pensive

i have schematics requesting a pair of resistors be matched to within .1% tolerance
i am soon to purchase a new multimeter and have perused their specifications/data sheets
i have seen accuracy of ohmeters specified to .1% and even .07% ohms
are there others with finer accuracy?
do any "inexpensive" multimeters with similar specs exist?
any recommendations from those with a familiarity?
thankyou
 
human prototype said:
i have schematics requesting a pair of resistors be matched to within .1% tolerance
i am soon to purchase a new multimeter and have perused their specifications/data sheets
i have seen accuracy of ohmeters specified to .1% and even .07% ohms
are there others with finer accuracy?
do any "inexpensive" multimeters with similar specs exist?
any recommendations from those with a familiarity?
thankyou

Why bother? Just buy some high precision resistors (0.1% or better). Even a pair of 0.01% resistors would cost much less than a high-precision multimeter. For a list of resistor manufacturers, check out 'http://www.diydb.org/links/component.html', under 'Resistors'. You'll need to work with one of their distributors to get your parts.

Good luck.
 
Forget meters!

Use a wheatstone bridge:

http://www.measurementsgroup.com/guide/glossary/wheatsto.htm

http://www.inform.umd.edu/EdRes/Topic/Chemistry/ChemConference/Software/ElectroSim/Wheatstone.html

You need only 2 very well matched resisors and one multi turn pot to calibrate it (in one branch the pot and the first matched resistor, on the other branch one reistor equivalent to half the pot and the second resistor). Trim the pot to have equilibrium (0v between the two middle part of each branch, use a high impedance millivoltmeter).

Once it is calibrated, replace one of the matched resistance with the one you want to measure.

If you want only match resistance and you don't care about absolute value, you can forget the matched resistance and use only the ones you want to match.

Use high quality metal film resistance (value should be within the value you measure) and cermet ajustable pot (twice the value), high quality binding post and take care of component temperature. Voltage should be low to avoid temperature rise, but enough to have sufficent sensibility (about a couple of volt).

When properly used, this is the most sensitive resistance meter...

[Edited by martinc on 07-30-2001 at 06:27 PM]
 
Thoth said:


Why bother? Just buy some high precision resistors (0.1% or better). Even a pair of 0.01% resistors would cost much less than a high-precision multimeter. For a list of resistor manufacturers, check out 'http://www.diydb.org/links/component.html', under 'Resistors'. You'll need to work with one of their distributors to get your parts.

Good luck.

but i might have to utilize lower tolerance components where i might end up searching for a needle in a haystack
maybe the extra effort in "hand-matching" the components might be cost-effective, or it might not
thankyou
 
I think you will find that the accuracy spec of most meters has to do with absolute, not relative error. Most meters should be more than capable of letting you match a pair of resistors, they just won't be able to tell you the actual resistance any better than their specified rating. To prove this, just try measuring the value of a resistor several times and see how much deviation you get in the readings.

A bigger problem than initial matching of the resistors is making sure they stay matched once in the circuit. Higher precision resistors will have tighter temperature specifications. Make sure you check how well compensated the resistors you use are for variation in temperature. For example you could hand match a pair of carbon film resistors to within 0.1% but what is the point if they are going to change 1 or 2 percent due to temperature variations.

Phil