Sous Vide Controller

An accurate temperature controller for low temperature long duration (sous vide) cooking.

Controller Design

I started by looking at Seattle Food Geek's Immersion Circulator and the core of the design is largely based off of his plans.

The key difference was that I wanted more flexibility so instead of wiring the relay straight to some immersion heaters, I wired it to an outlet that the heating device can plug in to. This allows me to use a rice cooker which uses less electricity to heat and has a more stable temperature than a plastic tub.

The rice cooker tends to heat fairly evenly so there was no need for a water pump or air bubbler to circulate the water, which helps reduce the complexity even more.

Minor modifications include using a C14 inlet for the power input, adding a fan for cooling the relay, and wiring the sensor to a 3.5mm jack for easy replacement.

Building the Controller

I started by ordering all the parts and once they arrived I began looking for a suitable enclosure. I settled on a 6x6x4 conduit box which had room enough for everything, but still wasn't too large.

After spending some time determining the arrangement of the parts, I used a Dremel to cut out the holes for all the parts and the fan. I chose to mount everything on the lid of the box for easy access; open the box and everything slides right out.

Once the parts were attached to the box they were wired together and then tested before the box was closed.


Tuning the Controller

Please read How PID Controllers Work for some background.

Once everything is assembled, the parameters of the PID controller need to be changed to correspond to your situation. Most PID controllers have an auto-tune function; however this does not always yield the desired results. Consequently I opted to tune the PID parameters manually.

I recommend reading the PID tuning guide for the Sous Vide Magic controller to learn how to tune your PID manually. At a high level the process is:

  1. Set P to 20, I to 0, D to 0, and find the optimum P value by halving the P value until the current temperature fluctuates around the target temperature.
  2. Next, set I to a large value (e.g. 600), reducing it if the change in temperature isn't corrected fast enough and increasing it if the temperature fluctuates wildly.
  3. Lastly, set D to be 25% or less of your I value. I used 10%.

So for my rice cooker I used P=10, I=300 and D=30. With these settings I found that the initial heating takes a while but the temperature is very stable once heated.

Using the Controller

To use the completed controller begin by filling your rice cooker (or crock pot) with water, inserting the temperature probe in the water, turn it on, and plug it into the controller.

Next turn on the controller and set the target temperature by pressing the set button and changing the temperature as appropriate with the up, down and left buttons. Press set again once you've selected the desired temperature. Now wait until the water warms up to your desired temperature and then add your food.

The traditional first dish for sous vide is an egg since they are simple, cheap, tasty, and have a shell which eliminates the need for a vacuum sealer. Cook the egg at 64.5° C for 45 minutes to get an egg with smooth whites, neither runny nor rubbery, and a thick, pudding-like yolk. Enjoy!

More Information

How PID Controllers Work

The core piece of my sous vide controller is a PID controller that actually senses the temperature of the water bath and regulates the heating accordingly. Since PID control can be complicated here is an explanation specifically in the context of sous vide cooking.

PID refers to the three variables that you have control over. I'll discuss each one in turn.

P - Proportional

In a normal thermostat, if the water temperature is less than the desired temperature the heat is turned on; and if the water temperature is greater than the desired temperature the heat is turned off. This usually causes large temperature fluctuations as the water temperature oscillates around the desired temperature.

Proportional control slowly ramps down the amount of heating that is provided the closer that the water temperature gets to the target temperature, which helps provide wild changes. So on a sous vide controller P represents the width of the temperature band that your heating is 'ramped down' over.

Let's say your target temperature is 60 and you have a proportional band of 10.

Instead of a simple thermostat where the temperature controller turns the rice cooker on until 60 then turns it off, once the temperature hits the proportional band (starting at 60-10=50) the controller turns the rice cooker on for decreasing periods of time.

So if the temperature is:

  • 50, the heat is full on
  • 55, the heat is on half the time (2 of every 4 seconds)
  • 57.5, the heat is on a quarter of the time (1 of every 4 seconds)
  • 60, the heat is off

This gradual decline in the heat prevents the temperature of the water from overshooting the target temperature. You could shrink or widen the proportional band to provide less or more of a ramp down when heating.

I - Integral

Now due to temperature loss, if you choose a wide (large) P value, the temperature of the water might never reach the desired temperature. Similarly, if you choose a narrow (small) P value the water temperature may stabilize above your desired temperature.

The I value is a time period (in seconds) over which the temperature is averaged. Based on this the controller adjusts the proportional band a few degrees in either direction to correct for under/over shoots in temperature.

Continuing the previous example;

If when using a temperature of 60 and P of 10 the temperature never rises above 57.5, an I value of 300 would allow the controller to check the temperature of the water every five minutes. Based on experience the controller could adjust itself so the temperature is ramped down starting at 55 instead of 50.

