RimsTuner Class Reference

Toolkit to automatically tune PID without a process model. More...

#include <RimsTuner.h>

Inheritance diagram for RimsTuner:

Public Member Functions
	RimsTuner (UIRims *uiRims, byte analogPinTherm, byte ssrPin, double *currentTemp, double *ssrControl, double *settedTemp)
	Consructor. More...
void	setFlowSensor (byte pinFlow, float flowFactor, float lowBound=-1, float upBound=100, float critalFlow=-1)
	Same as Rims::setFlowSensor. More...
Public Member Functions inherited from Rims
	Rims (UIRims *uiRims, byte analogPinPV, byte ssrPin, double *currentTemp, double *ssrControl, double *settedTemp)
	Constructor. More...
void	setTempProbe (byte probeType, float probeCoefs[], float res1)
	Set temperature probe (RTD, thermistor or custom) parameters. More...
void	setPinLED (byte pinLED)
	Set pin for heater LED indicator. More...
void	setFlowSensor (byte pinFlow, float flowFactor, float lowBound=DEFAULTFLOWLOWBOUND, float upBound=DEFAULTFLOWUPBOUND, float criticalFlow=DEFAULTFLOWLOWBOUND)
	Set pin for flow sensor and parameters. More...
void	setHeaterPowerDetect (char pinHeaterVolt)
	Set pin to detect if there is voltage applied on heater. More...
void	setTuningPID (float Kp, float Ki, float Kd, float tauFilter, int mashWaterQty=-1)
	Set tuning for PID object. More...
void	setMemCSPin (byte csPin)
	Set pin for flash memory chip select. More...
void	checkMemAccessMode ()
	Check if enterring in USB memory access mode. More...
void	run ()
	Start and run Rims instance. More...
float	getTempPV ()
	Get temperature from temperature probe (RTD, thermistor or custom). More...
float	getFlow ()
	Get flow from hall-effect flow sensor. More...
bool	getHeaterVoltage ()
	Check if heater is powered or not. More...
void	stopHeating (bool state)
	Stop heater no matter what PID output. More...

Protected Member Functions
void	_initialize ()
	Initialize RimsTuner before iterations.
void	_iterate ()
	Iterations for RimsTuner instance. More...
void	_refreshTuner ()
	Refresh relay identification and compute critical point parameters. More...
void	_relayInit ()
	Init relay for identification procedure.
bool	_relayAction ()
	Save a signal sample for amplitude evaluation and switch relay output if treshold is reached. More...
bool	_relayStartNewPeriod ()
	Start new relay identification period. More...
void	_relayEnd ()
	Evaluate PID coefficients and show them on UIRims.
float	_evalAmplitude ()
	Evaluate fundamental harmonic amplitude of previously saved samples. More...
void	_calcTuningPID (float T, float A)
	Calculate auto-tuned PID coefficients after tuning procedure. More...
Protected Member Functions inherited from Rims
void	_initSession ()
	Init all attributes and I/O for starting a brew session.
void	_endSession ()
	Attributes treatments for ending a brew session.
void	_refreshTimer ()
	Refresh time related values. More...
void	_refreshDisplay ()
	Refresh display used by UIRims instance.
void	_refreshSSR ()
	Refresh solid state relay. SSR will be refreshed in function of _controlValPtr (duty-cycle in percentage) and SSRWINDOWSIZE (mSec) values.
void	_serialPrintBrewData ()
	Print current data points values to the Serial logger. Serial port (UART) need to be initialized in the main sketch with Serial.begin()
unsigned int	_memCountSessions ()
	Count how many brew sessions were saved in flash mem. More...
unsigned long	_memCountSessionData ()
	Count how many data point were taken. More...
void	_memInitSP ()
	Initialize flash memory. More...
void	_memAddBrewData ()
	Add data point to the flash memory. More...
void	_memDumpBrewData ()
	Dump brew session data on USB serial port.
void	_memFreeSpace ()
	Show free memory on flash mem via USB serial port.
void	_memClearAll ()
	Clear all memory via USB serial port.

Detailed Description

Toolkit to automatically tune PID without a process model.

It tests differents values to the SSR and monitors the resulting temperature to automatically calculate proper PID coefficients. The resulting PID tuning is printed on the serial monitor at the end of the procedure. Open the serial monitor before stating the auto-tuning procedure.

The total required time for the auto-tuning procedure is unknown. It can last approximately from 30 minutes to 2 hours on the RIMS process.

It's based on two methods :

1. Relay feedback (with hysteresis) process identification
2. Ziegler-Nichols PID tuning method

For more details, see "Automatic Tuning of Simple Regulators with Specifications on Phase and Amplitude Margins" (Aström et al., 1984)

Warning

In most situations, manual PID tuning with a process model (using RimsIdent) is more robust and faster to disturbances.

