…I measured some coils and seem to have problems for low inductance values.
For the same transformer coil I get 11.73 mH on the HiL scale and 754 uH on normal L scale.
Any hint ?
My guess is 11.73 mH is the right value as primary gives 4.47 H and this is a 240V/12V transformer,
so I expect that the ratio of inductance will be roughly 400 (20^2).
Yes, 11.73mH is likely to be reasonably accurate.
If measurement result is lower for normal L mode compared to HiL mode, this indicates the inductor under test cannot function well at the (much higher) test frequencies employed by LC100-A normal L mode.Inductors and transformers intended for mains frequency operation (50/60Hz) must be measured with test frequencies in the audio range, preferably no higher than 1 or 2kHz. As much as possible the test frequency should be similar to the frequencies the inductor under test will encounter during normal operation.
Low frequency inductors/transformers have cores made from a stack of many
thin sheets of iron or steel. These thin sheets are known as
laminations. Although some very expensive wide-band audio transformers made with laminated iron/steel cores are functional up to 50kHz or a bit higher, this isn’t the case for typical 50/60Hz power transformers. Their high frequency performance is limited by eddy current losses in the laminated iron core along with stray capacitance in the windings.
These can only be measured by LC100-A HiL mode.Another popular core material is known as
powdered iron. These are often painted or wrapped with tape in bright
yellow, red, green, or blue, especially when the core has a toroid shape. These are functional up to about 100kHz and are commonly used in switching power supplies.
These should also be tested with LC100-A HiL mode.Ferrite cores are usually grey in color. They have a much larger frequency range which can extend up to many MHz. For ferrite cores the LC100-A can test them in either range.
Coils with no core (air core) can handle extremely large frequency ranges. Either normal L or HiL mode may be used when measuring air core inductors with LC100-A.
LC100-A test frequency range for normal “ small L “ mode is between 50kHz and 500 or 600kHz.
Test frequency for “ HiL “ mode is much lower, from roughly 100Hz up to 50kHz maximum.