help with technical tongue twister - Page 1
Forum section: electronics / beginners

author: AlfBaz
author_rank: Super Contributor
timestamp: June 03, 2014, 11:27:24 am
content: Ok, so I'm reading this pdf and I come across thisand then this graphshould that readQuoteorQuoteor is it right and I'm not reading it right, at any rate I'm sure the author was having a good chuckle when he wrote it

author: Simon
author_rank: Unknown
timestamp: June 03, 2014, 11:30:17 am
content: it certainly seems to contradict that graph

author: amyk
author_rank: Super Contributor
timestamp: June 03, 2014, 12:12:45 pm
content: I would go with "For film resistors, the decrease in dc resistance at higher frequencies decreases withincreasedecrease in resistance."

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 03, 2014, 04:46:15 pm
content: The whole sentence is flawed. The graph states "impedance", which is consistent. That's fine. But the sentence says "DC resistance" at AC, which isn't exactly DC resistance anymore, is it? Dur...Regarding the "decrease decreases" ambiguity, it's just that, ambiguous. One could argue for either direction, fundamentally because of the observation that, by strict mathematical definition, -20 islesser than, or one could say,smaller than, -10. But colloquially, -20 is understood to have a greater magnitude. Because it is a fundamentally ambiguous statement, one should avoid using such language altogether and specify clearly what one means.Tim

author: magetoo
author_rank: Frequent Contributor
timestamp: June 03, 2014, 08:44:20 pm
content: What a train wreck of a sentence.If your writing ends up being screenshotted and commented on, you are doing it wrong. Unless this was some sort of parody of technical writing..

author: Neilm
author_rank: Super Contributor
timestamp: June 03, 2014, 09:12:05 pm
content: Proof reading - we don't need no stinking proof reading.Mind you, I did see a draft (unpublished) of an international standard that had a couple of howlers in it. Corrected by the time it got to CDV

author: Neganur
author_rank: Unknown
timestamp: June 03, 2014, 10:12:08 pm
content: It makes more sense in the context of the text you're quoting (The Electrical Engineering Handbook Second EditionBy Richard C. Dorf ?) but it obviously is a case of going for coffee in the middle of a sentence.While explaining the high-frequency effects of different kind of resistors, the text is comparing impedance (i.e. AC) to DC resistance in relative terms, which is a measure for the useful frequency range of a resistor (=highest frequency at which the impedance still is within the stated (DC) resistance tolerance)The text explains that wire-wound resistors exhibit an increase in impedance over frequency (mainly inductive) and that composition resistors (which have low inductance) have capacitance due to the "many conducting particles which are held...by a dielectric binder".It then mentions film resistors and explains that the impedance "...remains constant until 100 MHz...and then decreases at higher frequencies." while referring to the figure 1.7 that you posted.So far it's all OK, but the author wants to say too many things at the same time with the next sentence. In my opinion he wants to:highlight the good frequency properties of film resistors (better than composite and wire-wound)explain that the impedance of film resistors degrades with higher resistance values (i.e. 100 kOhm ... 1 Mohm)explain that the rate of change of this "impedance as % of DC resistance" decreases with higher resistance values (*)(*): this has maybe nothing to do with fig 1.7, the drop in |Z|/R should cap out at -20 dB/decade (while still capacitive)I don't think he really meant to say that "the decrease in resistance decreases" but rather that the impedance as percentage of dc resistance decreases faster (i.e. the value Rac/Rdc decreases more) for higher values of resistance (i.e. it's worse for the 1 Mohm resistor than for the 100 kOhm resistor).So that the sentence:"For film resistors, the decrease in dc resistance at higher frequencies decreases with increase in resistance"was maybe meant to be:"For film resistors, the impedance as a percentage of dc-resistance at higher frequencies decreases with increase in resistance"Which is still not very nice to read, instead I would write:At higher frequencies, the impedance of high value film resistors degrades faster than the impedance of low value film resistors.

author: AlfBaz
author_rank: Super Contributor
timestamp: June 03, 2014, 11:32:56 pm
content: Quote from: Neganur on June 03, 2014, 10:12:08 pmYes that's the oneQuoteThis is one of the scenarios I thought he might have meant but wouldn't you have to introduce more poles to change the "rate"?QuoteI feel comfortable with this summation with regards to the graph but as this portion of the handbook is mostly revisory in nature I cant help but feel I'm missing something with reference to your 3rd point above