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Minor update and new examples using ZN_PID tuning method and adaptive control to reduce overshoot.
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Lines changed: 222 additions & 10 deletions

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‎examples/MAX31856_PTC_SSR/sTune_QuickPID_Adaptive/sTune_QuickPID_Adaptive.ino‎

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/********************************************************************************
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sTune QuickPID Adaptive Control Example
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This sketch does on-the-fly tunning and PID SSR control of a PTC heater
4+
using the ZN_PID tuning method. When sTune completes, we need the input
5+
to approach setpoint for the first time. As the input gets closer, the gains
6+
(tunings) are gradually applied. This helps keep the integral term to a
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minimum to help reduce initial overshoot. Final overshoot correction is made
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at the first crossover from setpoint. Here, a full AC cyle is dropped from
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the output and 100% PID control resumes with ½ AC cycle optimized SSR control.
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Open the serial plotter to view the graphical results.
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Reference: https://github.com/Dlloydev/sTune/wiki/Examples_MAX31856_PTC_SSR
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*******************************************************************************/
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#include <Adafruit_MAX31856.h>
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#include <sTune.h>
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#include <QuickPID.h>
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// pins
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const uint8_t inputPin = 0;
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const uint8_t relayPin = 3;
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const uint8_t drdyPin = 5;
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// user settings
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uint32_t settleTimeSec = 10;
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uint32_t testTimeSec = 500;
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const uint16_t samples = 500;
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const float inputSpan = 200;
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const float outputSpan = 2000;
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float outputStart = 0;
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float outputStep = 60;
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float tempLimit = 75;
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uint8_t debounce = 1;
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uint8_t startup = 0;
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// variables
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float Input, Output, Setpoint = 50, Kp, Ki, Kd;
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Adafruit_MAX31856 maxthermo = Adafruit_MAX31856(10); //SPI
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sTune tuner = sTune(&Input, &Output, tuner.ZN_PID, tuner.directIP, tuner.printOFF);
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QuickPID myPID(&Input, &Output, &Setpoint);
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void setup() {
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pinMode(drdyPin, INPUT);
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pinMode(relayPin, OUTPUT);
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Serial.begin(115200);
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delay(3000);
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Output = 0;
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if (!maxthermo.begin()) {
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Serial.println("Could not initialize thermocouple.");
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while (1) delay(10);
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}
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maxthermo.setThermocoupleType(MAX31856_TCTYPE_K);
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maxthermo.setConversionMode(MAX31856_CONTINUOUS);
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tuner.Configure(inputSpan, outputSpan, outputStart, outputStep, testTimeSec, settleTimeSec, samples);
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tuner.SetEmergencyStop(tempLimit);
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}
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void loop() {
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float optimumOutput = tuner.softPwm(relayPin, Input, Output, Setpoint, outputSpan, debounce);
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switch (tuner.Run()) {
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case tuner.sample: // active once per sample during test
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if (!digitalRead(drdyPin)) Input = maxthermo.readThermocoupleTemperature();
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tuner.plotter(Input, Output * 0.5, Setpoint, 1, 3);
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break;
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case tuner.tunings: // active just once when sTune is done
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tuner.GetAutoTunings(&Kp, &Ki, &Kd); // sketch variables updated by sTune
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myPID.SetOutputLimits(0, outputSpan * 0.1);
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myPID.SetSampleTimeUs(outputSpan * 1000 * 0.2);
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debounce = 0; // switch to SSR optimum cycle mode
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myPID.SetMode(myPID.Control::automatic); // the PID is turned on
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myPID.SetProportionalMode(myPID.pMode::pOnMeas);
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myPID.SetAntiWindupMode(myPID.iAwMode::iAwClamp);
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myPID.SetTunings(Kp, 0, 0); // update PID with the new Kp (P-controller)
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break;
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case tuner.runPid: // active once per sample after tunings
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if (!digitalRead(drdyPin)) Input = maxthermo.readThermocoupleTemperature();
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if (Input > Setpoint && startup == 6) {
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Output -= 17; // drop full AC cycle
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myPID.SetMode(myPID.Control::manual); // toggle PID control mode
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myPID.SetMode(myPID.Control::automatic); // PID uses new output value
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startup++;
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} else if (Input > Setpoint - 3 && startup == 5) {
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myPID.SetTunings(Kp, Ki, Kd); // 100% of gains
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startup++;
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} else if (Input > Setpoint - 6 && startup == 4) {
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myPID.SetTunings(Kp, Ki * 0.8, Kd * 0.8); // 80% of gains
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startup++;
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} else if (Input > Setpoint - 9 && startup == 3) {
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myPID.SetTunings(Kp, Ki * 0.6, Kd * 0.6); // 60% of gains
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startup++;
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} else if (Input > Setpoint - 12 && startup == 2) {
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myPID.SetTunings(Kp, Ki * 0.4, Kd * 0.4); // 40% of gains
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startup++;
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} else if (Input > Setpoint - 15 && startup == 1) {
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myPID.SetTunings(Kp, Ki * 0.2, Kd * 0.2); // 20% of gains
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startup++;
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} else if (Input > Setpoint - 18 && startup == 0) {
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myPID.SetTunings(Kp, Ki * 0.1, Kd * 0.1); // 10% of gains
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startup++;
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}
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myPID.Compute();
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tuner.plotter(Input, optimumOutput * 0.5, Setpoint, 1, 3);
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break;
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}
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}

