goddamn jd, you get hit by lightning ?
as pHaestus said, and I think you too now understand, the equip totally depends on what you wish to accomplish
- its not really so much 'what will work', for many things can be made to work, as how much accuracy is needed
so let me flip all the questions around and say, from my direct experience, what certain specific capabilities will enable one to do, and also what certain deficiencies will preclude one from doing
lets start with temperature: 2 principal applications:
- heat die/CPU/wb bp/hsf bp temps
- coolant temps
for heat die temps and such, 0.1°C resolution will work
BUT the instrument accuracy will probably be on the order of ±0.2 to 0.4°; this WILL play hell with one's calculations
-> do not think for an instant to 'ignore' accuracy (aka uncertainty), with sloppy thinking like "an instrument's error is always the 'same'", do read on this subject before buying anything - it is the same issue over and over
coolant temps are much more difficult because the increment being measured (that of interest) is much smaller, 0.01°C is necessary (and in fact insufficient if back-calculating power from a temp difference)
[I am now going from 0.01 to 0.001°C resolution for just this reason]
next: what sensors are appropriate for what resolution ?
for 0.1°C resolution with a TC only type T can be used (but yet again their accuracy is also ±0.2° or so; plays more hell with the calcs)
the Fluke 2190A is a good, and sometimes cheap, thermometer; but a multipoint selector will be needed also
(there are older models on eBay that can work, but the 2190A is better)
for 0.01°C resolution thermisters can be used, but they are rather special and rather expensive
-> and the indicators for 'matched' thermister reading ?
Very specialized, and pricey
a more common approach is with RTDs, but can only be 4-wire for this accuracy and require a good thermometer/ohmmeter
- note that the 24hr accuracy of a Fluke 2180A can be as low as ±0.02°C, everything calibrated of course
to go to 0.001°C can be as 'simple' as using a 6½ digit ohmmeter (the thermometers doing the conversion are VERY expensive)
for all of the above calibration is required
I have found it cheaper to buy the equipment and have the capability 'in house' so that it can be used as often as needed
- what's needed depends on the gear: calibrated mercury thermometer with TC, lab std resistors, lag bath, etc (its a chore)
call Omega and request their "Temperature" catalogue - tons of info (they have ss sheathed 'T' TCs in 0.040" dia)
they have a "Flow" catalogue also
flow meters are a problem which I think pHaestus has addressed
-> do remember: You can't make a silk purse form a sow's ear
the best low cost type is an industrial paddle wheel WITH a built in indicator
-> if the indicator is separate, how will you be able to calibrate it ?
answer: only by sending the whole thing off (big $$ !)
work with a pencil and see what the effect of 3% is (and is that 3%, or ±3% ?)
I can tell you this: repeatability is a B*TCH with 3% variation
you will not get the same results, close perhaps, but not the same
and the 'better' everything else gets, the worse the flow meter looks
this will drive you nuts !
[I have used 5 different types, form a Brooks rotameter to the mags - now have 4 - I use now.)
jd, glad to hear you wish to be a serious tester, feel free to contact me
(sometimes I have extra equip I've upgraded)
it will not be difficult to best what the 'review' sites do, for they have no equipment (and apparently less understanding)
- but I have totally rebuilt my test bench (The Ghetto Bench) 5 times and do assure you:
It will be much cheaper to get the 'right' equipment in the beginning.
good luck
|