You can enquire about your SCHMIDT^® flow sensor directly with SCHMIDT Technology or one of our partners. You will find the contact details on our website under the ‘Contact’ section → ‘Contact Sensors’, where they are categorised under ‘Germany’, ‘Europe’, ‘Asia/Pacific/Africa’ and ‘America’.

You are also welcome to send your enquiry to this address: sensors@schmidttechnology.de

SCHMIDT^® Sensors has been working with a large number of national representatives for many years. We aim to establish only one representative per country where possible. If you are interested in representing us in a country where there is currently no representative, please send your detailed application to: sensors@schmidttechnology.de

You can enquire about your SCHMIDT^® flow sensor directly with SCHMIDT Technology or one of our partners. You will find the contact details on our website under the ‘Contact’ section → ‘Contact Sensors’, where they are categorised under ‘Germany’, ‘Europe’, ‘Asia/Pacific/Africa’ and ‘America’.

You are also welcome to send your enquiry to this address: sensors@schmidttechnology.de

In general, to process your enquiry or order, we require your full contact details, the desired sensor configuration and quantity.

Typical configuration features are (depending on the model):

• Sensor length
• Remote electronics
• Measuring ranges (w_N and T_M)
• Accuracy
• Measurement direction
• Output signal (analogue output, pulse output, communication module)
• Connection options (mechanical and cable-side)
• Coating
• Gas correction
• ATEX
• O₂ application
• Operating pressure
• Operating temperature
• Customised programming

To process your enquiry and select the correct sensor, we require details of the process parameters and your specific measurement requirements. The more information you can provide, the more successful the final sensor selection will be. Key parameters include:

• Medium to be measured
• Temperature range of the medium (and behaviour: constant, variable, sudden changes)
• Cleanliness of the medium
• Humidity of the medium
• Pressurised or atmospheric application
• Installation parameters at the measuring point (space constraints, pipe, duct, measuring section, inlet and outlet sections, conditions upstream and downstream of the measuring point, material of the installation site, spatial restrictions)
• Expected flow velocity (or standard volume flow)
• Required measurement accuracy
• Factory calibration certificate or accredited calibration or certificate of compliance (2.1) only
• Environmental conditions (temperature, humidity, ambient conditions)
• ATEX
• Protective coating
• Cable length
• Output signals (analogue, digital, communication bus, which parameters)
• Flow direction detection

Please feel free to contact us to define the sensor: sensors@schmidttechnology.de

Die Konfigurationsmöglichkeiten jedes Sensors sind im jeweiligen Datenblatt und auf unserer Website beim Produkt zu finden. Zum Produkt gelangen Sie entweder über die Kopfleiste der Website unter „Nach Produkten suchen 🔍“ oder über die Rubrik „Produkte“ → „Strömungssensoren“ → … (bei Verwendung der Produktsuche achten Sie bitte auf die korrekte Schreibweise mit Trennpunkt, beispielsweise „20.500“).

Im unteren Bereich im Reiter „Bestellinformationen“ werden alle Konfigurationsmöglichkeiten aufgelistet. Die einzelnen Konfigurationsmerkmale mit vorangestellter Artikel-Nr. ergeben die gesamte Bestellnummer für den Sensor.

Über den Reiter „Downloads“ gelangen Sie zur Produktbroschüre. In dieser finden Sie die Bestellinformationen in der Regel auf den hinteren beiden Seiten.

Flow sensors from SCHMIDT Technology are generally not kept in stock and are manufactured to order according to your configuration requirements. The standard delivery time for small quantities is 5–10 working days after the order has been confirmed. For urgent deliveries or larger orders, please contact us at: sensors@schmidttechnology.de

If you are abroad, please contact the relevant SCHMIDT^® Sensors representative for your region. You can find the contact details on our website under the ‘Contact’ section → ‘Contact Sensors’, where they are categorised under ‘Germany’, ‘Europe’, ‘Asia/Pacific/Africa’ and ‘America’.

Volume flow refers to the volume of a flowing gas. In contrast, mass flow also takes into account the density of the flowing medium. In this case, therefore, the gas volume is measured independently of pressure and temperature.

The true velocity w_R indicates the actual velocity of the air – that is, how fast the individual air molecules are moving. The standard air velocity w_N, by contrast, takes into account the mass of the air flowing past, as the density of the medium changes with variations in temperature and pressure, and this directly influences the mass flow. By measuring w_R it’s not possible to detect a change in mass flow, caused by a pressure change for example_. Thermal anemometers such as the SCHMIDT^® flow sensors generally measure the standard flow velocity w_N, whilst vane anemometers, for example, generally measure the true air velocity w_R.

The formula for converting true air velocity to standard air velocity is:

w_N = w_R / ( (p_N / p_R) * (T_R / T_N) )

p_N: Standard barometric air pressure (1,013 hPa) [Standard]
p_R: Current local barometric air pressure (measured or average value)
T_N: Standard temperature (293 K) [Standard]
T_R: Current operating temperature (measured or fixed value)
w_N: Standard air velocity (measured value from the SCHMIDT^® flow sensor) [Standard]
w_R: Actual flow velocity (velocity of the air molecule)

The formula for converting standard air velocity to true air velocity is:

w_R = (p_N / T_N) * (T_R / p_R) * w_N

p_N: Standard barometric air pressure (1,013 hPa) [Standard]
p_R: Current local barometric air pressure (measured or average value)
T_N: Standard temperature (293 K) [Standard]
T_R: Current operating temperature (measured or fixed value)
w_N: Standard air velocity (measured value from the SCHMIDT^® flow sensor) [Standard]
w_R: True air velocity (velocity of the air molecule)

In most applications, it is necessary to transport a defined volume of air per unit of time in order to ensure the process runs safely. To achieve this, it is necessary to take into account possible changes in, for example, pressure or medium temperature, as these have a direct influence on the actual volume of air being transported. When an area needs to be kept clean or hazardous vapours need to be safely extracted, it is not the actual velocity of an air molecule that matters, but the air mass available to capture the unwanted components and safely discharge them. The same applies to cooling air and the transport of heat. Therefore, in most applications, w_N is the correct / relevant measurement parameter and not w_R.

