Wind Tunnel Construction

[BillA]

This will be a joint blog (biblog ?) by Ben and self describing our progress towards the construction of our respective wind tunnels. Contributions, comments, and criticism solicited as always.

This post will be an updated index/reference list of the source materials. (material from later posts will be moved or copied here)

Stds and Specs:
http://www.amca.org/crp/fans.asp (anyone have links to the docs themselves ?)
AMCA 210 - Laboratory Methods of Testing Fans for Rating Purposes.
AMCA 300 - Test Code for Sound Rating Air Moving Devices.
AMCA 301 - Method of Calculating Fan Sound Ratings from Laboratory Test Data.
http://www.iso.org/iso/en/CatalogueListPage.CatalogueList?ICS1=23&ICS2=120&ICS3=&scopelist=ALL
http://cart.amca.org/estore/download/amca_211.pdf

A ready-made guide:
http://www.me.pdx.edu/~gerry/epub/pdf/flowBenchManual.pdf

General wind tunnel references:
http://hightech.lbl.gov/Documents/CLEANROOMS/LBNL_FFUTestProc_v1.3.pdf has dwg of wind tunnel

Specific equipment references:
wind tunnel
http://www.fantester.com this is my target, ~250CFM leaves some headroom
http://www.fantester.com/man16.htm the actual manual
http://www.overclockers.com/articles750/ JoeC's use of a wind tunnel
http://www.climatictesting.com/Air%20Flow%20Test%20Stand.htm new
nozzles
http://www.helandermetal.com/air-flow-nozzle.htm other source ? (must be to spec, only)
fan
http://www.surplussales.com/Fans-Blowers/FansBlow-1.html assorted
heat exchanger
http://www.lytron.com/reg/files/Lytron_Catalog_hx_AL.pdf ES7070
blast gate
http://cgi.ebay.com/8-CAST-ALUM-BLAST-GATE-DUST-COLLECTORS-BLAST-GATES_W0QQitemZ7570534674QQcategoryZ11810QQcmdZVie wItem

Other air measurement stuff:
http://www.ddc-online.org/inout/inout_chapt02_ana_06flow.aspx
http://www.ebtron.com/pdf/white_papers/Airflow%20Measurement%20Comparison_052603.pdf
http://www.magnetrol.com/us/html/view_pdf.asp?pdf=mii\552
http://www.ashrae.org/template/AssetDetail?assetID=22561
http://www.pdhonline.org/courses/m192/fan_sourcebook.pdf

[BillA]

recommended minimum and maximum flows:

NOZZLE DIA ./ CFM @ 0.1 INCH W.G./ CFM @ 4.0 INCH W.G.
0.7 “ . . . . . . . 3.5 . . . . . . . . . . . . . . . 21.0
1.0“ . . . . . . . 6.7 . . . . . . . . . . . . . . . 42.0
1.6“ . . . . . . . 17.0 . . . . . . . . . . . . . . 110.0
2.0“ . . . . . . . 28.0 . . . . . . . . . . . . . . 172.0

max flow best @75% (3"WG)

[bigben2k]

[edited out link]

I'll be concentrating on the 16 inch'er, not for higher flow, but for the larger mounting area.

[BillA]

read the links Ben
the tunnel sectional area is 16x (min) the opening area
what size opening do you want ?

[BillA]

bought a -53VDC NMB blower for $20 as the air source ( http://www.surpluscenter.com/item.asp?UID=2006010314495497&item=16-1258&catname=electric ),
when I recognized that I could easily 'control' the air temp with parts on hand, the best kind

from a Lytron surplus MCS cooling unit I salvaged a ES0707 rad with a Comair Tarzan fan (yea, you can hear the scream)
fan http://www.comairrotron.com/ac_family.asp?FamilyID=66
ES7070 rad http://www.lytron.com/reg/files/Lytron_Catalog_hx_AL.pdf - nice to have rad specs, eh ?
the first (center) graph indicates, among other things, that an air flow rate of ~220CFM can be expected using this fan/rad combo
- I believe this is sufficient, with a Variac I can push it a bit

also added a link to an 8" blast gate I bought

would like a 5x5" opening, this means a 24" tube or a 20" sq duct
- am thinking that insulated duct may be the cheapest ?? (lg plastic pipe is pricey, got a source Ben ?)

EDIT
all these fans are far too small

[bigben2k]

I was looking at being able to test heatercores, and I have one that's 6" by 8" (a bit larger than most). That puts the diameter of my wind tunnel at 32". That's more along the lines of what I expected.

I stopped by the local hardware store last night, and found a 12" concrete former: $9. Waxed cardboard. anything bigger would be harder to find.

Reviewing the documentation last night, I'm realizing how critical it is that everything is properly sealed (for the pressure drop measurements). Then I pondered about how good a cardboard tube would be, and concluded that waxing ought to do well, but that if there's a way to apply a better kind of coating instead, it wouldn't hurt.

I also gave some thought on maintaining a seal at the nozzle plate. If the nozzle plate needs to be interchangeable (I haven't determined that yet), then it would be best to cut the tube in two and put a flange, so that I can bolt the nozzle plate. The flange would also act as a support (on a small diameter setup).

Today I'm going to try to sum up the requirements (from all the links above) in a simpler list, and source a 32" diameter tube.


Did you get a quote from helandermetal yet?

[BillA]

no hurry on that quote, what sizes you thinking of ?
look at the stuff Ben, copy it
the nozzle plate is fixed, nozzles bolted into it; accessed through a port
the 2 ends are identical, push or pull

[bigben2k]

I haven't sized the nozzles yet, but I'm looking at the same flow rates as you; so the same.

[BillA]

I just had a conversation about a 2500CFM app. !
?
what are you going to use as the air pump ?

[bigben2k]

A DC blower, probably automotive, with controls.

I'm looking at the blast plate, and wondering if I could do an iris instead (complicated and time consuming, I'll probably pass). Been watching Stargate too much.
http://www.turbosquid.com/FullPreview/Index.cfm/ID/256262

edit: nope it won't do, since it can't be sealed.

