大家好，

I am making the LC meter V2 designed by VK3BHR Phil RIce.

https://sites.google.com/site/vk3bhr/home/index2-html

I have seen many have done this and it works fine, but in my case it is not measuring inductance properly. For example a 90uH coil shows 52uH, 3.3uH shows 0.3uH. The measurement is completely wrong. Capacitance measurement is looking OK. Calibration was done using a 1% 100pF NP0 capacitor. I checked F1 and F2.

F1=00042879 (little lower than recommended value of 00050000 +- 5%)
F2 = 00032223（在F1的71％以内）

I have used all new components and L is a 100uH +/-20% toroid. C and Ccal are 1000pF NP0 +/-5%. I am using the PCB designed by VK3BHR. The relay is driven by a BC548B transistor as I cannot find a low current relay and I have checked the RELAY its clicking and contact resistance is less than 1 ohm. I am thinking that the +/-20% tolerance for the 100uH toroid is too high. What else could be wrong ? I will provide any other info that is useful for troubleshooting.

谁能帮助我找出问题。

谢谢
Ashok

Often, when people have trouble with the accuracy of this oscillator (the basis of the meter), the problem is the Q of the inductor. Reading inductors with large resistances leads to large errors in inductance measurements, similarly when measuring capacitance if the reference inductor has significant resistance it throws off the capacitance measurement. This is because resistance in the LC circuit makes the oscillator oscillate at other than the expected f = 1 / (2π √l c).

Let me know if you want me to dig up the definitive analysis by Chris Krah. I know it is somewhere on my hard drive...

HiDickCappels
感谢您的回复。我当然想对此进行更多分析，因此请与您分享您拥有的任何信息。这个项目对我来说非常重要，这是我测量RF过滤器电感器的唯一方法。我正在参加我的业余无线电许可考试，并且如果不准确测量电感，就无法完成建筑无线电。

Attached are a schematic and circuit description of an LC meter designed by Chris Krah in 2002. The effect of resistance in the inductor is addressed in Krah_LcmDoc(01-06-03).pdf in the circuit description of the oscillator and get interesting at equation 9.

谢谢for the documents. Now I need to disconnect up the L and measure its internal resistance.

谢谢for the documents. Now I need to disconnect up the L and measure its internal resistance.

You didn't say what kind of toroid core you used to wind the coil. The "Q" of the inductor you made with that core could easily be your problem.
Get rid of the toroid-core coil and get a leaded inductor such as this one:https://www.mouser.com/ProductDetail/Fastron/SMCC-101J-02/?qs=R2jSSvul3fDqs1EnZiUM9g==.
Its Q and DC resistance should get your LC meter up and running.

干杯，
Dave M

嗨，戴夫，

我使用了来自Multicomp的现成线圈。根据VK3BHR，电感器的内部电阻应低于1欧姆。附件是该环形电感器的数据表。它的内部电阻为0.3欧姆，但在数据表中，测试频率为10 kHz。在我的电路中，操作FREQ约为500 kHz。这可能是一个问题吗？您建议的电感器具有内部阻力多于一个欧姆。我可以有一些内部阻力小于1欧姆的东西吗？

嗨，戴夫，
I have found one TDK part. Specs are looking good having 0.7 ohm series resistance and recomended operating freq at 796 KHz, 100uH +/- 5%, self resonant at 3.5MHz. Waiting for this to arrive.

更新：
我已经用TDK部分代替了电感器，我提到了100UH，0.7OHM，2MHz SRF。还用1％聚苯乙烯电容器代替C和CCAL。将继电器转向单独的PCB（认为继电器线圈可能正在干扰100UH电感器）。现在，电路正常工作。感谢所有人的宝贵反馈，使这一反馈成功。

I was working with this circuit recently. Polystyrene caps make a big difference in stability.

@ashok.das81Also, be aware that those polystyrene caps are "kind of" polarized. Not in the way that electrolytics are, but one of the leads is, of course, connected to the outer plate of the cap and is near the outer surface of the cap. It will be affected by such things as your finger being too close if the cap is oriented "backwards". The end of the cap that is colored (probably red or orange) should be connected to the ground side.