The probe has "Cu50" on it, the rest is Chinese. The SG-808 calls for a "PT100 Cu50 Jpt100" at the appropriate connection point. So, I'm guessing it is a PT100 or compatible sensor.
Originally Posted by wiedzmin
The instrument box it is in is obviously some off the shelf generic thing, as you'll note the labels (see the on off switch) are hand written, and the PID is somewhat loosely installed. But it works perfectly. I did have to calibrate the probe (a setting on the PID). The factory setting is no adjustment, but mine was reading about 2.5 C too high. A simple adjustment got it to the exact same reading as my regular .1 C thermometer, across a variety of temperatures.
The PID controller is amazing. There is no hunting for the temperature, you set what you want, the temperature climbs up and just stops on the temperature you set. It does take a while to pull the chemistry up to temp in the bath, as one would expect. I could preheat the chems in a microwave, if I was in a hurry I guess. Or, I could start the bath at a high temp to pull up the chems. But it is simple enough to plan ahead, start the bath, put the chems in, and come back later when everything is at the right temperature, same as I used to do with the Jobo.
This is very interesting. Care to share some basic information on these?
I have been using a couple pumps and aquarium heaters in my kitchen sink but I want to make something that is better suited.
So, if I get this correct, you bring A/C power to the PID controller, and wire a relay and sensor (thermocouple?) to it. You wire your heating element to the relay?
PID monitors sensor and applies the power to the relay when the sensor reaches below your set temperature, supplying power to the heating element?
Essentially correct, yes. There are a variety of PID controller configurations. Some require an external relay, some have an internal one. The ones with an internal relay can be directly wired to the heating device, or more conveniently, to a power socket into which you would plug in the heating element. You can usually find a ton of them on ebay or other online sites. They are very common. I found one that was already built into a little instrument box, prewired, with the probe. That was so handy I jumped all over it.
Originally Posted by WayneStevenson
"PID" stands for Proportional, Integral, Differential controller. The heating algorithm is quite sophisticated. The PID controller can either auto tune or be manually tuned to the bath and heating element's capabilities. The result is that at least when tuned, the temperature does not overshoot the set value. It arrives at it and sticks, usually to within .1 degree C. It is quite impressive for such a small, relatively cheap box.
I've not found aquarium heaters to be sufficiently powerful for my water bath. I tried, gave up. Just not enough energy introduced quickly enough to get the bath and soup up to temp in a timely fashion, and I'm not certain it is powerful enough to hold the temperature stable while processing. I'm quite certain the PID controller and the heating element I have (which I think is a 1200 watt element, you can get various sizes) is sufficient. I do use a good pump. It works for aquariums or fountains. I don't know how well my pump will work if I try to do something like sous vide cooking in the same tank, which would require temps more like 80 degrees C minimum. That's hot enough I don't want to put my hands in the water, and I don't know if the submerged heater would operate in those temperature ranges. But I don't need that for photography, and if I do burn the pump out, it was only $10 and replacement is trivial. It just sticks to the bottom of the tank with suction cup feet.
I do plug everything into a ground fault circuit, just in case.
For the tank, it is a simple plastic storage bin from a home supply place. To get the heating element in, and supported horizontally, I made a large hole, cut a chunk of plastic (out of a plastic cutting board, about 1/4" thick) to reinforce the mount, glued it all in place, and then sealed it with silicone sealant. The result is that I don't need the water to be very deep to fully cover the heating element. Do note that these simple heaters will burn out almost instantly if powered up in the open air, so they must be under water. The downside to my system is that if I do burn it out, I have a goopy mess to cut through to extract and replace it.
The design on which I based mine had the heating element going in vertically from the top, attached to a separate unit that would clamp onto the bin. I didn't like that one, because it required the bin to be filled with water nearly to the top. If I'm using the Jobo 2509 (?) tank to develop sheet film, the water would be too high. I did consider it, and considered putting in a little submerged platform just for that tank, but decided it wasn't worth it. Better to mount the element low to begin with.
The size and depth of your tank depends on your need. If I was doing tray based processing, I'd construct a much larger container for the tempering bath, and build some sort of submerged shelf or platform for the trays, so that while the water would be deep enough for the heating element, it wouldn't be too deep for the trays.
(A larger volume might require multiple heating elements too.)
I don't have enough room in my bathroom for such a contraption, so this is it for me. I have enough room for Patterson - based roll film development, and for lights out dip and dunk using a combi-plan based system. One problem to solve with that system is the fact that the PID has very bright lights, as does the power switch. I'll rig an opaque cover for it.
Perfect. That is what I figured. I did some research on them last night to get a better idea of them.
And a GFCI were my first thoughts on it. Every time I put my hands in my sink with two $10 chinese heaters, and two $5 chinese pumps, I was always wondering if it would be the last thing that I ever did.
I have noticed you can wire an alarm or indicator light in to them to come on when the temperature is below threshold. Pretty slick.
