended to self-test their cleaning process on the sensor.
This application note shows for which type of cleaning and autoclave sterilization the sensor may be qualified. Allrecommendations are intended to be used as guidelines.

2 Cleaning Method Details
Various methods for sterilization and disinfection are present in the market. Sensirion tested three procedures
based on autoclaving, CIDEX® and STERRAD respectively. Other procedures are likely to work as well but eachindividual case should be thoroughly tested and verified.
The following table summarizes the statistical results of the cleaning tests performed. Test criteria to determinefunctioning of the sensors after cleaning are leakage rate and accuracy of the flow reading. Sensors pass ifleakage is <0.01 slm at 250 mbar over-pressure and if flow reading is within specification. Note that CIDEX® andSTERRAD cleaning did not produce any failure.
Cleaning Method
Autoclave
CIDEX®
STERRAD

Number of cycles
3010030Failure rate
<5%NoneNone

Sensirion does not guarantee the stability of the flow sensor using arbitrary methods and/or equipment forcleaning/sterilization. Validation of the flow sensor stability for cleaning procedures and/or equipment is the sole
responsibility of the customer. No validation of the cleaning procedure efficacy was performed by Sensirion.
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2.1 Autoclave Test
The sensor stability against autoclaving was tested in a Laboklav 80 MSLV by repeatedly cycling through thefollowing autoclave steps:▪
▪
▪

135 °C and -0.8…+2.15 bar gauge pressure for 5 min
Drying through evacuation for 5 min
Cool down to 50 °C

Testing was done with various batches. The statistics of 100 samples revealed an overall failure rate below 5%.
The figure below shows the exemplary flow-error of 30 units SFM3300-250-AW after autoclaving.

SFM3300-250-AW

Flow Error (%)

10%5%0%-5%-10%-250-150-5050Flow (slm)150250Figure 1. Exemplary flow-error of 30 units SFM3300-250-AW after autoclaving

2.2 CIDEX® Test
The stability of the sensor against cleaning in a liquid solution has been tested by repeatedly cycling the sensors
in CIDEX® activated dialdehyde solution for 10 cycles and an extended immersion, using the following steps:
▪
▪
▪

▪
▪

Complete immersion of clean and dry sensor in CIDEX® for 15 min at ambient temperature (~21 °C)
All cavities were brought in contact with CIDEX®
Sensor was removed and thoroughly rinsed with distilled water. This procedure was repeated twice, for a
total of three rinses. Each rinse was carried out for approx. 5 minutes in duration and a large volume of
fresh distilled water.
Subsequent rinsing in isopropanol to facilitate the drying process.
Sensor was entirely dried before re-connection and re-use.

After these 10 cycles, test measurements were performed for each sensor. The sensors were then re-immersed
for a prolonged period of >25 hours in CIDEX, which is equivalent to 100 cycles of 15 minutes.

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2.3 STERRAD Test
20 Sensirion SFM3300-250-AW sensors were sterilized in a STERRAD 100S machine. 2 samples were used ascontrol samples. Every 5 cycles 3 sensors were removed. A maximum of 30 cycles were tested. Samples weremeasured back before and after STERRAD procedure. For the entire flow range all samples remained within
specifications and no dependency on the number of STERRAD cycles was found. The following figure shows therelative average drift over all 18 samples versus the number of cycles.

Figure 2. Relative average drift over all 18 samples versus the number of cycles© Copyright Sensirion AG, Switzerland

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3 Cleaning Instructions
3.1 Autoclave Sterilization
Step 1: Disconnect all hoses, tubes and electrical connectors before initiating autoclave sterilization.
Step 2: Read and follow the instructions of your autoclave device. Follow all safety precautions.
Caution: As flow sensors are sensitive devices special care should be taken to avoid dirt and residues
from entering the sensor.
Step 3: Ensure to place the sensor in a vertical position during autoclaving in order to avoid water from collecting
inside the sensor housing.
Step 4: After autoclave allow the flow sensor to cool down and dry entirely before continued usage. We
recommend letting the sensor dry in a clean and low-humidity environment. Filtered, oil and contaminant-freepressured air may be used carefully to enhance drying, but may accelerate wear and drift. Drying the sensor in anoven at moderate temperatures (≤50 °C) is possible.
Step 5: Visually inspect the part after autoclaving. Parts which are mechanically damaged (visible cracks,distorted parts or altered colour) must be replaced.
Caution: Allow any liquid to evaporate entirely before re-connecting and using the sensor again.

