Florian Girmond, Managing Director of the Consumer Tests unit of HOHENSTEIN Laboratories GmbH & Co. KG

Optimal Results Under Pressure: A Digital Sensor at the Core of a New High-Tech Compression Tester

HOHENSTEIN, a textile-testing services provider, has been the leader in compression and functional-wear testing for decades. HOHENSTEIN required a sensitive digital sensor for the new HOSYcan testing system that would enable determining the compression power of textiles in a more customized and precise way. They opted for HBM’s FIT5A sensor because it measures force very accurately. Additionally, the measurement results can be conveniently analyzed and visualized owing to the included PanelX parameterization and analysis software. This enables the HOSYcan testing system to be started up easily and quickly.

The Effectiveness of Textiles

“When it comes to compression testing of textiles, we have been leading the way in the industry due to over 50 years of experience,” says Florian Girmond, the Managing Director of the Consumer Tests unit of HOHENSTEIN Laboratories GmbH & Co. KG.

From his tower room at the Hohenstein castle, Florian Girmond enjoys the view of the entire HOHENSTEIN Group facilities, which, since its establishment in 1946, has had its headquarters on the premises of the Renaissance castle in Bönnigheim, Germany. More than 600 of the company's worldwide staff of over 1,000 work at the German headquarters. The independent textile testing institute is run by the third generation of the Mecheels family and it holds important accreditations and certifications as a test facility. The laboratories’ range of testing and service offerings includes the testing of fit and workmanship of products, the development of functional wear, and the certification of personal protective equipment (PPE). Compression tests are primarily performed on medical textiles and sportswear, which involve the measurement of the pressure and pressure gradients that a textile exerts on a body part.

The Hohenstein castle

The Only Testing System that Ensures Standard-compliant Compression Tests

In the beginning of the 1980s, the HOHENSTEIN experts developed the HOhenstein SYstem (HOSY) for the testing of the impact of medical compression wear. Meanwhile, HOSY has established the standard in compression wear testing and has become the mandatory testing system for compliance with different standards such as RAL and DIN. HOHENSTEIN utilizes the system for its in-house textile testing services and also sells it to customers.

“HBM technology has always been integrated into the HOSY,” explains Gunther Kretzschmar, who has worked for HBM Sales and has also been the contact for Hohenstein for over 20 years.

HOHENSTEIN has now enhanced its testing system to meet an increased number of individual customer requirements and to make the HOSY compatible with IIoT (Industrial Internet of Things) applications. In doing so, the company has outlined specific requirements for the digital sensors that measure force. “The sensors must be very precise to enable us to obtain accurate measurement results,” explains Florian Girmond. Additionally, the individual sensors need to be narrow to ensure that a maximum width of 5 centimeters, including the mount for the textile jig, is not exceeded. It is also essential that the sensors have a high overload stability to avoid damage to the sensors in the event of unexpected load peaks. The sensors are compatible with the CAN bus technology applied in the testing system due to their CAN bus interface. Hence, they are a perfect fit for the new HOSYcan and can transfer the measured data quickly and efficiently to the software, which, in turn, calculates and visualizes the compression. “FIT5A is the digital sensor that matches our high demands,” says Florian Girmond.

Gunther Kretzschmar, Sales Engineer at HBM

Digital Sensor with an Extremely Short Settling Time

There are 20 tension testing units that have been arranged parallelly at the core of the new HOSYcan that uses the CAN bus technology. Textile tubular knitwear such as medical compression stockings or sportswear tops is clamped onto these units and extended in an absolutely non-destructive way. When the desired perimeter, between eleven and 150 centimeters, has been reached, the HOSYcan measures the required forces and, based on the measured values, calculates the compression that the textile exerts on the body. The results are listed in a table and, additionally, represented graphically in a compression profile. “We determine the tension force along the entire length of the test sample in sections of five centimeters each. This allows the calculation and visualization of pressure and pressure gradients at any position,” explains Florian Girmond. The precise digital sensor. with integrated electronics, is suitable for both static and dynamic measurements.

“The FIT5A has an excellent transient response and provides a stable measured value almost immediately owing to the use of integrated filter technology,” emphasizes Gunther Kretzschmar. “This enables the data at the individual measurement points to be retrieved faster. The complete testing procedure to which a textile test specimen is subjected can be completed more quickly.”

The FIT5A digital sensor can measure force in static and dynamic applications very precisely, has an overload protection of 1,000 percent, and an excellent transient response. Thus, it facilitates quick data acquisition.

Motion Simulation Made Possible, for the First Time

The FIT5A digital sensors have been integrated into the tension testing units, where they acquire tension force.

“An additional advantage of the FIT5A is that it enables completely new test sequences to be designed due to its fast data acquisition,” says Florian Girmond. “Now we can also simulate motion and measure the textiles’ corresponding compression behavior.”

The testing unit applies CAN bus technology to simultaneously transmit the measured values provided by the 20 tension testing units to the analysis software. “We knew right from the start that we would use a digital sensor with the CAN bus technology,” says Florian Girmond. “It is less sensitive to the electromagnetic fields emitted; for instance, those from nearby electric lines or radio waves.” The new CAN bus system enables the measured data to be processed directly in the sensor’s electronics and transmitted to individual channels. Additionally, the FIT5A swiftly measures and boasts of an overload protection of 1,000 percent of its capacity. This is important since the measurement is determined by the strain that the fabric is subject to and not by the force that is applied to achieve this. For this reason, the sensor’s overload range is achieved with certain textiles such as inelastic knee bandages; however, it is essential that the system continues to provide precisely measured data after exiting the overload range again.

Optimal Solutions through Close Contact with Customers

“We always stay in close contact with our customers to be able to find the optimal solutions,” says Florian Girmond and adds, “This also applies to our cooperation with HBM: We, as the customer, get the solution we need. HBM has provided us with a test specimen of the FIT5A sensor. We were able to quickly put it into operation and use it as the basis for our designs due to the convenient connector plug. During the start-up stage, Mr. Kretschmar provided comprehensive advice on the PanelX software and the many opportunities offered by the FIT5A.” Gunther Kretzschmar appreciates the collaboration with HOHENSTEIN, “The work environment at HOHENSTEIN is very positive. I am always pleased to join a meeting in the atmosphere of the former castle.”

The Customer: The Hohenstein Group

The Hohenstein Group is a global service provider that offers a broad range of services pertaining to textile testing, certification, and research. The company was founded in 1946 and is now managed by Prof. Dr. Stefan Mecheels, the third generation of his family. More than 5,000 customers worldwide benefit from the textile know-how of 1,000 plus staff members and a network of over 40 contact offices worldwide. Learn more about the Hohenstein Group

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