So far, gap measurements inside the pumps were not possible because of the extreme requirements. The sensors must be resistant to high speeds, high pressures up to 1,000 bar and temperatures above 100 °C. Furthermore, the pumps are extremely compact, which significantly limits the space available for integration of sensors. Thanks to the extremely small sensor designs and their high pressure and temperature stability, the eddyNCDT inductive miniature sensors are ideal for this application. The eddyNCDT 3300 eddy current measuring system, which is one of the most powerful systems in the world, is therefore used on the test rig for evaluating the pumps.