Auto Tune Pid Temperature Controller

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Auto Tuning Pid Temperature Controller
Auto Tune Pid Temperature Controller Manual
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Auto Tune Pid Temperature Controller Diagram

This example shows how to automatically tune a PID Controller block using PID Tuner.

Oct 01, 2006 A recent survey of Control Engineering subscribers who buy or specify loop controllers indicted that a user-initiated auto-tuning function is the most important feature of a PID controller behind the PID algorithm itself and the ability to communicate with external devices (CE, July 2005, “Loop Controllers: Lone Logic is More Connected”).
To achieve the best level of process control it is necessary to tune PID controllers, this can be done in a number of ways. Manual PID Tuning. Controllers will enable manual PID tuning meaning the P, I and D variables must be manually calculated by the engineer and set using the controller menu.This requires a reasonable level of knowledge and understanding from the user to be able to carry.
Increase the Integral Time value by 50%, or multiply the setting 1.5 times. From a cold start, test and verify that the Integral Time allows maximum elimination of offset with minimum overshoot. If not completely satisfied, fine-tune the value, up or down, as needed.
Jan 21, 2017 Since the temperature probe is located inline with the water line, the PID Controller maintains a steady temperature of the circulated water. Since the water dumping back into the Ice Chest is at or below the PID controller setting, I can be assured I won't have any hot spots in the water bath.

Description; The Newest PLATINUM Series Controller CNPT is Available Now! The CN76000 1/16 DIN PID controllers provide economical control for a wide variety of processes, includingheating, cooling, and heat/cool. When used with theproper transmitters, these devices can. Essentially, the controller “learns” how the process responds to a disturbance or change in set point, and calculates appropriate PID settings. In the case of a temperature controller like OMEGA’s CNi8 series, when “Auto Tune” is selected the controller activates an output. This is when the skills to tune a loop manually are necessary. As mentioned, most universal temperature and profile controllers provide an autotuning function as a standard feature. The controller automatically measures the process characteristics and tries to calculate the best PID parameters.

Introduction of the PID Tuner

PID Tuner provides a fast and widely applicable single-loop PID tuning method for the Simulink® PID Controller blocks. With this method, you can tune PID controller parameters to achieve a robust design with the desired response time.

A typical design workflow with the PID Tuner involves the following tasks:

(1) Launch the PID Tuner. When launching, the software automatically computes a linear plant model from the Simulink model and designs an initial controller.

(2) Tune the controller in the PID Tuner by manually adjusting design criteria in two design modes. The tuner computes PID parameters that robustly stabilize the system.

(3) Export the parameters of the designed controller back to the PID Controller block and verify controller performance in Simulink.

Open the Model

Open the engine speed control model with PID Controller block and take a few moments to explore it.

Design Overview

In this example, you design a PI controller in an engine speed control loop. The goal of the design is to track the reference signal from a Simulink step block scdspeedctrlpidblock/Speed Reference. The design requirement are:

Settling time under 5 seconds
Consult to see which Mac models are compatible with which versions of Windows. In its current incarnation, Boot Camp isn’t compatible with 32-bit versions of Windows.Other requirements follow:.An Intel Mac with OS X version 10.6 or later. Boot camp install windows on mac free. For now, Macs don’t support touchscreen computing.To install Windows 8 via Boot Camp, you still must have a legitimate Windows 8 license from Microsoft and a Win8 installation disc, assuming that you have an optical drive. If you don’t have an optical drive, you may be able to create a Windows installer from an ISO file downloaded from Microsoft on a USB flash drive that’s 8GB or larger. .At least 2GB of RAM and 20GB of available space on the Mac’s storage drive that you want to donate to Windows.A blank CD or USB storage device that you’ll use for Windows software driversIf you don’t run into snags, the entire installation should take about an hour.Windows 8 and Windows 8.1 are optimized for a touchscreen environment, though you can use it with a standard mouse and keyboard.
Zero steady-state error to the step reference input.

In this example, you stabilize the feedback loop and achieve good reference tracking performance by designing the PI controller scdspeedctrl/PID Controller in the PID Tuner.

Open PID Tuner

To launch the PID Tuner, double-click the PID Controller block to open its block dialog. In the Main tab, click Tune.

Initial PID Design

When the PID Tuner launches, the software computes a linearized plant model seen by the controller. The software automatically identifies the plant input and output, and uses the current operating point for the linearization. The plant can have any order and can have time delays.

The PID Tuner computes an initial PI controller to achieve a reasonable tradeoff between performance and robustness. By default, step reference tracking performance displays in the plot.

