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

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 conventional transducers, the desired output type must generally be specified at the time of ordering:

  • Voltage output (0–10 V)
  • Current Output (4…20 mA)

For devices with Automatic Output Switching This step is completely omitted. The transducer automatically detects, based on the connected load, whether a voltage or current signal is required—and adjusts itself accordingly.

In practice, this means:

One device, two output options—no manual switching required.

We have patented this unique technology: DE 10 2015 015 941 B4.

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?” Especially with larger systems or international projects, this decision isn’t always clear-cut—or it may change as the project progresses.

With AOS, this requirement is eliminated:

  • one device type for both signal types
  • a smaller variety of options in the product line
  • simpler spare parts strategy

This reduces complexity—both in planning and in purchasing.

2. Greater safety during installation and commissioning

A common problem in practice: The sensor is installed correctly—but the output signal doesn't match the control system. Typical consequences:

  • incorrect interpretation of a signal
  • No control or faulty control
  • additional effort required for troubleshooting

With Automatic Output Switching, that doesn't happen:

  • The device detects the connected infrastructure
  • adjusts automatically to the correct setting
  • minimizes typical wiring and parameterization errors

This is a real advantage, especially when it comes to time-sensitive commissioning.

3. Flexibility in response to changes in inventory

This often happens in existing systems:

  • Control systems are being modernized
  • Entry and exit cards are exchanged
  • Signal standards are changing

Without AOS, this often means:

  • Replace the sensor or
  • Reconfigure on-site

With AOS, the sensor continues to operate as usual. The adjustment is performed automatically via the connected controller.

This saves time, reduces downtime, and significantly 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.

Typical areas of application for AOS

Automatic Output Switching is particularly useful in:

Building automation (GLT / DDC)

  • Different control standards per project
  • Mixed signal worlds (0-10 V and 4...20 mA)
  • High requirements for simple commissioning

HVAC plant engineering

  • Series production with varying customer requirements
  • Reduction of variants in switch cabinet construction

Industrial and OEM applications

  • Different international standards
  • Flexible integration into various systems

Service and maintenance

  • Quick replacement without re-parameterization
  • Lower error rate in the field

Conclusion: less effort, more security

Automatic Output Switching is not a "nice-to-have", but a real practical feature for modern sensor technology.

The advantages at a glance:

  • Reduced number of variants
  • Easier planning and procurement
  • Low-error installation
  • Flexible use in existing and new systems
  • Faster commissioning

The added value is particularly evident in combination with more complex sensor solutions such as dual pressure transmitters.

In short:

AOS removes a typical source of error from the project - and makes sensor technology much easier to integrate.

All our products with AOS