Safety sensor technology for flexible response to demand changes – PILZ

Experts in mixing technology

Herbst is a medium-sized enterprise located in Buxtehude and enjoys a high reputation in the fields of mixing technology, custom and special-purpose equipment, process control equipment, plant construction, handling and unloading technology. With more than 30 employees, the company develops and produces various mixing equipment, such as planetary mixer, central mixer and horizontal mixer. Herbst produces equipment for many industries and provides its own test equipment for testing according to customer requirements.

Breaking stereotypes requires new safety concepts

The horizontal mixer is a machine that mainly stirs solid substances. The substances are fed through the nozzle or baffle on the upper part of the fixed cylindrical mixing drum and discharged through the lower part of the mixer. Several mixing tools are arranged along the central mixing shaft. When particularly intense mixing is required, a planetary mixing system can also be used. The mixture can be heated or cooled using a double jacket. When necessary, the horizontal mixer can also operate under vacuum or pressure.

In May 2018, Stephan Sch ö Ning, a project of Herbst company, experienced one thing. Although it was successfully solved, this luck did not happen every day: “a horizontal mixer is ready to be loaded and shipped. Suddenly, I got the news that this equipment will not be installed on the base as before, but directly installed on the ground and can enter and exit freely.” Stephan Sch ö Ning recalled that this change in installation location had a far-reaching impact, which meant that the existing safety concept had to be modified.


The horizontal mixer is developed by Herbst company according to the requirements of customers for mixing animal feed. It is a cylindrical mixing tank with a capacity of about 2500L, driven by a 30 kW motor, and the speed of the mixer is up to 50 revolutions per minute. The filling and discharge nozzles at the top and bottom are not important in terms of safety, but the first two service and cleaning baffles are different: although they have mechanical interlocking, the agitator can still run for a period of time after the baffle is opened, so there is a risk of injury to operators. “In the past, the agitator was installed on a base to ensure safe entry through the safety door and pirci’s safety door system psensgate. The non-contact sensor detects the position of the baffle. In this case, the entry time of personnel is greater than the time required to stop the agitator, so the equipment is safe,” Stephan Sch ö Ning explained.

The change of installation position invalidates the original safety concept, but the delivery and installation time of the equipment have been determined. Stephan Sch ö Ning added: “in this case, we must quickly find solutions to the real thorny problems we encounter”. At this time, our long-term partner pirci solved the problems with his expertise in security technology.

Solution: PSD system psenmlock plus

Two large baffles bend within the radius of the container and require a strong and flexible closing mechanism. We discussed many solutions and abandoned many solutions, including a key conversion system. Finally, pirci’s safety door system psenmlock can most effectively solve the problem in hand. Psenmlock realizes two functions in one equipment: safety protection locking and safety interlocking, holding force up to 7500n, flexible installation of mechanical actuator and high tolerance compensation. A noteworthy detail of the protective locking system is that it has led lights on three sides, and the clear readability provides convenience for diagnosis.

Based on the geometry of the baffle and the influence angle of the locking bolt, Herbst engineers developed a supporting mechanical solution. Psenmlock is installed on a mechanism with axial movement and spring influence, which increases the closing tolerance of the safety door system by 10mm. Psenmlock will be unlocked only after the system sends the signal that the agitator has stopped safely. Pirci can also manage the position of the baffle: the position information of each baffle is obtained by the psencode coding switch, and the safety relay pnozsigma is responsible for controlling and monitoring the safety signal.


Modular safety door system for all applications

Pirci’s modular safety door system provides customized safety door solutions, which perfectly meets different application requirements. It can combine different components to form customized safety door solutions, and perfectly adapt to various application purposes.

The safety door system package also contains a variety of accessories, such as different escape releases and door handles for rotating or sliding doors. The button unit pitgatebox can be combined with two kinds of safety door sensor groups psenmlock and psenslock to make the system more perfect. When combined with safety diagnosis equipment and pirci’s control technology, a complete and economical safety door solution is formed.

In addition to the safety door sensor psenmlock used for safety interlocking and safety protection locking, the safety door system also includes “series psenmlock”. It can be used in combination with the safety diagnostic machine SDD to control a single switch and / or door – fully in line with the spirit of industry 4.0.

Post time: Dec-09-2021