SCHMIDT Technology uses the following sensor head technologies for flow sensors: dumbbell head, chamber head, thermopile sensor head and double-pin sensor head. In addition, there are other technologies such as mpm or a cylindrical measuring head (similar to the dumbbell head principle).

The dumbbell-head sensor is based on the principle of a thermal anemometer. The sensor head consists of a medium temperature sensor installed in the probe tube and a heater located between the two dumbbell discs. The heater is maintained at a constant temperature above the measured medium temperature. Air flowing past the heater extracts heat from it, so that the heater must adjust and heat up. The energy required for this is an indicator of the flow velocity.

Due to its thermal mass, the dumbbell-head sensor is slightly slower to respond than other sensor-head technologies, but is otherwise robust and reliable. It is also easy to clean and does not need to be aligned with the direction of flow (360° radial flow coverage, ±45° angle).

Examples: SS 20.200, SS 20.225, SS 20.250, SS 20.500, SS 20.515

The chamber head sensor is based on the principle of a thermal anemometer. The sensor head consists of a glass-passivated sensor element housed in a small plastic or ceramic casing (chamber). The sensor element in the chamber head is protected by two deflector wires. A medium temperature sensor and a heater are located on the sensor element. The heater is maintained at a constant temperature above the measured medium temperature. Air flowing past the heater extracts heat from it, so that the heater must adjust and heat up. The energy required for this is an indicator of the flow velocity.

The chamber head is highly responsive due to the combined and spatially close arrangement of the temperature sensor and heater on a single element, and can cover a measuring range from 0.2 m/s up to 220 m/s. Thanks to the glass passivation, the sensor is highly robust against external influences.

Examples: SS 20.260, SS 20.261, SS 20.600, SS 20.651

The thermopile sensor head is based on the principle of a thermal anemometer. The sensor head contains a heated semiconductor chip in one of the two half-shells within the measuring chamber. On the semiconductor element there is a heater (in the centre) and two temperature sensors (to the left and right of it). A heat bell is generated above the heater, which is moved by the flow. The two temperature sensors measure the medium temperature. The flow velocity is then determined from the resulting measurement differences. By detecting the warmer area, the sensor also recognises the flow direction, thus enabling bi-directional flow measurement (particularly for flow measurement between cleanrooms). Thanks to its very slim design and the technology used, the sensor reacts extremely quickly and detects changes within 0.01 seconds. This, in turn, requires a clean environment (filtered air).

Examples: SS 20.400, SS 23.400 ATEX 3, SS 20.415, SS 20.415 Twin, SS 20.420

The double-pin sensor is based on the principle of a thermal anemometer. The sensor head consists of a medium temperature sensor and a heater, which are installed separately in two adjacent stainless-steel tubes. The heater is maintained at a constant temperature above the measured medium temperature. Air flowing past the heater extracts heat from it, so that the heater must adjust and heat up. The energy required for this is an indicator of the flow velocity.

Due to its thermal mass, the double-pin sensor is slightly slower to respond than other sensor head technologies, but is otherwise robust and reliable. It also features a sealed stainless-steel surface with very high resistance to aggressive and abrasive components in the measurement medium.

Examples: SS 20.700, SS 23.700 Ex, SS 20.715 

The mpm sensor is based on the principle of a thermal anemometer. The main body of the IL 30.0xx MPM InLine flow sensor contains three measuring tips. Two heaters are positioned on each of the two measuring tips on the left and right. The medium temperature sensor is located on the short measuring tip in the upper part of the assembly.

The four heaters are maintained at a constant temperature above the measured medium temperature. Air flowing past the heaters extracts heat from them, causing them to adjust and heat up. The energy required for this is an indicator of the flow velocity. An intelligent algorithm generates a linear output signal from the four individual signals. Even under the poorest installation conditions, mpm technology delivers a measurement result within the data sheet tolerances with a run-in distance of just 3 x D_i (pipe internal diameter), whereas a conventional single-point measurement exhibits deviations of up to ±30 %.

In clean applications, a bi-directional SS 20.400 thermopile sensor can be used to detect the flow direction.

For flow direction detection in industrial environments (non-clean / unfiltered air), two sensors with chamber head technology and an MD 10.015 display unit can be used. The two chamber-head sensors are installed at a distance of 10 x D_i (pipe internal diameter) in the centre of the pipe (the first sensor in the direction of flow, the second sensor against the direction of flow!). Both sensors are then connected to the MD 10.015 display unit, which is operated in bi-directional mode.

To ensure that the signal line between the SCHMIDT^® flow sensor and the monitoring system is in good working order, it should also be calibrated regularly. The SCHMIDT^® measuring section calibrators MK 40.415 consist of three calibrators with type-specific, fixed and precise reference currents of 8 mA, 12 mA and 16 mA. These are connected in sequence in place of the flow sensor that would otherwise be connected to the cable and supply the defined reference current directly. This allows a 3-point calibration of the measuring section to be carried out quickly and easily. The measuring section calibrators can be calibrated at SCHMIDT Technology.

A dumbbell-head sensor from SCHMIDT Technology is used when the sensor is to be mounted in any orientation, when a low lower measurement range limit of 0.06 m/s is required, for temperature ranges from -40 °C to +85 °C, where temperature fluctuations are low, and in pipes with a diameter of at least 100 mm. For use in aggressive media, where a protective coating is required and the measuring range does not exceed 50 m/s.

Examples: SS 20.200, SS 20.225, SS 20.250, SS 20.500, SS 20.515

A chamber head sensor from SCHMIDT Technology is used when operating pressures of up to 40 barg are present, a shallow insertion depth is required (from pipe diameter ≥ 25 mm), wide measurement ranges from 0.2 to 220 m/s are required, bi-directional measurement in an industrial environment is to be implemented, temperature ranges from -40 °C to +350 °C are to be covered, or communication modules are required.

