6 replies to this topic

[emannths]

Sorry for a n00b-ish question, but I don't think this has been covered here. I'd like to go the DIY route for a flexible temperature controller setup that I can use to control a number of appliances (not simultaneously). I'd like to control a simple SV setup and a water heater for coffee/tea for starters. If I throw together an inexpensive PID controller with a SSR and just plug the appliance-of-the-moment into the control box outlet, will this get the job done? Or will I run into tuning problems when switching appliances that will make this more trouble than it's worth?

For example, I'd like to have one device that combines both the Auber french press controller and Sous Vide Magic. Is this doable in a DIY setup using a controller like this?

Edited by emannths, 14 February 2012 - 08:25 AM.

[jmolinari]

it would have to retune for each appliance/heater/vessel combination. Or you could write down the P, I and D values for each appliance after autotuning once on each appliance, and input them manually, avoiding the autotuning, which in essence figures out those values for you.

[dcarch]

Why? PID controllers are cheap.

Instead of having only one to control all, I would get more than one just in case one breaks, I can have immediate back up units.

[Mark Muller]

Why? PID controllers are cheap.

Instead of having only one to control all, I would get more than one just in case one breaks, I can have immediate back up units.

dcarch

One PID to control them all, One PID to find them,
One PID to run them all and in the darkness bind them...

As to why, because many of us already have too many gadgets to store or remember where they are stored. So why have a PID for the Sous Vide rig, another for the smoker, and another and another...

As to whether this will work, it should work fine, provided you write down or otherwise store the P, I, and D values for each device you control (whether the values come from autotuning or your own experimenting), and set the PID to those values when you connect it to the device.

[emannths]

As to why, because many of us already have too many gadgets to store or remember where they are stored. So why have a PID for the Sous Vide rig, another for the smoker, and another and another...

As to whether this will work, it should work fine, provided you write down or otherwise store the P, I, and D values for each device you control (whether the values come from autotuning or your own experimenting), and set the PID to those values when you connect it to the device.

I haven't been able to find any controllers with memory to store multiple sets of parameters (other than expensive, overkill multiloop ones). Too bad. Almost makes me want to build a little Arduino project that handles the temp control and can save parameters. But I think a piece of paper should work just fine.

[jrshaul]

Mine (a cheap Chinese knock-off, I suspect) takes a minute or two to readjust.

Strictly speaking, a PID controller should keep a pretty accurate hold on temperature even if not precisely calibrated, and 1 degree celsius isn't the end of the world if you're making tea. Given the cost of a good PID controller and the need for a decent SSR, making your temperature controller interchangeable is a good idea.

Edited by jrshaul, 14 February 2012 - 11:24 AM.

[oldwhiteguy]

I have a homemade PID controller that I have used for sous vide (with hot plate and stock pot) as well as for controlling the air temperature inside a box that I used for salting prosciutto outdoors. I didn't even reset the PID parameters or use autotune for the box, but it worked fine. I probably "should" have - the thermal inertia of a stock pot is many times that of a few cubic feet of air. Incidentally, when tuning a PID controller, most control technicians will re-set the D (derivative) parameter to zero because a PI controller is much more forgiving of significant changes in thermal inertia, or load, or heating capacity, or set-point. Derivative control is generally only included for very critical industrial applications (such as plastic extrusion equipment) where fast response is crucially important.
To dcarch, yes, PID controllers are cheap, but mounting one in a project box, making the cutouts, assembling all the bits, power cords, wiring etc takes me an entire evening. I did have a controller burn out a couple of years ago; I had a spare, so I simply swapped it into my existing box. No need to have an entire spare assembly.