EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: ashok.das81 on February 03, 2021, 03:46:03 pm
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Hi all,
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 (within 71% of F1)
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.
Can anyone help me to find out the problem.
Thanks
Ashok
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You might try building the oscillator section from the AADE LC meter design:
https://pe2bz.philpem.me.uk/Comm01/-%20TestEquip/-%20Tester-NonActiveDevice/Cl-251-IndCap-MeterKit/lc-meter-project.htm
(search down to "The Oscillator")
It uses a LM311 comparator. Then you could verify the frequency of the various LC tanks involved.
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Thanks for the reply. Yes I am trying to do this. Then I will measure the frequency wing a separate counter to see how the LC tank oscillating