Products > Test Equipment
LCR Cal Test PCB
KungFuJosh:
A bunch of us have been comparing the accuracy and ranges of our LCR meters, and to compare to the "official" cal cert Martin72 received with his ST2830, I made my own test report and a test PCB to go with it.
I've been through 3 out of 4 versions of the board (skipped the 3rd after learning how to test dissipation factor). I'm now getting ready to make a 5th, and hopefully final version of the board. I could use some ideas and a little insight in finishing the last design.
There's some extra space on the R side, as I recently removed 1GΩ and 100MΩ test points. If somebody things I should keep one or both, let me know why you feel that way. I'm also considering adding 1pF back onto the C side, but it's lower than typically useful on these tests, but I do know the Shannon ST42 can test it fine.
Currently, my biggest question is finding a more reliable method for kelvin clip test points. What I have now is 3mm pads on top and bottom of the PCB running to the test components. For my kelvin clips to get a good connection, I have to add solder to both points around the board, and the resulting connection isn't amazing. It requires a little wiggling to get the best connection. I want something more stable.
Here's what the board design looks like currently:
KungFuJosh:
Here's the most recent example of my test done with V4 of the board.
Martin72:
That doesn't look too bad. :-+
Personally, I would stop at 10mH, 100µF, 1M Ohm.
And start at 100nH, 10pF and 1 Ohm.
While finding very small tolerances for resistors is not a problem, I had not found anything below 2% for capacitors, for example, and nothing below 5% for most coils.
What did you use, where can you find it?
KungFuJosh:
--- Quote from: Martin72 on July 04, 2024, 10:31:06 pm ---That doesn't look too bad. :-+
Personally, I would stop at 10mH, 100µF, 1M Ohm.
And start at 100nH, 10pF and 1 Ohm.
While finding very small tolerances for resistors is not a problem, I had not found anything below 2% for capacitors, for example, and nothing below 5% for most coils.
What did you use, where can you find it?
--- End quote ---
The first reason I got into testing inductance is for making Wah Wah pedals. Those inductors range from 500mH to 700mH, so I'll always include them. How accurate they are on their own doesn't matter. Once the board is finalized, it can be calibrated and then the calibrated value is the only thing that matters. I also test guitar pickups, and the (standard) ones I've done range between 3 to 5 Henries so far.
I'll put together a BOM including the parts. Everything except the wah inductor was from Mouser. Most, if not all (remaining) resistors were 0.1%. The rest is probably along the lines of what you said. High values tend to be worse, but I'll buy extras (including higher values) and find what tests to the desired value, and go with that in the end. Seeing 75µF or so when it's supposed to be 100µF is annoying.
I still think finding a better method for connecting kelvin probes is high priority. Or scrapping the kelvin probes entirely, whichever works better. 😉 I think having the lower values isolated might be enough on their own. I can test this by using the kelvin clips only touching the board top test points. Still though, I would prefer a better kelvin option.
I've seen some smaller pins that might work, but I dunno if that's the best way, especially if they get bent over time.
Thanks,
Josh
Martin72:
The pins that DMMCheck Plus uses are quite stable, I can still reach them easily with Kelvin clamps.
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