[christian_rice]

I managed to get the unit wired and programmed such that it keeps a steady temp without use of an external relay. I’ll provide some lessons learned for the record…

 

For anyone following this thread–don’t buy the thermocouple I mentioned earlier–I thought I was getting 24″ lead wires, but I got a 24″ probe lead. Ugh, ridiculously long probe. I consequently ordered a TJ36-CPSS-18G-6-CC instead, with a 6″ probe. It’s a type T, which is for temps much closer to what we’re doing, instead of a type K. That’s one small change of program on the controller, hopefully I’m getting the right thing this time.

 

Something one needs to know to make this work is that the relay function on the CN7533 completes a circuit from terminal 9 to terminal 10–the CN7533 does not internally provide power to any terminal lugs. I’m sure this is totally obvious to electronics buffs, it being a relay and all, but I was wondering about that for a little while. The controller instructions are not going to help an abject novice build anything useful.

 

I included a switch on the positive leg of my power cord, as per manual recommendation. Basically I bought a 12′ extension cord for $3 and an in-line rocker switch for $4 from Home Despot. I discarded the female end of the extension cord. The positive wire goes to terminal 1 and terminal 9. The neutral wire (aka “wide blade on a US power plug”) goes to terminal 2 and one wire of the heater element (in reality I used an additional terminal block so I could avoid splicing and wire nuts in my enclosure). Terminal 10 connects to the other wire of the heater element. The thermocouple connects to terminals 4 and 6 (omega.com has a reference page that illustrates the polarity color coding of their thermocouples).

 

Terminals 9 and 10 are OUT1. In the initial setup, OUT1 should be set to HEAT, which means when PV (process variable = temp measured) is less than SV (set variable = target temp), the relay closes, and the heater becomes active.

 

The actual opening and closing of the relay is further affected by the operation mode. PID autotune mode is very helpful, especially because there’s a lot of mass in my mercury cup heater connection assembly, especially relative to the volume of mercury being heated. The controller has to account for the fact that relay operation is not linked in real time to the mercury temperature–there’s a significant ramp lag. Autotune mode does some real math in the background, so “magically” makes this work.

 

I used a small ABS plastic project box from my local neighborhood electronics store. The heater pad leads were only about a foot long, so I soldered some extensions on there, and used shrink tubing to keep the wires neat. I wanted to keep the controller unit outside my portable fume hood, so it would be less likely to be attacked by whatever is in there, for what that’s worth…

 

Cheers.

 

[christian_rice]

Once again, very helpful. I downloaded and read the manuals before buying, but what I’ve got from you is orders of magnitudes more useful for me.

Thanks!

[christian_rice]

Thanks a bunch. From what I read, the grounded unit responds to temp variations faster–that should tighten the feedback loop.

I ordered the following from omega.com:

$20 KTSS-116G-24 thermocouple (K type, stainless steel, 1/16″ diameter, grounded, 24″ leads)

$26 SRFR-3/5 silicone/fiberglass heating disk, 3″ diameter, 5W/inch^2

$97 CN7533 1/32 DIN controller

I’m wondering if you used an external relay, or connected your heater directly to the controller. Perhaps the watt density of the heater also matters?

[christian_rice]

Once again, my previous post a bit premature…I found a 20×24″ sheet of rubylith at Blick in Berkeley for about $5, it doesn’t have much tack to speak of.

[christian_rice]

I could use some rubylith. I see it on eBay–am I concerned with thickness or tack-level? Do I just put two pieces together to avoid attracting massive quantities of dust?

[christian_rice]

I’m pretty sure Mike is referring to the color cycle of the plates, not which iodine pass you are on (if I comprehend the nature of your question). The more color cycles you go through, the thicker the sensitized layer, and the slower and less contrasty your plates will be.

See a thread at http://www.cdags.org/dagforum/topic.php?id=31 for more background.

So that would mean “the first rosy yellow” or “the first magenta” that results from total iodine sensitization that you can examine under light. If you break up the iodine pass into two halves, that is, xx seconds iodine, examine plate color (hopefully it’s yellow), then another xx seconds iodine with plate rotated 180 degrees, examine plate color (you should be approaching the desired color of rosy yellow or rosy magenta Mike refers to). Then bromine, and you can examine the plate again, to find a fairly deepened rose, or bromine a touch more. Then lights out, and iodine once more for 2/3 of the original total iodine time. You can’t really tell the plate color after the final iodine pass, or you’ll be adversely fogging your plate.

