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Old 12-08-2016, 09:30 AM
madlabs madlabs is offline
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Join Date: Jul 2016
Posts: 388
Sencore LC76, calibration and operation

I picked up a Sencore LC76 capacitor inductor analyzer for free. It didn't come with the power supply but it has a 12V input where the battery would go so I hooked it up to a 12V power supply. It lights up and fundamentally works but seems a little off in the pF range. I don't have a very good test setup, but here is what I have. I have a Fluke 117 and a cheap MK-328 tester. The 328 agrees with the Fluke quite well up in the nF range. The Fluke doesn't have pF range but testing some pF caps I have with the 328, including some 1% ones, the 328 seems to be right on the money. So I am measuring the Sencore against the 328. If I fiddle with the lead zero adjuster I can get it pretty close and it does fine on larger values. I think it is close enough for my purposes, it's not like I do anything exacting.

However, I am more interested in the accuracy of the leakage tester. That I really want to use. Since it is off in measuring capacitance values, does that effect the leakage test? Or are they separate circuits? Can one use a resistor to test the leakage? I tried this and it doesn't seem to match up. I took a 1m resistor, which measured out at 1,350,000 ohms. Then I tested it at 25, 50 and 100V. It should have read 96.6, 48.3 and 24.1uA respectively. But the Sencore showed 10, 80 and 140uA. Way off and far from linear. Is this a valid test of the leakage function? I should note that I measured the test voltages and they are fine.

I measure leakage in quite a few caps as well. Since I had the container of old parts from working on my Predicta handy, I tested a bunch of the old caps. They ranged from 0uA to 180ua to one that was over 10KuA and so out of range. Some of the values we 30, 19, 2,47 and 2uA. Then I tested a bunch of new 400V, .1uF film caps and they ranged from .3 to 1uA. Do these results make sense? While I see charts for aluminum electrolytics and tantalum caps, I don't see charts for paper, film, ceramic and mica. I take it that these one has to refer to the data sheet, but there must be some rules of thumb.

Then I starting playing with electrolytic caps. The Sencore agreed pretty well with the Fluke for value. Testing some slightly older but quality caps the leakage was well withing the charts and slowly ramped down. I was given a variety pack of cheap caps and most of them did fine. However, one whole bag of 100uF 50V caps kept climbing up and up until out of spec.. Quality control was out back having a smoke that day! Needless to say I tossed that bag and a good lesson that buying cheap caps (which I didn't) is stupid and to test caps before using them is a good plan.

So, any advice on using this gear or calibrating this gear? Any rules of thumb for different types of caps? Think I can use this gear for my crude purposes?

I haven't even started on the inductance and flyback and yoke tests but I will and I'm sure I'll have more questions!

Thanks!
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