[BillA]

some where on the site is a link to a surplus place from which I bought a huge one (at Swiftech), think it was from a Ford truck
this would be better than the Tarzan I think, I'll hunt
bingo
http://www.surpluscenter.com/item.asp?UID=2004121319144415&item=16-1279&catname=electric
$50 it is a beauty

[BillA]

another approach
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7577504580&fromMakeTrack=true
lower resolution

[bigben2k]

Can't find (readily) a 32" diameter tube. A 55 gallon drum would be ~22 inches:
http://www.zorinmaterial.com/products/products_detail.cfm?product=77

Estimating length to be 3X the diameter; I need a salvage yard, and a trailer! (have hitch, can rent trailer)

[BillA]

lets think on this a bit
got a torch, grinder, welder. etc ?

[bigben2k]

I'll sleep on it.

I was going to pick up a grinder anyways...

[bigben2k]

[edit: removed off topic ramblings]

Today I'm going to put the nozzle (dP) calculations in an Excel spreadsheet, and continue to try to source a tube.

[BillA]

bummer
look for plastic too in 24 -32" dia (I may go 32 w/you, but not a steel drum)

[bigben2k]

Thanks.
Agreed. The only way I see steel working, is if I can get both halves in the right size, and use JB Weld to put on a flange; not likely, and not practical.

I also prefer plastic. I'm leaving an option open for cardboard, but I don't think that'll be anywhere near as easy to find (nor practical) as plastic.

[BillA]

settling vanes/egg crate ?

[bigben2k]

settling vanes?!? You mean the flow straightener?

[BillA]

yea

[bigben2k]

If you mean this:
http://wbta.us/bigben2k/egg_crate.jpg
then yes, was thinking the same, with a preference for thin alu. Definitely not a DIY item (you reading this Brian?:) )

[BillA]

actually rather easy if you have a source of al flatstock
stack and cut on a bandsaw all at once, interlock together
(I have a bandsaw)
1 1/2 x 1/16" strip ?

[bigben2k]

Seems reasonable, but they make these (shapes) for office fluorescent lighting too (plastic or "chromed" plastic).

At 32", might be easier to make oneself, rather than try to find one big enough, or try to patch a couple together. Dunno.

[BillA]

I'd patch if cheap
?

[ProHandyman]

I'll check my lighting catalogue. I'm aware of older 2x4 and 4x4 commercial ceiling trouffers having 1,2 and 4" square aluminum. Not sure if still available though.

[ProHandyman]

googling finds many sources... here's one: http://www.americanlouver.com/eggcrate.html

[BillA]

Thanks PH

ok Ben, where can we scrounge some ?

[bigben2k]

I'll keep an eye out. Thinking of office surplus outfits (many around Houston). If I find any, I'll pick'em up for you; we ought to be due for a beer by then.

Putitng nozzle calcs on Excel isn't obvious; still at it.

[bigben2k]

About to go home. Came across a site that provides a BASIC program:
http://www.delta-tcompany.com/nozzles/program.php

The theory:
http://www.delta-tcompany.com/nozzles/paper.php

Will try to tackle the spreadsheet again tmo.

[Albigger]

May also try honeycomb core for flow straightener, if can source cheap enough.
first google link (http://www.plascore.com/honeycomb/default.asp) - comes in many sizes/materials.

At least two wind tunnels at my Univ. use some type of honeycomb material, if I had to guess about 2-3" thick.

I would be worried that light-fixture gratings wouldn't be thick enough, but not really sure of your goals / tolerances with this project.

[bigben2k]

I used the basic program to run a few numbers.

First:
The flow range to be covered is determined by the nozzle diameter. In order to have better resolution, the maximum flow should be near the 3.0+ inches w.g. range in differential pressure. ... If the differential pressure is below 1 inch w.g., select a smaller nozzle. If the differential pressure exceeds 4.0 inches w.g., select a larger nozzle or combination of nozzles. (from fantester (http://www.fantester.com/man16.htm))

so 1" is min, and 3" is max.

Using the program, I calculated the following flow rates:
DIAMETER Flow at 1" wc Flow at 3" wc
0.75" 11.8cfm 20.5cfm
1" 21.5cfm 37.5cfm
1.25" 33cfm 57cfm
1.5" 48cfm 83cfm
1.6" 54cfm 94cfm
2" 85cfm 147cfm
2.5" 133cfm 231cfm
3" 192cfm 333cfm Nozzles listed are from the standard size list from Helander (http://helandermetal.com/).

Back Monday.

[BillA]

what is that ?
what equations ?
std air ?

did you read post #2 ? it is from Fantester
recommended minimum and maximum flows:

NOZZLE DIA ./ CFM @ 0.1 INCH W.G./ CFM @ 4.0 INCH W.G.
0.7 “ . . . . . . . 3.5 . . . . . . . . . . . . . . . 21.0
1.0“ . . . . . . . 6.7 . . . . . . . . . . . . . . . 42.0
1.6“ . . . . . . . 17.0 . . . . . . . . . . . . . . 110.0
2.0“ . . . . . . . 28.0 . . . . . . . . . . . . . . 172.0

max flow best @75% (3"WG)

(running at lower pressure is going to be easier on the ears)

EDIT
Ben, have you looked for a fan pumping ~200CFM @ 4+"H2O ?
now I understand why they are in enclosures

[BillA]

Thoughts on the supply fan rating – 250 CFM being the nominal target

At max flow the dP across the nozzles will be 4�WC. This can be reduced by adding nozzle capacity, not sure w/o nozzle pricing how this relates to the cost effectiveness.
The internal straightening vanes drop I assume to be negligible.
As I intend to control the air temp, a heat exchanger will be used which has a pressure drop of 0.35�WC at 225 CFM, assuming ~0.45 at 250 CFM.
The 8� flexible air supply hose pressure drop is insignificant if the hose is kept straight.

