Actually, to not be to do metric what do not need branch is so clear, can substantially thinks tall nicety, tall accurate, small error is a meaning. But, to “ precision ” one word, can decompose composition to see 3 essential factor:

 

1.Temperature coefficient. Temperature change is the archenemy of resistor, temperature coefficient expresses with Ppm/ ℃ commonly, namely temperature changes 1 degree of corresponding resistor change hundred. 100ppm/ ℃ is 0.01%/ ℃ .

 

2.Ageing. Namely long-term stability, use Ppm/ commonly year will express, useful also %/ year come denotive. Leave factory again how accurate resistor, if ageing is big, so changed very quickly, also lose tall precise meaning.

 

3.Initiative adjust an error, this actually not quite important, how much is knowing error, otherwise becomes irrespective, when measuring, can amend. Accordingly, did not do in the article do not discuss.

 

Not quite tall to precision resistor, we need not be divided, say how much some resistor precision is generally. For instance the resistor of 0.1% precision, it is an integrated error, it is to say actually, fall in normal temperature (for instance 10 ℃ – 35 ℃ ) , 1 year in, include all errors, should still can make sure resistor is in 0.1% in.

 

But, to the place with high demand, the particular character of resistor will be checked, such gift are nice choose. The article will mix common high accuracy resistor according to temperature coefficient two index do ageing to be described.

 

Common accurate resistor has 3 kinds: Metallic film resistor, line is circled resistor is mixed a resistor.

 

Metallic film resistor is the commonnest, but it is resistor of accurate metal film betterly, the characteristic is temperature coefficient not quite, block value is stabler. But because film is thinner because this is opposite a few flimsier, helix cut and crimp share give an issue easily.

 

·The line circles resistor also is very commonly used, be high accurate equipment for a time even advocate hit resistance. Adoption resistor silk data has 3 kinds now:

– – constantan, older, heat-resisting but temperature coefficient is not quite good, the hot electromotive force with copper is taller.

 

– – manganin, have accurate manganin, although heat up but temperature is not quite high but temperature coefficient is very small, the hot electromotive force with copper is small, it is the line that introduces extensively circles resistor material.

 

– – Evanohm, be translated into Aifonuomu, it is chromium of a kind of nickel aluminum-copper alloy, OK also alloy of abbreviation nickel chromic resistor, temperature coefficient is the smallest, data is harder, weldability can be not quite good.

 

·Piece resistor, call tinsel resistor again, foreign manufacturer is a delegate with Vishay, it is to be in radical of pottery and porcelain piece stick on alloy resistor layer is engraved without sensitization next, used data of alloy of nickel chromic resistor not only, and underlay of pottery and porcelain does farther temperature compensation, make temperature coefficient very small, can accomplish <1ppm/ ℃ more very much. Homebred model is RJ711, performance is a few poorer.

 

Classify characteristic graph for accurate resistor below, fundamental data is to be based on his old collection, accumulate, the test is arranged and become. Cross axle is temperature coefficient, x-axis is ageing rate, accordingly, any resistor can have a place in this graph, stand by more left it is good that next horns show resistor is jumped over.

 

 

One introduction is made to these typical resistor respectively below.

 

1.Resistor of common metal film, bulk is compared commonly small, resistor film is thinner, temperature coefficient and ageing are general, besides tall block (> 1M) with low impedance (<5) beyond, 1% can assure.

 

2.Green gown resistor. This is the appellation of the resistor of film of a kind of metal that appears to the later period in 80 time, show bottle green because of the exterior and get a name, see in MF12 and MF14 avometer. But the actual measurement according to oneself, performance is average, ageing, deviation and temperature coefficient differ with red gown resistor very big.

 

3.Red gown resistor, code name RJJ, high stable low temperature spends film of coefficient nicety metal, volume is large, function is very good, through oneself test, old resistor, ageing has more than 0.5% rarely, temperature coefficient is controlled in 30ppm/ ℃ . Ask an attention, red gown resistor still has one kind is common precision, code name RJ, performance is average.

