S421 Thermal Mass Flow Sensor for Compressed Air and Gases (Inline-Sensor)

The Inline compressed air flow meter comes with a measuring section in different sizes and fits perfectly in your system.

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Affordable inline sensor to measure compressed air flow

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Fast response time and high precision

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Smartphone app for live readings and easy setup

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Seamless integration into the compressed air and gas system

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Optional flow conditioner, no need for a straight inlet

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No additional temperature and pressure compensation

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Isolated 4... 20 mA & Pulse; Modbus/ RTU; Modbus/ TCP; M-Bus

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In-line type with measuring section DN15 to DN80

The SUTO S421 Inline Thermal Mass Flow Sensor provides reliable compressed air and gas flow and consumption monitoring in main and header lines with a wide measuring range. With the high resolution and sampling rate, a fast and precise measurement is achieved.

Easy Installation and Optional Display

The installation is done through a measuring section with a pre-defined diameter, with R-thread or with flange connections. The flow sensor comes calibrated on the selected measuring section. The optional color display is designed to show all measured values like flow and total consumption on the screen. The display can also be used to manage the sensor settings, like gas types, output signal settings or reference conditions.

Measurement of two gases at the same time

The thermal mass flow sensor can save two calibration curves, this means the sensor can be used in two different gases without any loss of accuracy. This would allow for example compressed air flow to be measured and have the ability to switch to measure Nitrogen by simply changing the gas type via the S4C-FS app or using the sensors display.

Various Sensor Outputs

The S421 Thermal Mass Flow Sensor offers 4 different signal output options. It can have an isolated analog and pulse output to read out the flow and the total consumption. The Modbus/RTU and Modbus/TCP output options offers a state-of-the-art digital interface solution to connect the meter to high level controllers or software solutions. By using M-Bus as an output, the meter can be connected to existing metering networks easily.

Mobile configuration and real-time data

Various settings such as gas type, flow unit and reference standards, can be set ex-factory according to your needs. If settings need to be changed on site, they can be done using the free S4C-FS smart phone application. This enables users to change the settings of the flow sensor wirelessly on site. Flow meter settings are well protected from unwanted access with use of a unique QR access code for each meter.

Should you have any special requests, such as custom flow ranges or different gas types, please contact us here.

Read more

  • Compressed air / gas consumption and flow measurement in main and distribution lines
  • Compressed air allocation costs within distribution network


Accuracy1.5 % of reading ± 0.3 % FS (optional 1 % of reading)
Selectable unitsm3/h, m3/min, l/min, l/s, cfm, kg/h, kg/min, kg/s
Repeatability0.25 % of reading
SensorThermal mass flow sensor
Sampling rate10 samples / sec
Turndown ratio200:1
Response time (t90)0.1 sec
Selectable unitsm3, ft3, l
Reference conditions
Selectable conditions20 °C 1000 mbar (ISO1217),
0 °C 1013 mbar (DIN1343)
freely adjustable


Analog output
Signal4 ... 20 mA (4-wire), isolated
Scaling0 ... max flow, freely adjustable
Loadmax. 250 Ohm
Update rateValue updated ever 1 sec
Pulse output
SignalSwitch output, normally open, max. 30 VDC, 20 mA
Scaling1 pulse per consumption unit (selectable)
ProtocolModbus/RTU, Modbus/TCP
Update rateValue updated ever 1 sec
Voltage supply15 ... 30 VDC
Current consumptionmax. 200 mA


WirelessS4C-FS App for mobile phones
PC SoftwareUSB Service Kit + Software
OthersDisplay with 2 touch buttons
Integrated2.4” color graphic display with 3 touch buttons
Process connectionStainless steel 1.4404 (SUS 316L)
HousingPC + ABS
SensorCeramic, glass coated
Metal partsStainless steel 1.4404 (SUS 316L)
Electrical connection2 x M12 (5 pole); 1 x M12 (8-pole x-coded) for TCP
Protection classIP65
ApprovalsCE, RoHS, FCC
Process connectionS401: G1/2" (ISO 228/1)

S421: 带R型螺纹或法兰的测量部分
WeightS401: 0.9 kg

S421: 0.4公斤(不含测量部分)"。
Operating conditions
MediumAir, N2, O2, CO2 and other gases
Medium qualityISO 8573: 4.4.3 or better
Medium temperature-30 ... +140 °C
Medium humidity< 90 % rH, no condensation
Operating pressuremax. 5.0 MPa (> 1.6 MPa need installation device)
Ambient temperature-30 ... +70 °C, -10 ... +50 °C (with display)
Ambient humidity< 99 % rH
Storage temperature-30 ... +70 °C
Transport temperature-30 ... +70 °C
Pipe sizesS401: ½” ... 12” (bigger pipes on request) S421: ½” ... 3”

Volumetric Flow Ranges

Pipe SpecificationsS401S421
AnschlussgewindeDNDI (mm)S401-S (m3/h)S401-M (m3/h)S401-H (m3/h)Measuring range from to
½”DN15--0.5 ... 90 m3/h
¾”DN20--0.9 ... 170 m3/h
1”DN2527.30.5 ... 147.70.6 ... 294.70.6 ... 356.91.5 ... 290 m3/h
1¼”DN3236.00.9 ... 266.31.2 ... 531.51.2 ... 643.52 ... 500 m3/h
1½”DN4041.91.2 ... 366.71.5 ... 731.91.5 ... 886.23 ... 700 m3/h
2”DN5053.12.0 ... 600.12.5 ... 1197.63.0 ... 1450.04 ... 1000 m3/h
2½”DN6568.93.5 ... 1026.55.0 ... 2048.65.0 ... 2480.46 ... 1500 m3/h
3”DN8080.95.0 ... 1424.47.0 ... 2842.77.0 ... 3441.98 ... 2500 m3/h
4”DN100100.010 ... 2183.312 ... 4357.212.0 ... 5275.7
5”DN125125.013 ... 3419.618 ... 6824.418.0 ... 8263.1
6”DN150150.018 ... 4930.125 ... 9838.925.0 ... 11913.1
8”DN200200.026 ... 8785.633 ... 17533.342.0 ... 21229.5
10”DN250250.040 ... 13743.952 ... 27428.560.0 ... 33210.7
12”DN300300.060 ... 19814.880 ... 39544.1100.0 ... 47880.4


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S401 / S421

Info sheets
S401 / S421
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S401/ S402/ S415/ S418/ S418-V/ S421/ S430/ S450/ S452/ S460 /S461 /S462 – CE & UKCA DECLARATION OF CONFORMITY

S401/ S402/ S415/ S418/ S418-V/ S421/ S430/ S450/ S452/ S460 /S461 /S462 – CE & UKCA DECLARATION OF CONFORMITY
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S4C-FS App Android: V2.0.1

S4C-FS App Android: V2.0.1
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