Author

Francis Gagnon

Copyright

GPLv3 License

Examples:

rimsTunerBasic.ino.

Constructor & Destructor Documentation

RimsTuner()

RimsTuner::RimsTuner	(	UIRims *	uiRims,
		byte	analogPinTherm,
		byte	ssrPin,
		double *	currentTemp,
		double *	ssrControl,
		double *	settedTemp
	)

Consructor.

Parameters

uiRims	: UIRims*. Pointer to UIRims instance
analogPinTherm	: byte. Analog pin to temperature probe
ssrPin	: byte. Pin to control heater's solid state relay.
currentTemp	: double*. Pointer to a double that will be used for current temparature
ssrControl	: double*. Pointer to a double that will use to control SSR
settedTemp	: double*. Pointer to a double that will be use to store setted temperature

Member Function Documentation

_calcTuningPID()

void RimsTuner::_calcTuningPID ( float  T, float  A  )

protected

Calculate auto-tuned PID coefficients after tuning procedure.

Classic Ziegler-Nichols method is applied on the critical (or ultimate) gain and period. PID coefficients are converted from the ideal form to the parallel form. Derivative filter time constant is fixed at \(\tau = 0.1K_d\). For more info : http://tinyurl.com/mwamcj5

Parameters

T	: float. relay identification signal period in sec
A	: float. relay identification signal amplitudes

_evalAmplitude()

float RimsTuner::_evalAmplitude ( )

protected

Evaluate fundamental harmonic amplitude of previously saved samples.

The discrete Fourier serie (equivalent to FFT) is used to evaluate the signal amplitude of the first harmonic (more reliable than signal peak detection) :

\[ \begin{align} a_1 & = \frac{2t_s}{T} \sum_{n=0}^{N-1}y[n]\cos\left(\frac{2\pi nt_s}{T}\right)\\ b_1 & = \frac{2t_s}{T} \sum_{n=0}^{N-1}y[n]\sin\left(\frac{2\pi nt_s}{T}\right) \end{align} \]

where \(T\) is the \(y[n]\) period, \(N\) is \(y\) sample quantity and \(t_s\) is the sampling time. Then, \(y[n]\) amplitude \(A\) is evaluated with :

\[ A \approx \sqrt{a_1^2+b_1^2} \]

For more info : http://tinyurl.com/z3wtjyl

Returns

float. Calculated fundamental harmonic amplitude value

_iterate()

void RimsTuner::_iterate ( )

protectedvirtual

Iterations for RimsTuner instance.

Auto-tuning procedure duration is unknown (~0.5-2 hours). It starts at STEP0VALUE % for STEADYTIMELENGTH (long enough for temperature stabilization in steady-state.). Average temperature is measured at the end of the signal stabilization phase. Relay identification is then perform on the RIMS.

All information related to the tuning procedure is printed in the Serial monitor of the Arduino IDE. PID coefficients is printed at the end. Data is stored in the flash memory if correctly connected.

Reimplemented from Rims.

_refreshTuner()

void RimsTuner::_refreshTuner ( )

protected

Refresh relay identification and compute critical point parameters.

Because of Arduino lack of SRAM, it's impossible to store in an array all temperature measurements for a complete relay period (to evaluate signal amplitude afterward). Because of that, relay identification sampling time is increased at RELAYSAMPLEFACTOR*SAMPLETIME mSec (under-sampling). It should not induce precision problems since it is still quite fast relative to RIMS slow dynamics.

_relayAction()

bool RimsTuner::_relayAction ( )

protected

Save a signal sample for amplitude evaluation and switch relay output if treshold is reached.

Returns

boolean. True if the relay identification goes on, false otherwise.

_relayStartNewPeriod()

bool RimsTuner::_relayStartNewPeriod ( )

protected

Start new relay identification period.

Period and amplitude measurements are saved in arrays. Some variables is initialized for the next relay period and tuning is finished if limit-cycle is reached or if max relay periods is reached. Limit-cycle is considered stable if current period and amplitude measurement is whithin MODELPARAMTOL*100% (default of 5%) of the last measurement.

Returns

boolean. True if a new period is started, false if not.

setFlowSensor()

void RimsTuner::setFlowSensor	(	byte	pinFlow,
		float	flowFactor,
		float	lowBound = -1,
		float	upBound = 100,
		float	critalFlow = -1
	)

Same as Rims::setFlowSensor.

Redefinied to force criticalFlow at -1 and default bounds are fixed at -1 and 100 so you can auto-tune at any flowrate.

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The documentation for this class was generated from the following files:

• RimsTuner.h
• RimsTuner.cpp