Source for resistor kits

[(In)Sanity]

Hmm I must try my tests with a wider temperature range. Unfortunately this thermometer only goes to 120F, so I need to make a solid RTD circuit. Maybe I will finally do something with these peltier coolers that I have had sitting around for a year.

According to this document typically TCR is made from a 25-75 degree range. I suppose this makes sense because you are probably doing something wrong or very special if your PCB is above 75 degrees.
http://www.token.com.tw/pdf/resistor-ppm/resistor_ppm_terminology_glossary.pdf

I don't agree with that test range at all.  Real world gear is often subjected to much higher and sometimes lower temperatures.   A typical power amp or power supply,   LCD display,  Plasma TV..etc.etc.   I think you'll find over 100F in many of these items.  I've also found going above a certain point doesn't impact the measurement.   I've tested up to 130F so far and didn't see any change in the ppm's.   

On another note I just tested a thick film 180k Chinese 805 size SMD resistor,  and it scored in @ 19.6 ppm over 56F to 126F.    I have thousands of them,  so at least I have something to build with.   

Also from what I understand the higher the resistance the higher the ppm will be.   

If you put a positive tempco resistor in series or parallel with a negative tempco resistor do you end up with a more stable resistance ?  In theory you should.   Pretty sure that's the principles of basic temperature compensation where your offsetting drift in silicon with an opposite drift. 

Jeff

[ftransform]

Hmm I must try my tests with a wider temperature range. Unfortunately this thermometer only goes to 120F, so I need to make a solid RTD circuit. Maybe I will finally do something with these peltier coolers that I have had sitting around for a year.

According to this document typically TCR is made from a 25-75 degree range. I suppose this makes sense because you are probably doing something wrong or very special if your PCB is above 75 degrees.
http://www.token.com.tw/pdf/resistor-ppm/resistor_ppm_terminology_glossary.pdf

I don't agree with that test range at all.  Real world gear is often subjected to much higher and sometimes lower temperatures.   A typical power amp or power supply,   LCD display,  Plasma TV..etc.etc.   I think you'll find over 100F in many of these items.  I've also found going above a certain point doesn't impact the measurement.   I've tested up to 130F so far and didn't see any change in the ppm's.   

On another note I just tested a thick film 180k Chinese 805 size SMD resistor,  and it scored in @ 19.6 ppm over 56F to 126F.    I have thousands of them,  so at least I have something to build with.   

Also from what I understand the higher the resistance the higher the ppm will be.   

If you put a positive tempco resistor in series or parallel with a negative tempco resistor do you end up with a more stable resistance ?  In theory you should.   Pretty sure that's the principles of basic temperature compensation where your offsetting drift in silicon with an opposite drift. 

Jeff

I know that tempco matching technique is used for voltage references. In some circuits they will match them for greater stability over a temperature range. I have not heard it done with resistors but i'll be it is. I think that 75 C is reasonable, consider the electrolytic capacitor, which would be rather unhappy at those temperatures. You would need to use 130 C electrolytic, and even then the product would experience a short life span.

I want graphs for every resistor I use now lol.

[SeanB]

TC varies from batch to batch, so will need selection into matched pairs for use.

[(In)Sanity]

I think that 75 C is reasonable, consider the electrolytic capacitor, which would be rather unhappy at those temperatures. You would need to use 130 C electrolytic, and even then the product would experience a short life span.

I want graphs for every resistor I use now lol.

Ok,  I didn't put two and two together.  75C yes,  I thought you were in Fahrenheit.   BIG difference. 

Tested my first 10k 10 turn pot,   Chinese made "Baoter 3296".  I ran it from 55F to 126F and it came in at 64.98 ppm / C.   Not as bad as I was expecting.   Assuming I don't fall asleep I'll test some more.   This is a time consuming process due to the soak periods needed.   

[SeanB]

Check linearity, or at least mid position resistance where it will be at it's worst. Just two extra resistance measurements and will be interesting.

