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Controlled Cooling of Water Bath

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ciaran.mooney

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Afternoon,

I am currently doing a summer project in a University on crystal shape and size. This requires that I dissolve nickel and iron salts in water, and allow them to cool and recrystallise.

I want to be able to control the cooling rate of the salt solutions, so that I can see the effect on the crystals. Unfortunately I don't have any equipment that will do this.

I confess that I have no electronics experience, and hoping for someone to give me a circuit diagram that I can follow. I am interested in learning about electronics, but I hoped the need would not be as immediate as it is now. I am sure that this kind of equipment could be made in less than an hour by someone technically minded, but would take me weeks!

My idea was to emulate those "holiday light timers" you can get, where a lamp plugs into a time, that plugs into the wall. But instead of a lamp have a hot oil bath, and instead of a timer a temperature sensor.

The user changable settings would be:

* Start Tempeature
* End temperature
* Duration

The circuit should then calculate a rate of cooling, and carry it out. Essentially a linear graph of time vs temperature.

So I could set it to max = 75*C, min = 20*C, interval = 10 hours, and it would automagically work out the rate of cooling for me.

Is this possible with simple electronics? Or would I have to get my hands on some kind of IC and program it from a PC?

Thanks,

Ciarán
 
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hi Ciarán,
Sounds an interesting project.

How would a 10 hour timer and [20C to 75C] temperature sensor control the rate of cooling of your sample.?
 
Hi,

The 10 hour timer would not be independant of the two temperature settings.

Think of it as sitting next to a hot plate and manually turning down the "max temp" dial over a period of time.

If I set it to max = 75, min = 25, duration = 10 hours, what I would expect the circuit to turn that dial down 5 degrees every hour.

How I expect it to work is that the max temp would change over a period of time (5 degrees per hour), and circuit would control the hotplate by simply turning it off and on. The analogy would be with one of those lamp timers, except there would be a thermometer, rather than a timer.

I was thinking the easiest way would be with some kind of BASIC programmable chip, but I have no equipment, and initial costs would make a difficult route. I was hoping that a traditional electronic method could be built. Ie. I just buy a breadboard and a couple of components. This has to be <£30 ($60) project.

Any ideas how I could make this? My knowledge of electronics is terrible. Being a science student I understand resistors, capacitors, transitors, diodes etc, but I have no idea how to use them in the context of doing something with electricity!
 
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hi,
As you dont have any PIC programming or electronics experience, I would suggest that you consider using a PC/Laptop.

You could sense and control the project using the parallel port on a PC.

It would mean writing a PC program in Basic and constructing a small interface.
 
There are programmable temperature controllers that have a "ramp and soak" function. This allows the controller to adjust the temp over time in discreet steps. I saw a couple on eBay:

**broken link removed**

Don't have all the spec's on them but but it looks like if your heater is 10 Amps or less you could drive it directly with the 30-step one. The 64 step one would require an external relay...I think.

The price puts you a bit over budget, but given your circumstances, you can have it: fast, cheap, or easy...pick two. ;)

Ken
 
Thanks all for your suggestions!

KMoffett, I've been looing for something like that for days! I suspect we may have something similar in the department somewhere, I just have to go looking for it. Now I have a name it could be a lot easier. If it comes to it they are probably just within the budget of my supervisor, if I can convince him its the only way.

My programming experience on a PC is also limited, I can write a few simple scripts in Python. Although I am more worried about trashing a laptop by leaving it in a lab full of chemicals. (Specifically corrosive ones that I am using! :)). I may write a program anyway just to get my hands dirty.

I also looked up how cheap a PIC and a PIC programmer were, they are actually in my price range. And as I want to get into using them in the future I may buy one and also have a stab at it!

Thanks again for your help.
 
The part that I find most challenging is controlling the cooler. 20C end temperature won't be achieved just by turning the heater off.
 
as we talking about cooling (active way) what is the cooling source??

An oil bath whas mentioned in the first post but these are more used to heat things up

as mneary mention switching off a heater element is not cooling it's a form of controled heating

how big is the intendet set up ?

the resoirvoir, how many liters?
how acurate has the control to be, 1 degree celcius?

please give some more info

Robert-Jan
 
Hi,

Sorry I was not entirely clear.

I was planning on no active cooling, 20*C was used as a end temp because its around room temperature. The oil bath would be used to heat, but only turned on during the cooling programme to maintain a temperature. So yes, its more controlled-heating-backwards, from my point of view much simpler than finding a benchtop-cooling source.

The bath would be about 10-15cm diameter, and a 5cm deep, with the vials of my solutions sitting in the oil. Its not huge, and doesn't need to be.

It's crude but simple.

Accuracy would preferably be down to the degree, but that's actually quite difficult with this kind of set-up. Hysterises curves and all that would need to be employed. Even at the moment I the thermostated hotplate gives me a varying temperature of +-2-3degrees.
 
a bench top cooling source could be a big bucket with water (room temp) and you pump it through with a smal pump and a small hose in the bath

the hose i am thinking of is the kind of petrol tank to carburator hose on a motorbike

the small pump can be a windscreen washer pump which can be controled with a PWM control(pulse width modulated control) to control the flow and thus the temp of the water and the rate of cooling

Robert-Jan
 
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