I have done both the lehman approach (measuring duty cycle) and the lc tank approach (measuring frequency). As I was more interested in measuring low inductance (<100uh), the lc tank approach made more sense to me and the measurement cycle (time duration between successive measurements) can be so short that averaging is transparent to the user.
the lc tank approach is stable to the fourth digit, and the lehman approach is stable to maybe the 3rd digit. Both approaches are highly dependent on the gates used and supply voltage. the lehman approach requires extensive calibration.
Both will work if you don't need precise measurement of inductance.
In that case, either approach should work, all you need to measure is changes in inductance, not inductance itself.
For example, you can periodically measure the inductance (lehman) or frequency (lc tank), and use that as basis for your comparison to see if the inductance has changed.
With this approach, temperature stability doesn't matter - unless temperature can change drastically between measurements (aka the target is a container of hot water, etc.).
我用LM311做了个LC振荡测电感的，
most mcus have internal opamp / comparators that can be configured for this purpose. no need for an external part.
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I have done both the lehman approach (measuring duty cycle) and the lc tank approach (measuring frequency). As I was more interested in measuring low inductance (<100uh), the lc tank approach made more sense to me and the measurement cycle (time duration between successive measurements) can be so short that averaging is transparent to the user.
the lc tank approach is stable to the fourth digit, and the lehman approach is stable to maybe the 3rd digit. Both approaches are highly dependent on the gates used and supply voltage. the lehman approach requires extensive calibration.
Both will work if you don't need precise measurement of inductance.
多下大虾指导，我其实想做一个电感式接近开关，传感器探测面正前方有一个材料为15-PH的金属靶标，当靶标与探测头之间的距离发生变化时，传感器内的线圈电感量会发生变化，变化范围大概在4.9mH到5.05mH，变化量不超过150uH。其实如果采用雷曼式的话，对供电源的要求极其的高。但是如果用谐振的话真的很难抗住温度的影响。毕竟通常电容的温度系数比较高，尽管我有渠道可以买到比较高档的一类陶瓷。
就像我上面说到的，将电感充放电的时间转换为脉宽（即您所说的占空比信号）这个方法算下来真的很省体积，极少的外围器件就可以实现，您用门电路其实更直接，我是没有那么多空间使用门电路，只能选微控制器，C8051F301支持内部校准式的时钟，出厂前内部时钟校准为24.5M，这样我试图省掉高度（尺寸）消耗的晶振，研究到现在我已经迷失了，不知道当初一直坚持着这个方法到底行不行，但是毕竟这么多工作做了，不想放弃
In that case, either approach should work, all you need to measure is changes in inductance, not inductance itself.
For example, you can periodically measure the inductance (lehman) or frequency (lc tank), and use that as basis for your comparison to see if the inductance has changed.
With this approach, temperature stability doesn't matter - unless temperature can change drastically between measurements (aka the target is a container of hot water, etc.).
most mcus have internal opamp / comparators that can be configured for this purpose. no need for an external part.
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