Examples: SS 20.260, SS 20.261, SS 20.600, SS 20.651

Flow sensors with thermopile heads are exclusively suitable for cleanroom applications requiring extremely fast response times, bi-directional measurement with reliable direction detection and high-precision measurement results. Furthermore, when GMP-compliant design and cleanroom-specific mounting aids are required, and as a replacement or supplement for overpressure measurement from cleanroom to cleanroom (overpressure cascade) and for laminar flow monitoring and control.

Examples: SS 20.400, SS 23.400 ATEX 3, SS 20.415, SS 20.415 Twin, SS 20.420

A SCHMIDT^® flow sensor with a double-pin sensor head is used when particularly harsh conditions prevail in heavy-duty applications, aggressive media need to be measured, or the medium contains abrasive components.

When operating pressures of up to 16 barg are present, a shallow insertion depth is required (from pipe diameter ≥ 40 mm), wide measurement ranges from 0.1 to 220 m/s are required and temperature ranges from -20 °C to +120 °C need to be covered, or communication modules are required.

Examples: SS 20.700, SS 23.700 Ex, SS 20.715

SCHMIDT^® InLine flow sensors with mpm technology are primarily used in compressed air applications, where they also cope with highly restrictive installation conditions in connection pipes ranging from DN25 to DN50. They cover a temperature range of -20 °C to +60 °C and an air flow rate of 0.5 standard m³/h to 712 standard m³/h.

SCHMIDT^® Mass Flow Sensors Mini-IL are used in compressed air applications to measure standard mass flow directly at the point of use at operating pressures up to 8 barg and temperatures from -20 °C to +60 °C. The measuring range covers 0.2 standard l/min up to 500 standard l/min. For system connection, connection pipes or push-in fittings for pneumatic hose connections for DN8 and DN12 are available.

There is no one-size-fits-all answer to this question. Selecting the right sensor depends on the process parameters and the actual requirements of the measurement. Key parameters include:

• Medium to be measured
• Temperature range of the medium (and its behaviour: constant, variable, sudden changes)
• Cleanliness of the medium
• Humidity of the medium
• Pressurised or atmospheric application
• Installation parameters at the measuring point (space constraints, pipe, duct, measuring section, inlet and outlet sections, conditions upstream and downstream of the measuring point, material of the installation site, spatial restrictions)
• Expected flow velocity (or standard volume flow)
• Required measurement accuracy
• Factory calibration certificate or accredited calibration or certificate of compliance (EN 10204-2.1) only
• Environmental conditions (temperature, humidity, ambient conditions)
• ATEX
• Protective coating
• Cable length
• Output signals (analogue, digital, communication bus, which parameters)
• Flow direction detection

To define the sensor, please contact us: sensors@schmidttechnology.de

SCHMIDT Technology offers an online flow calculator on its website to help determine the required flow measurement range. You can find this in the ‘Service & Support’ section under the heading ‘Service & Support for Sensors’.

Two flow calculators are available:

• Volume flow → Flow velocity (based on standard volume flow, mass flow or operating volume flow in m³/h, m³/min, m³/sec, l/min, l/sec, CFM, kg/h or kg/min, with result in standard flow velocity w_N in m/s)
• Flow velocity → Volume flow (based on standard flow velocity w_N in m/s with result as standard volume or mass flow in m³/h, m³/min, m³/sec, l/min, l/sec, CFM, kg/h or kg/min)

Different gases and pipe / duct profiles can be selected. The calculation directly takes into account the relevant profile factor and any obstructions caused by the sensor.

If you calculate a flow velocity (m/s) from the volume flow (e.g. m³/h) without taking a profile factor into account, you will obtain a value that is too low (incorrect). This calculation assumes that the gas flows cylindrically through the pipe. In reality, however, it takes on a trapezoidal or parabolic shape, which is taken into account and corrected by the profile factor.

If the flow measurement range is exceeded, the sensor will not be damaged. A higher flow rate is still output linearly up to 110 % (11 V or 21.6 mA); beyond this, the signal remains constant.

SCHMIDT Technology offers an online flow calculator on its website for determining the standard volume or mass flow rate from the standard flow velocity. You can find this in the ‘Service & Support’ section under the heading ‘Service & Support for Sensors’.

Two flow calculators are available:

• Volume flow à Flow velocity (based on standard volume, mass or operating volume flow in m³/h, m³/min, m³/sec, l/min, l/sec, CFM, kg/h or kg/min, with result in standard flow velocity w_N in m/s)
• Flow velocity à Volume flow (based on standard flow velocity w_N in m/s, with results given as standard volume or mass flow in m³/h, m³/min, m³/sec, l/min, l/sec, CFM, kg/h or kg/min)

Different gases and pipe / duct profiles can be selected. The calculation directly takes into account the relevant profile factor and any obstructions caused by the sensor.

Due to the technology involved, thermal anemometers experience natural convection and associated thermal crosstalk at zero flow. This crosstalk is interpreted by the sensor as flow. The higher the operating pressure, the stronger these effects become.

By specifying the typical operating pressure of the application, this effect can be fully compensated for. It is therefore necessary to specify the exact pressure present during normal operation in order to achieve a stable zero point and accurate readings in the lower flow range. If the exact operating pressure cannot be determined, a slightly higher pressure should be specified to ensure a stable zero value. If the operating pressure has decimal places, round up to the next higher value.

The majority of the effect is already eliminated at flow velocities > 1 m/s; at > 2 m/s, the effects are no longer present.

For pure oxygen applications with O₂ > 21 %, the SCHMIDT^® flow sensors SS 20.600 and SS 20.700 can be used with the ‘grease-free’ configuration option. For the SS 20.600, the application is limited to a maximum pressure of 20 barg, and for both sensor models to a maximum temperature of +60 °C. It should be noted that the sensor’s temperature range extends up to +120 °C and that at +60 °C only approximately 57 % of the output signal is generated.

The two SCHMIDT^® flow sensors, SS 20.700 and SS 23.700 Ex, can be used in applications where ‘paint-wetting impairment substances‘ must be avoided, when the ‘PWIS conform’ order option is selected.