[ftransform]

this "panasonic" trimpot is disappointing -732 ppm when it the divider is set to 500ohm - 1500ohm, from 19c to 46c

Did you use loctite on yours before heating it?
http://industrial.panasonic.com/www-data/pdf/AOH0000/AOH0000CE2.pdf
that's what they claim it is.


UNLESS I made a typo and wrote 2 instead of 1. In that case the tempco would be -18.
I'm letting it cool down to room temperature again to see whats going on.

[(In)Sanity]

this "panasonic" trimpot is disappointing -732 ppm when it the divider is set to 500ohm - 1500ohm, from 19c to 46c

Did you use loctite on yours before heating it?
http://industrial.panasonic.com/www-data/pdf/AOH0000/AOH0000CE2.pdf
that's what they claim it is.


UNLESS I made a typo and wrote 2 instead of 1. In that case the tempco would be -18.
I'm letting it cool down to room temperature again to see whats going on.

Actually so far I've only tested the end to end resistance and temp co only.   Today I'll test some divisions.    I wanted a baseline to see just how much the mechanical wiper impacts the overall stability.   I tested end to end a 1k 10 turn trim pot from the same manufacturer and obtained 110 ppm/C.   I may test divisions on this one first. 

Jeff

[(In)Sanity]

Ok,  so I did a test of the 1k 10 turn put at the half value center tap vs end to end.   

End to end was 110 ppm and half value was136 ppm.

I also just got a set of 600 "Metal film" resistors in from Amazon.   The scrape test is not all that encouraging.   The direction of the temperature coefficient is positive..which is good.

I'll report back on the temp co.

Jeff

[(In)Sanity]

Sorry about all the back to back posts. 

So which two of these are carbon film ? 
















I you guessed the middle one and the bottom one you would be right.   The others are metal film.   The middle one was marketed and sold as being metal film.   The second to the bottom one looks identical to the middle one with the exception that it appears to be real metal film.   Both are not very good quality using metal leads for example.   The second to the bottom is coming in around 240~ ish ppm/C temperature coefficient.

[ftransform]

I think you need more light in your pictures it is very difficult to tell. Cameras suck at this, you really need a bright bulb real close to it imo.

I remeasured that panasonic trimpot, it turns out that it is -250ppm. The value did however drift by 1 ohm after it warmed up again. I wonder if loctite would prevent this.

[(In)Sanity]

I actually used a Canon 60D,  but I used the built in flash and didn't use manual settings.   I have a canon speedlite flash of good quality that I could use.   I'll see what I can do. 

Jeff

[(In)Sanity]

Is this photo any better at telling the difference ?

[nanofrog]

Is this photo any better at telling the difference ?

Pretty hard to tell from just scraping it IMHO.

For example, take a look at a cross section photo of this carbon film resistor (http://en.wikipedia.org/wiki/File:Carbon-resistor-TR212-1.jpg). It's a dull grey, not black as one might expect.

[(In)Sanity]

Is this photo any better at telling the difference ?

Pretty hard to tell from just scraping it IMHO.

For example, take a look at a cross section photo of this carbon film resistor (http://en.wikipedia.org/wiki/File:Carbon-resistor-TR212-1.jpg). It's a dull grey, not black as one might expect.

At this point I agree.   I actually found some low value resistors in my original questionable batch of resistors that when scrapped without a doubt look like metal.   No grey at all and they are shinny.   But then I have the one in the photo that looks more carbon then metal.   They test out as very poor quality and that's what counts.

In the end I would suggest to anyone to test the resistors in a fashion that makes you happy.  If your using them for pullup (or down) resistors with logic circuits..who cares.  If your using them as a voltage dropper with LED's...who cares.   If your going to build a precision op-amp circuit stop what your doing and order from a respectable company with proven parts.   You get what you pay for,  but sometimes it's good enough. 

