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crundy
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Re: Food! (was Charcutiers of the worlds unite)

Tue Apr 10, 2012 4:03 pm

Well, here's my setup, warming up ready for the lamb (on the bottom left):



One thing I did note; using a slow cooker doesn't give you "accurate" temperature control. Even after the relay turned it off it climbed to 2.1C above the cutoff temperature. Didn't seem to dip too much below the (target - diff) temperature though. I guess you should set it 1C lower than you want, assuming that will still be above 55C to kill any C.Botulinus bacteria of course.

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rurwin
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Re: Food! (was Charcutiers of the worlds unite)

Tue Apr 10, 2012 6:35 pm

It sounds like you need to tune that PID controller.

It will oscillate around the setpoint, getting closer each time. By tuning the P and I coefficients you can get it to ring less and settle down faster. You should not need to tune D. In fact you shouldn't need D at all.

If my customers can tune a loop to hold coolant temperature at 98C without boiling on a 300kW engine, you should be able to get within 1C of your setpoint on this rig.

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scep
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Re: Food! (was Charcutiers of the worlds unite)

Tue Apr 10, 2012 6:54 pm

It does need tuning - 2 degrees when you are cooking an egg SV is a lot! Though it's better to be over - rather 'mushy' meat after a 4+ hours bath than a case of C. perfringens cramp-squits

Some good cooking time tables  here

E
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Re: Food! (was Charcutiers of the worlds unite)

Tue Apr 10, 2012 7:04 pm

So how was it Crundy?

Crundy said:


Well it isn't a non-stick coating. The wok is solid and as it's magnetic I suspect it's some kind of brushed cast iron. It was great when I first got it, and I could pop it on the induction cooker and get it insanely hot to cook a stir fry in a few minutes, but now things stick to it, even though I season it properly every time I use it.


You may well already know this, I did a bit of research on seasoning before I inherited my nans pan, and from what I can tell it's possible to break down the polymer coating the oil forms if the temperate gets too high for the oil used.

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crundy
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Re: Food! (was Charcutiers of the worlds unite)

Tue Apr 10, 2012 7:08 pm

I don"t think It"s the pid, I think It"s the slow cooker. The trouble is the bowl the food sits in is ceramic and so it takes a while for the heat from the element to permeate through to the water. Therefore by the time the controller has detected the temperature is at the cutoff and flips, there is still a lot of heat working its way across the ceramic. I might try putting the probe closer to the bottom of the dish and setting the slow cooker to medium rather than high and see how I get on.

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rurwin
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Re: Food! (was Charcutiers of the worlds unite)

Tue Apr 10, 2012 9:52 pm

A well tuned PID can take account of that sort of problem.

That's the case when D might be useful. It reduces the rate at which the temperature rises.

The basic procedure is given here, although I generally don't bother with the maths and just do it by trial and error.

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scep
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Re: Food! (was Charcutiers of the worlds unite)

Tue Apr 10, 2012 10:52 pm

The whole point of a PID instead of a thermostat is that it has brainzzzzz! E.G If it knows the pot always goes 1.7 degrees over it will switch off in a timely manner so it doesn't.

As rurwin says, it can deal with that (with fuzzy logic and adaptive prediction and stuff – OK, so I have no idea, just making it up, but you get the gist )

Let us know how you get on.

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crundy
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Re: Food! (was Charcutiers of the worlds unite)

Wed Apr 11, 2012 8:54 am

Ah, mine isn't a pid controller, it's just a basic thermostat, so any tuning I do will have to be on the slow cooker itself. Are there any decent cheap pid controllers about?

Lamb was nice anyway. The wife wasn't too impressed. She's a "well done" kind of meat eater. Well, she does like sous vide duck breast, but not lamb.


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Re: Food! (was Charcutiers of the worlds unite)

Wed Apr 11, 2012 9:18 am

@Crundy:

Lamb looks nicely defrosted....  
I'm just a bouncer, splatterers do it with more force.....

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rurwin
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Re: Food! (was Charcutiers of the worlds unite)

Wed Apr 11, 2012 10:45 am


Are there any decent cheap pid controllers about?


It"s called a RaspPi and a Gertboard

Or if you don"t want to write that program,there's loads on eBay, but they are all the same. They have only 0.2% Full-Scale measurement accuracy; that's not great when the full-scale of even a PRT100 is over 800C.

If you can, snap this one up. It"s accurate to 0.1% FS, and FS with a PRT100 can be ~400C. I would trust West far more than an unbranded one. You can find the user manual on the RS website, just search for the part-number listed on the eBay page.

This is another good name, rather more expensive but new instead of used.

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crundy
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Re: Food! (was Charcutiers of the worlds unite)

Wed Apr 11, 2012 11:04 am

rurwin said:



Are there any decent cheap pid controllers about?


It"s called a RaspPi and a Gertboard

Or if you don"t want to write that program,there"s loads on eBay, but they are all the same. They have only 0.2% Full-Scale measurement accuracy; that"s not great when the full-scale of even a PRT100 is over 800C.

If you can, snap this one up. It"s accurate to 0.1% FS, and FS with a PRT100 can be ~400C. I would trust West far more than an unbranded one. You can find the user manual on the RS website, just search for the part-number listed on the eBay page.

This is another good name, rather more expensive but new instead of used.


Ta!

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crundy
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Re: Food! (was Charcutiers of the worlds unite)

Wed Apr 11, 2012 11:09 am

There's quite a few cheapo ones on there, like this. Do I take it these are crap and/or dangerous?

