Volume flow transducer

Volume flow transducers measure air volumes indirectly via the differential pressure and provide a processable output signal for building automation, HVAC systems and industrial air ducting. They are used wherever air flows not only need to be displayed but also reliably recorded for control, monitoring or documentation purposes - for example in ventilation and air conditioning ducts, in clean room and medical technology, in filter systems, spray booths or commercial kitchens. Modern devices often not only cover the volume flow, but also differential pressure, filter monitoring and, in certain applications, even level detection based on pressure measurement.

Guide and useful information on flow transducers

Volume flow transducer for HVAC

Author: S. Becker | Status: 06.03.2026

In a nutshell

A volume flow transducer does not measure the air volume flow directly with an impeller or thermal element, but calculates it from a recorded differential pressure. This is based on the established relationship between pressure difference and volume flow in ventilation and system technology: the volume flow increases with the square root of the differential pressure, supplemented by a k-factor of the respective sensor or flow element. This makes these devices particularly suitable for duct applications, filter monitoring and ventilation systems with a defined measuring section.

For planners, integrators and maintenance engineers, it is particularly important that a suitable volumetric flow transducer not only maps the measuring range, but also matches the installation situation, the desired output signal and the control task. The cleaner the pressure recording, the more stable the signal. The better the measuring range, damping and k-factor are selected, the more resilient the subsequent control or monitoring will be.

Typical fields of application are

Volume flow measurement in supply and exhaust air ducts
Demand-based fan control via 0-10 V or 4-20 mA
Filter monitoring via differential pressure or degree of contamination
Negative and positive pressure monitoring in sensitive rooms
Applications in clean rooms, medicine, laboratories, kitchen exhaust air and industrial ventilation

Content

Why is flow measurement so important in practice? Typical applications in HVAC, clean room and industry Selection guide from practice - Which pressure transmitter is the right one? Installation, pressure acceptance and influence on measurement quality

What is a volume flow transducer?

A volume flow transducer is a field device that generates an electrical standard signal from a pressure difference. In practice, the dynamic Pressure with a static Pressure compared. The measuring transducer calculates the volume flow from this difference and passes it on to the DDC, BMS, PLC or frequency inverter as an analog output signal. Depending on the device version, 0-10 V or 4-20 mA are available, for example; sometimes supplemented by relay contacts and a display.

The main advantage lies in the system integration: instead of just providing a local measured value, the transducer supplies a standardized signal for control, limit value monitoring and trend recording. This is particularly relevant if air volumes are not only to be calibrated once, but also monitored or actively controlled during operation.

Why is volume flow measurement so important in practice?

In ventilation systems, the volume flow is a key control variable. It directly influences how much supply air or extract air is actually conveyed and therefore also comfort, energy efficiency, pressure conditions and process reliability.

This has concrete effects in building automation:

In air conditioning systems, the volume flow rate determines the actual air exchange rate.
It stabilizes defined pressure conditions in clean rooms and laboratory areas.
In filter applications, a change in differential pressure indicates at an early stage when the system status is deteriorating.
For fans and frequency inverters, the output signal serves as a reference variable for demand-based control.

In B2B applications in particular, it is not just the display of a value that counts, but its technical usability. A properly designed volume flow transducer reduces unnecessary readjustments, improves the control dynamics and creates reliable data for operation and maintenance.

Measuring principle: Volume flow from differential pressure

Many volume flow transmitters work on the basis of a piezoresistive measuring element for differential pressure measurement. This measuring principle is tried and tested in air measurement technology and enables a compact design with good accuracy and high reliability. In the device examples shown here, the volume flow is calculated using the relationship V = k - √Δp. The k factor is adapted to the respective flow element or manufacturer reference.

In practice, this means

The differential pressure is the measured primary variable.
The volume flow is the calculated variable derived from this.
Without a suitable k-factor, the volume flow rate display cannot be loaded.
A clean recording of dynamic and static Pressure directly influences the measurement quality.

An important point in the selection is therefore the distinction between linear pressure output and square root output characteristic. A linear characteristic curve makes sense for pure differential pressure measurement. To determine the volume flow, the device configuration must take the root relationship into account. In the example devices, this is done via device settings, DIP switches or menu-guided parameterization.

Typical applications in HVAC, clean room and industry

Volume flow transducers are particularly useful where air volumes need to be monitored or controlled continuously and a compact, robust field device is required.

Ventilation and air conditioning ducts
Here, they are used to record supply and extract air volumes, to monitor duct conditions and to provide feedback to the building management system. In conjunction with frequency inverters, the volume flow can be used as a reference variable for demand-dependent fan control.

Filter monitoring
In filter stages, the differential pressure changes with increasing soiling. Devices with an additional filter function can directly derive a degree of soiling or a limit value for the filter change from this. This makes maintenance planning easier and prevents both premature and late filter changes.

Clean room and medical technology
The focus here is on stable pressure conditions and reproducible air volumes. A properly parameterized volume flow transducer supports the monitoring of sensitive pressure zones and provides a measuring signal that is easy to integrate in terms of signal technology.

Spray booths, commercial kitchens and industrial air ducting
Robust measuring devices that deliver a stable signal even under changing operating conditions are required in these areas. Switchable filter times, multi-range switching and zero point adjustment are particularly helpful here.

