# What would "perfect control" of an oven look like? **URL:** \ **Category:** Factual Questions\ **Created:** [September 19, 2015, 4:08am UTC](https://boards.straightdope.com/t/what-would-perfect-control-of-an-oven-look-like/731729 "2015-09-19T04:08:13Z")\ **Posts on this page:** 12\ **Page:** 3
**Author:** ![Pork\_Rind](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pork_rind/32/111_2.png) [@Pork\_Rind](https://boards.straightdope.com/u/Pork_Rind)\ **Post date:** [September 21, 2015, 3:54am UTC](https://boards.straightdope.com/t/what-would-perfect-control-of-an-oven-look-like/731729/41 "2015-09-21T03:54:11Z")
> [@Habeed](#): > > As long as you kept those project files somewhere, you didn’t really lose the system… True enough. In fact, even though I still have the parts list and schematics, it almost doesn’t matter as there are several places to buy the whole setup [prebuilt](http://www.auberins.com/index.php?main_page=product_info&products_id=380). To be honest, what I actually regret is that I’ll have to spend the money all over again. That wasn’t my first adventure in PID controllers though. I had my espresso machine set up similarly. And I know there’s at least one other Doper with a PID controlled Rancilio Silvia. But I’ll be damned if I remember who. ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [September 21, 2015, 4:12am UTC](https://boards.straightdope.com/t/what-would-perfect-control-of-an-oven-look-like/731729/42 "2015-09-21T04:12:28Z")
> [@Pork\_Rind](#): > > That wasn’t my first adventure in PID controllers though. I had my espresso machine set up similarly. And I know there’s at least one other Doper with a PID controlled Rancilio Silvia. But I’ll be damned if I remember who. Ah, the reference standard coffee geek setup for many years. As noted, PID controllers have nothing intrinsically to do with computer control. Integrators and differentiators are standard building blocks in analogue computers. A quad op-amp and a handful of passives is all you need to build a perfectly useful PID controller. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [September 21, 2015, 4:22am UTC](https://boards.straightdope.com/t/what-would-perfect-control-of-an-oven-look-like/731729/43 "2015-09-21T04:22:48Z")
> [@Pork\_Rind](#): > > That wasn’t my first adventure in PID controllers though. I had my espresso machine set up similarly. And I know there’s at least one other Doper with a PID controlled Rancilio Silvia. But I’ll be damned if I remember who. Not me, but I did put together a PID Sous Vide unit. The PID controller was off the shelf, though, and I just had to add a few parts (solid state relay, thermocouple, etc.) for the complete setup. Works pretty well, though there’s an initial overshoot. It claims to be “self-tuning”, but whatever the case, I need to turn down the I constant. It’s solid once it locks in the temperature. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [September 21, 2015, 11:03am UTC](https://boards.straightdope.com/t/what-would-perfect-control-of-an-oven-look-like/731729/44 "2015-09-21T11:03:45Z")
> [@Dr.Strangelove](#): > > Just as an example, the speedometer in an older car is a totally analog way of computing a derivative (the derivative of distance is speed, of course). As you might know, it uses a magnet in an aluminum cup to convert spinning motion into a torque; the torque is applied to a spring and the net result is a roughly linear relationship between rate of rotation vs. angular displacement. You could, with some care, use the same technique to compute the D input for our controller. Older cars also computed the RMS of a signal. That’s how the fuel gauge used to work. If your fuel level sensor is a potentiometer, and your fuel gauge is simply an ammeter or voltmeter, then the meter’s needle will be constantly bouncing left to right as the fuel jostled around in the tank. The engineers needed a way to damp the signal. They could have used a LP filter of some sort, but they settled on something much more clever. Instead of using an ammeter or voltmeter for the fuel level gauge, the potentiometer controls the current through a _heater_. A thermometer measures the temperature of the heater. The thermometer is the fuel level gauge. Ingeniously simple and reliable. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [September 21, 2015, 11:33am UTC](https://boards.straightdope.com/t/what-would-perfect-control-of-an-oven-look-like/731729/45 "2015-09-21T11:33:30Z")
Nm ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [September 21, 2015, 11:39am UTC](https://boards.straightdope.com/t/what-would-perfect-control-of-an-oven-look-like/731729/46 "2015-09-21T11:39:14Z")
> [@Dr.Strangelove](#): > > Not me, but I did put together a PID Sous Vide unit. The PID controller was off the shelf, though, and I just had to add a few parts (solid state relay, thermocouple, etc.) for the complete setup. Works pretty well, though there’s an initial overshoot. It claims to be “self-tuning”, but whatever the case, I need to turn down the I constant. It’s solid once it locks in the temperature. “Ghetto sous vide” with beer cooler…ah, those were the days. The Anova is $100 now. I always wondered why the Polyscience was so damn expensive. Still don’t know. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [September 21, 2015, 11:55am UTC](https://boards.straightdope.com/t/what-would-perfect-control-of-an-oven-look-like/731729/47 "2015-09-21T11:55:27Z")