From http://www.connel.com/freeware/airduct.shtml
This is what you input
Flow Rate 250 CFM
Velocity 714 FPM (based on 8� dia)
Pressure 14.7 PSI
Temperature 60 F
Duct length 10 FT
Duct Roughness 0.01 FT (canvas, wire wound)

These are the results
The duct diameter is: 8.01 inches
The air density is: 0.0764 pounds per cubic feet
Reynolds Number = 51056.22
Friction Factor fa = 0.04308519
Friction Factor f = 0.04458125
loss PSI = 0.00077848
loss inches of H2O = 0.02157016
loss inches of H2O per 100 ft = 0.21570163

To the above must be added the expected max drop across the DUT; difficult to imagine more than 0.4 as such pressure requires a very noisy fan. (most apps will see a dP <0.2�WC using an axial fan)

All of this suggests ~5�WC, w/o the rad and a lower DUT pressure perhaps 4�WC could do.
This is not a typical blower as most top out at 1.5 or 2�WC.
…………………………………………†¦â€¦â€¦â€¦â€¦

Another question is about the air control mechanism.
Blast gates seem recommended, I guess because they are cheap. Is there any reason why the motor cannot be speed controlled ? (a LOT less noise)

[bigben2k]

I haven't looked much into the blower, but I did note a concern about it being to push air with some decent pressure, as possibly a more important/relevant spec than the cfm: 4"wc is not obvious, for any fan.

An axial fan would fail miserably, without a doubt, at any diameter and in any configuration. A blower ought to do well, but I suspect that it would have to be of a fair diameter, in order to achieve a pressure of 4"wc. I'm guesstimating 8" diameter, possibly more, hence the large box (also a noise suppressor). I'm all for DC control, but these are limited, so I believe that the blast plate is still needed. Agreed on the duct; an elbow is going to be the equivalent of ~24 feet of the same duct!

As for the calculation, I used the Basic program (http://www.delta-tcompany.com/nozzles/program.php), with these:
Duct Diameter: 32 (could be wrong, but impact is negligeable)
Throat diameter: [insert nozzle size]
Upstream static pressure: 14.7
Upstream static temperature: 70
name of gas: air
The program then returns gas viscosity, upstream gas density, beta, gamma, and the critical pressure ratio.

then I put in the dP (0.1, 1, 3 or 4, "wc) and it returns:
downstream static pressure, pressure ratio, exit velocity, Mach#, downstream static density, Reynolds, Mass flow rate, CD, the flow rate (converted in various units), and the "pressure recovery".

I see that 0.1" wc as a minimal pressure drop for the nozzle, in the sense that a dP that is any lower, will not produce results that are meaningful. I'm going by the fantester instructions, which state that 1.0"wc is the minimum dP, before one should switch to a smaller nozzles. I'm interpreting the instructions as:
min dP: 1.0"wc and max dP: 3.0"wc (across any nozzle). This seems to fall inline with a "desired measuring range".

Today I've got a lot of catching up to do, having been offline since Thursday, but I'll look into pressure drops of larger blowers, and see how to get to 4"wc+. Sidenote; might be able to use a combination of two (or more) 5" blowers, with DC control.

[edit: removed off topic ramblings]

[bigben2k]

Confirmed (went over ebm-papst product line); can't do 4" with a single blower, regardless of diameter. It'll have to be multiple blowers. This makes DC control easier (turn some on/off).

[BillA]

no
google radial blower
I bought this to see http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7544689100

[bigben2k]

Dandy, but 3 phase isn't practical for me.
http://www.allproducts.com/tami/chuanfan/05-pf.html
http://www.kooltronic.com/b-blower/hprad/hprad.htm

cute animation:
http://www.rtpumps.com/rtpumps/web/home.nsf/systemcontentview/index.html?Open&DirectProductURL=C1256ED700496AB1C1256EE5007976A9

I'm going to pursue the multiple blower configuration:
1-easier DC control (turn some on/off)
2-variable voltage of an EBM-Papst (spec'd at 24 volts) can be from 9 volts to 32 (much "play" room)
3-should be cheaper than a specialty unit (unless I can get lucky on eBay, as you did).

I'm assuming, for now, that running a pair side-by-side isn't going to be an issue.

[BillA]

get a phase converter

[BillA]

well I got a blower lesson (link in #37)
super construction, but . . .
made in Italy by Nassetti USMCA, an Italian conglomerate gone bust in the '90s
they did not actually make the fan but it will be difficult to find who did to get the specs (I speak Italian but surf poorly, don't know the right keywords)

I had assumed (wonderful word) to change the motor to a TENV for the torque with a speed control, BUT it does not have a std NEMA frame

back to eBay it goes

[bigben2k]

Bummer. No rpm indication either?

[edit: removed off topic ramblings]

Otherwise I completed my New Year's resolution to "clean house"; got the (drug addicted) brother-in-law gone, the live-in boyfriend kicked out, and the step-daughter opted to follow the boyfriend. Am strapped for cash, but otherwise at peace :D .

[BillA]

bleh, good cleansing

[bigben2k]

[edit: removed off topic ramblings]

[bigben2k]

[edit: removed off topic ramblings] My boss quit; I am boss-less :D but applying for it.


I've been scouring eBay for a blower. Nothing useful yet, but the Grainger website (www.grainger.com (http://www.grainger.com)) comes in handy for specs. I'm still keeping in mind finding a 32" tube; I think this is going to come down to a lucky find, while driving around town.

More links that may come in handy, for those interested:
http://www.ceesi.com/pubs_gasflow.aspx
http://ts.nist.gov/ts/htdocs/230/233/calibrations/mechanical/PUBS/NCSL_4e03.pdf

[bigben2k]

Today I thought I'd spend a bit of time on the nozzles.

First I'd like to clarify wether we are indeed going to keep the dP during testing between 1.0 and 3.0 "wc, as per the fantester guidelines, or if we're doing something different.

I'm also thinking about nozzle selection; what's the word on using multiple one at the same time? Ok for 2? Ok for 3, 4? (I understand how it would work; this is an accuracy concern only).

Knowing that, I can figure out the minimum number of nozzles, their sizes, and the right combination to get to 250 cfm. Do we have a minimum cfm requirement?

I expect to be mobile again Wednesday; I'll start to scour the area for tube and egg crates.


Speaking of which...
...The chamber has flow straightening screens installed upstream and downstream of the nozzle array. The screens break up turbulence in the airstream and provide a uniform flow approaching the nozzle array. Each set consists of three screens with open areas of 60%, 50% and 45%. ... Any thoughts if we're going to be ok with the egg crate, or if we're way off here?

[BillA]

review the spec in the first post

the screens have 2 purposes, the increasing density is to make the pressure more uniform
note the max velocity differences permitted (need a thermal anemometer over 400CFM as I recall)

[bigben2k]

According to the paper from the Portland State University... using up to 3 nozzles is still within the standard. That answers one question I had.

