the self inductance of WW resistors has been a hot topic here - as makers rarely specify how much inductance their products have nor publish impedance curves.
For most WW resistors over a few hundred ohms, inductance issues rarely arise - but for ones under 100 ohms and in the larger wattage ratings, it can be wise to check.
One resistor is this category is sold by WES Components under the code "
100W8 " and is a 100 watt ( free air rated ) tubular ceramic type, wound with a 2.3 mm flat strip conductor. The wind diameter is 28 mm and the length from beginning to end of the wind is 110mm. There are 31 turns of strip.
The WES catalogue claims they are " non -inductive" but this is complete nonsense.
They make useful dummy loads for audio amplifiers and if submerged in water will happily dissipate up to 1000 watts - being a hollow tube helps a lot with water cooling.
Using an on-line calculator ( see below) gives an estimated inductance of
6.0 uH.
But as there are significant ( 1.3 mm ) gaps between each turn on the resistor, the inductance value ought to be less than the calculated one. However, the opposite proved to be the case as the resistors show an inductance of 9.4 uH (with a 1uF cap series resonance occurred at 52 kHz).
The reason is rather obvious, when you do one more simple test on the resistor.
Anyone know ?
.... Phil