‎examples/MAX6675_PTC_SSR/sTune_QuickPID_Adaptive/sTune_QuickPID_Adaptive.ino‎

Lines changed: 106 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,106 @@
1+
/********************************************************************************
2+
sTune QuickPID Adaptive Control Example
3+
This sketch does on-the-fly tunning and PID SSR control of a PTC heater
4+
using the ZN_PID tuning method. When sTune completes, we need the input
5+
to approach setpoint for the first time. As the input gets closer, the gains
6+
(tunings) are gradually applied. This helps keep the integral term to a
7+
minimum to help reduce initial overshoot. Final overshoot correction is made
8+
at the first crossover from setpoint. Here, a full AC cyle is dropped from
9+
the output and 100% PID control resumes with ½ AC cycle optimized SSR control.
10+
11+
Open the serial plotter to view the graphical results.
12+
Reference: https://github.com/Dlloydev/sTune/wiki/Examples_MAX6675_PTC_SSR
13+
*******************************************************************************/
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#include <max6675.h>
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#include <sTune.h>
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#include <QuickPID.h>
18+
19+
// pins
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const uint8_t inputPin = 0;
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const uint8_t relayPin = 3;
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const uint8_t drdyPin = 5;
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const uint8_t SO = 12;
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const uint8_t CS = 10;
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const uint8_t sck = 13;
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// user settings
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uint32_t settleTimeSec = 10;
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uint32_t testTimeSec = 500;
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const uint16_t samples = 500;
31+
const float inputSpan = 200;
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const float outputSpan = 2000;
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float outputStart = 0;
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float outputStep = 60;
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float tempLimit = 75;
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uint8_t debounce = 1;
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uint8_t startup = 0;
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// variables
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float Input, Output, Setpoint = 50, Kp, Ki, Kd;
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MAX6675 module(sck, CS, SO); //SPI
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sTune tuner = sTune(&Input, &Output, tuner.ZN_PID, tuner.directIP, tuner.printOFF);
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QuickPID myPID(&Input, &Output, &Setpoint);
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void setup() {
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pinMode(drdyPin, INPUT);
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pinMode(relayPin, OUTPUT);
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Serial.begin(115200);
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while (!Serial) delay(10);
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delay(3000);
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Output = 0;
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tuner.Configure(inputSpan, outputSpan, outputStart, outputStep, testTimeSec, settleTimeSec, samples);
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tuner.SetEmergencyStop(tempLimit);
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}
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void loop() {
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float optimumOutput = tuner.softPwm(relayPin, Input, Output, Setpoint, outputSpan, debounce);
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switch (tuner.Run()) {
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case tuner.sample: // active once per sample during test
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Input = module.readCelsius();
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tuner.plotter(Input, Output * 0.5, Setpoint, 1, 3);
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break;
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case tuner.tunings: // active just once when sTune is done
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tuner.GetAutoTunings(&Kp, &Ki, &Kd); // sketch variables updated by sTune
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myPID.SetOutputLimits(0, outputSpan * 0.1);
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myPID.SetSampleTimeUs(outputSpan * 1000 * 0.2);
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debounce = 0; // switch to SSR optimum cycle mode
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myPID.SetMode(myPID.Control::automatic); // the PID is turned on
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myPID.SetProportionalMode(myPID.pMode::pOnMeas);
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myPID.SetAntiWindupMode(myPID.iAwMode::iAwClamp);
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myPID.SetTunings(Kp, 0, 0); // update PID with the new Kp (P-controller)
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break;
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case tuner.runPid: // active once per sample after tunings
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Input = module.readCelsius();
78+
if (Input > Setpoint && startup == 6) {
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Output -= 17; // drop full AC cycle
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myPID.SetMode(myPID.Control::manual); // toggle PID control mode
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myPID.SetMode(myPID.Control::automatic); // PID uses new output value
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startup++;
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} else if (Input > Setpoint - 3 && startup == 5) {
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myPID.SetTunings(Kp, Ki, Kd); // 100% of gains
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startup++;
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} else if (Input > Setpoint - 6 && startup == 4) {
87+
myPID.SetTunings(Kp, Ki * 0.8, Kd * 0.8); // 80% of gains
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startup++;
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} else if (Input > Setpoint - 9 && startup == 3) {
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myPID.SetTunings(Kp, Ki * 0.6, Kd * 0.6); // 60% of gains
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startup++;
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} else if (Input > Setpoint - 12 && startup == 2) {
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myPID.SetTunings(Kp, Ki * 0.4, Kd * 0.4); // 40% of gains
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startup++;
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} else if (Input > Setpoint - 15 && startup == 1) {
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myPID.SetTunings(Kp, Ki * 0.2, Kd * 0.2); // 20% of gains
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startup++;
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} else if (Input > Setpoint - 18 && startup == 0) {
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myPID.SetTunings(Kp, Ki * 0.1, Kd * 0.1); // 10% of gains
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startup++;
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}
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myPID.Compute();
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tuner.plotter(Input, optimumOutput * 0.5, Setpoint, 1, 3);
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break;
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}
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}

