B
bitrex
Guest
Microcontroller-based strategies like this work OK for high-Q inductances:
<http://www.pa3fwm.nl/technotes/tn11b.html
But don't work too good for little random-wire very lossy inductances,
of values around 0.5uH to 5uH, at the lower excitation frequencies that
microprocessors can easily provide from direct pin-switching system
clock-derived outputs. e.g. inductaors that have self-resonant
frequencies in the 100s of MHz.
I was thinking the small inductance could have its effective Q boosted
via boostrapping, perhaps (I'm kinda down on negative impedance
circuits, now, you can make some cute circuits with them but they all
obv. tend towards being unstable and are "fiddly" and I'm uncomfortable
using them in "real work")
and then you could measure a certain range of small inductances by
applying a clock to a tank circuit thru a resistor, and putting the
original clock plus the output from the tank into a phase detector a la
a PLL and look at the integrated leading or lagging phase "up/down"
signal to infer the inductance.
It might need little external hardware other than the Q-booster in some
implementation. Clock out to the tank and leading/lagging phase signal
back in to the uP to an onboard comparator/phase detector and integrator.
For my particular solution needs whatever form it takes, it would be
best to trade of absolute accuracy for precision/repeatability.
<http://www.pa3fwm.nl/technotes/tn11b.html
But don't work too good for little random-wire very lossy inductances,
of values around 0.5uH to 5uH, at the lower excitation frequencies that
microprocessors can easily provide from direct pin-switching system
clock-derived outputs. e.g. inductaors that have self-resonant
frequencies in the 100s of MHz.
I was thinking the small inductance could have its effective Q boosted
via boostrapping, perhaps (I'm kinda down on negative impedance
circuits, now, you can make some cute circuits with them but they all
obv. tend towards being unstable and are "fiddly" and I'm uncomfortable
using them in "real work")
and then you could measure a certain range of small inductances by
applying a clock to a tank circuit thru a resistor, and putting the
original clock plus the output from the tank into a phase detector a la
a PLL and look at the integrated leading or lagging phase "up/down"
signal to infer the inductance.
It might need little external hardware other than the Q-booster in some
implementation. Clock out to the tank and leading/lagging phase signal
back in to the uP to an onboard comparator/phase detector and integrator.
For my particular solution needs whatever form it takes, it would be
best to trade of absolute accuracy for precision/repeatability.