The nozzles used are: 0.75", 1" and 1.6". That gives this tester the following cfm ranges:
(as stated by the man)

0.75" only: 9 to 19 cfm
1.0" only : 15 to 35 cfm
1.6" only : 39 to 96 cfm

0.75" and 1.0" : 24 to 40 cfm
0.75" and 1.6" : 48 to 71 cfm
0.75" and 1.0" and 1.6" : 63 to 150 cfm

A simple addition, as expected, but max for {0.75" and 1.0"} ought to read 54 cfm (instead of 40), and max for {0.75" and 1.6"} would read 115 cfm (not 71). Not sure why there's a difference.:hammer:

The cfms calculated are consistent with a dP range of 1.0"wc to 3.0" wc (both our calculations appear to be off, but mine are closer :p ). I don't understand why the graphs in that paper have a pressure range between ~0 and ~45 Pa: 1.0" wc is 249 Pa.:confused:

Am I missing something here? I'd like to master the calculations. That'll be my goal this week. I'll retry the calcs at 60F and 32F, to see if I can sort out the differences.


I read you (clear) about the screens: I just wanted your opinion on wether the egg crate would suffice for us, or if we should consider looking at twpinc.com (I've ordered samples from them in the past, for water filtration). Going over the site quickly, it is possible to replicate the 60, 50 and 45% open area in mesh, but it might be pricey (i.e. in aluminium, ~4.00$ per square foot, off of a 36" wide roll).


I don't understand you on "max velocity differences permitted". We won't be anywhere near 400 cfm, right?

[BillA]

ck, preserver
no idea on the calcs, have not seen them

[BillA]

bought a blower
http://cgi.ebay.com/Dayton-2C820-Radial-Blade-Blower-1-3-HP-Baldor-Motor_W0QQitemZ7586400313QQcategoryZ1267QQssPageNa meZWDVWQQrdZ1QQcmdZViewItem

[bigben2k]

Yep, am tracking same model. Darn, 220v...

[BillA]

at $40 + $19 shipping, buy another motor

[bigben2k]

Why didn't I think of that... it's got a standard 1/2" shaft.

[BillA]

because you always make things more difficult
??

[Etacovda]

because you always make things more difficult
??

** Etacovda laughs

[bigben2k]

bought a blower
http://cgi.ebay.com/Dayton-2C820-Radial-Blade-Blower-1-3-HP-Baldor-Motor_W0QQitemZ7586400313QQcategoryZ1267QQssPageNa meZWDVWQQrdZ1QQcmdZViewItem
BTW, there's a small discrepancy that you might want to be aware of:

The Grainger site lists the motor as 1/2 HP, and the eBay listing has the blower setup with a 1/3 HP motor. I don't think it'll make much difference, unless you plan to push the edge of the 5" wc pressure drop.

I should win a 2C820 too, unless someone outbids me on it. I'm finding a 120 Vac motor for it:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7588113994
(might get another one than that, seller is fuzzy on the specs)
and controller:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7589764727

[BillA]

yea, if the fan is operated at very low back-pressure it will burn up the motor - easily

that speed controller is for ceiling fans, will not work
get a 1 to 3 phase speed controller, $150 + and use the 3 phase motor with a blast gate

spent yesterday looking for a copy of AMCA 210-99, $90
tried an interlibrary loan but from OK is unlikely, probably a ref copy

the diffusers are screens with different gage wire and spacing
the 500 CFM unit from fantester uses a 16" tube, ~ok for 2 120mm fans in parallel; w/o the blower or gate $6900

a 32" dia concrete form tube is $116.80 for a 12' length
a 34" spiral formed steel duct 7' long is $129.00
either would need bulkheads, etc., etc., etc
am now thinking to go for 20 to 24" dia, looking for a surplus aluminum pipe now - easier to weld

awaiting a quote on the nozzles, not yet sourced the screens

[BillA]

nozzle prices from Helander

.687 $63.53
.750 $69.88
1.000 $76.23
1.250 $82.58
1.500 $88.94
1.600 $88.94
2.000 $101.64

adding taps in 1" and above about doubles the price
plugs are $10.50 ea

so ~$400 for 500 CFM worth

[bigben2k]

I was afraid of the Helander prices. I'm going to buzz Jon. Taps are out, but the plugs are a common hardware store (Lowe's) item, albeit maybe not in all sizes.

http://www.electricmotorwarehouse.com/phase_inverter.htm
I'm thinking variac with the 1/2 HP 120v motor; think it'll work? I need a cheaper option than $150. Even a belt or chain drive with stepped wheel would be cheaper than that converter.

Keeping my fingers crossed on the blower; am being outbid. Hopefully the seller has more (been listing them for a while now).

Good find on the concrete former; local? Can we split one, or is 6' too short? Darn, it's a bit short... Really need 7 feet, at 32".

I could make bulkheads from commonly available plexiglass sheets, cutting and stacking multiple parts. A bit tricky, but cheapest of all. Thinking fiberglass & resin to seal the bulkhead to the tube. I'd have no problem using JB Weld on alu (the stuff is available in larger quantities).

I believe that standard/common screens are of the 75 or 67% opening, variety. Again, cheaper to stack them, and combine an egg crate. i.e. 2 stacked before the egg crate, then 3 stacked after. (duplicated on both sides of the nozzle wall). Any thoughts?


Am planning a stop for the phenolic this week, and possibly some surplus shops for the egg crate, time permitting. I believe that CDscrapmetal is closer to you.


Got a new toy: http://tasktoy.com

[BillA]

what size/thickness phenolic you need ?
I have a fair amount

would suggest 20 or 24" dia

run the blower flat out with a blast gate
you need to learn "simple"

[bigben2k]

3/8" preferably, but will settle for anything right now. Need a 3" wide strip, enough to construct a box.

I'm also leaning towards a smaller diameter; 32" is not handy (bordering on ludicrous), and would have wheels, like fantester's biggest unit. I have no problem/concerns/qualms exceeding the specifications, if testing an 8" by 6" core, on a 24" diameter tunnel.

Got a source for 24" concrete formers? At 24", we could split a 12' length.

Yeah, I'll get the motor first, then try it out. If I want to add motor control, I'll do it later. Lost the blower; better luck on the next one.

[BillA]

eh ?
3/8 x 3 x ?