To judge the color of the plate, you can have a 40 watt incandescent bulb maybe five or six feet away. Hold the plate so it reflects a whiteboard or white paper, and look at the surface of the plate.

You could also make a test plate with different bromine times, to find at which point your plate is fastest. It’s a curve, and fog is induced beyond a point. Use a small strip of card stock to block bromine sensitization to make a test strip of sorts.

If you wait an hour or two after sensitization to make an exposure, your plate can pick up speed, up to a whole stop. But don’t want after exposure to dev it, as the image is fading away.

There’s lots of places one can set up tests, so it’s good that plates can be reused…

Hope this helps, corrections welcome.

[christian_rice]

Here’s a web page for 3M cartridges to protect from mercury vapor and chlorine gas. It has some detailed instructions. I just googled “respirator with mercury filters.”

Click to access mediawebserver

Note that the cartridge says it is only useful up to certain concentrations–above which you are in trouble. If you don’t have adequate means of keeping mercury levels below the required level, wandering into a space full of mercury will be bad for you.

You can make a fume hood out of a large plastic storage container and a decent exhaust fan. I’m sure something passable could be done cheaper than buying a professional hood. I’m planning to build my own from raw materials–probably acrylic sheets, but I, like you, am open to suggestion.

[christian_rice]

From everything I’ve read that you’ve posted, I think your English is quite functional.

[christian_rice]

So much for Wikipedia…ok, I admit I trust it too much to cover for my ignorance of chemistry. So why do we use heat in the gilding process?

[christian_rice]

Thanks, Li. That is a different formulation, though I do see HAuCl4 popping up in searches on gilding, as well, so the learning continues each day.

A Wikipedia search on Gold_chloride details the various forms, and does indicate HAuCl4 decomposes to HCl + AuCl3 with heat. And mixed with sodium thiosulphate, I suppose the elemental gold becomes available.

So it seems there’s a number of ways to go. I guess the important part is to give the gold an opportunity to become free when heated. All of which makes me want to go sign up for some chemistry classes at the local college…

“If auric chloride AuCl3 be mixed with a solution of sodium thiosulphate then the gold passes into a colourless solution which deposits colourless crystals containing a double thiosulphate of gold and sodium which are easily soluble in water but are precipitated by alcohol…This salt which is known as Fordos and Giles’s [sic] salt is used in medicine and photography.” — The principles of chemistry, Volume 2, Dmitry Ivanovich Mendeleyev

Also, from http://www.ncbi.nlm.nih.gov/pubmed/11625558 :

[From photography to chrysotherapy: Fordos and Gelis salt].

Devaux G.

Abstract

In 1840, the French physicist Hippolyte Fizeau (1819-1896) proposed an auric chloride and sodium thiosulfate-based reagent to fix daguerreotypes. In 1843, two French pharmacists, Mathurin-Joseph Fordos (1816-1878) and Amedee Gelis (1815-1882), isolated its main ingredient in crystalline form and analysed it as a sodium aurothiosulfate. They recommended the use of an aqueous solution of this product to fix photographic negatives. In this way, the deterioration by sulfuration that negatives underwent with Fizeau’s solution could be avoided. Fordos and Gelis salt came back in the news in 1924 when Prof. Holger Christian Mollgaard (1885-1973) from Copenhagen suggested it under the term Sanocrysine for use in tuberculosis.

(it goes downhill from there, a la “That’s a great idea, Sir Bedivere!” said the king, “This new learning intrigues me. Tell me again how a sheep’s bladders can prevent earthquakes.”)

[christian_rice]

Nevermind

AuCl3 pops up in the dagforum. My bad.

[christian_rice]

A nice lead, the San Jose shop, thanks Andy–I’ll check that out. I’d love to check out your castle sometime, maybe there’s cause for a bay area dag meetup? One last question about San Jose Scientific–did they want to know if the bromine was going to a residence? If so, how did you handle that? Or should I not ask? Not that that’s your situation, AFAIK…

And thanks, Rob for the encouragement.

I’ve been chasing down a lot of leads, and it does seem that the academic/educational sector is the well-lit path, because I’ve now got access to bromine. Not my own bottle, but it’s a start, and that means I don’t have to keep it in my house for now, nor did I have to bubble chlorine gas through dissolved pool tablets

[christian_rice]

Hey, Todd, we were at Peter’s Valley this past summer together. I’ve been building my tool set, including gilding stand, mercury pot, and buffing stand with mills, lathes, and TIG welding. If you are still looking for any of these items, let me know, and I can post some pics, let you decide if you’d want something. My prototypes show my learning curve in the industrial arts, but I’m getting a lot better.

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