The net effect of moving the lower end of the P band up to 55 is to provide more heat. Based on this, it should allow the water temperature to stabilize at the desired temperature.

This running average helps correct any temperature errors and provides smooth temperature control over long periods of time.

D - Derivative

Lastly, if you added a large quantity of cold food to the water bath the temperature would begin to drop very quickly. The I value would correct for this movement over a number of minutes, but sometimes a quicker response to rapid temperature changes is desirable.

The D value is a shorter time period (in seconds) over which the temperature is averaged to determine the trend of temperature changes. Typically the D value is 25% or less of the I value, and is closer to 10% for sous vide cooking. Based on trends in temperature change the controller will apply more or less heat to help maintain consistency.

Continuing the previous example;

Once the water bath has reached the desired temperature, cold food is added to the water and the temperature begins to drop. If the D value is 30, then within 30 seconds the controller would notice that the temperature has begun to fall and would begin to provide more heat to compensate.

This provides a faster response than waiting for the I value (5 minute average) to respond to the change in temperature, increasing the temperature stability.

This short average helps correct for sudden movements in temperature and restores a stable temperature faster than just I control.

Summary

Based on ramping down the heat close to the target temperature (P), correcting for long term errors in temperature (I), and watching for short term fluctuations (D); PID controllers can maintain a very stable temperature over an extended period of time.

These settings will be specific to each cooking device (rice cooker vs crock-pot); however they can be determined via trial and error for optimal results.

20
Jan 2012

Corporate Personhood - Wendell Berry

Fri, 01/20/2012 - 20:50 — Sean Carney

Corporate personhood, despite being a fairly old concept, has been getting a lot of attention lately. Wendell Berry adds the following to the discussion:

The folly at the root of this foolish economy began with the idea that a corporation should be regarded, legally, as “a person.” But the limitless destructiveness of this economy comes about precisely because a corporation is not a person. A corporation, essentially, is a pile of money to which a number of persons have sold their moral allegiance. Unlike a person, a corporation does not age. It does not arrive, as most persons finally do, at a realization of the shortness and smallness of human lives; it does not come to see the future as the lifetime of the children and grandchildren of anybody in particular. It can experience no personal hope or remorse, no change of heart. It cannot humble itself. It goes about its business as if it were immortal, with the single purpose of becoming a bigger pile of money. The stockholders essentially are usurers, people who “let their money work for them,” expecting high pay in return for causing others to work for low pay.

Corporate Personhood - Wendell Berry

18
Jan 2012

SOPA: Returning Us to the Golden Age of Bulletin Board Systems

Wed, 01/18/2012 - 17:45 — Sean Carney

The Daily WTF has a commendable explanation of the effects of SOPA and the potential dismantling of the domain name system;

You see, back in the day, if you wanted to get online and access electronically-stored information like digitized photographs, electronic bulletin boards, and informational databanks, there was only one thing you needed: a telephone number. You’d simply fire up your favorite telecommunications program (mine was Telix), have it dial that phone number, and after a refreshing symphony of beeps and hisses, you were online.

Each phone number transported you to a quaint, peaceful community that was almost entirely self-sufficient. There was no “hyperlinking” between systems: you simply wrote down the phone number, signed-off of the current system, and then dialed into the new system. And let me tell you, there are few experiences in life that can parallel the utter bliss of discovering a new phone number and a new electronic resource.

...

SOPA and PROTECT-IP offer hope in returning to the golden age of telecommunications, and to the days before the Information Superhighway polluted the online culture with this domain name nonsense. Let the Domain Name System a natural death and prepare yourself for the Internet Protocol Number (IPN) renaissance. All you need to do is start a notebook that lists electronic resource names and their corresponding IPN. And let the first entry in your notebook be

     The Daily WTF     74.50.110.120

We can only hope that our legislators introduce common sense guidelines to ban HTTP (and HTML/JavaScript) as well so we can all return to the more sensible GOPHER standard.

As a translation for non-technical users; If the Americans decide to implement the extremely nearsighted SOPA legislation, it would set the Internet back by over twenty years.

16
Jan 2012

After months of waiting, winter arrives.

Mon, 01/16/2012 - 18:25 — Sean Carney
11
Jan 2012

The Christian Industrial Complex - Shane Claiborne

Wed, 01/11/2012 - 22:44 — Sean Carney

Some thoughts by an ordinary radical on "Jesus junk".