Burris Contractors Supply (281) 657-8900

[bigben2k]

3/8" x 3" x 3", 6 times.

[BillA]

1/4" ok ?
why so large ?
put the phenolic next to the slug (?) with an air gap

[bigben2k]

1/4 is perfect.

I got the heater inside the box, and doing a vacuum. It might end up being only 1" tall, not sure yet. I can PayPal you something.

[BillA]

I'll wack off a piece tomorrow, I'm in Shoreacres - want to pick up ?
no $, you owe me
lol

[bigben2k]

I'll save the meeting for another time. You have PM with my new address. Offer stands, at least for shipping.

[BillA]

why do you keep avoiding the titty bars ?
NO other reason to live in Houston
(I live in Shoreacres, lol)

[bigben2k]

Moral objection, being married notwithstanding. How about that bar in Kemah, the one with the 20 foot tall fishtank?

Am working on a PID setup for air temp. More when I have the controller in hand.

[BillA]

don't get too exicited, they make more than we do

ck your PM

[Brians256]

Darn straight they make more than we do. With strippers, you get screwed not laid.

Ben, how much do you know about tuning a PID system? This may get interesting when you actually try it.... :D

[bigben2k]

The PID control is going to be another learning effort. I understand the general principle, and I downloaded the manual for the unit I spotted on eBay. It comes with a "pulsed voltage output SSR drive", forward and backward, and can be configured manually, or let the fuzzy logic circuit figure it out. The only part I'm not clear on, is how I'm going to integrate a heater to the whole thing, nor what kind of heater. The unit is spec'ed with a 1 second response time, minimum: I'm not even sure if it's going to be enough, or if I can somehow make it work with a slow response heater. Right now I'm still trying to figure out the details of the "pulsed voltage output SSR drive"; it'll pretty much make or break the idea.

Looking at it backwards, I'm targeting for it to maintain a 25 deg C air inlet temp, with minimal fluctuations. I have yet to define what "minimal" is, but I can figure it out, that's not a problem.

Interesting indeed; if this works out, the same effort could be used in a water cooling loop. The dynamics are a bit different, but the application is the same.

Temp probes gallore coming... and I haven't tested my GPIB network yet!

[bigben2k]

Went through the PID manual last night, got 2 pages of notes. Will know more when I have the unit in hand. Auto-tune is going to be limited (needs a 40 deg C span) , but fuzzy and PID will be available.

Stopped by Lowes today:
-egg crates available, ~1/2" squares, ~1/4" thick. 2' by 4' sheets, ~$10.

-screens available; door screen (reticular implant estimates 85% opening) and "dog-resistant" screen, reticules to ~67% (brick pattern). $5 to $10 for a roll. Manufactured by Phifer (http://www.phifer.com/).

-picked up a "test plug", 1 1/2". Expands to 1 5/8", at best. No smaller sizes available there. $2.

Today I'm going to source an SSR, and continue to try to master the calculations.

Uncle Sam is blessing me with a fat return:D

[bigben2k]

Bought a 1" plug at a local auto parts store. $3. Other sizes available, but none smaller.

I should find out at the end of today wether or not I'll win the controller I've been eying.

This week; keeping on the flow calcs, and paying Bill a visit.


Sidenote: went through the Leybold (http://www.leybold.com/) vacuum primer (200 page, is there anything better to do on a Saturday night? :D), for the heat die / test chamber. Most informative! Spent Sunday repairing my bumper.:hammer:

[bigben2k]

Victory!

FUJI PYX-9 FUZZY CONTROLLER
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7590593467

The manual (http://wbta.us/bigben2k/pyxman.pdf)
(PDF, 98 pages, 669kb)

More info (http://www.alphacontrols.com/Products.htm?ID=72)

[bigben2k]

Just got back from visiting Bill; thank you Bill for a very informative learning session!

To update everyone else, since Bill is going to have access to a wind tunnel, I've bought the blower, blast gate, and hose that he had already acquired.

I'll be experimenting with the temperature controller that I just acquired, but after discussing it with Bill, it's now clear to me why it is going to be a problem. In short, Bill showed me his environmental chamber and the design of it. It is composed of a refrigeration unit and a heater unit. The air is recirculated in such a way that it is first cooled, then heated back up to the desired temperature. The reason for doing it that way (cool then heat) is to eliminate any fluctuations. The Haake chiller works the same way.

Thinking about it on my drive to work, the temperature controller probably won't be able to maintain a very steady temperature (which I've suspected). I'll test it out (in a small makeshift setup) and report results.

I have to make notes about everything Bill showed me today.:nod:

[bigben2k]

I took the blower apart last night and this morning. Good news, it's reversible (the housing can be mounted on either side). In plain english, I can screw up on the rotation (CW or CCW) for the replacement motor, and make up for it.

The not-so-good news is that the blower wheel isn't balanced. There's been an apparent effort made to balance it (i.e. small disks drilled out on the perimeter) but not good enough; the wheel freely rotates to the same position. The outside hub appears to be perfectly centered, but the inside one is off.

I'll look at this issue again, when I have the replacement motor (no spare shaft to play with, right now).

Otherwise I may have found a (free) source (co-worker) for a plastic tube in 24" diameter, but the length is in question.

Now focusing on the temporary rig for the temperature controller test.

[bigben2k]

Am getting parts for a test rig.

Gonna have to be patient on the replacement motor; they're more scarce than I anticipated. In the mean time, I'm reselling unused components.


Does anyone have opinions on a plastic nozzle? (I may be able to get them fabricated).

[BillA]

those nozzles are critical, absolutely to spec - or cal the tunnel, ~$4000
lets get that spec first

re the balance, dynamic is what is relevant
wait 'till you can spin it up

[bigben2k]

Got a replacement motor:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7592920115

Leeson 1/3 HP, 1 Phase, 1/2" Shaft, TEFC (Totally Enclosed Fan Cooled), 3450 RPM, G48 Frame Motor, 115/208-230 Volt, New in Box
More info: www.leeson.com/ (http://www.leeson.com/)

(the item had the wrong picture posted, here's a correct one: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7595637153)

Been in touch with Jon; he's out, not equipped for spinning (a reminder that turning and spinning are not the same!). Progressing on the heat die though.

I hear you on the balance, but right now I expect it to vibrate. Grommet time. will see, shortly.

