Electronics > Metrology

Any resistor series, that are stable wrt time/temp, but not precision values

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julian1:
I want to make resistor dividers, that have low drift over time and have high temperature stability. If calibration and trim can be handled with monotonic/precision DACs - then part tolerance on measured R values is less important.

I discovered Vishay VPG http://au.mouser.com/search/refine.aspx?Ntk=P_MarCom&Ntt=113825677 but the prices are a bit alarming to a newbie.

Great temperature stability of 0.2 PPM / C, but I really don't need 0.01% value tolerance.

Are there any less expensive resistor series on the market that are designed to meet this kind of need?

acbern:
Your question is very unspecific. What is low drift over time and high temperature stability? What do you need?
These epoxy encapsulated VPG resistors may be above 10ppm/year in drift. Better drift-wise are usually wirewounds, but standard types typically in the 3-5ppm/K range.

T3sl4co1l:
There are some resistor packs with precision ratios and only modest overall tolerance, but it really isn't a problem, for macroscopic networks, for all elements to be accurate in the first place.

If you need high stability, you might as well get the high accuracy too.

Tim

Cerebus:
Vishay have the NOMCA series, 8 resistors in a surface mount package, under £4 GBP each in small quantities. These are the best bang-for-buck that I've found so far in matched resistor networks.

25ppm tempco overall, 5 ppm tempco tracking
0.1% basic tolerance, 0.05% ratio tolerance.
Stability 0.05%/1000hrs, ratio stability 0.015%/1000hrs.

All the resistors in the package are the same value but you can make a set of dividers by using parallel and series combination that are going to take advantage of the matched ratio tempco and stability ratings while being on the same substrate. Only available in 1k, 2k, 5k, 10k, 20k and 50k off the shelf, but Vishay will make them to order in any value but of course that would come at a price

Depending on your design, it might take a bit of cunning to make the particular layout of these suit your purposes. Again, depending on your design, you might get better overall performance out of these than out of say, several Vishay dedicated MPM dividers which have 2ppm ratio tracking each, but obviously wouldn't have tracking between separate packages.

If you need better stability or tracking performance than these then you are going to have to step up in price.

julian1:

--- Quote ---you can make a set of dividers by using parallel and series combination
--- End quote ---

It's obvious when explained, but I wouldn't have immediately thought of this.
 

--- Quote ---take advantage of the matched ratio tempco and stability ratings while being on the same substrate.
--- End quote ---

The idea being that if they're on the same substrate - then they're at the same temperature, so temperature effects should cancel in a divider configuration. Much like thermally-bonding a npn and pnp pair. Thanks.
 

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