Need advice putting this device together

ronfinch · Jun 23, 2010

I am looking to put together something that will enable me to accurately control the temperature of water inside a container such as an electric slow cooker, at pretty low temperatures 65 - 70 centigrade.
I am looking to buy the components and fit it together myself simply to save money...

I believe I need the following:

i. Digital PID with SSR output, I obviously need to be able to set the temperature/it needs to display it. A timer and or high and low temperature alert are not essential but would be good. As would maybe be an autotune/self-tuning function for the PID...
ii. Solid state relay of some appropriate power rating. 1 of the sets I saw specified (40A), 24-240V AC. The unit will only be used in the UK I do not know if this affects the Voltage rating I need
iii. A temperature sensor probe - one of the kit specified a PT100 temperature sensor probe with a M8 Fixing Screw, Flexibe Spring and an Armored Wire Cable.

Can anybody help me out with advice as to units I can buy? Haven't been able to get the advice I think I need, am hoping an electrician/someone interested in electronics could help me out here....

Thanks very much if you can.

nickblake · Jun 23, 2010

check out vellaman kits , or ceebek , im shure they do temerature controll kits , also available at CPC online

pmac10 · Jun 23, 2010

try rs components online, a pid controller would have an analogue output, how accurate do you need to be? would p or pi control be enough?? i could recommend a simple on/off controller using a pt100 probe which controls a contactor for a heating element. if you want to keep costs down this may be the way to go, if you require greater accuracy i could advise you further

Yooj · Jun 23, 2010

Why do you require PID functionality for a 'simple' temperature control.

If it is not a simple project, can you explain the type of control you require.

What type of vessel are you looking at, what is the size of the vessel in literage, and what type of heating profile do you require, i.e. rapid heating will require more extreme heating and thus finer control?

How are you planning to heat the water...electrically I am assuming?

You mention that the temp control is arounf 65 - 70 deg c...therefore is this you hysterisis? or would it be acceptable to be 63 - 73 for example, or are you saying that you need to set the temp to say 68 deg, and you need a constant temp maintained +/- 0.1 deg for example.

If you do not need such fine control, then why not just a simple heating element, and a simple thermostat with a simple temp sensor with readout, all of which could be procured from RS Components.

The thing that leads me to think that this is not just a simple project is your requirement for PID control.

Yooj

Andyfm · Jun 23, 2010

What you cooking -- Crystal Meth ????

ronfinch · Jun 24, 2010

First off thanks for the replies appreciate it - sorry I havent replied sooner. Will check out the companies/websites mentioned.

pmac10 said:
how accurate do you need to be? would p or pi control be enough??

Need it to be as accurate as possible - around a degree or so centigrade would be great.

Could a p or pi (the cheaper options I assume) keep it within a degree or so?

Why do you require PID functionality for a 'simple' temperature control.

There are all in one devices available but they are pretty expensive (for me) and not available in the UK. I also don't know what I might get charged in import duty so would love to put together a kit myself if possible. The kits available all mention PID control, so I assumed that was essential. As mentioned above if a control with less accuracy will work for me then great. What do you think?

What type of vessel are you looking at, what is the size of the vessel in literage, and what type of heating profile do you require, i.e. rapid heating will require more extreme heating and thus finer control?

I want to heat the water using a slow cooker. The one I currently have has a capacity of 3.5 litres. Higher literage I have been told would make for more stable temperature so I might move up to 5 or maybe 6 litres if I could find a unit that has this capacity.
I don't need to heat rapidly but want to maintain as stable a temperature as possible over a period of hours.

or are you saying that you need to set the temp to say 68 deg, and you need a constant temp maintained +/- 0.1 deg for example.

If you do not need such fine control, then why not just a simple heating element, and a simple thermostat with a simple temp sensor with readout, all of which could be procured from RS Components.

The thing that leads me to think that this is not just a simple project is your requirement for PID control.

Yooj

Yes I am looking to set the temperature at say 68 degrees, then stay within a degree or so of that. If there is some other way of doing it and you have the time would love to hear your advice.

What you cooking -- Crystal Meth ????

Not crystal meth or anything illegal in any way! Suppose it is an unusual request and am more than happy to explain.
I am really keen to try sous vide cooking - which is basically cooking meat/proteins generally inside vacuum packed bags at fairly low temperature over longish periods of time. Am a keen cook but a bit skint.

Here is the device whose functionality I would like to get close to replicating. This one is pretty fancy - mine doesnt have to be this good... Want to try it out first

http://freshmealssolutions.com/inde...ategory_id=15&option=com_virtuemart&Itemid=31

Thanks again for the replies - appreciated.

pmac10 · Jun 24, 2010

i think you might be getting a bit confused here, a pid controller is not an all in one device, it is a method of control (Proportional/integral&Derived), and a cheap one will probably cost the same as the device you linked to. add on top of that the pt100 probe, possible power supply,wiring,heating element and an enclosure to put it in, i cant see a way to do it for less than that american one pictured (bar pilfering the company's maintenance store).

any further questions fire away, maybe i am mis-interrupting your intentions??

ronfinch · Jun 24, 2010

I might have some things confused, but I do realise the pid is a method of control not an all in one device. Perhaps I didnt word my response clearly. I mentioned the pid/pi issue in response to other posts querying what I was looking for. And I linked to that all in one unit to show what I needed the device to do.

I found these item on ebay Sous Vide Incubator Slow Cooker Temperature Controller on eBay (end time 06-Jul-10 15:30:29 BST)

I think I will see if I can get those items in the UK (rather than shipping from canada as per the ebay link) perhaps from the websites recommended to me earlier in the thread.

If not I will buy an all in one unit.

Thanks for the response.

pmac10 · Jun 24, 2010

you can certainly get all the items i mentioned in the uk, these are standard items we carry in our maintenance stores and all the websites mentioned should carry them, i know for a fact rs components does, what im saying is buying these components in your local electrical wholesaler will still work our more expensive.
by the way i checked out the spec of the item you posted and its flippin bargain, it also has options for P,PI and PD control built in not to mention the auto tune you spoke of, pid tuning ain't much fun.