Gonna put up some items on eBay to get rid of unused things (including that 220 v motor), and make costs back.

edit: motor listing: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7595805284
shameless plug: My old ISA GPIB card: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7595813019

[bigben2k]

Picked up an inclined manometer:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=7594051088
Dwyer Mark II
0-3"
(just for a visual indicator)

Got a couple of watchers on the motor.

[bigben2k]

Gerry produced more than one paper:
http://www.me.pdx.edu/~gerry/class/ME449/weekly/pdf/flowRateSlides.pdf (http://www.me.pdx.edu/%7Egerry/class/ME449/weekly/pdf/flowRateSlides.pdf)
(PDF, 27 pages, 210 kb)

More general.

Edit: his main page:
http://www.me.pdx.edu/~gerry/

Now teaching an Applied CFD class.

[bigben2k]

A few more hits of interest:
http://www.eere.energy.gov/buildings/appliance_standards/residential/pdfs/furnaces_boilers/furnace_boiler_app8_6.pdf


The AMCA documentation on 210-99 standard is available, for a price ($90):
http://cart.amca.org/publications/product.asp?PN=210/N

NASA's KSC library has a copy of 210-99, but not available for loan.

Rice shot down my online request for a loan. I might have to pay them a visit.

A Chinese library (Wanfang) seems to have a copy but there's no way to it. $3.00 (!)


The AMCA certification program documentation:
http://cart.amca.org/publications/product.asp?PN=211F/ND
and
http://cart.amca.org/publications/product.asp?PN=611F/ND
(I haven't read them all yet)

[bigben2k]

I received the replacement blower motor last week. Friday, I installed it, and was able to take it through a quick test run. It works well. It's quieter than I expected, similar to a household vacuum cleaner; very tolerable.

I picked up another manometer:
Meriam Instruments 40GD10
link (http://www.meriam.com/products/default.asp?m=3&d=0&p=50)
($0.99 + $17.81 shipping & handling)
I hope to get more precise readings from it, until I go digital.

I also got a set of four SSR (Solid State Relays), model D1D20:
($30.01 + $8.49 S&H)
Specifications (http://www.crydom.com//userResources/productFamilies/39/crydom_1dc.pdf)
(PDF, 2 pages, 48 kb)
I'll be using these along with my Harrison PSU (0-36Vdc, 0-5A) to heat up some nichrome wires, in that test run with the Fuji temperature controller.

Still working on the tunnel tubing. A pair of 55 gallon drums is starting to look attractive.

Money is becoming tight, and I'm going to have to cool off the acquisitions for a while.


Saturday, I was able to test some of my other testbench instruments: the three RTD temperature transmitters, the industrial RTD probe, the whole lot of small PSUs (5v, 12v, 15v, and 24v, DC).
(see list here (http://wbta.us/forums/index.php?topic=57.0))

Picked up a pair of lithium batteries for my Sponsler flowmeter ($17 with shipping). The meter won't power up without them.

I will be picking up a set of thermocouples, and two Fluke 2190A from Bill (graciously calibrated!).

Am going to have to pickup:
.826 specific gravity, red oil for both manometers (can probably get locally).

250 ohm precision resistors for the RTD transmitters (the 4-20 mA output is through the power connection, (!) ).

[bobo5195]

Gerry looks like the dude there are a couple of things on his website that are quite useful for me.

he uses the same cfd program (star cd) that we use. It is an awful awful program but it was developed in the early 90's by one of the profs (he also did alot of stuff on engine intake modeling as well for all the car nerds out there and that is where the program comes from i believe)

[bigben2k]

Sounds in line with his work; a wind tunnel for Peterbuilt freight trucks.

I'd like to see more about the TIM joint tester that a group of his students put together: http://www.me.pdx.edu/~gerry/research/TIMtester/
Most puzzling.

[bigben2k]

Help, I need someone's input!

I need a solution to mount the nichrome wire, something cheap, that won't burst into flames :p

I'm going to pickup an assortment of nichrome wire with gauges 30, 33, 34, 36, and 38. The temp controller is going to drive the SSR DC, and my Harrision PSU will power (0-36 v, 0-5 amps) the nichrome wires.

I've got a couple of heavy cardboard tubes, 80 mm diameter, and ~ 6 inches long. I'll slap a spare 80 mm fan at one end, mount the nichrome wire assembly in the middle, then the thermocouple at the end.

What I don't have, is a cheap way to mount the nichrome wires, probably in some kind of ziz-zag arrangement. Does anyone have any ideas?

All I can think of right now, is some kind of flimsy wood frame with steel screws. either that, or sacrifice a hair dryer or the spare toaster.:D McMaster has ceramic sheets that I might be able to cut, somehow...

[Brians256]

Cheap? Use coat hangars or wire and then attach by putting loops around standard insulators that you find for electric fences.

[bigben2k]

I like it, keep 'em coming.

[bigben2k]

Came across an NIST paper about calibration of the nozzles:
http://www.cstl.nist.gov/div836/836.01/PDFs/1998/NCSL_4e03.pdf

[bigben2k]

Did I post these yet?
http://www.ceesi.com/pubs_venturis.aspx
http://www.ccdi1.com/efa-flow/064/064-desc/064-desc.htm
http://in3.dem.ist.utl.pt/lxlaser2004/pdf/paper_22_5.pdf
http://www.flowmaxx.com/
(that last one's mostly useless)

[bigben2k]

I thought I'd share a few thoughts I had about temperature control. (I'm having to re-write this; my wife's laptop crashed when I was almost done :mad: ).

First a recap: I have a temperature controller with an input for a thermocouple (among others), and a PWM (Pulse Width Modulation) SSR (Solid State Relay) drive output. The output is varied on the duty cycle in what I'm assuming is 1% increments (I'll be verifying that experimentally). The frequency can be set to a maximum of 1 Hertz (not great, but I'll live).

Going over the details of the test setup that I'm preparing (an 80 mm fan blowing into a heavy cardboard tube, with a nichrome heating wire arrangement in the middle, and the thermocouple at the end) I came to realize what difficulties Bill told me that he encountered trying to maintain a steady air temperature prior to acquiring the environmental chamber.

The temperature controller is a pretty clever device. Beyond the obvious, it can be programmed to respond proportionally to a temperature i.e. it can be programmed to apply the right amount of heat to make up for a specific difference in temperature. Not only that, it also has a self-tuning feature so that it can program itself (saves me a lot of work :D).

