Tool/software: WEBENCH® Design Tools
For a school project I am using the LDC 1614 with a self designed coil to measure distances between 0 up to 20mm.
I designed the coil as follows: outer diamter = 40mm, 2 layers, 32 windings, inner/outer-ratio=0.3, trace width and clearance = 8mil, c = 330pF.
I exported it as an altium file. After receiving the pcb-coil I measured it over the calculated frequency range of about 814kHz up to 2MHz.
I observed inductance, q-factor and Rp resp. Rs.
The curve characteristics of the inductance in function of frequency was continuous as expected, except for a specific frequency range. At around 930kHz all of the tested parameters suddenly jumped to another value. E.g. the parameter Rs jumped from around 24Ohm down to 23Ohm. After this jump the courve followed the excpected course. At a frequency of around 1MHz the jumped repeated but in the opposite direction. After the second jump the curve followed the excpected course until the end of the measurement. I can exclude a measurement error since this exact same behaviour was observed on five pcb-coils and I also measured the reference-coil: J of the reference coils of Texas Instruments. This coil didn't show any of this behaviour. No conductive material was near the coil while measuring. Only the coil was measured without the presence of a capacitor. The used measurement device was: Gwinstek LCR 8110G
Do you have an Idea what problem it could be? Did you also test coils from webbench-designer exported coils?
The shape of these coils (altium export) was kind of a circular approximation with multiple straight lines. Can you imagine that this behaviour was cased due to this non-continous shape of the coil?
If desired I can also upload measurement-graphs.
Many thanks,
Adrian
