Prof. Dr.-Ing. Dr. h. c. Uwe Hampel

Experimentelle Thermo­fluiddynamik
Tel.: +49 351 260 2772

Eckhard Schleicher

Lei­ter Experimentaltechnik
wissen­schaftlicher Mitarbeiter, VEFK
Tel.: +49 351 260 3230

Work package 5.1 - Gas-fraction and temperature measurements in chemical reactors

Principal Investigators: Dr. M. Schaulin (TU Dresden), E. Schleicher (HZDR)

Main Scientific Goals:

Flexible printed circuit board technology based temperature and dielectric sensors have been designed and manufactured. The development included the selection of a suitable Polyimide substrate, photo lithographic structuring of a laminated resist, thin-film Platinum plating, lift-off, and short pulse laser structuring of the individual sensor structures.
The analysis of the chemical resistance show that the single sensors developed fail after around 70 hours. The sensor is built on of different laminated functional layers. An analysis of the damage mechanism indicated that the bonding layers of the stacked sensor design be attacked chemically at the end faces. Due to the numerous little tubules traveling vertically through the coatings, large end faces exposed. To achieve chemical resistance the work concentrated on two approaches:

The first approach does the bonding entirely without any bonding film. By the use of PTFE, different functional layers are fused together in a fusion bonding process. The process required a controlled vacuum assisted high temperature press. PTFE is a chemically resistant and a wide range temperature-resistant material. The material can also be strengthening by aramid fibres. The sensor acquires properties such as high quality sealing rings commonly used in chemical plants. During the preliminary investigations it was found that there were movements and deformations inside the core layer. The cause is the flow characteristics of the material compound at the fusion bonding process. This has negative effects on the machining process since the specified precision of the contours required for creating openings has been violated. A robust process management is prevented thereby.

The second approach protects the end faces of the polyimide based sensor by a protective layer. A thin coating is applied. There were sensor matrices designed for phase- and temperature measuring. The sensors are designed for the experimental reactor used at the Institut für Verfahrenstechnik der TU Dresden. In order to achieve the required measuring accuracy the resistive sensor was connected by a special multiplexer using four-wire principle. The sensor matrices are currently being established under the terms of the second approach.

A robust, high precision sensor interface for in-situ temperature measurements in process engineering has been designed, manufactured and characterized in detail. Wiring and interference are minimized by directly connecting thick film technology based sensing elements to the interface PCB. The interface features are fully digital calibration, operating temperature compensation and noise canceling, a low-noise supply scheme for a wide range of operating voltages, parallel operation of up to 120 units on a self-managing CAN, and a user-friendly generic serial ACM USB connection for plug-and-play operation. The temperature sensor interface achieves an absolute accuracy of 50 mK by employing a novel dual slope, calibration method.