The required sensor length depends on the installation situation. In a pipe- or duct-mounted application, the centre of the pipe or duct is the preferred measuring point. Therefore, the sensor length should be selected as half the diameter of the pipe or duct plus the mounting. For pipe-mounted installation with a welding socket and through-bolt joint connection, approx. 70 mm must be allowed for the mounting accessories.

Example: Pipe diameter 200 mm → ½ D = 100 mm + 70 mm ‘through-bolt joint mounting’ = minimum 170 mm probe length.

For high-temperature applications and when using the ATEX sensors  SS 23.400 ATEX 3, SS 20.500 Ex, SS 20.600 Ex and SS 23.700 Ex, an additional probe clearance length of at least 50 mm must be taken into account. This results in the following for the above example: 170 mm + 50 mm = minimum probe length of 220 mm.

The easiest way to get answers to your technical questions is to send us an email to sensors@schmidttechnology.de . You will normally receive a response to your enquiry on the same day.

You can also reach us by telephone on +49 7724 899-170.

Our website lists additional contacts and points of contact both in Germany and abroad.

Flow sensors from SCHMIDT Technology can be repaired. However, as most potential repair issues may affect the sensor’s measurement capability and accuracy, subsequent re-adjustment and calibration of the sensor are necessary. Therefore, no spare parts are available for self-repair, and repairs can only be carried out by SCHMIDT Technology. Please contact us in advance: sensors@schmidttechnology.de

Most potential repair issues can affect the sensor’s measurement capability and accuracy. Consequently, the sensor must be readjusted and recalibrated afterwards. Spare parts for self-repair are not available, and repairs can only be carried out by SCHMIDT Technology. Please contact us in advance: sensors@schmidttechnology.de

To return flow sensors for repair or calibration, you will need

• an RMA number
• a completed and signed decontamination declaration
• and, for returns from a non-EU country, additional instructions regarding customs declaration.

Please ensure to contact us before returning the goods: sensors@schmidttechnology.de

The decontamination declaration required for sensor returns is always included in paper form with every new sensor. In addition, a digital version is available as an online fillable PDF document on our website under the heading ‘Service & Support for Sensors’ à ‘Product downloads’ à ’Service return and decontamination declaration of flow sensors’.

For most sensors, the serial number is printed on a label on the electronics housing (beginning with SN). For sensors without an electronics housing and with a permanently attached cable, the serial number is printed on a cable label near the cable outlet. Cleanroom sensors have the serial number laser-marked.

Certain features (soft keys) can be changed retrospectively. These include, for example, the measuring range, accuracy, gas correction, switching threshold and customer-specific programming (depending on the model). To change the configuration, the flow sensor must be returned to us. Please contact us in advance: sensors@schmidttechnology.de

SCHMIDT^® flow sensors can be calibrated. Please contact us in advance: sensors@schmidttechnology.de

SCHMIDT^® flow sensors can be calibrated in any calibration laboratory with suitable wind tunnels. For sensors for pressurised applications, attention must be paid to the calibration method and wind tunnel used (we recommend calibration on a pressurised wind tunnel).

Recalibration or adjustment of the sensor in the event of detected deviations (e.g. due to contamination of the sensor element) is only possible at SCHMIDT Technology in St. Georgen. Please contact us in advance: sensors@schmidttechnology.de

A calibrated wind tunnel is required to calibrate a flow sensor. As this cannot be provided on-site at the customer’s premises, on-site calibration is not possible. Only reference measurements and verifications can be carried out on-site at the customer’s premises. For on-site verification, SCHMIDT Technology offers the SS 20.450 Verification Probe.

A calibration carried out in the unaltered state upon receipt of the calibration item is referred to as an ‘as found’ calibration or ‘incoming calibration’. A calibration carried out following an adjustment is referred to as an ‘as left’ calibration or ‘outgoing calibration’

SCHMIDT Technology can calibrate and adjust the measuring section calibrators. Please contact us in advance: sensors@schmidttechnology.de

SCHMIDT^® flow sensors can be adjusted if required (re-adjustment; sometimes referred to as ‘re-calibration’). This procedure can only be carried out by SCHMIDT Technology. Please contact us in advance: sensors@schmidttechnology.de

Adjustment is the process of setting the sensor to a specific measurement range with the required measurement accuracy (e.g. ‘0 … 10 m/s with accuracy class 1 %’).

Calibration is simply the measurement of the sensor’s accuracy at defined measurement points (verification).

Both adjustment and calibration require a high-quality and suitably accurate wind tunnel. On-site at the customer’s premises, only verification, validation or reference measurement is possible.

Adjustment is also referred to as alignment

Due to the measuring principle, sensors from SCHMIDT Technology are maintenance-free and contain no moving parts and do not drift. Unless otherwise specified by the customer, we recommend repeating the calibration every 12 months. The sensor must be sent to SCHMIDT Technology for this purpose. Please contact us in advance: sensors@schmidttechnology.de

Calibration certificates do not, by definition, have an ‘expiry date’. The calibration certificate shows the actual and target values at the time of calibration. It is up to the user to decide when a calibration certificate needs to be renewed. As a rule, the typical duration is one year.

The SCHMIDT^® calibration laboratory is accredited by DAkkS in accordance with DIN EN ISO/IEC 17025.

SCHMIDT Technology offers factory calibrations as well as accredited calibrations (accredited to DIN EN ISO/IEC 17025). High-precision wind tunnels are used to carry out the calibrations, which are regularly calibrated using a Laser Doppler Anemometer (LDA). The LDA itself is in turn regularly calibrated by PBT, an accredited body. In this way, SCHMIDT Technology consistently ensures the highest precision and repeatability of its calibrations and adjustments. Detailed information on our calibration services can be found on our website under the heading ‘Service & Support for Sensors’ → ‘SCHMIDT^® Sensor Adjustments and Sensor Calibrations’.

Factory calibrations are offered for all SCHMIDT^® flow sensors (with the exception of the HVAC 100).