How to select the right volume flow transducer

1. select measuring range to suit the application
If the measuring range is too large, the resolution in the relevant working window will deteriorate. A measuring range that is too small leads to overload or incorrect measurements. Device examples from the operating instructions cover ranges up to ±1000 Pa or ±5000 Pa, depending on the type; some versions offer several switchable measuring ranges via DIP switches.

2. adapt the output signal to the automation environment
In practice, 0-10 V and 4-20 mA are particularly relevant.
0-10 V is widely used in building automation and is easy to integrate. 4-20 mA is often of interest when longer cable lengths, higher interference immunity or industrial signal chains are required. The example devices show both signal worlds: 0-10 V in a version with a switching output and 4-20 mA in compact transmitters with an active output.

3. consider the installation situation and device design
Whether pressure connections are at the top or bottom, whether a cable gland or M12 connector is required, whether a display is needed or not - all these factors influence installation, accessibility and service. For outdoor installation, weather and sun protection is expressly recommended in the instructions.

4. evaluate parameterization and operability
Devices with a display, menu-guided configuration or DIP switches make commissioning and customization easier. Relevant here are, among others:

Selection of Pressure- or volume flow function
Entering the k-factor
Switching measuring ranges
Selection of signal filtering, e.g. 1 s or 10 s
Setting switching points or limit values
Manual or automatic zero point adjustment

Installation, pressure acceptance and influence on measurement quality

A volumetric flow transducer can only measure as well as the pressure pick-up is designed. This point is often underestimated in practice. Depending on the application - such as volume flow measurement, filter monitoring, fan monitoring or room pressure monitoring - the way in which the pressure connections are designed and connected differs.

The following applies to volume flow measurement:
The P1 connection records the dynamic Pressure in the direction of flow, while P2 represents the static Pressure should be as unaffected by flow effects as possible.

This means in practice:

Incorrect hose assignment falsifies the measured value.
Unfavorable positioning of the pressure tapping can increase flow influences.
Kinked or leaking hose connections impair the signal quality.
Heat sources, direct sunlight or EMC influences can affect the measuring stability.

The decisive factor is therefore not only the measuring device itself, but also the interaction between the measuring point, pressure tapping, hose routing and commissioning. A properly executed installation is the basis for stable and reproducible volume flow values.

Differentiation from differential pressure transmitters

Not every differential pressure transducer is automatically a volume flow transducer. The difference lies in the function and parameterization.

A differential pressure transducer primarily maps the pressure difference as a control variable. A volume flow transducer uses this pressure difference to calculate a volume flow rate and output it accordingly.

This is particularly important if:

a k-factor must be stored,
a root-extracted characteristic curve is required,
a direct output in m³/h, l/s or similar units is desired,
the device function between Pressure, volume flow, filter and level should be switchable.

So if you want to measure or control specific air volumes, you should pay attention to a volume flow function designed for this purpose and not just the pressure measuring range.

Find the right solution for your application

In practice, it's not just about using any volume flow transducer - it's about using exactly the right solution for your system, your control strategy and your operating conditions.

This is precisely where the difference lies: a well-chosen and coordinated measuring system ensures stable control loops, traceable measured values and less effort during commissioning and operation.

As a field device manufacturer for HVAC and building automation, we know the typical requirements from projects, retrofit situations and series applications. Our volume flow transmitters are therefore consistently designed for practical suitability:

Matched measuring ranges for typical duct and filter applications
Flexible output signals for BMS, DDC and industrial interfaces
Simple parameterization for fast commissioning on site
Robust designs for long-term use in the field
Functions such as filter monitoring, attenuation and zero point adjustment integrated directly in the device

For you this means less coordination effort between planning and operation, faster commissioning and reliable measured values during operation.

During the selection process, we provide targeted support along the decisive points:

Which controlled variable is the focus - pure volume flow or combined Pressure/filter monitoring?
Which signal world is required - 0-10 V in building automation or 4-20 mA in an industrial environment?
What is the range of the actual volume flow during operation?
What are the requirements for installation, accessibility and operation on site?

On this basis, you will find exactly the right device design from us - technically coherent, tried and tested and optimally integrated into your system.

Select volume flow transducer now

FAQ

How does a volume flow transducer measure the air volume flow?

Usually via differential pressure. The device records the pressure difference and calculates the volume flow from this using a square root relationship with a k-factor. This makes it particularly suitable for air ducts and defined measuring sections.

What is the difference between a volume flow transducer and a differential pressure transducer?

The differential pressure transducer primarily supplies the pressure value. The volume flow transducer uses the differential pressure as a basis, converts it into an air volume and provides this as a processable output signal.

Why is the k-factor important?

The k-factor determines the conversion from differential pressure to volume flow. Without a suitable k-factor, the calculated air volume cannot be loaded. Depending on the manufacturer or flow element, this value may be defined differently.

Can volume flow transmitters also be used for filter monitoring?

Yes, many devices in this class also cover differential pressure and filter monitoring functions. This allows not only the air flow to be recorded, but also the contamination status of filters to be assessed.

We also manufacture individually

Do you have special requirements? As a manufacturer with our own production in Germany, we are always able to produce outside the standard range.

contact

Secure payment methods

Do you have a question? We will be happy to help you:

+49 911 519 470

Mo. - Fr. 7.00am - 5.00pm CEST

e-mail FAQ

Volume flow transducer

Volume flow transducer for HVAC

Author: S. Becker | Status: 06.03.2026