class ReflowStateMachine(object):
# Reflow profiles
LEADED_PROFILE = 'leaded'
LEAD_FREE_PROFILE = 'leadfree'
# Constants
TEMPERATURE_ROOM = 50
SENSOR_SAMPLING_TIME = 1000
SOAK_TEMPERATURE_STEP = 5
SOAK_MICRO_PERIOD = 9000
def __init__(self, reflowProfile, thermocouple=None, relay=None, lcd=None):
self.__reflowProfile = None
if (reflowProfile == self.LEAD_FREE_PROFILE):
self.__reflowProfile = ReflowLeadFreeProfile()
else:
self.__reflowProfile = ReflowLeadedProfile()
self.__reflowOvenPidContext = PIDContext(_input=0.0,
_output=0.0,
_setpoint=0.0)
self.__reflowOvenPid = PID(self.__reflowOvenPidContext,
Kp=self.__reflowProfile.PID_KP_PREHEAT,
Ki=self.__reflowProfile.PID_KI_PREHEAT,
Kd=self.__reflowProfile.PID_KD_PREHEAT,
direction=PID.DIRECT)
self.__thermocouple = thermocouple
self.__relay = relay
self.__lcd = lcd
self.__windowSize = 2000
self.__windowStartTime = datetime.now()
self.__nextCheck = datetime.now()
self.__nextRead = datetime.now()
self.__timerSoak = 0.0
self.__reflowState = ReflowState.REFLOW_STATE_IDLE
self.__reflowStatus = ReflowStatus.REFLOW_STATUS_OFF
self.__timerSeconds = 0.0
def Reflow(self):
reflowCycleComplete = False
now = datetime.now()
while (reflowCycleComplete == False):
# Time to read the thermocouple?
if (datetime.now() > self.__nextRead):
# Read thermocouple next sampling period
self.__nextRead += timedelta(
milliseconds=self.SENSOR_SAMPLING_TIME)
# Read current temperature
try:
self.__reflowOvenPidContext.Params[
PIDContext.Input] = self.__thermocouple.ReadCelsius()
except Exception as e:
# Thermocouple error
self.__reflowState = ReflowState.REFLOW_STATE_ERROR
self.__reflowStatus = ReflowStatus.REFLOW_STATUS_OFF
if (datetime.now() > self.__nextCheck):
# Check the Input within the next second
self.__nextCheck += timedelta(milliseconds=1000)
# If reflow process is ongoing
if (self.__reflowStatus == ReflowStatus.REFLOW_STATUS_ON):
self.__timerSeconds += 1
if (self.__lcd is not None):
self.__lcd.Clear()
self.__lcd.Print(ReflowState.Messages[self.__reflowState])
self.__lcd.SetCursor(0, 1)
if (self.__reflowState == ReflowState.REFLOW_STATE_ERROR):
self.__lcd.Print("No thermocouple connected!")
else:
self.__lcd.Print(
str(self.__reflowOvenPidContext.Params[
PIDContext.Input]) + "C ")
# Reflow oven controller state machine
if (self.__reflowState == ReflowState.REFLOW_STATE_IDLE):
if (self.__reflowOvenPidContext.Params[PIDContext.Input] >=
self.TEMPERATURE_ROOM):
self.__reflowState = ReflowState.REFLOW_STATE_TOO_HOT
else:
# Intialize seconds timer for serial debug information
self.__timerSeconds = 0
# Initialize PID control window starting time
self.__windowStartTime = datetime.now()
# Ramp up to minimum soaking temperature
self.__reflowOvenPidContext.Params[
PIDContext.