The following figure shows the PID Tuner dialog with the initial design:

Display PID Parameters

Click Show parameters to view controller parameters P and I, and a set of performance and robustness measurements. In this example, the initial PI controller design gives a settling time of 2 seconds, which meets the requirement.

Adjust PID Design in PID Tuner

The overshoot of the reference tracking response is about 7.5 percent. Since we still have some room before reaching the settling time limit, you could reduce the overshoot by increasing the response time. Move the response time slider to the left to increase the closed loop response time. Notice that when you adjust response time, the response plot and the controller parameters and performance measurements update.

The following figure shows an adjusted PID design with an overshoot of zero and a settling time of 4 seconds. The designed controller effectively becomes an integral-only controller.

Complete PID Design with Performance Trade-Off

In order to achieve zero overshoot while reducing the settling time below 2 seconds, you need to take advantage of both sliders. You need to make control response faster to reduce the settling time and increase the robustness to reduce the overshoot. For example, you can reduce the response time from 3.4 to 1.5 seconds and increase robustness from 0.6 to 0.72.

The following figure shows the closed-loop response with these settings:

Write Tuned Parameters to PID Controller Block

After you are happy with the controller performance on the linear plant model, you can test the design on the nonlinear model. To do this, click Update Block in the PID Tuner. This action writes the parameters back to the PID Controller block in the Simulink model.

The following figure shows the updated PID Controller block dialog:

Completed Design

The following figure shows the response of the closed-loop system:

The response shows that the new controller meets all the design requirements.

You can also use the Control System Designer to design the PID Controller block, when the PID Controller block belongs to a multi-loop design task. See the example Single Loop Feedback/Prefilter Compensator Design.

How the heating control operates

Each heating controller in RepRapFirmware 1.15 and later can work either in bang-bang mode or in PID mode. When operating in PID mode, it can get its PID parameters in either of two ways:

Use two sets of PID parameters computed from a first-order + delay time (FOPDT) model of the heating system. The FOPDT model parameters may be derived using auto-tuning, or configured manually using M307.

Use one set of legacy PID parameters configured manually using M301. This provides backwards-compatibility with previous versions, and provides a fallback if the behaviour of your heating system cannot be approximated well enough by a FOPDT model.

After power up or reset, the bed heater controller is in bang-bang mode and the extruder heaters use the model-derived PID parameters. If you use the M301 command to set the legacy PID parameters, the controller for that heater switches over to use them. If you run a successful auto tune or you set the model parameters manually using the M307, the controller switches back to using model-derived PID parameters.

To see which set of parameters is being used, run M307 H# where H is the heater number, and that will tell you either that the model is in use (so model-based PID parameters are being used for that heater), or not in use (so legacy PID parameters are being used).

Each heating controller performs temperature monitoring to try to detect fault conditions such as a heater of thermistor falling out of an extruder heating block. The temperature monitor relies on the model parameters to decide what is reasonable behaviour. Therefore, even if you decide to use legacy PID parameters or bang-bang control, you should still define an approximate model of the heater to provide good heater monitoring without false alarms.

Setting the model parameters by auto tuning

Auto tuning is initiated by the M303 command:

Firmware 1.18 and later

The S parameter is the temperature to heat up to. The default value depends on which heater you are tuning. During auto tuning, the heater will be run at the specified power until this temperature is reached and then it will be switched off; so the temperature will overshoot the target somewhat

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There is also an optional P parameter, which is the PWM value to use. Unless your heater is greatly over-powered, use the default PWM value of 1.0.

Firmware 1.17 and earlier

The S parameter is the maximum allowed temperature. Auto tuning will be abandoned if the temperature exceeds this value.

The P parameter is the PWM fraction to use. You should choose it such that when the heater is run at this PWM for an extended period, a typical printing temperature will be reached but the maximum specified by the S parameter will not be exceeded. The default value of 0.5 is satisfactory for a heater of modest power. If you have a particularly powerful hot end heater, reduce it as necessary to avoid excessive temperature rise. Conversely, when tuning a weak bed heater that can barely reach 100C, increase it.

All firmware versions

Only one heater may be auto tuned at a time. Before commencing auto tuning, the heater to be tuned must be at or near room temperature and its temperature reading should be stable.

Send M303 with an H parameter (and optionally P and S parameters) to start the auto tune process. A message will be generated when auto tuning is completed or abandoned. You can also run M303 with no parameters to see the current status of auto tuning.

