Limitations of permanent magnet incorporated potential difference probe
for liquid metal flow investigations in presence of the AC magnetic field
The permanent magnet incorporated potential difference probes (PMP) has been tested for liquid metal local velocity measurements in flows driven by AC magnetic field at frequencies ranging from 5 to 50 Hz and at much higher frequency 2400 Hz. Magnetic force density acting on the rare earth permanent magnet in AC magnetic field may reach extremely high values. Resulting demands to mechanical properties of the probe support should be regarded.
Account should be taken of the local fluid flow perturbation generated by electromagnetic forces resulting from: 1) AC current interaction with permanent magnet DC magnetic field; and 2) DC current interaction with AC magnetic field.
Caution should be taken with the AC signal component induced in the loop formed, on the one hand, by the fork of the probe electrodes and, on the other hand, closed via liquid metal. The AC signal component, regarded as a noise for velocity measurement, may be even for orders higher than the fluid velocity information carrying DC signal. Without proper signal conditioning procedure the signal preamplifier may become saturated by high amplitude AC signal.
The PMP was found to be applicable for investigations of liquid metal under impact of AC magnetic field, but only with thorough critical analysis of probe limitations under specific conditions of actual experiment.