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Old 10th September 2006, 10:40 PM   #1
Nordic is offline Nordic  South Africa
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Talking Resistor matching tip

Resistors often come in long stips...

When buying new ones, I take a pen and my multimeter and measure each one (without removing it from hte paper strips), then write down tha last digit from the multimeter display below each resistor... quick and painless.. Then in future when I need a matched set I just find two with the same number....
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Old 13th January 2007, 01:55 AM   #2
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Great simple little tip! Till now, I'd just find the best two matches, then have to do it all over again the next time!

PS Trying to find your thread on the voltage regulators. Finnaly gaot mine going.
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Old 13th January 2007, 12:09 PM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
then connect them in series (using terminal blocks) for super matching or into a measuring bridge. Better than 0.1% matching is easily achieved.

Any thoughts on absolute accuracy? or how to get close?
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Old 13th January 2007, 04:09 PM   #4
Ron E is offline Ron E  United States
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I think one way for a DIY to get more accurate measurements is to start with something like this:
http://focus.ti.com/docs/prod/folders/print/ref102.html
...and build from there.

For resistors it would be best to have a connecterized resistor measured with an NIST traceable meter, then used as a reference for the type of voltage divider ckt described by andrew, or a bridge ckt. With the bridge, once zeroed, you could match very closely indeed, even with unknown bridge resistors.

For low ohms, you need a kelvin ckt or a constant current source.
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Old 13th January 2007, 04:16 PM   #5
AndrewT is offline AndrewT  Scotland
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help,
Kelvin ckt?
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Old 13th January 2007, 05:19 PM   #6
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Quote:
Originally posted by AndrewT
help,
Kelvin ckt?
4 terminal measurements - 2 for a current source, 2 for voltage sense,

Good DVMs and PSUs (higher res) always have them.

Here is my resistance box I made over 30 years ago, the lower values have 4 connections to eliminate lead resistance.
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