Warning! During auto tuning there is minimal protection against heating faults. Therefore you should not leave the printer unattended during auto tuning.

If auto tuning is successful, new model parameters are set and the PID parameters computed from them are used. You can see these parameters by running the M307 H# command, where # is the heater number M307 will also indicate that the model is in use, meaning that the PID parameters displayed by M307 are used, not the PID parameters displayed by M301.

Tuning a hot end heater typically takes between five and ten minutes. Tuning a bed heater may take more than half an hour, depending on the thermal capacity of the bed. You can cancel tuning by sending M0.

After you have run auto tuning and checked that the heater control is working well, run M500 to save the heater parameters in config-override.g (this is supported in firmware 1.17 and later). Alternatively, construct a M307 command with the model parameters and add it to config.g. For example, if after tuning you run M307 H0 and see this:

Auto Tuning Pid Temperature Controller

then you should add the following to config.g to preserve this model:

The B0 parameter tells the system to use PID (the default on power up is bang-bang for the bed heater). If you need to limit the maximum PWM of the heater, add an S parameter to the M307 command, for example S0.8 will limit the PWM to 80%.

Make sure there is no M301 command for the same heater after the M307 command, otherwise the model will not be used.

Troubleshooting auto tuning

If you are using firmware 1.17 or earlier and auto tuning fails because the maximum temperature you specified in the M301 command (or the default) is exceeded, you will be prompted to use a higher maximum temperature (S parameter) or lower PWM (P parameter). You should wait until the hot end is within 10C of room temperature before trying again. The higher your hot end heater power, the lower the P value you need. The default of 0.5 works well for a 30W heater on a typical hot end (E3Dv6) run at its nominal voltage. A 40W heater might need P=0.4, and a 60W heater P=0.25. If your power supply voltage is higher than the nominal heater voltage then you should reduce P further. For example if you are using a 12V heater with a 13.2V supply, you should reduce P by 20% to account for the 10% higher voltage.

If auto tuning fails with a message that the temperature is not rising fast enough, this indicates that either you are using too low a P value in the M303 command, or the dead time in the existing model is much too low for your heater. You can increase the dead time using the M307 command. For example, sending M307 H0 D30 will increase the dead time to 30 seconds. The actual dead time will be known after a successful auto tuning.

Setting the model parameters manually

Model parameters can be changed and reported using the M307 command. Examples:

The H parameter specifies the heater.

The A parameter is the model gain, which is the ultimate temperature rise divided by the PWM fraction. For example, a gain of 350 means that at a constant 50% PWM, the temperature would eventually reach ambient temperature plus 350 * 0.5 degC.

The D parameter is the dead time, which is the delay between a change in PWM and an appreciable effect on the rate of temperature change.

The C parameter is the model time constant. This may be thought of as the time taken for the temperature rise to reach 63.2% of its ultimate value after the heater is switched on from cold at constant PWM, less the dead time.

You can limit the PWM by adding a suitable S parameter, for example S0.8 will limit the PWM to 80%.

To use bang-bang mode instead of PID, change B0 to B1. In bang-bang mode, the S parameter is still used to limit the PWM when the heater is turned on.

Measuring the gain

If necessary, use M301 to set some PID parameters that let you achieve a steady temperature. You can set the I term to zero if it helps - this means you won't reach the temperature you set, but that doesn't matter.
Set the heater to a temperature you typically use and wait until the temperature is stable. It doesn't matter if it is still creeping up slowly, but it must not be oscillating.
Send M573 P# (where # is the heater number) to report the average PWM.
The gain is: (actual_heater_temperature - ambient_temperature)/average_pwm.

Manual adjustments to the heater model parameters

If necessary you can make manual adjustments to the M307 model parameters, as follows:

If during initial heating the temperature undershoots the target, reduce the A parameter. If it overshoots the target, increase the A parameter. Try increasing/decreasing it by 5% or 10%.

If the response to temperature changes caused externally (e.g. the print cooling fan turning on) is too slow, reduce the D parameter. If the temperature is not stable but oscillates around the target temperature even when the print head is stationary, increase the D parameter. Try increasing/decreasing it by 30%.

Setting legacy PID parameters

This mode is intended as a backup, for use if model-based tuning is not working well enough. The parameters are configured using the M301 command. Example:

The H parameter is the heater number. Usually, 0 is the bed heater, 1 is the extruder 0 heater, and so on.

P, I and D are the standard proportional. integral and differential coefficients, scaled by 255 for compatibility with older firmware. A negative P value means use bang-bang control.