EOL's

And you should not ever.

"Robert L Bass" a écrit dans le message de news: snipped-for-privacy@4ax.com...

No, not from you Your not the group

No Robert, the tolerance of a resistor applies to the percentage that it may deviate from it's rating. And then all the other issues I mentioned can apply. Carbon will change over time, especially when subjected to heat and humidity. The tolerance applies to the percentage of deviation from the value shown on the resistor. You know what I meant.

Al

No, Al. The percentage of deviation is a manufacturing issue. The resistor will remain at whatever it was when it was made for time immemorial. Tolerance is not an indicator of the resistor's propensity to change value over time (as you originally stated).

No, Al. The issue where you first stumbled was your understanding (or rather your lack thereof) of what the tolerance is. Tolerance is an indication of the greatest amount that the resistor may differ from its stated value when it is made.

The heat needed to significantly alter the value of a carbon film resistor would be sufficient to ignite the house. As to humidity, that's another area you don't seem to understand. Carbon film resistors are not absorbent. The shell is sealed. Humidity won't affect the inside of the resistor because it isn't exposed.

At the time of manufacture -- NOT over the lifetime of the resistor in a circuit.

I know what you think you mean. I also know you're completely wrong about tolerance. I suggest you study the matter a while. Then come back and correct yourself.

Of course, you can also take the ASA-standard approach and make up "anecdotal evidence" of non-existent field experience with ever-changing resistors, punctuated with personal insults and the usual ASA stupidity. If you're unsure how to proceed with that technique, contact Olson. It's his area of expertise.

How much experience do you really have at servicing electronic systems, Robert? I was trained as an associate engineer in electronics, the man between the engineers and the manufacturing floor. My experience also includes the manufacturing and repair of X-ray equipment as well as all kinds of analogue and digital electronic systems. I worked as a NuTone Service Center as well as other manufacturers.

Your assessment of the "resistor" is not practical but rather theoretical. Humidity and temperature most definitely play a major part in the stability of carbon in a resistor. This is one of the most fundamental facts taught in electronic school in lab. It's also one of the facts you are bound to discover when servicing electronic systems on the work bench. Exposure to lightning is also another factor, but only because of the heat that such an intense current will cause inside the carbon of a resistor component.

Al

obviously not numbnut or the OP would not have posted his question.

He's just trying to be a thorn, Al. Don't let him get under your skin. He also 'says' he didn't believe in the green corrosion that sometimes gets on resistors and can affect their operation and cause them to break. As you say his knowledge is purely theoretical, no real life experience outside of the slammer.

I don't mean to belittle you as you are obviously trying to do to me, but you really show how little practical field or bench repair experience you have when you say that high temperatures, combined with high humidity cannot affect resistance in a carbon resistor.

Although it may not be common for a field resistor to change value based on high ambient heat and high levels of humidity, it can and does happen in the real world. To tell anyone that this is not so is doing them a disservice. Also, perhaps this man's resistor suffered an induced high current due to a nearby lighting strike, in which case the excessive heat caused by the high current could have super heated the carbon, causing its properties to change.

What I've told him I stand behind from both my electronic training and my experience in the field, which includes 4 years of schooling, 18 years of field experience, and more than 15 years of work in trade journalism working with the men and women who work in the field in security. I also hold a technican's class amateur radio license, KC80CV.

I stand behind my statement 100% unless someone else who has some real engineering knowledge can step up and refer me to an on-line source of information that says, as you have, that temperature and humidity, combined with time, cannot change the value of a carbon resistor. That's my final word until that day comes.

Al

I know he is trying very hard to yank my chain. I can see why so many of you truly tire of him. He's attacked me several times in this news group and I've tried to be a gentleman about it by not responding in kind. I don't play games with people, but he can sure stretch one's composure. :-)

Back in the 90s I had asked him to do a sidebar on power supplies for one of my technical stories when I was with SDM Magazine. He said he would do it and so I continued on my other work. I contacted him several times about the issue and he continued to insist that he would get it to me. When we came down to crunch time I called him and he said he hadn't done it yet. When I pressed him he became angry and stated that he always knew I had other people do my work for me. I told him promptly that I can write the thing myself but was only trying to give him some exposure in SDM. I hung up and promptly wrote the darn thing myself in 10 minutes time. Since then, he's tried to cause others to question my technical knowledge in this news group. He's certainly a card, is he not? :-)

Thanks for the return comment.

Al

Don't feel too bad, as you know ; No good deed goes unpunished. A card, yea that's one way of putting it. I wonder where that expression came from, "he's a card" ?

It is not terribly unusual to find an EOL on a fireloop that has drifted far enough out of specs so as to cause a loop trouble or a short.

Hmmm, I lost Bass in the Noise... Al is coming through with a 5/9 + 30 DB ..... 73 Al, Russ KN6SD

off to the races...

I used to run into that all the time with DSC 1550's

OK!!! OK!! Ok!

As the Original Poster on this topic I was hoping that this would have been simple calm discussion. But NOOOOO!!

You guys amaze me to no end. Therefore I did what I was trying to avoid and did a Google search to try and find the answer to my question. After searching on [resistor value tolerance] I received 446,000 hits. I did not read them all, nor did I find my answer, but I did find some supporting information on both sides of the fence. Could it be that everybody is RIGHT????

I have included some of my findings below. You can all read to your hearts content and try and find the part that may support your own special thoughts.

