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.
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.
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.
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.
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.
Nm
“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.
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.
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, or 1941 if you were a defense contractor.
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, 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.
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.
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.