Acoustic/ultrasonic testing is now a common method in the field of nondestructive testing for detecting material defects or monitoring ongoing mechanical changes in a structure during operation. In many applications, piezoelectric transducers are used to generate mechanical waves inside the specimen. Their actual operating frequency is highly dependent on the dimensions of the transducer. Larger dimensions of the piezoelectric transducer allow for a lower operating frequency. However, these dimensions limit the use of piezoelectric transducers in certain applications where the size of the transducer is restricted due to limited installation space and when low-frequency excitation is required. One application that places these requirements on the transducer is the monitoring of mechanical seals. Here, the transducer must be mounted on the stationary ring of the seal. In this paper, a continuously operated electromagnetic acoustic transducer (EMAT) is presented as an alternative to piezoelectric transducers as a transmitter. The advantage of a EMAT is that it meets the requirements of limited sensor size (sensor area < 10 × 6 mm) and can excite mechanical waves with frequencies below 10 kHz. A structural analysis of the stationary ring shows that the first two mechanical resonances occur around 4 and 5.5 kHz. An experimental study meterologically demonstrates the ability of the EMAT to excite these first two mechanical resonances of the ring. A comparative simulation agrees well with the measurement.

A new storage pump replaced 3 multistage pumps to transport water between the Kreuzeck and the Reisseck power plant sides. Located in the valley of the two reservoirs, it provides impressive performance data for single-stage operation at n = 3000 rpm. Hydraulics already utilised for significantly lower heads are the basis of this pump. The pump was adapted to the new location, and CFD-based development was applied. Within the scope of a model test, the performance data (Q-H-Eta and Q-H-Sigma) were to be confirmed and measured, including the inflow and outflow situation. In addition, the pressure pulsations had to be verified. Finally, installing air vessels should reduce pressure pulsations on the suction and pressure sides. Furthermore, modifications in the bladed areas of the impeller and the guide vane section should enhance this reduction.

Turbines or pumps in hydropower plants achieve peak efficiencies of far more than 90% depending on the specific speed and the type of machine. Based on model tests or numerical simulations, the efficiency of a prototype machine has to be guaranteed and measured with the best measurement technique available. The choice of the appropriate efficiency measurement method does not only depend on the expected measurement uncertainties and tolerances set in a contract, it is also a question of the effort required for such a measuring campaign and of technical challenges, e.g., limitations imposed by plant operating conditions as draining of the system or constant load operation. Concerning hydraulic turbomachines, modern measuring technology offers different methods for efficiency measurements at a turbine unit. Primarily through the development of real-time capable data acquisition systems, it is possible to perform high-precision measurements rather quickly, whereby minimal downtimes can be achieved. In the first part, the specific measurement methods available in different standards are presented in an overview, and then in the second part, the achieved accuracies of a very complex thermodynamic measurement are compared with a low-cost clamp-on acoustic Doppler measurement using a concrete example.