SCHMIDT Technology offers accredited calibrations for the following sensors:

• All thermopile head sensors (except: Duplex / Twin sensors)
• All dumbbell-head sensors (except: flow switch SS 20.200)
• Chamber-head sensors: SS 20.260 and SS 20.651
• Double-pin head sensor: SS 20.715 LED

A 2.1 certificate of compliance essentially confirms that the sensor has been tested and, upon delivery, operates within the tolerances specified in the data sheet. It is issued after each adjustment procedure (alignment; compliance with specifications; in accordance with DIN EN 10204).

A factory calibration certificate specifies the individual calibration points with the respective deviation from the target value and lists the references and standards used for calibration.

A DAkkS-accredited calibration certificate can only be issued by a DAkkS-accredited calibration laboratory such as that of SCHMIDT Technology. The DAkkS-accredited calibrations are carried out in compliance with guideline RL-ST-220 (Accredited calibration procedure for thermal anemometers). A laser Doppler anemometer (LDA) is used for the calibration itself – currently the most accurate standard available for measuring gas flow.

A factory calibration certificate lists the individual calibration points with their respective deviations from the target value, and lists the references and standards used for calibration.
In everyday language, a factory calibration is often referred to as an “ISO calibration”. This can lead to misunderstandings in the context of accredited calibration in accordance with DIN EN ISO/IEC 17025. It is recommended to use the terms “factory calibration” and “accredited calibration”.

A DAkkS-accredited calibration certificate can only be issued by a calibration laboratory accredited to DIN EN ISO/IEC 17025, such as that of SCHMIDT Technology. The DAkkS-accredited calibrations are carried out in compliance with guideline RL-ST-220 (Accredited calibration procedure for thermal anemometers). A Laser Doppler Anemometer (LDA) is used for the calibration itself – currently the most accurate standard available for measuring gas flow.

In the case of factory calibration, the calibration points are fixed by the manufacturer and cannot be freely defined. In the case of accredited calibration, either predefined SCHMIDT^® standard calibration points or your own calibration points can be specified.

In a factory calibration, the tolerance limits are fixed by the sensor configuration and cannot be freely defined. In an accredited calibration, either the predefined sensor tolerance limits or your own tolerance limits can be set.

SCHMIDT^® Measuring Section Calibrators MK 40.415 are used to calibrate the measuring section (signal line) between the flow sensor and the plant control system (PLC / monitoring).

Flow sensors from SCHMIDT Technology are generally available in two accuracy classes: “Standard accuracy” and “High precision”. Depending on the sensor model, the two classes differ further in terms of the percentage accuracy class (3 % and 1 %, or 5 % and 3 %).

When ‘Standard adjustment with correction’ is selected, the flow sensor is adjusted and calibrated to an accuracy class of 3 % in air and then provided with a gas-specific correction. The gas-specific correction was determined in detail through metrological measurements during an extensive measurement campaign in the respective real gas.

Flow sensors from SCHMIDT Technology are generally available in two accuracy classes (‘standard accuracy’, ‘high precision’). Depending on the sensor model, they differ in their accuracy, expressed as a percentage (3 % / 1 % or 5 % / 3 %). In addition to the difference in percentage accuracy, sensors with high-precision adjustment are adjusted and calibrated at more points than sensors with standard accuracy. The adjustment is therefore more precise and has a finer resolution.

As a rule, when defining the accuracy class, a percentage value is first specified (±1 %, ±3 %, ±5 %). This percentage value refers to the current measured value. The percentage value is followed by an additional error margin relating to the flow sensor’s measuring range, known as the ‘full-scale error’ (fmr error = error in respect to full measuring range). The ‘full-scale error’ can (depending on the measuring range) be a further percentage of the measuring range or a fixed value in m/s. Adding both error margins together gives the possible total error of the sensor at the respective measuring point.

No, with regard to the flow measurement of thermal anemometers, the gases nitrogen, oxygen and ozone behave like air and no gas correction factor needs to be applied.

The closer one gets to the zero point, the greater the influence of zero-point errors from the electronics and sensors on the result. A consistent specification of ±1 % of the measured value is physically impossible to achieve – even though some competitors include such specifications in their technical data.

Reproducibility refers to the deviation when the measured value is obtained repeatedly under the same conditions. In many applications, reproducibility is far more important than actual absolute accuracy.

Thermal flow sensors measure the heat dissipation generated by the gas flowing past them. As different gases have different heat capacities and therefore generate varying amounts of heat dissipation, this must be taken into account during measurement. Ideally, the manufacturer will have incorporated a gas correction into the sensor, so that the sensor’s output signal already corresponds directly to the actual gas value. If a sensor calibrated to air by default is used with a different gas, the measured value must subsequently be processed using a correction factor.

If you require a gas-specific correction factor for your flow measurement, please contact us. We are also able to calculate correction factors for special gas mixtures. Your contact at SCHMIDT^® Sensors: sensors@schmidttechnology.de

Ozone (O₃) is highly corrosive and can destroy the sensor. Under certain circumstances, use in ozone is possible. Please contact us in advance: sensors@schmidttechnology.de

No, with regard to the flow measurement of thermal anemometers, the gases nitrogen, oxygen and ozone behave like air and no gas correction factor needs to be applied.

Raw biogas is very humid and, in combination with certain gases such as H₂S, highly corrosive. The use of flow sensors in raw gas is only recommended to a limited extent. However, following dehumidification / treatment, the double-pin sensor head is very well suited to this application (Note: Only for pipes larger than DN 40). Furthermore, the mixture may be flammable. For biogas, the ATEX option SS 23.700 Ex is generally recommended. The accuracy of the sensor also depends heavily on the gas composition. Please contact us in advance: sensors@schmidttechnology.de

It is not possible to tamper with the calibrated measuring range of the SCHMIDT® flow sensor. This ensures that the adjusted and calibrated state is maintained upon leaving the factory. Should the flow sensor exhibit a deviation, it can be calibrated and, if necessary, re-adjusted at SCHMIDT Technology.

To ensure the best possible measurement results, SCHMIDT^® flow sensors are adjusted and calibrated to the flow measurement range specified by the customer. The user is not intended to alter the calibrated measurement range at a later stage, in order to maintain the sensor’s accuracy over the long term.

