In PID control, the operation variable is determined by combining the functions of P (proportional), I (integral), and D (derivative).

By changing the PID constant such as the proportional band, integral time, and derivative time that determine its function, the process by which the temperature approaches the target value also changes.

PID tuning is the process of using this relationship to approach the desired control response.

This is not a task to find the "correct PID constant."

When we talk about PID tuning, it might seem like there's a single "correct PID constant" for each piece of equipment.

However, control response that is important differs depending on whether the goal is to reach the set temperature as quickly as possible or to minimize over.

Furthermore, even with the same equipment, control response may change if operating conditions such as the set temperature, load, and materials are altered.

Just because you can't control the temperature as you want doesn't necessarily mean the problem lies with the PID constant. Before changing the PIDs, check the entire control loop.

Is the PV correct?

The first thing to check is the PV (Perceptual Voltage). If the temperature sensor is not accurately measuring the target you want to control, adjusting the PID (Personal Indicator) using that PV will not yield the desired results.

We will check the sensor's mounting position, insertion depth, response, thermal influence from the surroundings, and the condition of the sensor and wiring.

How is the music video progressing?

Next, let's look at the music video. Just looking at the PV, all we can gather is the fact that "the temperature doesn't rise."

However, if PV does not rise to the set value while MV is around 100%, it indicates that the controller is already requiring a large amount of operation.

In this case, in addition to the PID constant, you also need to check the heater capacity, heat loss, load, and other factors.

Is the equipment working as shown in the music video?

Even if the controller is outputting the correct MV, the temperature will not change as expected if the operation parameters are not reflected in the actual equipment.

If the equipment uses electric heaters, control loop includes operation devices such as thyristor regulators and SSRs, the power supply, and the heater itself.

Have the driving conditions changed?

If control status changes after previously being stable, check if conditions such as material, input amount, flow rate, set temperature, ambient temperature, and door opening/closing have changed.

Even with the same PID constant, the response may change if the conditions of control system change.

When adjusting PID settings, don't just look at the PV; try to check the MV on the same timeline as much as possible.

What we can learn from the PV

By viewing the PV (Percentage View), you can check the speed at which the SV over View) approaches the SV, overshoot, hunting, settling time, offset, and more.

PV is information used to see the results of control.

What we can learn from the music video

By looking at the video record (MV), we can see what operation control system required to achieve that result.

In PID tuning, control state is evaluated by observing the changes in PV and MV over time.

It's important not to judge the quality of control based on a single indicator. For example, trying to speed up the rise time might result in a large over; multiple evaluation items may be involved.

"The temperature doesn't reach the set temperature easily" is a common symptom encountered when adjusting PID settings. However, the first thing to check is not the PID constant, but the MV (Motion Volume).

If the MV is already large

If the MV is near 100% but the PV is rising slowly, the controller is already demanding significant heating.

In this case, we check the heater capacity, power supply, operation equipment, heat loss, the heat capacity of the control object, load, etc.

Changing the PID constant will not exceed the available heating capacity itself.

If there is time in the MV

If PV is far from SV but MV is not rising sufficiently, it is worth checking the PID settings and other control settings.

over is a phenomenon where page views (PV) temporarily exceed site views (SV).

In PID calibration, we don't just check "how many degrees Celsius it exceeded," but also how it exceeded the SV (Sensitivity Variable).

• It rose rapidly and far exceeded
• I slowly approached SV and then crossed it.
• Stabilized immediately after exceeding the limit.
• Even after exceeding that point, it continued to fluctuate up and down.

Even with the same over, the waveform characteristics can differ. Instead of judging based on a single rule like "over = change a specific PID constant," we consider the cause while looking at the PV and MV waveforms.

Hunting refers to a state where the PV (Perceptual Frequency) fluctuates periodically up and down near the SV (Substantial Frequency).

Even if the temperature reaches near the set value, if it continues to fluctuate up and down, it may not be stable control.

Both the PV and MV are vibration intensely.

control device's operation itself may be fluctuating significantly. We will examine the relationship between the PID's function and the waveform in detail.

The music video is stable, but the promotional video is vibration.

If PV is fluctuating despite MV not changing significantly, we will also check for factors other than PID, such as disturbance or changes in equipment.

Even though the symptom is the same—hunting—the areas to check will differ depending on whether it's a PV or an MV.

Even if the PV reaches near the SV, it may fluctuate up and down for a long period of time afterward and not stabilize easily.

What we want to check at this point is the "setup time." The setup time is the time it takes from the start of control until the PV settles into a stable state near the SV.

Here, we need to distinguish between "it takes a long time to reach SV" and "it takes a long time to stabilize after reaching SV."

In the former case, equipment capacity and other factors are also relevant. In the latter case, we will carefully examine the behavior of PV and MV around the setpoint, including PID settings and disturbance.

offset is the steady-state difference that remains between SV and PV even after control has stabilized.

Using only P-action requires a certain degree of deviation to maintain the operation variable, which can result in a residual offset. I-action is used to reduce this persistent deviation.

However, instead of immediately changing the input just because there is a difference between the SV and PV, we also check the sensors, settings, higher limit and lower limit limits of the output, and whether the equipment can perform the necessary operation.

In PID tuning, the ability to compare the settings before and after the change is more important than the change itself.

Clearly state what has been changed.

When the P.I.D. is changed, the system records which parameter was changed, from which value to which value.

Don't make too many big changes at once.

Significantly changing the PID constant can also drastically alter control response. Adjustments should be made gradually while checking specifications of control object and controller.

Compare under the same conditions.

If the SV, load, material quantity, initial temperature, and ambient conditions differ significantly before and after changing the PID constant, it becomes difficult to determine whether the waveform difference is due to the PID change.

Record the adjustment results.

Keeping records makes it easier to perform PID adjustments not as a guesswork, but as a process of comparing changes with results.

If changing the PID does not result in the desired response, we will re-examine factors other than the PID.

Some controllers offer an auto-auto tuning function, which can be useful when you need to determine the PID constant from scratch.

In auto tuning, the PID constant are determined using the response of control system.

However, since the calculated PID constant may not be optimal under all operating conditions, it is important to verify control response under actual operating conditions.

What is auto tuning? The mechanism and precautions for automatically adjusting PID constant.

What I've explained so far is the general approach to PID tuning.

CHINO has published "8 types of PID adjustment methods" based on specific temperature control waveforms using the DB series and KP series.

You can see specific examples of how the waveform changes when the PID is changed, regarding temperature vibration, over, and settling time.

See 8 different PID tuning methods