I grew up in the Bible Belt. When I became a Christian, I learned I didn’t have to stop buying stuff — I just had to start buying Christian stuff. An entire world of retail spending possibilities lay before me: the Christian industrial complex. There were Christian t-shirts, bumper stickers, even Christian candy — “testa-mints” — peppermints wrapped in a Bible verse. We were taught “secular” was bad, and supplied with charts that countered popular mainstream bands with a Christian alternative. We burned our old tapes (which is what we listened to back in those days) and went to the Christian albums. We were often sadly disappointed. They just didn’t sound like Metallica. As a friend of mine quipped: “All these Christian artists say, ‘God gave me this song,’ and then you listen to it and know why God gave it away.” I later learned that Christian art doesn’t have to be a mediocre counterfeit of the original. And, I learned that Christianity is not about conforming to the world, but about being transformed by a God who is crazy about the poor, fond of toppling the powerful, and raising the lowly … and who I’m pretty sure would feel conflicted wearing a “God bless Rome” shirt or doting an “Army of One” sticker on the bumper of his SUV… I mean, hybrid. I mean donkey. Never mind.

I became convinced that the world will not know we are Christians by our bumper stickers and T-shirts, but by our love.

In light of all the exciting movements addressing world hunger and peace, many with Christians in the forefront, I really believe Christian stores should be pioneers and innovators, rather than chameleons. Selling fair-trade coffee is a good start. But we have a long way to go. I just saw an iPod shaped like a cross. Ugh.

The Christian Industrial Complex - Shane Claiborne

After hearing Shane speak in Winnipeg a number of months ago, I can now read this while imagining his voice.

9
Jan 2012

Zen and the Art of Accounting - Calm Blue Oceans

Mon, 01/09/2012 - 22:43 — Sean Carney

7
Jan 2012

Coming Soon: Adventures in Sous Vide

Sat, 01/07/2012 - 22:42 — Sean Carney

For the past few days I have been experimenting with a decidedly esoteric cooking method: sous vide. Sous vide (French for 'under vacuum') is a cooking method in which food is sealed in airtight plastic bags and the immersed in a water bath to cook.

The benefit of this cooking method is very precise temperature control. In almost all cases, the temperature of the water bath is the same as the desired temperature of the cooked food. This means that it is nearly impossible to overcook or burn food and allows for long cooking times.

As an example, I cooked a steak a few days ago at 54.5° C for 3 hours. 54.5° happens to be the ideal temperature for a medium rare steak, so when I cut into the steak after cooking it was pink all the way through. Since the steak cannot overcook, I could have left it in the water bath for a few extra hours without any real difference. According to Emily this was the second best steak she ever ate, beating the steak from Hy's Steakhouse but not 529 Wellington.

There are a number of setups for sous vide cooking. The most basic is to put a pot on the stove and carefully watch the temperature and adjust the heat accordingly. Less tedious solutions involve temperature controllers which can be used to control the temperature of slow cookers and rice cookers to within ±0.1°. Temperature controllers can either be bought ready made or assembled from scratch depending on your budget and preferences. For those with a larger budget, all in one units with both a water bath and temperature controller can also be purchased.

On account of both budget and preferences, I elected to build my own temperature controller. The controller is nearly complete and I will be posting more information about the construction, configuration and use of it as time goes on. Stay tuned.

5
Jan 2012

Are we calling this a "win-win"? - Jamie Wright

Thu, 01/05/2012 - 23:55 — Sean Carney

Jamie Wright's thoughts on poverty tourism short term missions work:

I want to fill a rental van marked “Tourist” with unbelievably rich people and then I want to bring them to your middle-class neighborhood to take pictures of you and your kids and your house and your cars.

I’ll act as the unofficial tour guide to their trip, walking them slowly down the street, pointing out the shocking differences between their lifestyle and yours. “This man,” I will say with a gesture of my upturned palm, “cuts his own lawn.”

“These kids share a bedroom.”

“Many of these families require two incomes… just to survive.”

I’ll tell them bluntly, “Most of these people will never ride in a helicopter, meet the president, or own a show horse.” And they will glance at each other with looks of angst and sadness, they’ll shake their heads at the injustice of it all.

And then I’ll let the details of your simple life sink in as they snap pictures of your no-thrills mid size SUV and your quarter acre lot. I’ll stand aside so they can get pictures of each other, smiling, with their arms around your kids in hand-me-downs. Ooh, and maybe they can take turns helping you cut your hedge or clean your bathroom, and then you could show some of them how to make a sandwich - That would be so great for the video they’re gonna take back to show at the Super Elite Rich People Church.

But don’t worry. There will totally be something in it for you. The rich people are going to paint all of the houses on your block. For real. They’re going to pay for it and do all the work and everything. Also? They’re gonna do a puppet show for your kids, and give them candy and crap.

It’s a win-win.

Are we calling this a "win-win"? - Jamie Wright