52 votes

Why do consumer ovens use thermostats instead of PID + PWM?

Mechanical thermostats are capable of switching high currents with very long life in that application. They are inexpensive and accurate enough. They don't mind the high ambient temperatures and don't ...
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25 votes

Why aren't Stepper motors used in closed-loop systems and PID control?

The main point of a stepper motor is that you get discrete steps. However, the cost is larger size and lower efficiency than a continuous motor of the same torque. Stepper motors also have a low ...
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24 votes
Accepted

What are the effects of removing P, I, and D from a PID controller respectively?

If you start with a PID and: remove the D action: the controller won't respond quickly to quick changes in the input. This is sometimes desired if the input is noisy and you don't wont the output to ...
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  • 1,409
21 votes
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Can a PWM with 1% resolution in a PID heater loop achieve better than 1% temperature accuracy?

It depends on the time constant of the load. A heated load will often respond in 10s of seconds. If you generate 30% PWM for one second, then 31% PWM for the next second, that will look like 30.5% ...
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  • 142k
19 votes
Accepted

Confusion in PID loop for the case of zero error?

No, e(t) being zero does not imply that u(t) is also zero. It only implies that the output of the "P" process is zero. Remember, the "I" and "D" processes have memory — they depend on the past ...
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  • 165k
16 votes
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PID algorithm: how to account for fast input value changes after a long delay

Your problem is called Integral Windup, it's a common control problem. In a non-linear or otherwise bounded region, the controller can't track the setpoint, and the integral increases to a large value....
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  • 7,158
16 votes

Why do consumer ovens use thermostats instead of PID + PWM?

A thermostat is already PWM, just slow. The element can be on or off, and the only thing that allows your oven to be set to 500°F or 250°F is varying the duty cycle. That's PWM. You could reduce the ...
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  • 55.5k
13 votes

Why aren't Stepper motors used in closed-loop systems and PID control?

This is not actually particularly rare. In industrial systems, stepper motors with encoder feedback are relatively common. And for hobbyists, there is e.g. the Mechaduino project. There are several ...
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  • 4,719
12 votes

Why do P/PI/PID Controllers exist when we can manually code in software (say an Arduino).

The question is really about the difference between a hack and a product. An Arduino on its own is a caseless, non-shielded device that has no input/output protection. To modify its behaviour you ...
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  • 45k
12 votes
Accepted

Please explain in layman's terms how a PID accounts for inertia in temperature control

I had to + Glen's comment. He consistently has his brain in the right place, IMHO. There is nothing harder to deal with in a PID than a \$\Delta t\$ delay. I've been dealing with lamp-heated ...
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  • 70.2k
11 votes
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Why is frequency not measured in db in bode's plot?

Frequency is not a measure of signal amplitude or power hence, talking about "this or that" frequency in decibels makes no sense. If somebody says "increase the frequency by 3 dB"; ...
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  • 384k
11 votes

Why is frequency not measured in db in bode's plot?

We could start using dBHz and see how it feels. My guess is it won't make life any simpler or help understanding. NOTE however : logarithmic frequency scale is already in use, and has been for a while ...
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11 votes

Why do consumer ovens use thermostats instead of PID + PWM?

Why do consumer ovens use thermostats instead of PID + PWM? The answer is the word 'Consumer', which means cheap and low specification. Professional ovens for (say) resin curing will use PID control. ...
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  • 142k
10 votes
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Integral only control (as opposed to PI or PID)

Another way to look at your question is when would you use PI control with the P term 0. The answer is basically "Whenever you think you can get away with it.". This main risk with only integral ...
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9 votes

Yogurt on a PID controller

The real problem seems to be your mechanical setup, not the PID control detail. PID control may not even be what you want at all. I'd start by putting the container of yogurt culture inside a water ...
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9 votes

Can a PWM with 1% resolution in a PID heater loop achieve better than 1% temperature accuracy?

Yes. Given the fact that relative to other regulations (voltage, current, etc.), temperature regulation is quite slow, what you can do is use a microcontroller (i'm guessing you already do), but add ...
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  • 1,658
9 votes

Why aren't Stepper motors used in closed-loop systems and PID control?

Provided you don't miss a step, a stepper motor should give you a deterministic movement. You can run it N steps forwards and N steps backwards and it will be in the same place. This is because the ...
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  • 45k
9 votes

Where to put the PID windup guard?

Integrator anti-windup is a measure you need to take because of output saturation or other limits in the system, and such limits are nonlinear behavior. When you start doing nonlinear control, a lot ...
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  • 36.3k
9 votes

Motor fader PID control

A control system is only as good as it's sensor, run the sensor open loop and remove the control input. Create your own input to the sensor and slide it slowly (or find a way to slide it slowly ...
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  • 63.7k
9 votes
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How stable are PID loops really?

There's no inherent oscillation in the output. A perfect PID controller controlling an ideal 2nd order system has a closed-loop transfer function that either moves asymptotically to the setpoint (...
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8 votes

Kp, Ki, Kd for software PID control

All credit for this is from the (now unfortunately dead) Balancing Robots for Dummies thread on the Arduino forum. The PID controller is as follows: ...
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  • 216
8 votes
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I'm confused a bit on basic control stuff for a PID controller

Your control is quite good despite if you feel in other way. I do think that a P-control with feed forward LUT (Look Up Table) would solve 98% of your need. Try this way: For each temperature ...
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8 votes

Why do consumer ovens use thermostats instead of PID + PWM?

The more meaningful way to measure temperature variation would be with a probe inserted just below the surface of some baked goods. I don't see any advantage unless you are broiling very close to ...
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8 votes

What are the effects of removing P, I, and D from a PID controller respectively?

The P term is the term which provides the main drive to drive the process in a direction which reduces the error signal. Integral response is inherently slow and so the proportional term is needed to ...
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  • 5,238
7 votes
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Integral and Derivative terms in PID control

The Short answer The constants for your PID controller as well as the error signal can be negative or positive , as your system adjusts to your PID control signal it will produce decreasing error and ...
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  • 5,419
7 votes
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Misconceptions about PID Controllers

The input to the PID controller is not a position. The input to the position sensor is a position. The input to the PID controller is a signal that represents a position. It could be a voltage, or a ...
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  • 142k
7 votes

Can a PWM with 1% resolution in a PID heater loop achieve better than 1% temperature accuracy?

Oddly worded question, but what I think you are asking is will the temperature of the load increment by 1% steps with a PWM of 1% step resolution. i.e. 2.828C per step. Although it sounds like it ...
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  • 45.7k
7 votes

What happens if PID loop is too fast?

When you execute a PID with higher sampling rate you can encounter two things: The integrator may not work properly if the new delta is very tiny. This is due to the final resolution of floating ...
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6 votes

PID Control implementation for charging battery really necessary?

You said yourself that depending on what part of the charging process you are in, you keep the current constant or try to maintain that voltage. That's going to require some kind of controller, ...
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6 votes
Accepted

PID : What does « ultimate gain Ku » in Ziegler–Nichols method mean?

Let we take for example a P-controller, which is simpler to understand. The output of the controller is the amplified error. \$Y_{\text{out}}=K(X_{\text{SP}}-X_{\text{PV}})\$ Where \$K\$ is the gain, \...
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