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Smart Tweezer LCR ST1 -measurement question

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    Smart Tweezer LCR ST1 -measurement question

    first version of smart tweezers lcr st1-

    When I check capacitance out of circuit smd 0805 for example schematic says 22uf, I pulled 3 off a board 22uf 20% 6.3v and they all measure about 16uf on the RCL the documentation says accuracy capacitance 10pf to 100uf <3.0%
    0.5pf to 4999uf <5.0% Is this right readings for the meter?

    The resistors 0402 for example 10k 4.7k are almost spot on
    33uh on schematic inductor reads 31uh out of circuit.

    10uh to 99mH <3.0%
    0.5 to 999mH <5.0% accuracy inductance
    Last edited by macattack600; 02-19-2016, 10:53 PM.

    #2
    Re: Smart Tweezer LCR ST1 -measurement question

    I don't understand what the question is. Are you asking about a reading of 16uf for a 22uf cap?

    Comment


      #3
      Re: Smart Tweezer LCR ST1 -measurement question

      if they are smd electrolytics they are probably just crap.

      Comment


        #4
        Re: Smart Tweezer LCR ST1 -measurement question

        Originally posted by tw2005 View Post
        I don't understand what the question is. Are you asking about a reading of 16uf for a 22uf cap?
        Yeah I'm getting 16uf for what the schematic says is 22uf any chance you've worked with these rcl tweezer before? I posted the documentation accuracy of the meter i'm using.
        Last edited by macattack600; 02-19-2016, 11:57 PM.

        Comment


          #5
          Re: Smart Tweezer LCR ST1 -measurement question

          no,
          but if your looking at used electrolytics and expecting them to read as marked, forget it.
          your tools are most likely not lying - it's the caps are deteriorated.

          Comment


            #6
            Re: Smart Tweezer LCR ST1 -measurement question

            well i'm not sure if the 0805 is electrolytic I think it's ceramic electrolytic is usually unmarked right this is surface mount no marks
            Last edited by macattack600; 02-19-2016, 11:49 PM.

            Comment


              #7
              Re: Smart Tweezer LCR ST1 -measurement question

              electrolytics are metal cans,
              if you have a rectangle, and it's black or yellow with markings then it's tantalum.
              if it's just coffee coloured and has no + /- markings then it's ceramic.

              Comment


                #8
                Re: Smart Tweezer LCR ST1 -measurement question

                I tested some electrolytics 2 of 4 tested right out of circuit so I know your right I wonder why the ceramics tested much lower the meter is made for smd components especially

                Comment


                  #9
                  Re: Smart Tweezer LCR ST1 -measurement question

                  ceramics are crap, most can drift over 40% +/- at different temperatures.

                  Comment


                    #10
                    Re: Smart Tweezer LCR ST1 -measurement question

                    that explains it I think the meter is still calibrated correctly its a handy tool to give you idea of smd components still have to take out of circuit to get the right reading ,ugh thanks.

                    Comment


                      #11
                      Re: Smart Tweezer LCR ST1 -measurement question

                      The ST1 does have some issues measuring ceramic caps. Mine always reads a lot lower, but the ST5 fixed this. Exerpt here:

                      "... The only case when this little limitation is important is characterization of ceramic capacitors. It is a well known problem and it existed in the previous releases of Smart Tweezers, from model ST1 to ST3 where 0.35 V rms test signal was used. It is known that insufficient test signal amplitude may lead to up to 30% lower measured ceramic capacitor value than the actual value as it is described in the Smart Tweezers manual."

                      Comment


                        #12
                        Re: Smart Tweezer LCR ST1 -measurement question

                        Originally posted by stj View Post
                        ceramics are crap, most can drift over 40% +/- at different temperatures.
                        Wow, a really thoughtful evaluation. Almost every electronic device known to man includes ceramic caps in the design. There are working parameters for nearly everything in the engineering world, and if you know what they are, amazing things can happen. The tweezers are not defective; you are simply seeing physics in action.

                        Directly to the point of the thread, all ceramics are voltage dependent to some degree depending upon the type. Here is an instructive video addressing that very subject!

                        https://www.youtube.com/watch?v=2MQyQUkwmMk
                        Last edited by Longbow; 02-21-2016, 08:32 AM.
                        Is it plugged in?

                        Comment


                          #13
                          Re: Smart Tweezer LCR ST1 -measurement question

                          Misleading marketing of MLCC's is also to blame. Most cap datasheets do not spec the voltage coefficient of capacitance and in practice you'll never achieve the advertised value. Good article on it:
                          "Temp and voltage variation of ceramic caps, or why your 4.7-uF part becomes 0.33 uF"

                          Comment


                            #14
                            Re: Smart Tweezer LCR ST1 -measurement question

                            Hey thanks I figured that was the case
                            Last edited by macattack600; 02-21-2016, 09:49 PM.

                            Comment


                              #15
                              Re: Smart Tweezer LCR ST1 -measurement question

                              There is no misleading marketing or conspiracy behind ceramic capacitors. True, most people don't want to delve into the spec sheets if they are putting together a simple project. On the other hand, just as in all engineering, it takes some homework if you want your ceramic cap to do what you want it to. In practice you WILL in fact achieve the little number stamped on the capacitor if your choice is correct for the circuit frequency, signal amplitude and d.c. offset.

                              I recently rebuilt an HP signal generator with calibrated attenuator. It would do 10 Hz at the bottom end. The generator differential output was coupled to the attenuator with 2 4000 uF electrolytics. At first I was surprised no to find some ceramics or mica capacitors in parallel, but if you plot the reactance of a 4000 uF electrolytic capacitor on the way up to 20 MHz, you will see additional capacitors are not necessary. The 4000 uF figure drops off quickly and becomes very low past 1 or 2 MHz, but that doesn't mean that electrolytics are crap. It means that even with very low equivalent capacitance at higher frequencies, there is plenty of coupling throughout the operating range of the device, which is what you wanted in the first place. What a concept! Sprague didn't hide the information on what their 4000 uF capacitor does at 20 MHz!
                              Is it plugged in?

                              Comment

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