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rurwin
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Re: Food! (was Charcutiers of the worlds unite)

Wed Apr 11, 2012 11:53 am

The accuracy of those is only 0.5%  of full-scale, and full-scale for a K-type thermocouple is 1540C. I would want to see a detailed user manual before I recommended one of those.

You are right at the limit of accuracy that is easily achievable. Even my company, which charges tens or hundreds of thousands, does not quote better than 0.1%FS. We generally manage better than 1C, but not by much; 0.1C is difficult to achieve.

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crundy
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Re: Food! (was Charcutiers of the worlds unite)

Wed Apr 11, 2012 12:28 pm

Wait do you have to buy a relay for those PIDs as well? Does that mean they're pretty messy to set up?

TBH I'm fine with +/-1C variation, but just over 2C with my current setup is a bit much.

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Re: Food! (was Charcutiers of the worlds unite)

Wed Apr 11, 2012 1:01 pm

There are various options and you have to check the manufacturer's part number carefully. At least some of the cheap ones have a relay (3A at 240V = 720W). The West one has a relay (2A at 240V = 480W), the Omron one has voltage output for an external relay.

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scep
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Re: Food! (was Charcutiers of the worlds unite)

Wed Apr 11, 2012 1:25 pm

Crundy said:


There's quite a few cheapo ones on there, like this. Do I take it these are crap and/or dangerous?



I'd avoid those C100s  - as well as the accuracy, some people have reported receiving ones that don't have a solid State relay (SSR) output even though they say they do.

I'd bid on that West one, it's very nice, top quality. It's also very poorly advertised, so you might get lucky: if you can get it for a cheeky £30 or less you'll be laughing. Though I'm betting that the current bidder is prepared to pay £71.23 for it ) And you'll need a SSR (about a fiver)

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scep
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Re: Food! (was Charcutiers of the worlds unite)

Wed Apr 11, 2012 1:27 pm

Crundy said:



Lamb was nice anyway. The wife wasn't too impressed. She's a "well done" kind of meat eater. Well, she does like sous vide duck breast, but not lamb.


That lamb looks spot on!

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scep
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Re: Food! (was Charcutiers of the worlds unite)

Wed Apr 11, 2012 1:37 pm

Crundy said:


Wait do you have to buy a relay for those PIDs as well? Does that mean they're pretty messy to set up?

TBH I'm fine with +/-1C variation, but just over 2C with my current setup is a bit much.


Depends on that slow cooker - if it's a few hundred watts then you can wire it straight to the PID -  dependant on PID (as rurwin's post). Otherwise you will need a relay (solid state best: more reliable, no clicky clicky). But this can go in the PID case (which is another purchase!), it's not messy, just another component.

As for PIDs, n2006p are fairly well regarded for the price for all sorts of DIY stuff - SV, reflow ovens, kilns, brewing etc. Got mine for 17 quid incl (Hong Kong job). Has a 3A relay, accuracy is 0.2FS%. Description of a typical set up here (he does go on a bit, but it does show clearly how to control high wattage device.)


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Re: Food! (was Charcutiers of the worlds unite)

Wed Apr 11, 2012 7:36 pm

scep said:

As for PIDs, n2006p ..., accuracy is 0.2FS%.
But the n2006p has only one range for each type of sensor. FS for PRT100 is -200C - 600C = 800 degrees. 0.2% of that is 1.6 degrees. The branded types offer other ranges where FS is smaller. For example the West one has a mode with a range of -128.8 – 537.7C = 666.5degrees, so 0.1%FS accuracy = 0.6665 degrees.

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scep
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Re: Food! (was Charcutiers of the worlds unite)

Wed Apr 11, 2012 8:04 pm

rurwin said:

But the n2006p has only one range for each type of sensor. FS for PRT100 is -200C - 600C = 800 degrees. 0.2% of that is 1.6 degrees. The branded types offer other ranges where FS is smaller.

And a BMW RS comes with heated grips and cute, wireless, pressure monitoring tyre caps. But at 14 grand I think that I'll make do with my £5000 V-Strom

The n2600p is 17 quid and whatever the specs, the community seem to like it. So for the cost of a few rolls of vacuum bags I'll be able to make my own mind up. Nowt to lose really...

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Re: Food! (was Charcutiers of the worlds unite)

Thu Apr 12, 2012 10:33 pm

rurwin said:


If you can, snap this one up.


I did !

Seeing as no one else was bidding with 15 mins to go I had a bash. (There was some action with 10 mins to go – sorry if this was you Crundy, mine was a fire and forget snipe!)

So cheers rurwin, I owe you a beer  - guess I got that BMW after all . I'll put the cheap clone to good use somewhere else

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Re: Food! (was Charcutiers of the worlds unite)

Sat Apr 21, 2012 11:41 am

Symington's Table Cream. Any aficionados here? I've just eaten a chunk of it for lunch (out of my most excellent Kemal Ataturk mug - I have a lovely Victorian jelly mould, but it's a bit short of a pint) and I feel like my great-grandmother reincarnated.

Of course, when you think about it, it's just a panacotta. Jolly nice, though.
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scep
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Re: Food! (was Charcutiers of the worlds unite)

Sat Apr 21, 2012 4:05 pm

Never heard of it. Sounds like something a great-grandmother would have slathered over her face before she went to bed

(just looked it up - looks like Angel Delight with added gelatine!)

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liz
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Re: Food! (was Charcutiers of the worlds unite)

Sat Apr 21, 2012 5:22 pm

I applaud the way the packet makes it very obvious that it's basically made out of vanilla, sugar and half a boiled-down pig.
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