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???
02/22/06 14:17
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 		 #110482 - Distributor of your confidence
Responding to: ???'s previous message
Bruce said:
Have you given any thought as to how one might use these measurements to work the problem in reverse? That is, to determine the accuracy of the manufacturers equipment?

Sorry for being late, Bruce!

Many years ago we ordered some dozens of TL072C from a distributor in our region. The TL072C is specified to have an offset voltage of typical 3mV and maximal 10mV. But when we tested our circuit, we recognized abnormal offset voltages. The strange was, that we couldn't find any OPamp showing an offset voltage of less than 3mV. Everything from -10mV to -3mV and from 3mV to 10mV, but nothing in the range from -3mV to 3mV!

We contacted our distributor and asked him about the reason. He told us, that sometimes they select OPamps showing narrow tolerated offset voltages. The rest of the batch they sell as 'standard' OPamps then. He told us that this would be legal, because the sold OPamps would not violate the maximum specifications.

So, if you trust that a from batch of Opamps the most candidates of them will show rather little offset voltage, because the manufacturing tolerances are assumed to be Gaussian distributed, then you can experience a big surprise, if the 'distributor of your confidence' has fumbled with the chips.

Kai

List of 157 messages in thread
TopicAuthorDate
Measuring capacitance very precisely.            01/01/70 00:00      
   "I want the best money can buy, but I do            01/01/70 00:00      
      In this specific case I disagree.            01/01/70 00:00      
   Bridge?            01/01/70 00:00      
      Bridge!            01/01/70 00:00      
   AC bridge            01/01/70 00:00      
      Error Sources            01/01/70 00:00      
         Blumlein Bridge            01/01/70 00:00      
            Blumlein Bridre.            01/01/70 00:00      
               Bridge excitation            01/01/70 00:00      
            Blumlein            01/01/70 00:00      
   Let the statistics be your friend...            01/01/70 00:00      
      frequency meter            01/01/70 00:00      
      Product as a Transfer Standard            01/01/70 00:00      
         Distributor of your confidence            01/01/70 00:00      
            Suppliers like that ...            01/01/70 00:00      
               why blame the suppliers            01/01/70 00:00      
                  Not at all            01/01/70 00:00      
                  Hah!            01/01/70 00:00      
      Statistics for reference determination.            01/01/70 00:00      
         You got it!            01/01/70 00:00      
   questions            01/01/70 00:00      
      he wants to select to 0.1% from 1% stock            01/01/70 00:00      
         that is a bad idea            01/01/70 00:00      
            Hmm            01/01/70 00:00      
      That's a good way            01/01/70 00:00      
         posts cross timed            01/01/70 00:00      
            It makes sense to select them            01/01/70 00:00      
      No sorting of Caps.            01/01/70 00:00      
         then, are you not using the wrong approa            01/01/70 00:00      
            Time constant            01/01/70 00:00      
            Re: Eliminate cap sorting            01/01/70 00:00      
               Example            01/01/70 00:00      
               you do not need precision, you need rate            01/01/70 00:00      
         Would it not be easier the other way?            01/01/70 00:00      
            Difficult            01/01/70 00:00      
               Yes Digital Difficult.            01/01/70 00:00      
                  I think the point has been missed again.            01/01/70 00:00      
                     Demo ?            01/01/70 00:00      
                        Difficult to change now.            01/01/70 00:00      
                           Don't worry            01/01/70 00:00      
                              Re: Dont Worry.            01/01/70 00:00      
                                 How to calibrate an integrator?            01/01/70 00:00      
                                    Re: How to calib. an integratrator.            01/01/70 00:00      
                                       Answers            01/01/70 00:00      
                                    256Hz too fast.            01/01/70 00:00      
                                       Integrator and RMS using DSP            01/01/70 00:00      
                                          Whats available easily.            01/01/70 00:00      
                                             dsPIC30F2010            01/01/70 00:00      
                                                500 kSPS            01/01/70 00:00      
                                                   This little PICcy got eaten, the SILabs            01/01/70 00:00      
                                                      Is that useful?            01/01/70 00:00      
                                                         Planning to use dspic.            01/01/70 00:00      
                                                         Speed ?            01/01/70 00:00      
                                                            But for what purpose?            01/01/70 00:00      
                                                               MAC            01/01/70 00:00      
                                                                  it is amazing            01/01/70 00:00      
                                                                     Here is the analysis            01/01/70 00:00      
                                                                        the content, not the words            01/01/70 00:00      
                                                                           analysis please            01/01/70 00:00      
                                                                              since you, just like me, have no idea ab            01/01/70 00:00      
                                                                                 Ah! The Horatio quote version 2!            01/01/70 00:00      
                                                                                    again, you focus on words, not content            01/01/70 00:00      
                                                                                       Which is why I asked...            01/01/70 00:00      
                                                                                          If what you are saying is that I can not            01/01/70 00:00      
                                                                                          I had to.            01/01/70 00:00      
                                                                                             You said it!            01/01/70 00:00      
                                                                              Analog integrator            01/01/70 00:00      
                                       How do you calculate the RMS?            01/01/70 00:00      
                                          RMS in detail.            01/01/70 00:00      
                                          Out of interest.            01/01/70 00:00      
                                             wot you want a RMS demo,steve??            01/01/70 00:00      
                                                FIXED point            01/01/70 00:00      
                                                   fixed point is almost as bad            01/01/70 00:00      
                                       Alternative            01/01/70 00:00      
                                          NCO again            01/01/70 00:00      
                                             Would be nice            01/01/70 00:00      
                                                Timer2 of 89C52            01/01/70 00:00      
                                                   clever            01/01/70 00:00      
                                                      Oops! Incomplete statement            01/01/70 00:00      
                                                         Clock feedthrough            01/01/70 00:00      