‎library.json‎

Lines changed: 1 addition & 1 deletion
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@@ -1,6 +1,6 @@
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{
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"name": "sTune",
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"version": "2.3.1",
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"version": "2.3.2",
44
"description": "Open loop PID autotuner using a novel s-curve inflection point test method. Tuning parameters are determined in about ½Tau on a first-order system with time delay. Full 5Tau testing and multiple serial output options are provided.",
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"keywords": "PID, autotune, autotuner, tuner, tune, stune, inflection, step",
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"repository":

‎library.properties‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
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name=sTune
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version=2.3.1
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version=2.3.2
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author=David Lloyd
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maintainer=David Lloyd <[email protected]>
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sentence=Open loop PID autotuner using a novel s-curve inflection point test method.

‎src/sTune.cpp‎

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/****************************************************************************************
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sTune Library for Arduino - Version 2.3.1
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sTune Library for Arduino - Version 2.3.2
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by dlloydev https://github.com/Dlloydev/sTune
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Licensed under the MIT License.
55
@@ -113,8 +113,8 @@ uint8_t sTune::Run() {
113113
float lastPvAvg = pvAvg;
114114
pvInst = *_input;
115115
pvAvg = tangent.avgVal(pvInst);
116-
float pvInstResolution = abs(pvInst - lastPvInst);
117-
float pvAvgResolution = abs(pvAvg - lastPvAvg);
116+
float pvInstResolution = fabs(pvInst - lastPvInst);
117+
float pvAvgResolution = fabs(pvAvg - lastPvAvg);
118118
if (pvInstResolution > epsilon && pvInstResolution < pvInstRes) pvInstRes = pvInstResolution;
119119
if (pvAvgResolution > epsilon && pvAvgResolution < pvAvgRes) pvAvgRes = pvAvgResolution;
120120

@@ -192,7 +192,7 @@ uint8_t sTune::Run() {
192192
_TuMin = _Tu * 0.1667; // units in minutes
193193
_tdMin = _td * 0.1667; // units in minutes
194194
_R = _tdMin / _TuMin;
195-
_Ku = abs(((pvMax - pvStart) / _inputSpan) / ((_outputStep - _outputStart) / _outputSpan)); // process gain
195+
_Ku = fabs(((pvMax - pvStart) / _inputSpan) / ((_outputStep - _outputStart) / _outputSpan)); // process gain
196196
_Ko = ((_outputStep - _outputStart) / pvMax) * (_TuMin / _tdMin); // process gain
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198198
_kp = sTune::GetKp();
@@ -507,11 +507,9 @@ float sTune::softPwm(const uint8_t relayPin, float input, float output, float se
507507
if (msNow - windowStartTime >= windowSize) {
508508
windowStartTime = msNow;
509509
}
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511-
// SSR optimum cycle controller (AC half-cycle control)
510+
// SSR optimum AC half-cycle controller
512511
static float optimumOutput;
513-
if (!debounce && setpoint > 0 && input > setpoint) optimumOutput = output - 8;
514-
else if (!debounce && setpoint > 0 && input < setpoint) optimumOutput = output + 8;
512+
if (!debounce && setpoint > 0 && input > setpoint) optimumOutput = output - 9;
515513
else optimumOutput = output;
516514
if (optimumOutput < 0) optimumOutput = 0;
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