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Out of spec resistors

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I am working on a decade resistor box project and  I bought a bunch of 1206 0.1% tolerance resistors.  I had to go to four of the main distributors and use 4 different well known top manufacturers to get things that were in stock.  These range from 0.1 ohm to 1M and I bought 500 of each size(.01 & 1.0 are 1%).  So I just got my new fluke bench meter that is freshly calibrated and I thought just for the fun of it I will test some to see what they look like.  I picked the 10K ones and started measuring them by using the kelvin probes poked thru the back side of the tape strip.  I got 17 out of 100 were out of spec on the high side.  I called the distributor  and in about an hour two techs from the manufacturer call me about the problem.  The ask me about my instrument and measuring technique and find nothing I am doing wrong.  Since I don't know how good the Fluke kelvin probes were I volunteered to get regular kelvin clips and measure them again.  Same out of spec readings.  By now all the other values have showed up and I measure a bunch of each value, all are in spec.   And two of these values were the same brand as the out of spec 10K resistors.  Per the manufacturers request I sent the 17 with my measurements for them to measure but it sure seems like these will be out.  I am somewhat new to electronics so Is this common? Do you have to inspect all your product when it comes from top name suppliers and manufacturers?

this is very interesting.

I remember Dave having problems with his microcurrent probe and the 0.1% resistors.
Is something going on at the resistor manufacturer.
Or are they all sourced from the same factory?

It does happen.  Dave talked about his bout with it almost a year ago:


I watched eevblog #133.  I was not going to name names, but since my supplier was Digikey and the brand was Bourns I think the names are now relevant. The two other Bourns values I got were from other suppliers and they checked out OK.  I made up a set of Kelvin clip leads using the Meuller gold kelvin clips. I also made a switch unit to reverse the polarity of the drive current.  This allows you to get rid of thermal EMF errors by taking a reading with one polarity and then reversing the current direction and taking a second reading then average the readings (at 10K this is overkill). This drops out the voltages generated by the Seebeck effect of all the connection points. I also set my Fluke 8846A up in math mode to average 40 readings. for each measurement direction.

Conrad Hoffman:
With the fresh meter cal you should be in good shape. It's always nice to have a standard to use, just to be sure everything is still OK. I always keep a calibrated resistor around so I can sleep soundly at night. You don't need Kelvin probes to measure a 10K. They come into play at lower values, depending on your meter resolution and accuracy. I'll usually go for the Kelvin probes below 1 kohm for high precision stuff, and 100 ohms for 4 digit level stuff. Out of spec parts are rare today, but it does happen. It can be quite interesting to record all the measurements and make a bell curve. I've done that for thru hole parts and what's interesting is the curve is sometimes not bell shaped at all. It makes me think there was a selection process going on and part of the population was abducted!


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