A bit about the output.

The output of the controller drives an SSR (Solid State Relay). The SSRs that I ordered are of the DC drive for DC output (a bit unusual, since most SSRs drive an AC output).They can handle an output maximum of 100 volts and 20 amps. Maximum turn-on time is 0.1 msec and max turn off time is 1.0 msec, well within the maximum frequency of the controller's output: 1 Hertz. (Unfortunately, it'll be at least two weeks before I receive them GR). While they are usually mounted to heatsinks, right now I don't expect to run too much power through them.

I got an assortment of nichrome wires. 10 feet of each gauge (30, 33, 34, 36, and 38 AWG, of different metals, more on that later). I calculated the applied power at several voltages and lengths, and everything looks in line for me to use my Harrison PSU (0-36 volts, 0-5 amps).

The controller output voltage is within the SSRs input range. I've calculated the amperage draw, and I expect that it will fall within the controller's max output rating (but I'll have to check it experimentally).

What became clear to me, came when I looked at the details of the above, in terms of PWM. There are three variables of interest here: the frequency, amplitude, and the duty cycle.

In my test setup (where I'll raise the air temp to 25 deg C), I am working with one assumption; that there is an infinite supply of air at 20 deg C. Below are the reasons why that is a problem.

The PWM frequency ought to be fairly high, so that any temperature change can quickly be corrected. Also, the duty cycle cannot be 0 or 100%. If the duty cycle tops out, then the temperature has fallen below the SV (Setpoint Value) and the temperature is no longer being controlled. Conversely, if the duty cycle hits 0% (or otherwise fluctuates between 0% and 1%), temp control is (essentially) lost.

*** In short, the heater must always be ON, for the temperature to be controlled. ***

While it might be tempting to state that a 50% duty cycle would be ideal to keep a safe margin "either way", this isn't actually the case: the temperature is "in control" as long as the duty cycle is 1%, 99% or anything in between. But there's more.

Let me use an example where I'm running a relatively high amount of power to the heaters, and I end up with a very low duty cycle. To correct it, I lower the applied power, which increases the duty cycle.

(In actuality, it isn't quite that simple: since the applied power has changed, the heater response has also changed, so the controller has to be re-programmed or re-tuned).

Enter the refrigeration unit.

While visiting Bill, he explained to me the function of his environmental chamber (BTW, the Haake 82 water chiller works the same way). In short, it's made up of a refrigeration unit (the usual compressor, evaporator, condenser arrangement) that runs "flat out", as he put it. The recirculated air is cooled, then heated back up by an arrangement of nichrome wire coils, to the desired temperature.

Without the refrigeration unit, keeping in mind that the heater must always be ON, it should become clear that that arrangement cannot function, where the fluid (air or water) is recirculated.

I've determined that the refrigeration unit serves many purposes.

While I'm sure that the temperature controller and heater (alone) arrangement can work well, I believe that there are a number of issues that arise, when the inlet and outlet temperatures are very close to each other.

1st, as we all know, the transfer of heat within a very small temperature difference is difficult because it is a very slow process. Picture two stacked blocks of copper where one is at say 23 deg C and the other is at 24 deg C, and try to imagine how long it would take for both blocks to be at the same temperature. Now imagine the same blocks, 100 deg C apart, and try to imagine how long it would take for both blocks to be within 99 degrees from each other. Obviously it's quicker in the latter (it's obvious, right? :D ).

I figure that the nichrome wire heater works best when it operates at a significant temperature difference. Further, given some relatively minor inlet temperature variation, the same heater should easily (read quickly and just as effectively) be able to heat the fluid back up. What I'm getting at, is that the combination of the temperature controller and heater arrangement, may not be able to deal with a significant change in the heater effectiveness, as happens when the heater is called to apply heat levels that vary over a wide range, or more specifically, near and far from a very low range.

Another factor that can apply here, is that the DUT (Device Under Test) may throw in its own share of heat or cooling, but the heater should still be applying a significant amount of heat. The DUT effect is a factor in the design of the recirculator. If the DUT is expected to induce heat, then the whole assembly might be preset with a lower duty cycle.

To go back to the (false) ideal of a 50% duty cycle...

50% duty cycle is actually ideal, to minimize the temperature fluctuations, but isn't necessarily relevant.

See the graphs below, where green is the average temp, and blue/purple the actual temp. Sorry for the rough graphs, I hope you all get the point. Note the peak high and low.

graph 1 50% duty
http://wbta.us/bigben2k/50pctduty.GIF

graph 2 low duty cycle.
http://wbta.us/bigben2k/1pctduty.GIF

While 50% might seem ideal, it may not be relevant if the DUT (by design) is unable to be affected by the amplitude and frequency of the temperature fluctuation, but if any fluctuations exist, one should be aware of them.

As previously stated, while 50% is ideal, the design may have to accomodate a DUT that adds a heat load, which means that it would be configured with a higher than 50% duty cycle.

I've also determined that the response time of the temperature probe plays a critical role. As I've previously found out, RTD type probes usually have a slower response time than other types, probably because they are encased and/or shielded, where thermocouples can be found bare. In order for the temperature probe to report a new temperature, its mass must be brought to the new temperature. What can help in getting a better response time, is the fluid's flow rate; the higher it is, the quicker the response will be (note that any flow rate also induces heat). I believe that the temp probe response time is by far the most limiting factor in maintaining a steady temperature.

The test setup.

My test setup effort will mostly consist of varying the applied power, then re-configuring the controller each time, until I hit a duty cycle around 50%, then measuring and noting the fluctuations.

I will first start by trying to calculate the necessary power, based on the the energy required to heat a certain flow rate of air by 5 deg C.

I'll be using a type T thermocouple, 40 AWG (0.0031 inch diameter) that I recently ordered from Omega.com (a $12 item!). I'm hoping that the type and small size of this probe will make for a responsive setup.

With all of the above, I believe that I am well on my way to maintain a steady temperature, once I incorporate a refrigeration unit.


A note about analog.