Jeff

[ftransform]

Did you use any kind of advanced control for the peltier or was it the most simple implementation of on/off? How good does it hold the temperature inside a small chamber that way?
I'd love to do curves from 10-75C but the temperature regulation part is a bit intimidating. I had PI control in mind but the software part of the project kind of discourages me. On/off in responce to my RTD can I can do, but all the control system stuff is a bit daunting.

[(In)Sanity]

Did you use any kind of advanced control for the peltier or was it the most simple implementation of on/off? How good does it hold the temperature inside a small chamber that way?
I'd love to do curves from 10-75C but the temperature regulation part is a bit intimidating. I had PI control in mind but the software part of the project kind of discourages me. On/off in responce to my RTD can I can do, but all the control system stuff is a bit daunting.

I had a simple control system my first go around,  I had taken it all apart (breadboard) so this time I opted to just use constant current and let it hit the top and bottom of cooling and limited heating.   For cooling I was pushing about 60 watts,  for heating 10 watts.   Once it hit it's limits it was very stable.   I added some foam to the chamber to reduce the volume more.  I'll toss together another controlled setup in the future.   Too many things to do.   

Jeff

[ftransform]

Did you use any kind of advanced control for the peltier or was it the most simple implementation of on/off? How good does it hold the temperature inside a small chamber that way?
I'd love to do curves from 10-75C but the temperature regulation part is a bit intimidating. I had PI control in mind but the software part of the project kind of discourages me. On/off in responce to my RTD can I can do, but all the control system stuff is a bit daunting.

I had a simple control system my first go around,  I had taken it all apart (breadboard) so this time I opted to just use constant current and let it hit the top and bottom of cooling and limited heating.   For cooling I was pushing about 60 watts,  for heating 10 watts.   Once it hit it's limits it was very stable.   I added some foam to the chamber to reduce the volume more.  I'll toss together another controlled setup in the future.   Too many things to do.   

Jeff

Volume reduction is a good simple idea that I am ashamed not to have thought of. I noticed that a good stable max point is reached with a lightbulb, I suppose that a peltier cooler is no different.

Have you ever found a graph of resistance vs temperature for a normal (carbon/metal/wire) resistor? It's surprisingly difficult to find, all I seem to run into is graphs of thermistors and "increased tcr" types. I want to see how linear the change in resistance of a regular resistor is from experimental values. Eventually I will make my own once I get to this project but I am curious now.

[(In)Sanity]

Have you ever found a graph of resistance vs temperature for a normal (carbon/metal/wire) resistor? It's surprisingly difficult to find, all I seem to run into is graphs of thermistors and "increased tcr" types. I want to see how linear the change in resistance of a regular resistor is from experimental values. Eventually I will make my own once I get to this project but I am curious now.

Do a search for "temperature coefficient resistor" in Google Images. 

[(In)Sanity]

Just stumbled on this article.

http://www.eetimes.com/electronics-news/4199812/Strengths-and-weaknesses-of-common-resistor-types

I also think it's important to note based on this article and others I've now found that it would appear you don't want to test below 25C to get your PPM reading.   It almost appears as if it's two different responses.

[M. András]

bought a resistor kit for testing purposes, well  its advertised as metal film but most likely carbon film they have a nice negativ tempco. tested around 10 different value all of them dropped on the readings using my fluke 289 and soldering iron for more quicker and wider response from the resistors http://www.ebay.com/itm/300863774703?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649. wondering what the seller will say about this

[(In)Sanity]

I tossed a bunch that I got off ebay.  I ended up with a few batches off Amazon that appear far better in quality.   Still you get what you pay for,  so while they are better they are still not really good.   I do have some SMD resistors that I got from ebay that have proven to have very nice temp-co's.    A soldering iron test is going to tell you the direction,  but it's not going to give you a very good test of stability.   I guess it might work as a course reference against a known higher quality resistor.   

Jeff

[M. András]

gonna buy anyway some good quality yageo 1%metal films 0.6watts from a local electornics store i wanted to use these as throw away test they stock the whole e24 range so i jump in with 100 each, unfortunatly they dont stock the whole range in smd