Do you define resistor TC the same way Guildline does? - Page 1
Forum section: electronics / general

author: splin
author_rank: Frequent Contributor
timestamp: April 22, 2020, 11:05:52 pm
content: From the Guildline 9334A standard resistor datasheet:http://www.guildline.com/media/k2/attachments/30165-00-85_K1Z9334A.pdfQuote(My bold)This bewilders me - is their definition of TC (for resistors) a traditional industry standard that has changed over time by other companies/organisations whether due to error, misuse or whatever or simply their own unique standard?Their definition simply makes no sense to me - the datasheet labels the TC as ppm/C but the above quote defines it as ppm per two degrees - misleading and confusing at the very least.

author: bob91343
author_rank: Super Contributor
timestamp: April 23, 2020, 01:10:37 am
content: When I see stuff like this I assume the manual was written by a high school student on summer vacation and the engineer didn't take the time to read it.It's clear to me that the plus and minus signs need to be used intelligently. So 1 ppm/deg C means just that, whether up or down. Every degree results in a 1 ppm resistance change.The temperature coefficient of resistance of copper, and many other metals, runs roughly 0.393%/deg C so a 10 degree temperature change results in a resistance change of about 4%, up if warmer and down if cooler. Manganin and Constantan are much lower, and carbon tends to be in the opposite direction.So forget this hocus pocus about plus and minus. (Hm that may be a good title for a song.)

author: guenthert
author_rank: Frequent Contributor
timestamp: April 23, 2020, 05:26:38 pm
content: Quote from: bob91343 on April 23, 2020, 01:10:37 amIndeed. I don't know the culture at Guildline at the time the document was written (some manuals from HP and IBM from the sixties, seventies are a joy to read and often truly enlightening), but from my own experience at former employers in more recent times, the manuals were written by 'tech writers' which may or may not have had a tech back-ground and may or may not have been involved during development. Those documents were then meant to be proof-read by engineers, but that wasn't a task they enjoyed. Most resulting documents were of little help and often factually wrong and misleading. There even was once a 'best practices' document available to customers, which we internally called 'best to avoid practices' (and I'm guilty in having that one let slip).In the nineties a company we partnered with sent us one of their engineers to stay with us for a week to pick his brain, as the quite exhaustive documentation of their library was outdated and in too many places wrong. Uh well, thanks, I guess.

author: Andreas
author_rank: Super Contributor
timestamp: April 23, 2020, 07:52:31 pm
content: Quote from: bob91343 on April 23, 2020, 01:10:37 amQuote from: bob91343 on April 23, 2020, 01:10:37 amThis is the temperature gradient (derrivation) of the temperature, not the temperature coefficient.The temperature coefficient is usually defined per "box method"Usually with 3 temperatures: minimum, nominal and maximum (operating) temperature.So in the example above:22 deg = - 0.4 ppm23 deg = 0 ppm24 deg = +0.4 ppmwe can put all 3 value pairs into a rectangular box with 2 degree width and 0.8 ppm height.To calculate the temperature coefficient we use the middle height of the box (+/-0.4 ppm) and divide by the temperature width (2 degrees) which gives +/- 0.2 ppm/K as temperature coefficient. (even when the temperature gradient is +0.4 ppm/K)It gets even worse when the resistor is optimized for "room temperature" with a parabolic shape.22 deg = -0.4 ppm23 deg = 0ppm24 deg = -0.4 ppmin this case we get +/- 0.1 ppm/K as temperature coefficient with the box method. (Even when the gradient near 22 deg might be much larger).with best regardsAndreas

author: Cerebus
author_rank: Super Contributor
timestamp: April 23, 2020, 08:29:49 pm
content: Quote from: Andreas on April 23, 2020, 07:52:31 pmErm, no, that is exactly thetemperature coefficient of resistance\$\alpha\$ in the classic equation:\$R(T) = R_0[1+\alpha (T - T_0)]\$(Note: This formula is a simplification of more general formulae for the temperature dependence of resistance, but is good enough for rough work.)The usage ofcoefficientto describe the 'coefficient' in the box method is not strictly correct, even if it is generally understood, because it's not a coefficient, there's nothing meaningful to multiply by that coefficient to get a result. There has to be something being multiplied by a coefficient in an algebraic formula before it becomes a coefficient because that's exactly what the word coefficient means.

author: Andreas
author_rank: Super Contributor
timestamp: April 23, 2020, 09:08:35 pm
content: Hmm,what does the content of a "advertising brochure" er "data sheet" of a resistor to do with math or physics?+/-0.2 ppm/K or simplified 0.2 ppm/K sell much better than 0.4 ppm.with best regardsAndreas

author: Cerebus
author_rank: Super Contributor
timestamp: April 23, 2020, 09:30:41 pm
content: Yes, but it was you, not some brochure, who said that:Quote from: Andreas on April 23, 2020, 07:52:31 pmI.e. That the temperature coefficient, wasn't a temperature coefficient, when it is. And then went on to define the temperature coefficient as that derived with the box method. Also, I haven't a clue quite what you were trying to get at with "the temperature gradient (derrivation) of the temperature" - \$\frac{dt}{dt}\$