Reading and testing ceramic capacitors- need help.

[Om_Audio]

I am trying to read/test some cheap ceramic caps I got and am having trouble. I am hoping someone to add to my knowledge here.

I have looked at dozens of cap codes charts, read my DMM manual, and am stuck. Might just be limitation of my DMM?

The readings I get are not consistent with the charts or codes I have looked at. Also the DMM (you have to use "REL" mode for very low value caps) if it shows a value in nF, it will not show any value in uF which is -higher- so why would it not show the same value with decimal moved 2 places to the right? Right?  

Any insight or info much appreciated!
C

DMM I have is Radio Shack 22-812 w following spec for capaciatance- I do not fully understand what the limits of this DMM are even after looking at this spec:


Some of the caps-


Images showing some tests (note this DMM can be calibrated which I have not done but don't imagine it is needed)
(images removed)

Post showing calibration and other stuff:
http://www.candlepowerforums.com/vb/showthread.php?261833-Playing-with-the-RadioShack-22-812-Meter

[sgmezei]

Well for what its worth the first two numbers are the same as the first two bands on a resistor code. The third number is how many zeros go after the numbers.

So, the blue 561 cap is "56" with one zero, so it is 560pf
the caps that just have 2 digits are low values, so the cap with just "10" on it is a 10pf cap

In my experience multimeters aren't great for cap values. Thats why I bought this project at spark upon recommendation from another forum member.
https://www.sparkfun.com/products/9485

Works great!

[Om_Audio]

Thank you so much! I am going to get that kit. Do more expensive multimeters handle caps better?
I am always looking for the simple "man on the street" explanation for things, not.sure why it seems so hard to come by on the net. I suggested creating a doc or resource for DIY that was written this way, in conversational style with common sense and experience based language.
Thanks again man,
C

[pickdropper]

Thank you so much! I am going to get that kit. Do more expensive multimeters handle caps better?
I am always looking for the simple "man on the street" explanation for things, not.sure why it seems so hard to come by on the net. I suggested creating a doc or resource for DIY that was written this way, in conversational style with common sense and experience based language.
Thanks again man,
C

Expensive meters aren't necessarily good at measuring down into the picofarads.  You really need to look at the specs of the meter (and hope it's in calibration).  I have a fairly pricey Fluke that isn't terribly accurate on the lower end of things.

You may want to check out LCR meters.  Those can be a bit better, but they do get expensive quickly.

[Om_Audio]

Thats why I bought this project at spark upon recommendation from another forum member.
https://www.sparkfun.com/products/9485

Works great!

Care to share how you boxed it up? I ordered the kit today.
Thx,
C

[sgmezei]

I actually have yet to box it up. Just use it on my desk and put it away. I have been too lazy to use a dremel and cut out a square hole for the screen.

[TNblueshawk]

My thought on the cap accuracy is the DMM is good enough for me to 'get me in the range' so to speak. In other words if I'm in the ballpark and I'm not sure many times the DMM is close enough to let me know what the cap is likely. If I was designing circuits and needed to be spot on kind of thing then the DMM is not the way to go.

I have a lot of those caps you have Om. I got a ton of them from somewhere, sort of a grab bag but I don't remember where.

[Om_Audio]

My thought on the cap accuracy is the DMM is good enough for me to 'get me in the range' so to speak. In other words if I'm in the ballpark and I'm not sure many times the DMM is close enough to let me know what the cap is likely. If I was designing circuits and needed to be spot on kind of thing then the DMM is not the way to go.

I have a lot of those caps you have Om. I got a ton of them from somewhere, sort of a grab bag but I don't remember where.

Ya, I think I have like 3 or 4 caps for the Sabertooth that are low enough that the DMM I have gives me no reading at all or is way off to the point where I simply cannot trust it. I ordered the kit mentioned above, I'm excited to be able to get accurate readings. It is actually a part of my learning process to see the values.
I went on a spree at Radio Shack a few times and bought some random assortments- that's where those came from. At the time I thought it might have been a waste of money but actually the part bags have come in handy. Way more expensive than online but good to have a local shop to go to when you get all excited.

C

[Om_Audio]

So I assembled this kit tonight and it works good. Thanks Scott for the tip!
I added the leads which are handy. I do notice some caps actually swing a lot and some swing over 100p at times and other caps are almost dead solid while being tested. Do you notice this on yours? I'm not using the ideal power supply at 1000ma but it is the only one I could find with center pin as positive- seems to be fine though- voltages on IC pins 7 and 20 are just under 5V and pin 10 shows just under 2.5V so I know the ocillator is ok.
Anyway, I def find it interesting to see how far off some caps are from their rated and how like I said some caps just don't seem to present stable capacitance. The blue 561 shown above is especially so- all of them I have behave this way and even stranger I have left it on my DMM it reads up to 769 right now. If I warm it up with my fingers it starts dropping. Just cool to learn all these little idiosyncracies of things!

[TNblueshawk]

Dang, that was fast. I ordered that kit too. I let some folks over at BYOC know and they reminded me of some folks that put their into an enclosure when a cap kit was making the rounds awhile back.

http://www.buildyourownclone.com/board/viewtopic.php?f=9&t=41447

[Om_Audio]

Ya I was reading in the manual that putting it in a metal enclosure and grounding it would make it more accurate with smaller cap values. The trouble is the heights of some things are above the display and then the socket to place the caps to be tested is way below the level of the display. You might consider raising the display a bit to be above everything (caps/tranny/DC jack) and then find a way to extend or raise the socket for the caps. Using the test leads would be easiest. Anyway be aware before you solder if you are planning on boxing it up later. I just soldered the caps in backwards and holy s**t I never seem to get any better at removing/repopulating parts it is really difficult. (I might end up trying one of those blade solder tips).
Thanks for that link, I watched the Peak video demos on youtube and man those are awseome units!
C

[sgmezei]

Wow you got that fast dude!

I have not had any trouble with my meter as of yet and it seems to be very accurate. Have you been zeroing it when you turn it on?

I don't know how to put this into an enclosure without having it be a PITA! Let me know if you do.

[Om_Audio]

Wow you got that fast dude!

I have not had any trouble with my meter as of yet and it seems to be very accurate. Have you been zeroing it when you turn it on?

I don't know how to put this into an enclosure without having it be a PITA! Let me know if you do.

Ya I zero it, it just seems on certain resistors it never settles and the displayed values keeps changing. On some caps it is minor like only the hundreths place changes but on some other caps it swings a LOT. Most caps read quickly and shows a stable result right away, so I am really thinking it is the cap not the unit. I have had to reset it a few times after testing a few caps it won't give a correct reading and power cycling the unit fixes it.
If and when I box it up I will def share the results- I agree it seems a PITA to do it in metal nicely

C