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A certificate of compliance 2.1 essentially confirms that the sensor has been tested and, upon delivery, operates within the tolerances specified in its data sheet. It is issued after each adjustment procedure (alignment; compliance with specifications; in accordance with DIN EN 10204).

At SCHMIDT Technology, adjustment and calibration procedures refer to standard conditions of 20 °C and 1,013.25 hPa.

When cleaning SCHMIDT^® cleanroom sensors, ensure that you use cleaning agents that dry without leaving any residue (isopropanol, deionised water, etc.). Avoid leaving cleaning agent residues on the sensor element, as these can form deposits that may lead to measurement deviations.

It is recommended, where possible, to cover the sensor head with the protective cap or, at the very least, to disconnect the flow sensor from the power supply before cleaning begins until it has dried completely. Drying the small thermopile sensor head measuring chamber can be aided and accelerated by carefully blowing it out with gentle bursts of compressed air (strong bursts of air must be avoided at all costs to prevent damage to the sensor element).

Never shake or tap a wet thermopile sensor, as this may damage the sensor element.

Do not clean the device whilst it is connected to the mains, as this may cause residues to burn onto the sensor element.

• Disconnect the sensor from the power supply.
• The sensor tube can be wiped with a damp, lint-free cloth (use a cleaner that dries without leaving any residue or isopropanol).
• Take care to wipe in the correct direction (from the sensor head towards the electrical connection) and avoid allowing cleaning fluid to enter or be pressed into the sensor head.
• To clean the sensor head, use a glass of deionised water (DI water) or isopropanol and swish the sensor head around in it for a few minutes.
• Then support the drying process of the small thermopile sensor head measuring chamber by gently blowing it out with soft bursts of compressed air (it is essential to avoid strong bursts of air to prevent damage to the sensor element).
• Never shake or tap a wet thermopile sensor, as this may damage the sensor element.

If this does not work, the sensor can be professionally cleaned by trained SCHMIDT^® specialists.

Mechanical cleaning of the sensor head by the user is expressly not recommended.

• Disconnect the sensor from the power supply.
• The sensor tube and sensor head can be wiped with a damp, lint-free cloth (use a cleaner that dries without leaving a residue or isopropanol).
• Do not apply any lateral force when cleaning the dumbbell head, as this may cause the dumbbell head to break off.

• Disconnect the sensor from the power supply.
• The sensor tube and sensor head can be wiped with a damp, lint-free cloth (use a cleaner that dries without leaving a residue or isopropanol).
• When cleaning the double-pin sensor head, do not apply any lateral force, as this may cause the thin tubes to break.

• Disconnect the sensor from the power supply.
• The sensor tube can be wiped with a damp, lint-free cloth.
• To clean the sensor head, use a glass of deionised water (DI water) or isopropanol and swirl the sensor head in it for a few minutes (not suitable for SS 20.651 with ceramic sensor head).
• Then assist in drying the sensor head measuring chamber by gently blowing it out with soft bursts of compressed air.
• If this does not work, the sensor can be carefully cleaned mechanically. To do this, use narrow strips of a microfibre cleaning cloth or a clean pipe cleaner and moisten them with a little isopropanol. Insert the damp cleaning strip into the sensor head and carefully move it back and forth through the sensor head with light pressure.

• Disconnect the sensor from the power supply.
• The sensor tube and sensor head can be wiped with a damp, lint-free cloth (use a cleaner that dries without leaving a residue or isopropanol).

• Disconnect the sensor from the power supply.
• Carefully blow out the removed sensor with gentle bursts of compressed air.
• Do not clean the internal measuring probes mechanically or with moisture.

SCHMIDT^® flow sensors cover a very wide measurement range. This ranges from a lower detection limit of 0.05 m/s to a maximum flow rate of 220 m/s. The individual measurement range options depend on the sensor model and the sensor technology used.

The temperature measurement range is from -40 °C to +350 °C (depending on the model).

Operation outside the specified limits can damage the sensor and is therefore regarded as a critical error. The error behaviour when the temperature measurement range is exceeded is sensor-specific and is described in the relevant operating instructions.

In practice, the moisture content of the medium plays hardly any role in flow measurement with SCHMIDT® sensors. It only becomes a factor at extreme values. Therefore, if increased air humidity is to be expected, particularly in combination with an elevated medium temperature (e.g. 55 % RH at 80 °C), this may lead to increased deviations.

In flow sensors, the temperature is regulated to an over-temperature (e.g. 40 K). If the medium temperature suddenly changes by 20–30 K, there is a time delay in the flow sensor’s re-adjustment. During this re-adjustment period, the flow measurement values are outside the tolerance.
The temperature response is expressed in K/min. A value of 8 K/min, for example, means that changes of less than 8 K/min have no effect on the flow measurement.

The permissible operating temperatures for each sensor can be found in the data sheets and operating instructions and generally range from -20 °C to +70 °C. However, there are also sensors with permissible operating temperatures of -10 °C or 0 °C to +60 °C. A sufficiently long cooling section (insulation length) must be provided to prevent the high / low medium temperature from affecting the sensor electronics.

The relative humidity of the medium must not exceed 95 X% RH, and the moisture must not condense and settle on the measuring element.

In practice, the moisture content of the medium plays hardly any role in flow measurement with SCHMIDT® sensors. It only becomes a factor at extreme values. Therefore, if increased air humidity is to be expected, particularly in combination with an elevated medium temperature (e.g. 55 % RH at 80 °C), this may lead to increased deviations.

Flow sensors with a thermopile sensor head have the fastest response time, at 0.01 seconds. Flow sensors with chamber head technology have a response time of 1 second, dumbbell head sensors 3 seconds, and flow sensors with a double-pin sensor head 10 seconds. The technical capabilities depend heavily on the thermal mass of the sensor head design.

Depending on the sensor model, SCHMIDT^® flow sensors can be used in positive pressure up to a maximum of 40 barg. The available pressure ratings are 6 barg, 10 barg, 16 barg and 40 barg.

As long as there is a measurable flow in negative pressure, this can be measured depending on the sensor model. The limit for this is a negative pressure of up to 300 mbar, depending on the situation.