 

4.Common thread circles resistor, use manganin or constantan resistor silk, blame is sealed (go up only lacquer) , because line means is general thicker ageing target is accordingly good, but it is too good that temperature coefficient does not calculate, it is 15ppm/ ℃ arrives between 35ppm/ ℃ commonly.

 

5.Narrow line is circled, resistor silk uses accurate manganin commonly, sealed hind stability gets rising, checked many 0.01% resistor actually, great majority still can maintain after several years in 0.02% in. Temperature coefficient also reachs higher level because of select material and craft, it is 5ppm/ ℃ arrives between 20ppm/ ℃ about. Taste the price newly about 5 yuan / .

 

(additional, homebred still a kind of tall sealed line is circled, stability is betterer)

 

 

 

6.Low TC (temperature coefficient) the line circles resistor, common at vintage abroad (for instance Fluke) in all sorts of accurate instruments, employ alloy of nickel chromic resistor, temperature coefficient is very low, arrive in 1ppm/ ℃ commonly between 5ppm/ ℃ , some resistance marked each times actual measurement temperature coefficient. Ageing is not big also, be in basically 20ppm/ year in, secondhand the price about 10 yuan / . After such resistor undertakes demarcate, can be used as average level resistor.

 

 

 

7.Hermetically sealed line is circled, resistor silk material is Alexandrine, but use metallic case sealed (down-lead is hind solder) because this stability is very tall,put an end to moisture and oxidation completely, achieve 8ppm/ or so years, temperature coefficient also is mostly in 1ppm/ ℃ , use extensively at old generation high order and degree in metric instrument and standard resistor, I have a special implied meaning to had made detailed introduction. Secondhand the price about 50 yuan / .

 

 

8.Model seals a resistor. Because use alloy of nickel chromic resistor and compensation technology, what temperature coefficient can do is very low, even <1ppm/ ℃ . But because this resistor is sealed not quite good accordingly aging characteristic is not very good, can assure 25ppm/ only year, the model is worth 12.5ppm/ year. Taste the price newly to make an appointment with 50 yuan / , secondhand about 20 yuan / . Such resistor often also is had a fever by acoustics friend is used, because besides afore-mentioned character, still have super- low noise and without the good character such as feeling.

 

 

 

 

 

 

 

 

9.Gold seals a resistor, this is current the resistor of highest grade, internal composition is Alexandrine but use cermet sealed (the appearance is similar brilliant brace up) , put an end to outside ageing element thoroughly, at the same time technology of 0 temperature coefficient makes temperature coefficient is achieved very difficult measure the level that come out. Ageing model is worth 2ppm/ year, some achieves 0.5ppm/ year the following. Taste the price newly about 400 yuan / , western country executes block to our country, forbidden entrance is used at martial end, also used even 8 avometer 3458A of half merely (become in-house standard resistance) .

 

 

 

 

 

 

 

 

 

 

Should see, even if is same kind resistor, not different manufacturer, coetaneous product, the difference is very big also, the range that a type just seeks as far as possible here just.

 

Add: What resistor had better avometer of pressing with a finger use?

 

Choice resistor should read the order and degree of avometer, use the 1/4 of grade or 1/5 commonly, for instance of 2.5 class choose 0.5% , of 1 class choose 0.2% or 0.25% .

 

What the line circles is best, stable and temperature coefficient is small, but block cost is high do very hard, because this much is of low block value,circle with the line. What see resistor having 5M still is circled with the line exclusively is MF35.

 

Voltage measures the need 3M such as archives to be worth resistor to the tall block of 5M, can choose metallic film only commonly. And the metallic film of tall block high accuracy is more difficult also, film of need tall block (such stability should become possibly poor) , large volume. Film of conventional accurate metal of red gown RJJ is very appropriate.

 

If,spare condition falls very pursuit function, can choose film of metal of 6 annulus 1M the resistor of 0.1% many undertake establishing ties.