                                                            Maxim App note            01/01/70 00:00      
                                                               Nice links, thanks!            01/01/70 00:00      
                                                               AD9832            01/01/70 00:00      
                                                            sine vawe            01/01/70 00:00      
                                          Re: Alternative.            01/01/70 00:00      
                                             Will work            01/01/70 00:00      
                                          Re: 64Hz Gain 1.126.            01/01/70 00:00      
                                             Maximum input voltage range            01/01/70 00:00      
                                                Re: Max. Input voltage Range.            01/01/70 00:00      
                                                   You have got it            01/01/70 00:00      
                                                      indeed, and            01/01/70 00:00      
                                                         Is the resistor in gnd really needed.            01/01/70 00:00      
                                                            Negligible with CMOS Opamps            01/01/70 00:00      
                                                               Re: Negligible with CMOS Opamps.            01/01/70 00:00      
                                                                  Most opamp datasheet do specify            01/01/70 00:00      
                                                                  Input Bias Current            01/01/70 00:00      
                                                                  Impedance matching            01/01/70 00:00      
                                                                     Re: Impedence Matching.            01/01/70 00:00      
                                                         yess balancing is required and to that..            01/01/70 00:00      
                                          4u7 Cap polarity and type.            01/01/70 00:00      
                                             Foil caps are needed            01/01/70 00:00      
                                                Available Capacitors.            01/01/70 00:00      
                                                   This one            01/01/70 00:00      
                                                      What are these MK equivalents            01/01/70 00:00      
                                                         MKT, MKP, MKC, KT, KP, KC,...            01/01/70 00:00      
                                                            Thanks Kai,            01/01/70 00:00      
                                          Ground Planes.            01/01/70 00:00      
                                             Have you had problems?            01/01/70 00:00      
                                                RE: Have you had problems.            01/01/70 00:00      
                                                   Keep the oscillator away from output            01/01/70 00:00      
                                                      Board Layouts.            01/01/70 00:00      
                                                         Recommendations            01/01/70 00:00      
                                                            Corrected Board            01/01/70 00:00      
                                                               I try to draw it for you            01/01/70 00:00      
                                                                  RE: I try to draw it.            01/01/70 00:00      
                                                                     Here it is            01/01/70 00:00      
                                                                        RE: Corrected Ver 2.0            01/01/70 00:00      
                                                                           Answers            01/01/70 00:00      
                                                                              Re: Corrected Ver. 3.0            01/01/70 00:00      
                                                                                 Some hints            01/01/70 00:00      
                                                                                    Re: I am in trouble.            01/01/70 00:00      
                                                                                       Sorry!            01/01/70 00:00      
                                                                                       Is this schematic correct.            01/01/70 00:00      
                                                                                          Corrections            01/01/70 00:00      
                                                                                             Re: Correction.            01/01/70 00:00      
                                                                                                Mylars will do            01/01/70 00:00      
                                                                                             Corrected Board and schematics Ver 4.0            01/01/70 00:00      
                                                                                                Why not doing it like this?            01/01/70 00:00      
                                                                                                   Re: Corrected boards ver 5.0            01/01/70 00:00      
                                                                                                      Some hints            01/01/70 00:00      
                                                                                                         Corrected board ver: 6.0            01/01/70 00:00      
                                                                                                            Please remove it...            01/01/70 00:00      
                                                                                                               Yes removed Gnd plane from mount hole.            01/01/70 00:00      
                                                                                                                  Looks good now            01/01/70 00:00      
                                                                                                                     Does than mean Green signal.            01/01/70 00:00      
                                                                                                                        Yes            01/01/70 00:00      
                                                                                                                           Thanks Kai.            01/01/70 00:00      
                                                                        trying to understand that            01/01/70 00:00      
                                                                           DC impedance of ground plane            01/01/70 00:00      
                                          bipolar swings how and where?            01/01/70 00:00      
                                             Here            01/01/70 00:00      
                                                explain a bit please            01/01/70 00:00      
                                                   Explaination            01/01/70 00:00      
                           Me ?            01/01/70 00:00      
                        Exactly!!            01/01/70 00:00      
   as requested a demo.....,sort of            01/01/70 00:00      
   simulation results of the demo...sort of            01/01/70 00:00      
      Thanks Jez.            01/01/70 00:00      
   Changing Q7 to Q9.            01/01/70 00:00      
   AD7142/AD7745            01/01/70 00:00      
      Only good for a few pF            01/01/70 00:00      
         My apologies            01/01/70 00:00      
            No need to apologize!            01/01/70 00:00      
         Nice part            01/01/70 00:00      
   Built Precision Sine Wave Generator.            01/01/70 00:00      
      Good luck            01/01/70 00:00      

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