The available output signals depend on the sensor model. The following are available:

• Analogue output (4–20 mA; 0–10 V; Auto U/I)
• Pulse output (frequency output)
• ModBus
• Profibus
• DeviceNet
• Ethernet
• M-Bus
• I/O-Link
• SCHMIDT^® digital interface
• Bluetooth^® technology

Yes, the analogue outputs of SCHMIDT^® flow sensors are distributed linearly across the selected measuring range, whereby the start of the measuring range (0 m/s) corresponds to 4 mA or 0 V and the end of the measuring range corresponds to 20 mA or 10 V (could differ with bi-directional measurement option).

The same applies to the medium temperature output (e.g. -20 °C = 4 mA or 0 V; +120 °C = 20 mA or 10 V).

The main materials (in contact with the medium) used in SCHMIDT Technology flow sensors are stainless steel, epoxy resins, plastics and glass. Anodised aluminium and plastics are used for the electronics housings, which do not come into contact with the medium.

Flow sensors from SCHMIDT Technology are largely made of stainless steel and other highly resistant materials and are therefore already resistant to many media. Optionally, the sensors can be coated with either polyurethane (PU, black) or Parylene (clear), making them resistant to various aggressive media. The coating options depend on the model.

Protective coatings can be useful if chemically aggressive components are present in the gas being measured, to protect the sensor head from long-term damage. Despite intensive and extensive testing, a coating is not a panacea and its use must be assessed on a case-by-case basis. Please contact our technical advisors at sensors@schmidttechnology.de for further information.

Protective coatings are used for media containing chemically aggressive components. If stainless steels in particular are at risk of corrosion, the sensor benefits from the order option ‘Parylene fully coated’.

No, the Parylene coating on the SCHMIDT® flow sensor is not visible and can only be detected by means of resistance measurement.

Thermal flow sensors output the standard flow velocity in w_N as the measurement result and detect the heat dissipation generated by the flow at the sensor element. If more molecules pass the sensor element due to an increase in pressure, the heat dissipation increases accordingly. Therefore, pressure compensation is not required.

If the temperature or pressure of the medium changes, this also alters the density and thus the standard flow velocity w_N. For example, if the medium pressure increases from 1 bar gauge to 2 bar gauge, the volume of air transported per unit of time also doubles (assuming the actual velocity w_R remains constant). A vane anemometer, on the other hand, measures the actual flow velocity w_R and cannot detect an increase in pressure. To determine the correct volume in this case, knowledge of the pressure parameter is important, whereas this is not the case for w_N.

• The heat transfer inherent in chamber head technology causes natural convection in a vertical downstream application, resulting in thermal crosstalk, depending on the operating pressure.
• This thermal crosstalk manifests as ‘suspicious’ flow at very low flow rates and disappears as the flow velocity increases. At zero flow, this also results in a slightly excessive medium temperature.
• The effect is limited to low flow velocities < 2 m/s.
• To ensure reliable measurement of zero flow, vertical installation with downward flow must be avoided.

Note: For cleanroom applications, this can be compensated for by vertical adjustment.

Flow sensors from SCHMIDT Technology are generally designed for indoor use. Due to their protection ratings (≥ IP 65), sensors with large electronic housings may be operated outdoors at the user’s own risk. In such cases, the sensor must at least be protected from direct exposure to the elements, such as rainfall and sunlight, and care must be taken to ensure compliance with the operating parameters.

Yes, all products in the SCHMIDT^® sensor range are silicone-free.

The decision, as to whether an ATEX zone classification applies, rests solely with the operator. SCHMIDT Technology generally recommends using an ATEX sensor for flammable gases.

Depending on the model, ATEX zone 2 (gas) and ATEX zone 22 (dust) are covered.

SCHMIDT Technology flow sensors generally cover CE and UKCA approvals. Some sensor models are also ATEX-compliant and cover the following ATEX certifications:

SS 23.400 ATEX 3:

• Gases (zone 2): II 3G Ex ec IIC T4 Gc

SS 20.500 Ex, SS 20.600 Ex, SS 23.700 Ex:

• Gases (zone 2): II 3G Ex ec ic IIC T4 Gc
• Dusts (zone 22): II 3D Ex tc ic IIIC T135°C Dc

For ATEX applications in clean areas, we recommend the SS 23.400 ATEX 3 with ATEX certification for zone 2 (gases).

For applications in industrial environments, we recommend using the ATEX sensors SS 20.500 Ex, SS 20.600 Ex or SS 23.700 Ex. All three sensors are approved for ATEX zones 2 (gas) and 22 (dust). For heavy-duty applications involving aggressive or abrasive media, the SS 23.700 Ex is the preferred choice. In applications where there is a risk of contamination of the sensor head, the SS 20.500 Ex and SS 23.700 Ex sensors are ideal. For fast response times in industrial ATEX applications, the SS 20.600 Ex is recommended. SCHMIDT Technology will be happy to advise you on selecting the right sensor for your ATEX application. Please get in touch: sensors@schmidttechnology.de

Ja, die Baumusterprüfbescheinigungen sind beim jeweiligen Sensor im Download-Bereich abgelegt. Geben Sie dazu auf der Website oben im Feld „Nach Produkten suchen 🔍“ die Produktbezeichnung ein (bitte auf die korrekte Schreibweise mit Trennpunkt achten, z. B. „20.500“) und scrollen Sie nach unten. Im Reiter „Download“ stehen Baumusterprüfbescheinigungen und weitere Dokumente sowie 3D-Daten zum kostenfreien Download zur Verfügung.

• When operating the SS 23.400 ATEX 3, strict adherence to the product specifications must be ensured (e.g. operating temperatures, medium temperatures, approved media, electrical connection, earthing, etc.).
• To maintain ATEX approval in ATEX zones, the sensor must be operated exclusively with an original connection cable from SCHMIDT Technology (part of the approval test).
• During installation, a minimum clearance length of 50 mm must be ensured and taken into account when configuring the probe length (part of the approval test).

