‘Functional safety’ is the key phrase when safety questions are raised concerning accident prevention on machines and systems. When developing its products, Johannes Huebner Giessen complies strictly with the requirements of the European Machinery Directive 2006/42/EC as well as the associated standards, which are also increasingly becoming recognized international standards. The Machinery Directive regulates a uniform level of protection as well as requiring CE marking and a Declaration of Conformity to comply with the relevant standards such as DIN EN ISO 12100:2010 (Safety of machinery).

With the U-ONE-SAFETY Johannes Huebner Giessen has developed the next generation of the U-ONE encoder system; in doing so it supports machine builders and system operators in preventing workplace accidents.

Nowadays, safety measures are more and more required in the dry bulk industry. Safety is ensured by Johannes Huebner Giessen’s U-ONE-SAFETY.


Safety-critical situations invariably arise when it is necessary to physically intervene while the machine is running to rectify faults during setting up procedures or performing test runs. The speed and position-changing movements of a machine part can pose a risk to safety from which operating personnel need to be protected. The easiest solution at first glance is to simply isolate 

the drive power of the respective motors, meaning shutdown the system. However, this is not always the best or the most economic solution. Productivity stands and falls with the number of hours a system is in operation. Moreover, larger systems have long, drawn-out initialization procedures when restarting, so that more valuable time is wasted. If it is not an option to shut down the machine, hazardous movements must be performed at safely-limited speeds, rotational speeds or positions, often in inching mode or in combination with simultaneously operating an enabling switch. Activating the safety functions presented below ensures risks to safety are reduced permanently.



  • SLS – Safely- Limited Speed: the SLS function prevents the motor exceeding defined speed limits. Monitored functions that exceed the limit value are detected and the drive is shut down safely.


  • SSM – Safe Speed Monitor: the SSM function supplies a reliable output signal to indicate if the motor speed is below a defined limit value. The output signal is reset if the limit value is exceeded; no other reaction follows.
  • SDI – Safe Direction: the SDI function prevents the motor shaft moving in an unintended direction. Any movement in the wrong direction is detected and the drive is shut down safely.




  • SLP – Safely Limited Position: the SLP function prevents the motor exceeding defined position limit(s). Monitored functions that exceed the limit value are detected and the drive is shut down safely.
  • SCA – Safe Cam: the SCA function supplies a reliable output signal to indicate if the position of the motor shaft is within a defined range. The output signal is reset if the limit value is exceeded; no other reaction follows.


System operators and machine builders are faced with the question of how to practically and economically implement these safety functions while maintaining the necessary Performance Level (PL) and Safety Integrity Level (SIL). Purely implementing these features by means of a safety PLC is often not desired, because that significantly increases the complexity of the system — and as a result the dependence on experts who are able to programme the controls accordingly, and who are often not on-site to intervene when needed.

By contrast, the U-ONE-SAFETY makes it easy to implement movement and position dependent safety functions. Depending on requirements U-ONE-SAFETY monitors the safety functions SLS (Safely-Limited Speed), SSM (Safe Speed Monitor), SDI (Safe Direction), SLP (Safely-Limited Position) and SCA (Safe Cams) — and is configured according to customer specifications. Monitoring the speed and position of the deployed traversing and hoisting equipment are typical tasks in the bulk goods sector. When hoisting gear is lowered, SLP monitoring, for example, can ensure defined limit positions are reliably monitored. When configuring the U-ONE-SAFETY the traversing range is initially calibrated. Subsequently, it is possible to define several points within this range at which reliable safety monitoring is desired. For instance, when hoisting gear moves loads it is often permissible to travel at greater speeds at mid height than after a defined slow-down point is reached close to a final position switch, at which point travel speeds must be slower.


In particular the safe position and error switches as well as the safe absolute encoder interfaces are new features in comparison with the previous version of the U-ONE-SAFETY. In addition, the system offers a reliable speed switch as well as optional current or incremental outputs. It is possible to simply and reliably programme the respective parameters utilizing the configuration software included in the scope of supply — without having to intervene in the higher-level controls. Thomas Brandenburger, head of the project management department, explains:“With integrated safety logic and safe switching outputs U-ONE-SAFETY is far more than just a normal encoder. The user is able to very easily implement speed and position dependent safety functions without needing a lot of programming know-how. And in the event a device needs to be replaced the stored parameters can easily be transferred to the new device — it can’t get more straightforward than that.”


With integrated dual channel architecture and internal cross- checking the U-ONE-SAFETY is ideally suited for applications up to safety category 3 and Performance Level (PL) d to DIN EN ISO 13849 as well as Safety Integrity Level (SIL) 2 to DIN EN 61508. The advantage of dual channel architecture: the safety function is always retained even when an error occurs. Two separate sensors generate a signal independent of one another. Two logic units cross-check if the values are identical. Finally, the signals are fed to a switching output (speed and position switches are possible), which also boasts dual channel architecture. “This integrated, system-wide dual channel architecture is the basis for the classification in safety category 3. That means it is possible to deploy the U-ONE-SAFETY in a much wider spectrum of applications”, says Brandenburger. Certification means it is possible to classify the device as a safety component during the safety review required by the standard, something that significantly reduces the burden of assessment on the part of the customer.

It is possible to combine the different functions, output signals and interfaces within the scope of a modular concept to create the right solution for the respective application. Two different versions of the system are available: the U-ONE-SAFETY- Compact that sees modules attached to the basic unit within a compact casing; then there is the U-ONE-SAFETY-LWL that features a basic unit in a robust casing, which is connected to the corresponding modules in the switchboard enclosure via fibre optic cabling.

“With U-ONE-SAFETY the customer receives all of the functions and interfaces he requires in a single compact device”, explains Brandenburger. U-ONE-SAFETY is suitable for both new installations and upgrade projects. This system means there is no longer any need for mechanical cam switches, mechanical cam controllers, intermediate or limit switches. Characteristics such as the rugged construction, the high degree of protection, even when the terminal box is open (thanks to the fully encapsulated base), and robust O-ring-seals in the terminal box cover ensure the U-ONE-SAFETY is the right solution for use in extreme environments – in particular in steel and rolling mills, in mining, in crane technology and in the bulk goods sector. Moreover, all of the devices offer high connection flexibility with safe cable entries – on both sides.