I plan to use an oil heater or water heater element for my baths. They can be removed easily, do not require soldering, and usually have their own rubber gasket and lock nut. And I have no idea what developer, or fix, etc. will do to them. Especially the pumps. So making everything easily replaced is important.
One in particular that I am looking at is 4kw. Meant for much larger volumes. Do you think it would be a good idea?
MacGyvering a tempering bath for color development
These are also great for sous vide cooking. In fact there's a relatively cheap out of the box model PID controller on amazon. It's called the dorkfood I think. I have one from auber instruments and love it.
Of course never mix food and developing chems. But sometimes the technologies of food and photo making are the same.
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Sorry for highjacking. But I'm sure I'm not the only one here completely loving your setup, who would like to do their own.
I see relay outputs of the PIDs but they do not specifically state that they are solid state. Some show voltage and amp, some just say relay. So that must be what you were talking about with the internal relay. Seem to only be able to handle 750w and under at 110 with the built in ones.
So, I can run a 4000w / 220V element (which would require a 30amp circuit), at 110V / 1000W (halve voltage, gives you quarter wattage) from what I understand.
So it will run on a 15amp circuit, and take 9amps to run. I think I should run 14 guage to stick with code.
Last edited by WayneStevenson; 03-12-2013 at 05:53 PM. Click to view previous post history.
Unless it's caffenol!
Originally Posted by drumlin
I actually did use the contraption for sous vide eggs. But even though I used fresh water (I dump at the end of every session), I did put the eggs in a plastic bag to isolate them from the water (bag with air evacuated by carefully, slowly immersing it in water, sealing it as the water reached the seal. This can be done in a separate body of water.)
I tend not to spill much chemistry into the water bath - a drip here, drop there. So I'm not too worried about damage to the pump or heating element. Chems will be so dilute that I can't imagine any harm will come.
I find the little heater I have can maintain temps easily at "egg level" sous vide temperatures (I used 63.5 C for one hour). I haven't tried raising the temp to 80 C. I'm a bit concerned it will struggle a bit at that temperature, and I don't know if the aquarium pump will survive the heat. But try it I will at some point. I am considering inserting the whole tub inside a styrofoam cooler I have, in which it fits quite well. That should help with heat retention, especially at higher temps, and should generally allow me to use less electricity overall.
While the heater will bring up the water on its own, I also recommend helping it out by starting with water that is close to the desired temperature. Saves a lot of time, and energy. I think it also saves time to accelerate the chems to temperature by either starting them in a separate, much hotter bath, perhaps in a sink, and then transferring them to the tempered bath when they are close to the desired temp. It takes a long time for a jug of room temperature chemistry to come up to the working temperature, just sitting in 38 C water.
Regarding a bigger heater: I'm not sure it is necessary, but I do think you would want a PID that drives a higher capacity relay than the internal one if you use a big heater. For development, you mostly are interested in holding a constant temperature, rather than moving the water mass to different temperature levels. The former doesn't take a lot of energy, the latter benefits from a big heater. But you might also be using a much larger bath, so it really depends on your design's requirement.
The 80 C test was successful. I did insert the tub into a styrofoam container. The container is a common one here in China used for shipping meat, basically a big, square styrofoam cooler, with a lid. This does help keep the heat in, I think, though it wouldn't be as efficient as a purpose built ice chest.
If you want to do this and also have something that could work for sous vide (i.e., a high heat environment), you might consider starting out with an ice chest, instead of a plastic storage container. It should be much more energy efficient. the reason I shied away from them is that they tend to be pretty deep (high walls, narrow footprint), which I find a bit of a bother when processing film. A more powerful heater might give you some comfort too. I think it is important to make sure that the water flow can move the heat into the bath efficiently. If you have a big heating element, you might need more flow.
The last thing I want to add to this are a couple of shields to protect the heating element and the temperature probe from being banged about. The probe in particular is easy to bump, and it has a lot of leverage against the very thin through-hole in the wall of the container (I should probably reinforce that hole a bit better than I did).
First parts of mine have arrived. Well, some heater elements. Should have everything here within a couple weeks I hope.
Last night I set mine up into an 8x10 tray with aquarium heaters for testing. Works beautifully. I made the mistake of ordering relays that have DC input. I read somewhere that DC relays could take AC 110 current. But I now think that it may have been the other way around as I fried the relay I was testing with. I actually tested it with an 18V AC output I had on a DC model train controller I have. It worked. Once I wired up 110 to it, it was done with.
So I cut the end off a 6V AC/DC adapter and soldered connectors onto it. Once my AC input relays that I just ordered come in, the footprint will get smaller.
The thermocouple was out of calibration with the REX C100 PID controller by 2 degrees celcius. Using several thermometers in both the heated bath, and ice water.
I tried another thermocouple with the same results. The manual didn't document how to adjust compensation which I found rather odd, but I did find a setting that wasn't documented. After setting it a couple times, I found that that was exactly what I was looking for. It's not calibrated to my IR thermometer that I use which is within a half degree of 6 other thermometers that I have.
I need to get some plastic sheeting now so I can build some tanks.