• When operating the SS 20.500 Ex, strict adherence to the product specifications must be ensured (e.g. operating temperatures, medium temperatures, approved media, electrical connection, earthing, etc.).
• A suitable cable must be used for the electrical connection in accordance with the operating instructions. SCHMIDT Technology offers these cables as accessories, but other cables that meet the specifications may also be used.
• The enclosed impact protection sleeve is mandatory for maintaining ATEX approval and must be installed correctly (part of the approval test).
• During installation, ensure a minimum clearance length of 50 mm and take this into account when configuring the probe length (part of the approval test).

• When operating the SS 20.600 Ex, strict adherence to the product specifications must be ensured (e.g. operating temperatures, medium temperatures, approved media, electrical connection, earthing, etc.).
• A suitable cable must be used for the electrical connection in accordance with the operating instructions. SCHMIDT Technology offers these cables as accessories, but other cables that meet the specifications may also be used.
• The enclosed impact protection sleeve is mandatory for maintaining ATEX approval and must be installed correctly (part of the approval test).
• Communication modules are not available for the ATEX version of the sensor.
• During installation, ensure a minimum clearance length of 50 mm and take this into account when configuring the probe length (part of the approval test).

• When operating the SS 23.700 Ex, strict adherence to the product specifications must be ensured (e.g. operating temperatures, medium temperatures, approved media, electrical connection, earthing, etc.).
• A suitable cable must be used for the electrical connection in accordance with the operating instructions. SCHMIDT Technology offers these cables as accessories, but other cables that meet the specifications may also be used.
• The enclosed impact protection sleeve is mandatory for maintaining ATEX approval and must be installed correctly (part of the approval test).
• During installation, ensure a minimum clearance length of 50 mm and take this into account when configuring the probe length (part of the approval test).

SCHMIDT® ATEX flow sensors require no additional equipment beyond the supplied accessories for safe, approved operation. The specifications for the connection cable as set out in the operating instructions must be observed.

Flow sensors from SCHMIDT Technology are very easy to install. The extensive range of accessories includes a wide variety of through-bolt joints, welded sockets, mounting flanges and cleanroom mounting accessories for ceiling or wall mounting.

It is not possible to answer this question, as it is unclear what effects this will have inside the pipework. In the event of unfavourable installation conditions, it may be advisable to switch to a SCHMIDT^® InLine flow sensor with mpm technology.

Due to the technology involved, thermal anemometers generate natural convection. The laminar flow must work against the resulting upward flow, and only once the convection has been overcome can the flow be detected by the sensor. For laminar flow applications, this effect can be compensated for by adjustment in the vertical wind tunnel (otherwise deviation of -10 % to -20 %).
This effect is limited to ‘energy-intensive’ sensors – thermopile technology is not significantly affected by it.

• In the context of energy efficiency in cleanrooms, the focus is on the generation of ultra-clean air.
• Particularly during downtime or periods of reduced activity, air consumption should be reduced to a minimum without incurring an increased risk.
• Differential pressure technology reaches its limits here (possible error ±100 % at 0.3 Pa).
• There is a direct correlation between differential pressure and flow velocity (15 Pa ≙ 5 m/s; 5 Pa ≙7 m/s; 1 Pa ≙ 1.2 m/s; 0.1 Pa ≙ 0.5 m/s).
• The SCHMIDT^® SS 20.400 flow sensor allows for a significantly lower flow velocity (possible error at 0.3 Pa between ±8 % and ±15 % depending on the measuring range, compared to ±100 % for the differential pressure sensor)
• Furthermore, the bi-directional measurement ensures reliable detection of unwanted backflow from 0.05 m/s.

For further information, please contact us: sensors@schmidttechnology.de

The cleanroom sensors SS 20.400, SS 23.400 ATEX 3, SS 20.415, SS 20.415 Twin, SS 20.420, SS 20.450, SS 20.515 and SS 20.715 are all suitable for cleanroom use and can therefore be sterilised with H₂O₂. Where possible, it is recommended to protect the sensor heads with the protective cap supplied.

SCHMIDT Technology offers a utility model rights protected SS 20.415 Twin duplex laminar flow sensor. This allows laminar flow in the cleanroom to be double-checked – even where space is limited. The SS 20.415 Twin enables two redundant laminar flow sensors to be operated at a single measuring point.

The wire safety bar or protection bracket is used to protect the dumbbell sensor head when it is located in an area subject to frequent handling (glove access, staff, etc.) and there is a risk that the dumbbell sensor head could be knocked and damaged. The wire protection bracket is not suitable for other sensors and is not required.

The SCHMIDT^® LED measured value display is available in 4 versions. A model MD 10.010 and a model MD 10.015, each in two versions with 24 V DC and 85 to 230 V AC. The model MD 10.010 has only one connection option for an analogue input, one analogue output and one relay output. The MD 10.015 model offers two analogue inputs, two analogue outputs and two relay outputs.

The SCHMIDT^® MD 10.020 measurement display module is designed for use with the SCHMIDT^® module interface (e.g.
IL 30.0xx MPM, SS 20.700 or, with an interface splitter, with SS 20.400, SS 20.715, IL 30.20x Mini-IL).

The SCHMIDT^® Bluetooth^® module BT 10.010 is designed for use with the SCHMIDT^® module interface (e.g. IL 30.0xx MPM, SS 20.700 or, with an interface splitter, with SS 20.400, SS 20.715, IL 30.20x Mini-IL). The free SCHMIDT^® Sensors app is also required for operation (download from the App Store).

Passendes Zubehör zu jedem Sensor ist im jeweiligen Datenblatt und auf unserer Website beim Produkt zu finden. Zum Produkt gelangen Sie entweder über die Kopfleiste der Website unter „Nach Produkten suchen 🔍“ oder über die Rubrik „Produkte“ → „Strömungssensoren“ → … (bei Verwendung der Produktsuche achten Sie bitte auf die korrekte Schreibweise mit Trennpunkt, beispielsweise „20.500“).

Im unteren Bereich im Reiter „Zubehör“ werden alle Zubehörteile aufgelistet. Über den Reiter „Downloads“ gelangen Sie zur Produktbroschüre. In dieser finden Sie das Zubehör in der Regel auf den hinteren beiden Seiten.