Personally I am moving on to more important issues of the day, like What's for Lunch.

Please find some of the research below.

Have a nice day and a better tomorrow.

Les

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(engineering) From Wikipedia, the free encyclopedia Jump to: navigation, search Tolerance in engineering is an allowance, given as a permissible range, in the nominal dimension or value specification of a manufactured object. The purpose of a tolerance is to specify the allowed leeway for imperfections in manufacturing the part or component.

The tolerance may be specified as a factor or percentage of the nominal value, a maximum deviation from a nominal value, an explicit range of allowed values, be specified by a note or published standard with this information, or be implied by the numeric accuracy of the nominal value. Tolerance can be symmetrical, as in 40±0.1, or asymmetrical, such as

40+0.2/-0.1.

It is good engineering practice to specify the largest possible tolerance while maintaining proper functionality, since closer or tighter tolerances are more difficult to manufacture and hence cost more to either build or buy.

Tolerance is different from safety factor, but an adequate safety factor will take into account relevant tolerances as well as other possible variations.

[edit] Electrical component tolerance An electrical specification might call for a resistor with a nominal value of 100? (ohms), but will also state a tolerance such as "±1%". This means that any resistor with a value in the range 99? to 101? is acceptable. It would not be reasonable to specify a resistor with a value of exactly 100? in any case, because the exact resistance will vary with temperature, current and other factors beyond the control of the designer.

are constructed to provide predetermined resistances. Most common resistors are guaranteed to be within 5% of their marked value. ('Metal-oxide' resistors with a blue body are guaranteed to meet their marked value plus, or minus 1%.)

Although you may find any of the above colors in the third band, red, orange, and yellow are the most common. In some cases, the third band will be silver or gold. You multiply the first two bands by 0.01 if it is silver, and 0.1 if it is gold. The fourth band, which is the tolerance band, usually does not present too much of a problem. If there is no fourth band, the resistor has a 20-percent tolerance; a silver fourth band indicates a

10-percent tolerance; and a gold fourth band indicates a 5-percent tolerance. Resistors that conform to military specifications have a fifth band. The fifth band indicates the reliability level per 1,000 hours of operation.

come in standard values such as 1K, 2.2K, 4.7K, and so on. Why these values? Consider a range of resistors with a 10% tolerance. The resistors are designed with values such that a 10% variance of one resistor would meet or overlap with the 10% variance of the next resistance value.

To clarify, the 10% tolerance range for a 1K resistor would be 0.9K to 1.1K. So the next resistor value going up the scale would be 1.2K since it's 10% tolerance range would be 1.08K to 1.32K. The lower end of the tolerance range for the 1.2K overlaps a little with the upper end of the range for the

1K.

In the case of a range of resistors with a 5% tolerance, there would have to be more unique values to allow for overlap. Starting with the 1K resistor, the next resistor value up the scale would have to be 1.1K to allow for an overlap. Resistors with a 20% tolerance on the other hand would have bigger jumps between values. Starting with the 1K resistor, the next value up the scale would be 1.5K. In this case, the upper value for a 1K would be 1.2K, while the lower value for a 1.5K would be 1.2K.

values Standard resistors are manufactured in values from a few milliohms to about a gigohm; only a limited range of values called preferred values are available. In practice, the discrete component sold as a "resistor" is not a perfect resistance, as defined above. Resistors are often marked with their tolerance (maximum expected variation from the marked resistance). On color coded resistors the color of the rightmost band denotes the tolerance:

silver 10% gold 5% red 2% brown 1%. Closer tolerance resistors, called precision resistors, are also available.

[edit] 5-band axial resistors 5-band identification is used for higher tolerance resistors (1%, 0.5%, 0.25%, 0.1%), to notate the extra digit. The first three bands represent the significant digits, the fourth is the multiplier, and the fifth is the tolerance. 5-band standard tolerance resistors are sometimes encountered, generally on older or specialized resistors. They can be identified by noting a standard tolerance color in the 4th band. The 5th band in this case is the temperature coefficient.

is the extent to which the resistor value sways from the original value. You may think as to why the resistance value should change from the printed value? Well, we live in a world that is far from perfect and resistors are no exceptions. Their value changes mainly due to the change in temperature.

You mean like you just did??

I agree, but it's more rare when you use low-tolerance or precision resistors. Those who use 20% resistors are more likely to find this kind of situation. Most of the time such drift is not excessive and out of a panel's ability to forgive. Sometimes it can be a problem, for sure.

Al

Les,

I only gave you the benefit of my years in the field and my electronic training. I don't really care who is right so long as you get the right answer.

It's like james bond said many years ago, "never say never" :-) Anyway, thanks for the information. Hope you solved your problem, hope you figured out why the EOL did that to your satisfaction. If I can ever be of assistance, just send me an e-mail.

Al

This is RLB doing what he does best, he takes a statement from a poster, distorts it, deliberately misquotes it and attempts to ridicule the original poster while at the same time trying to impress others with his newgooglefound knowledge. The bottom line is that the value of a resistor can change over a period of time, even someone as obtuse as RLB should be able to understand that if you start with a resistor that is 20% off its nominal value, it will take less of a change to put its value outside the tolerance range of the control panel than a resistor that starts off within 5% of its nominal value. This in a nutshell is what I believe Al originally meant in the first place.

Doug L