Automatic Output Switching (AOS): Why Automatic Signal Detection Offers Real Benefits in Building Automation

June 15, 2026

In building automation and industrial measurement technology, a sensor’s output signal is often seen as a seemingly minor detail—yet in practice, it can determine the integration effort, error susceptibility, and flexibility of an entire project. This is precisely where Automatic Output Switching (AOS) comes into play.

AOS describes a transmitter’s ability to automatically detect and switch between 0–10 V and 4…20 mA without requiring manual configuration. This feature was specifically developed to meet the demands of building automation and has proven itself in real-world applications.

What initially sounds like a convenience feature is, in reality, a technically sophisticated, S+S-patented solution that significantly simplifies planning, installation, and operation—especially in projects with different signal standards or changing requirements.

Back to blog

What does Automatic Output Switching actually mean?

With classic transmitters, the desired output type must usually be specified when ordering:

Voltage output (0-10 V)
Current output (4...20 mA)

For devices with our patented Automatic Output Switching this step is completely eliminated. The measuring transducer automatically detects whether a voltage or current signal is required based on the connected load - and adjusts itself accordingly.

In practice, this means

One device, two output variants - without manual switching.

Why AOS is so relevant in practice

1. fewer variants, less planning effort

In many projects, the question arises early on:
"Do we need 0-10 V or 4...20 mA?"
This decision is not always clear-cut, especially in the case of larger systems or international projects - or changes over the course of the project.

With AOS, this stipulation no longer applies:

One device type for both signal types
Less variety in the product range
Simpler spare parts strategy

This reduces complexity - both in planning and in purchasing.

2. increased safety during installation and commissioning

A classic problem in practice:
The sensor is mounted correctly - but the output signal does not match the control unit.
Typical consequences:

Incorrect signal interpretation
No or incorrect regulation
Additional effort for troubleshooting

This does not happen with Automatic Output Switching:

the device recognizes the connected infrastructure
automatically adjusts itself correctly
Minimizes typical wiring and parameterization errors

This is a real advantage, especially for time-critical commissioning.

3. flexibility in the event of changes to the portfolio

It often occurs in existing systems:

Control systems are being modernized
Input/output cards are swapped
Changing signal standards

Without AOS, this often means

Replace sensor or
reconfigure on site

With AOS, the sensor remains unchanged in use.
The adjustment is made automatically via the connected control unit.

This saves time, reduces downtime and considerably simplifies retrofit projects.

Technical background: How does AOS work - and what makes it special?

Automatic switching is based on the detection of the connected load.

If a typical load resistance for current signals is detected → switchover to 4...20 mA
If a high-impedance load is detected → Switch to 0-10 V

The device therefore analyzes the electrical environment and decides independently which output signal is required.

The crucial point here:
Automatic Output Switching is not a generic function, but a specifically developed technology for building automation.

AOS was developed by us and introduced to building automation in this form for the first time. The underlying circuit and mode of operation is patented, ensuring reliable and clearly defined switching logic.

For the user this means

Switching takes place automatically when connecting
No additional parameterization necessary
Stable signal provision during operation

In contrast to simple "switchable" devices, where only manual selection between signal types is required, AOS takes over the decision automatically and unambiguously on the basis of the real connection conditions.

In short:
AOS removes a typical source of error from the project - and at the same time brings a patented, tried-and-tested technology to the sensor system that has been specially developed for the requirements of building automation.

Why automatic switching makes technical sense

Automatic switching between 0–10 V and 4–20 mA combines the advantages of both signal types in a single device.

The 4–20 mA current signal offers high immunity to interference, particularly over long cable runs and in EMC-prone environments, as well as the ability to monitor the cable. Voltage signals such as 0–10 V, on the other hand, can be integrated particularly easily and cost-effectively for short connections.