An analog controller would (essentially) connect the temp probe directly to the heater, where more power is applied when the temperature drops. However, I believe that it would have to be finely tuned, so that the heater and the temperature probe response is matched, otherwise the system would over/under compensate for itself, which would cause fluctuations. A similar effect is known in flight, where the plane dips forward and back. Otherwise, a proportionally controlled heater like that would probably be ideal for steady temperatures, if it is possible, because a digital (PWM drive) output is a sure way to fluctuations (although they would be easier to identify).

Ok that's all for now.

[bigben2k]

Argh! Someone stop me!

I "accidentally" picked up another Fluke 2190A:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7601329663
with a 2300A this time. I just made a minimal bid, I didn't expect to win!

I also picked up a differential pressure transmitter:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7600553910
(Dwyer 647, Wet/Wet Differential Pressure Transmitter)
unfortunately, I only noticed afterwards that the accuracy is very poor. Oh well.

[bigben2k]

Still waiting on the relays.


I calculated the needed power as follows:
The knowns:
-typical cfm of an 80 mm fan: 35
-density of air: 1.2 kg / m^3
-heat capacity of air: 1004 Joules / kg
-1 Watt/hour = 3600 Joules

I then calculate the needed power to be 20 Watts. 19.9 actually, but this is a rough estimate, as it doesn't account for barometric pressure, heat transfer resistance, secondary losses, or actual airflow rate.

As I mentionned before, the target is 50% duty cycle, so I'll setup the nichrome wire to apply 40 Watts at full load.

Using one foot of 30 gauge nichrome wire, and applying 2.5 amps would result in a voltage of 16.3 V. This would result in a wire temperature of ~760 deg C.

Using one foot of 33 gauge nichrome wire, and applying 1.8 amps would result in a voltage of 23 V. This would result in a wire temperature of ~870 deg C.

Both temps are within the maximum specs for these wires.

The numbers don't feel right, so I'll double check them again.

I have yet to figure out a mounting solution for this wire, but I've determined that I can use screw terminals to connect it, as long as the screw terminal isn't cheap plastic.

[bigben2k]

...and many months later!

I'm about to complete construction of the simulator, to flex the temp controller. (Otherwise the temp controller will be re-dedicated to a water heater).

I need some suggestions, on cutting these things:
http://wbta.us/bigben2k/ceramic_tubes1.jpg

They are:
Alumina (Al2O3) ceramic
1" long by 0.19 inches in diameter
Hole diameter is 0.13 inches

I need to cut them in 1/4" length or less. The best success I've had so far, is with a grinding wheel on a Dremel, but still very, very slow.

Anyone?

[billbartuska]

I need to cut them in 1/4" length or less. The best success I've had so far, is with a grinding wheel on a Dremel, but still very, very slow.
Anyone?Put a variable speed, reversible drill in a vice and then cut with the Dremel. May not be faster, but you'll get nice square cuts. A little water for cooling may help.

[bigben2k]

I stopped by Lowes today, and came across a jigsaw blade by Bosch, special for ceramics.
http://www.boschtools.com/accessories/

I'll mount the ceramic tube in a drill to secure it, and see if I can chop it that way.

I'll report results Sunday.

Thanks,
Ben

[bigben2k]

Sometimes, the simplest solution works best:

The $8 jigsaw blade was useless :( but the drill chuck happily crushed these tubes to the length I wanted. :D

[bigben2k]

A quick update:

I'm still building the simulator. I picked up a couple of power terminals, and I'll be using pieces of a hacksaw blade to route the power in and out of the tube. Nuts and bolts will secure the hot wire inside.

I lined the inside with a steel wire, and used JB weld to secure it. I'll be able to use JB weld again to secure the ceramic tubes, and mount the wire. Then I'll add some aluminium tape to line part of the inside (just because I have it, and it's a cardboard tube). Then I can fire it up, and run some tests.

Pics later.

[bigben2k]

Assembly complete, and I had my first test run last weekend.

I was only able to maintain a steady temp within +/- 0.4 deg C and could only set the temp within a very narrow range (i.e. 2 or 3 degrees above ambient, no more, no less). As soon as the house AC kicked in, it dropped the room temp by 3 deg C, and the system couldn't keep up anymore.

It was interesting to see the hotwire flex, on those moments when the controller was running it at ~50% duty cycle.

What I observed is that the TC I used would return temps that would jump by 0.2 deg C for no apparent reason. I was going to try my miniature RTDs, but they turned out to be thermistors, and won't link up to the Fuji temp controller.

I'll have a few more runs at it, as is, but I plan to replace the temp probe with an RTD. I might add an RTD to measure the inlet temp. I'll also review the temp controller features; it's a bit more powerful than I expected.

[bigben2k]

Another update.

I removed the eyelet slug at the end of my thermocouple, to see if I could get a quicker response. It didn't seem to have any impact.

I've got a set of RTD probes on the way, but I'm still going to try my original idea of using my 40 gauge thermocouple (normally I wouldn't use them here, because they're very small, and a small thermocouple like this can oxidize quickly in relatively low temperatures ( > 100 deg C, which ruins the TC probe), but I'm running with "near room" temps here, so should be fine.

Otherwise I'm still seeing 0.2 degree C temperature reading jumps, and I haven't identified why yet. I'll plug my scope on it, and see if it'll help me figure out what's going on.

I might also try replacing the 1 foot long nichrome wire with recently acquired nichrome coil, to apply more power. If successfull, I might be able to apply enough heat to get a 40 deg C temperature rise, which would allow me to have the temperature controller run a self-programming routine.

Going over this thread, I realized that I've already spent over $100, just to create a test rig. :eek:


On related topics, I've begun tooling up for phase change, and I'll be building the cooling unit myself, for the environmental chamber that I'm putting together. Details in the forums: http://xtremesystems.org/

[bigben2k]

An update:

Link to my thread on xtremesystems.org:
http://www.xtremesystems.org/forums/showthread.php?t=113725
(mostly acquisition, for now).

I acquired a couple of (what I though was) RTD probes, but they turned out to be thermistors, and they won't hook into the Fuji controller. So I got a pair of two wire PT 100 2-wire RTD probes.

I've moved to a new place, and having the carpet replaced with tiles Tuesday. Then I get to setup everything all over again.

Otherwise I've acquired a lot more tools and testing elements, including a vacuum pump (to build the phase change in the environmental chamber) and a (PCI) multi-function Data Acquisition card (which unfortunately requires a special cable, more on that later).


More later, hopefully with pics.