measuring a ceramic resistor - Page 1
Forum section: electronics / beginners

author: JaseG
author_rank: Contributor
timestamp: October 31, 2016, 09:55:25 am
content: I'm in the process of making a simple dummy load circuit and I have a ceramic resistor that looks just like this:http://d2ydh70d4b5xgv.cloudfront.net/images/8/6/5-general-ceramic-cement-power-wirewound-stand-up-resistor-1-ohm-10w-d8a9b360373de2c936b0e1546db86c57.jpgThe one I have says 10W1 \$\Omega\$J on it so I'm assuming it's 1 ohm, and I would expect it to draw 500ma at 0.5 volts. However, when I tried to do this practically it was a different story. I had to push 3 volts through it to get 1 amp on my meter and power supply indicator.I measured the resistor with my meter and it reads at 1.1 ohms which is out of spec, but I don't exactly have top shelf gear so I'm not fussed about that. .It certainly wasn't 3 ohms which would have made sense.What could I possibly be doing wrong?!? is there a special way to measure a resistor like this?

author: tatus1969
author_rank: Super Contributor
timestamp: October 31, 2016, 10:09:07 am
content: plus your meter also adds resistance. try 10A range on your meter if it has, this adds less resistance.

author: JaseG
author_rank: Contributor
timestamp: October 31, 2016, 10:17:54 am
content: of course! Just measured the resistance between my supply and the resistor. 2ohms. boom!I initially tested in the mA range as well and this changed the value considerably. 10A range reads as expected.3 volts / (1ohm resistor + 2ohm wire) = 1 amp. Physics has been restored.

author: Dave
author_rank: Super Contributor
timestamp: October 31, 2016, 10:35:03 am
content: Do you perhaps have access to two multimeters? Put one in series with the power supply and have it feed a constant current into the resistor. Probe the voltage across the resistor right where the wires pop out of the ceramic body. Divide the two measurements to get the final result.

author: Cliff Matthews
author_rank: Unknown
timestamp: October 31, 2016, 10:37:05 am
content: Series connect it with another resistor (say 1k and pre-test its value with DVM), apply 10v, measure total current and Vdrop on each. Ohms law tells the rest..

author: Ammar
author_rank: Regular Contributor
timestamp: October 31, 2016, 11:00:46 am
content: Quote from: JaseG on October 31, 2016, 09:55:25 am/*Pedandtry warning*/Voltage is measured across an element, between two points, it is a potential, as in you had to put three volts across it. Current moves through an element, as in 1 amp passed through it. Apologies for my fussiness./*End Pedantry warning*/

author: JaseG
author_rank: Contributor
timestamp: November 01, 2016, 08:33:47 pm
content: @Ammar haha. No need to apologise, you're right and I appreciate the point you're making.It ended up working out ok. I threw it all together on a bread board and after realising I had a busted op amp I was able to bodge it up on it's own board. The end result works as expected and matches the maths close enough for my purposes. The only thing I need to do is add a voltage reference so that the max current doesn't change based on the input voltage.http://jasongilholme.com/wordpress/wp-content/uploads/2016/11/20161101_175501-1280x720-1024x576.jpg

author: Ratch
author_rank: Regular Contributor
timestamp: November 01, 2016, 10:15:43 pm
content: Quote from: Ammar on October 31, 2016, 11:00:46 amI know what you mean by pedantry. Charge flows or moves, but current does not flow twice. The phrase "current flows" means "charge flow flows", which is redundant and ridiculous. One should instead say "current exists" or "current is present"Ratch

author: vk6zgo
author_rank: Super Contributor
timestamp: November 01, 2016, 10:36:59 pm
content: Quote from: Ammar on October 31, 2016, 11:00:46 amYou do realise you just went on a watch list!

author: Algojervia
author_rank: Unknown
timestamp: November 02, 2016, 12:13:07 am
content: Quote from: JaseG on October 31, 2016, 09:55:25 amNot being native to English this might be completely wrong but haven't we passed from electronics into semantics now and is not a valid parallel that we do speak of flowing streams. Thous even if it might be redundant one might suspect that it is your statement that is ridiculous or do you argue that we all should start talking about the relaxing sounds of a present stream.

author: Ratch
author_rank: Regular Contributor
timestamp: November 02, 2016, 01:46:04 am
content: Quote from: Algojervia on November 02, 2016, 12:13:07 amYou have to decide whether the above is a technical response, or a slang description which includes redundant words and sometimes misdefined meanings. Although slang might be understood by everyone, it usually fails to describe correctly what is really happening with respect to the laws of physics. A good example of slanglish is the way NASA describes their astronauts "walking" in space. If their tethers broke, would the astronauts walk away? There is nothing wrong with considering semantics when writing or speaking about technical subjects. After all, semantics is the meaning of words. As for the example you gave, I would say "the stream became present when it it rained". Or, "the river came into existence after the ice age".Ratch

author: Brumby
author_rank: Unknown
timestamp: November 02, 2016, 03:56:45 am
content: Semantics are important when semantics need to be important.Common usage of a term will often depict an unambiguous understanding - despite it having semantic problems. Standing on the semantics soapbox in these situations will usually result in alienation and can add confusion.I would suggest this is more likely to come from newbies who are in the process of picking up the jargon and may take some phrases too literally. We should all - and I include the newbies - be careful how such discussions are conducted so that understanding is found ... and not a war.I don't find any problem with "Walking in space" or "crossing a stream" that is nothing more than a dry watercourse. We know what is meant - without ambiguity - and that's what really matters.

author: Ratch
author_rank: Regular Contributor
timestamp: November 02, 2016, 12:40:38 pm
content: Quote from: Brumby on November 02, 2016, 03:56:45 amSemantics are always important even when they are disregarded or sloppily used.QuoteI don't see how using clear unambiguous language can result in confusion and alienation. Perhaps you can expound on that averment.QuoteA correction, dispute, or disagreement is not necessarily a war. Arguments, and persuasions can be made without starting Wild War III (WWIII). The foundation of correct understanding is a correct definition.QuoteSometimes it matters and sometimes it doesn't. Slang has no place in a correct technical description of an event or object. If you are casually describing something or writing poetry, then fine, use slang.Ratch