> [@Shalmanese](#): > > There’s something to be said about just throwing more thermal mass at the problem. Having a heavy enough and well insulated enough oven means you can just preheat it to the desired temperature well in advance and any swings end up being inconsequential to the end result. > > Consumer ovens are actually deliberately terribly insulated. The reason is, if you have a recipe that calls for baking at 400F for 20 minutes, then dropping to 275F, you don’t want it to take an hour to get down to 275. _Ovens for scientific or craft applications tend to be far better for temperature stability_. Italic added. Which is why copper pans are so much better for almost all stovetop cooking, which is dancing around with split-second heating times. Which is also why copper stock pots and dutch ovens and the like are such a waste of money. Of course, a full cast iron stock pot isn’t very useful either. Italics: pizza ovens professional, and “pizza stones” hobby. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [September 21, 2015, 1:19pm UTC](https://boards.straightdope.com/t/what-would-perfect-control-of-an-oven-look-like/731729/48 "2015-09-21T13:19:08Z")
> [@Leo\_Bloom](#): > > Italic added. > Which is why copper pans are so much better for almost all stovetop cooking, which is dancing around with split-second heating times. > > Which is also why copper stock pots and dutch ovens and the like are such a waste of money. Of course, a full cast iron stock pot isn’t very useful either. > > Italics: pizza ovens professional, and “pizza stones” hobby. Well, actually, that’s not the reason! Copper isn’t used because of it’s thermal mass, but it’s excellent conductivity. ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [September 21, 2015, 6:46pm UTC](https://boards.straightdope.com/t/what-would-perfect-control-of-an-oven-look-like/731729/49 "2015-09-21T18:46:40Z")
So, about a PID. When they covered the various Op amp circuits in school, I noticed there’s fixed ratio proportional multipliers, integrators, and differentiators. Each of these circuits, a single resistor governs the gain or ramp up. So…does that mean you could build a PID autopilot with just 3 op amps and 3 knobs to control the 3 coefficients? Is that how they used to actually do it? You’d need a separate autopilot per axis of movement…but I read that early autopilots would just control altitude or rudder only. Apparently, you could get op amps off the shelf as early as [1953](https://en.wikipedia.org/wiki/Operational_amplifier#Historical_timeline), or 1941 if you were a defense contractor. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [September 22, 2015, 12:12am UTC](https://boards.straightdope.com/t/what-would-perfect-control-of-an-oven-look-like/731729/50 "2015-09-22T00:12:40Z")
> [@Habeed](#): > > So…does that mean you could build a PID autopilot with just 3 op amps and 3 knobs to control the 3 coefficients? You need an adder as well, though there might be a way to assume the P gain is at unity and fold it into the final gain stage. But essentially, yes. PID controllers are pretty straightforward devices and work surprisingly well for their simplicity. Although PID controllers as such were really only worked out in the early 20th century, a fair amount of the theoretical underpinning was worked out by James Clerk Maxwell in the 19th century. Maxwell wrote the paper [On Governors](http://www.maths.ed.ac.uk/~aar/papers/maxwell1.pdf), and in it addresses governors (for steam engines, etc.) with proportional, integral, and differential components. Some of these were semi-accidental–the lubricants were sometimes so viscous that they offered a significant differential signal on their own. Others were more intentional. Regardless, Maxwell mostly worked out the theory of stability behind these governors. ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [September 22, 2015, 1:00am UTC](https://boards.straightdope.com/t/what-would-perfect-control-of-an-oven-look-like/731729/51 "2015-09-22T01:00:06Z")
There’s nothing that says you actually have to use op-amps. They are just a convenient and (now) cheap way to create the basic building blocks. Convenient in that they allow you to gloss over a large fraction of the grief in design. But building a PID controller from raw transistors (or tubes) without the intermediate use of op-amps (whether integrated or discrete) is quite reasonable. Similarly, mechanical building blocks can be made to do the same thing, or as **Dr. Strangelove** points out, a close enough approximation. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [September 22, 2015, 1:12am UTC](https://boards.straightdope.com/t/what-would-perfect-control-of-an-oven-look-like/731729/52 "2015-09-22T01:12:55Z")
> [@Leo\_Bloom](#): > > Italic added. > Which is why copper pans are so much better for almost all stovetop cooking, which is dancing around with split-second heating times. > > Which is also why copper stock pots and dutch ovens and the like are such a waste of money. Of course, a full cast iron stock pot isn’t very useful either. > > Italics: pizza ovens professional, and “pizza stones” hobby. > > > [@beowulff](#): > > > > Well, actually, that’s not the reason! > > Copper isn’t used because of it’s thermal mass, but it’s excellent conductivity. I _thought_ that’s what I said. You want thermal mass in Dutch ovens (in stock pots, to w certain extent, it’s immaterial). Cast iron or (for braising with wine) enamel over iron is way cheaper and more efficient thermodynamically. You don’t need such a responsive tool with copper. This is a hijack, but PM me if you want and I could direct you to thermodynamics analyses galore. [Previous page](https://boards.straightdope.com/t/what-would-perfect-control-of-an-oven-look-like/731729.md?page=2)