LCR Cal Test PCB

[KungFuJosh]

PCB finished size ?

150mm x 120mm, not too small.

[Martin72]

That leaves the vexed question of calibration....
I see several possibilities.
The first option is to send in the assembled board and have it measured.
Second possibility:
Those of us who are "blessed" with an LCR bridge that has 0.05% basic accuracy and is therefore well below the component tolerances, use their device as a reference - But would also have to have it calibrated first to be on the safe side.
Then, of course, there is the third option:
You don't care, the main thing is that you have something to measure.

[mawyatt]

If the PCB can fit inside those small USPS boxes that ship for ~$5 anywhere in US, you could have folks around the country make measurements with different meters for comparisons, kinda like folks do with the Voltage Source Cal group.

Also consider a thermistor on the PCB.

Best,

[KungFuJosh]

If the PCB can fit inside those small USPS boxes that ship for ~$5 anywhere in US, you could have folks around the country make measurements with different meters for comparisons, kinda like folks do with the Voltage Source Cal group.

Also consider a thermistor on the PCB.

It should definitely fit in the small flat rate priority box which is ~$8 to ship anywhere in the US.

I've never used a thermistor before. What type should I get, and how should I set it up? ...and is it really better than measuring ambient temperature?

Thanks,
Josh

[mawyatt]

Wow that flat rate has gone up since last we used!!

Thermistors are used to measure temperature of the thermistor element, and are usually inexpensive (<$1) and most folks have a DMM that can use them. If the thermistor is mounted to your PCB then the readings should give a rough indication of the PCB temperature.

Best to study up on thermistors (lots of on-line tutorials) as there are an almost infinite variety of such!!

Thermistors are non-linear and most DMMs use Steinhart-Hart equation:

1/T = A + B(lnR) +C(lnR)^3, where T is Kelvin and A, B and C are Thermistor Parameters.

Common types are NTC 10K and 5K @ 25C.

Here's an example SMD from TDK.

https://www.digikey.com/en/products/detail/tdk-corporation/NTCG163JF103FT1/614632

Best,

[KungFuJosh]

Here's an example SMD from TDK.

Thank you, that's what I needed. I understand the (very) basics of thermistors, but there's a wide range of accuracy, value, etc. I didn't want to guess at what specs would be acceptable.

I don't want to use anything smaller than 0805, I assume this should be fine?: https://www.mouser.com/ProductDetail/594-NTCS0805E3103FLT

Should I use the same connection setup as the other solo items?

Thanks,
Josh

[mawyatt]

Suspect that should work with most DMMs. Since the expected PCB temperature should be 25C +-5C this should give a reasonable indication of PCB temperature.

Of course humidity also becomes a factor, but that's another level to consider as you dive down the Rabbit Hole of Precise Measurements

Edit: Should have mentioned no need for 4 wire measurements to Thermistor, 2 wire measurement should be fine.

Best,

[KungFuJosh]

I'm changing the 1mF to 2824 (was 2812). That way people can choose between either 10% at 6.3V or 20% at 10V. The old one was 6.3V 20%.

[KungFuJosh]

Assuming no glaring issues, this may be the final version of the V5 board. Feedback is always welcome.

I also attached 2 BOMs. One for Mouser, and one for JLC PCBA service. Most of the JLC parts seem fine, a few I'm not sure about (haven't heard of a couple brands before). They also didn't seem to state the value for their thermistor. I might mix and match parts from both sources, or skip the PCBA.




ETA: After seeing what it would cost to preorder parts for PCBA, I will not be using that service. Yikes. 

Thanks,
Josh

[mawyatt]

Just noted, don't forget holes in the corners for nylon standoffs.

Best,

[KungFuJosh]

Just noted, don't forget holes in the corners for nylon standoffs.

Fiiiiiiiiiiiine. 😉

Is 3.5mm good for you?

[Martin72]

@Josh:

1mm drill hole..

Will 1.5mm still work for you? I don't mind changing it, do you have the sheet for the pins?

They will then sit loosely in it, but yes, 1.5mm is also possible.
Data sheet/origin is at work, I won't get to it for another 2 weeks.

[KungFuJosh]

I noticed an issue with my dissipation factor test results. For some reason when I ordered the parts for V4, I substituted the 50Ω with a 47Ω and the 160kΩ with a 158kΩ. Those two test results were lower than they were supposed to be, which is not surprising.

I corrected those values on the Mouser BOM, and here's the project link: https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=6851743830

All parts come out to less than $30, which is nice. Unless you want test pins, and then it will cost twice as much. 😉😉

The 1mF cap is backordered until August, but I'm guessing that won't matter.

Here's (hopefully) the final V5 board version:


Thanks,
Josh

[KungFuJosh]

I ordered the new PCBs and parts. I should be able to make a new board next week. I ordered some extra PCBs in case anybody in the US wants one.