3.2 CIDEX® Cleaning
Step 1: Disconnect all hoses, tubes and electrical connectors before beginning with liquid agent cleaning.
Step 2: Read and follow the instructions of how to prepare, activate, use and dispose of the CIDEX® solution.
Follow all safety precautions.
Caution: As flow sensors are sensitive devices special care should be taken to avoid dirt and residues
from entering the sensor.
Step 3: Entirely submerge clean and dry sensor in CIDEX® solution. Gently move the sensor within the cleaning
agent to allow solution to enter all cavities. Soak sensor in CIDEX for 15 min at ambient temperature (~21 °C).
Step 4: Remove sensor from bath and take care to pour excess cleaning agent from sensor housing. Thoroughly
rinse with distilled (!) water. Repeat this procedure twice, for a total of three rinses. Each rinse should be carriedout for a minimum of one minute in duration, and a large volume of fresh (!) distilled (!) water. Subsequently rinse
in isopropanol alcohol in order to facilitate the drying process.
Step 5: Let the sensor dry in a clean and low-humidity environment. Filtered, oil and contaminant-free pressured
air may be used carefully to enhance drying speed, but may accelerate wear and drift. Drying the sensor in anoven at moderate temperatures (≤50 °C) is possible.
Step 6: Visually inspect the part after cleaning process. Parts which are mechanically damaged (visible cracks,distorted parts or altered colour) must be replaced.
Caution: Allow any liquid to evaporate entirely before re-connecting and using the sensor again.
Note: Please refer to the CIDEX® solution instructions for more details on how to prepare, activate, use anddispose of the CIDEX® solution.

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3.3 STERRAD Cleaning
Carefully follow the handling instructions of your STERRAD device and consider post cleaning test procedures
outlined in this application note after each STERRAD cycle and before each use.

3.4 Other methods of sterilization
Other methods of sterilization have not been evaluated by Sensirion. If you are interested in evaluating othermethods or substances, please contact Sensirion.

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4 Post Autoclave/Cleaning Recommendation
For each flow sensor Sensirion gives a recommended range of autoclaving and cleaning cycles which typically
can be performed with the sensor remaining within the specifications. Since the autoclave procedure is harsh andleads to accelerated aging of the sensor it is possible that a single sensor over- or underachieves the typicalnumber of cycles. Residues from the cleaning processes may affect the accuracy of the sensor. Therefore,
Sensirion recommends different post cleaning / pre-use tests to ensure correct operation:
a)

b)
c)

Offset test with zero flow and sensor in horizontal position. Recommended:▪ SFM3200-AW offset < 0.1 slm▪ SFM3300-AW offset < 0.2 slm▪ SFM3400-AW offset < 0.05 slm
Measure a defined flow point with references to other sensors or critical regimes.
Leakage test1: According to requirements within customer’s application.

The highest certainty of detection is reached by performing all three tests. However, it is possible to combine any
two or select only one of above tests if a lower certainty is acceptable. The recommendations given are only aguide and should be adapted by the medical device manufacturer according to the use case.

5 Considerations for integrating flow sensors into medical devices
The autoclave and cleaning procedures described above should be used as a guideline for cleaning anddisinfection of the sensors as these are verified procedures. Nonetheless it is recommended to carry out own
tests to ensure the cleaning procedures and equipment is suitable for using with the flow sensors. Our
recommended post cleaning test procedures can help to perform own tests. All other handling instructions andrecommendations in the datasheets should be followed as well.
For more details, please contact Sensirion.

1 If leak tightness is critical in customer application, it remains customer’s sole responsibility to leak-test the sensor before usage. It issolely the customer’s responsibility to ensure that the sensor does not create a critical situation for a patient or user.

© Copyright Sensirion AG, Switzerland

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6 Revision history
DateAug 2015
Aug 2015
Mar 2017
July 2017
Jan 2021

AuthorDATDATSAWSAW
MaKom

Version Changes
1.0
Released
1.1
Corrected errors
2.0
Added STERRAD results, overall update of the application note
2.1
Made application note compatible with SFM3400-AW
2.2
New format

7 Headquarters and Subsidiaries
SENSIRION AG
Laubisruetistr. 50
CH-8712 Staefa ZH
Switzerlandphone: +41 44 306 40 00
fax:+41 44 306 40 30
info@sensirion.com
www.sensirion.com

Sensirion Korea Co. Ltd.
phone: +82 31 337 7700 3
info@sensirion.co.kr
www.sensirion.co.kr
Sensirion China Co. Ltd.
phone: +86 755 8252 1501
info@sensirion.com.cn
www.sensirion.com.cn

Sensirion Inc., USA
phone: +1 805 409 4900
info_us@sensirion.com
www.sensirion.com

Sensirion AG (Germany)
phone: +41 44 927 11 66
info@sensirion.com
www.sensirion.com

Sensirion Japan Co. Ltd.
phone: +81 3 3444 4940
info@sensirion.co.jp
www.sensirion.co.jp© Copyright Sensirion AG, Switzerland

To find your local representative, please visit
www.sensirion.com/contact

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