SetPoint] = self.__reflowProfile.TEMPERATURE_SOAK_MIN
# Tell the PID to range between 0 and the full window size
self.__reflowOvenPid.SetOutputLimits(
0.0, self.__windowSize)
self.__reflowOvenPid.SetSampleTime(
self.__reflowProfile.PID_SAMPLE_TIME)
# Turn the PID on
self.__reflowOvenPid.SetMode(PID.AUTOMATIC)
# Proceed to preheat stage
self.__reflowState = ReflowState.REFLOW_STATE_PREHEAT
elif (self.__reflowState == ReflowState.REFLOW_STATE_PREHEAT):
self.__reflowStatus = ReflowStatus.REFLOW_STATUS_ON
# If minimum soak temperature is achieved
if (self.__reflowOvenPidContext.Params[PIDContext.Input] >=
self.__reflowProfile.TEMPERATURE_SOAK_MIN):
# Chop soaking period into smaller sub-periods
self.__timerSoak = datetime.now() + timedelta(
milliseconds=self.SOAK_MICRO_PERIOD)
# Set less agressive PID parameters for soaking ramp
self.__reflowOvenPid.SetTunings(
Kp=self.__reflowProfile.PID_KP_SOAK,
Ki=self.__reflowProfile.PID_KI_SOAK,
Kd=self.__reflowProfile.PID_KD_SOAK)
# Ramp up to first section of soaking temperature
self.__reflowOvenPidContext.Params[
PIDContext.
SetPoint] = self.__reflowProfile.TEMPERATURE_SOAK_MIN + self.SOAK_TEMPERATURE_STEP
# Proceed to soaking state
self.__reflowState = ReflowState.REFLOW_STATE_SOAK
elif (self.__reflowState == ReflowState.REFLOW_STATE_SOAK):
# If micro soak temperature is achieved
if (datetime.now() > self.__timerSoak):
self.__timerSoak = (
datetime.now() +
timedelta(milliseconds=self.SOAK_MICRO_PERIOD))
# Increment micro setpoint
self.__reflowOvenPidContext.Params[
PIDContext.SetPoint] += self.SOAK_TEMPERATURE_STEP
if (self.__reflowOvenPidContext.Params[PIDContext.SetPoint]
> self.__reflowProfile.TEMPERATURE_SOAK_MAX):
# Set agressive PID parameters for reflow ramp
self.__reflowOvenPid.SetTunings(
Kp=self.__reflowProfile.PID_KP_REFLOW,
Ki=self.__reflowProfile.PID_KI_REFLOW,
Kd=self.__reflowProfile.PID_KD_REFLOW)
# Ramp up to first section of reflow temperature
self.__reflowOvenPidContext.Params[
PIDContext.
SetPoint] = self.__reflowProfile.TEMPERATURE_REFLOW_MAX
# Proceed to reflowing state
self.__reflowState = ReflowState.REFLOW_STATE_REFLOW
elif (self.__reflowState == ReflowState.REFLOW_STATE_REFLOW):
# We need to avoid hovering at peak temperature for too long
# Crude method that works like a charm and safe for the components
if (self.__reflowOvenPidContext.Params[PIDContext.Input] >=
(self.__reflowProfile.TEMPERATURE_REFLOW_MAX - 5)):
# Set PID parameters for cooling ramp
self.__reflowOvenPid.SetTunings(
Kp=self.__reflowProfile.PID_KP_REFLOW,
Ki=self.__reflowProfile.PID_KI_REFLOW,
Kd=self.__reflowProfile.PID_KD_REFLOW)
# Ramp down to minimum cooling temperature
self.__reflowOvenPidContext.Params[
PIDContext.
SetPoint] = self.__reflowProfile.TEMPERATURE_COOL_MIN
# Proceed to cooling state
self.__reflowState = ReflowState.REFLOW_STATE_COOL
elif (self.__reflowState == ReflowState.REFLOW_STATE_COOL):
# If minimum cool temperature is achieved
if (self.__reflowOvenPidContext.Params[PIDContext.Input] <=
self.__reflowProfile.TEMPERATURE_COOL_MIN):
# Turn off reflow process
self.__reflowStatus = ReflowStatus.REFLOW_STATUS_OFF
# Proceed to reflow Completion state
self.__reflowState = ReflowState.REFLOW_STATE_COMPLETE
elif (self.__reflowState == ReflowState.REFLOW_STATE_COMPLETE):
# Reflow process ended
self.__reflowState = ReflowState.REFLOW_STATE_IDLE
# Exit the state machine loop
reflowCycleComplete = True
elif (self.__reflowState == ReflowState.REFLOW_STATE_TOO_HOT):
# If oven temperature drops below room temperature
if (self.__reflowOvenPidContext.Params[PIDContext.Input] <
self.TEMPERATURE_ROOM):
# Ready to reflow
self.__reflowState = ReflowState.REFLOW_STATE_IDLE
elif (self.__reflowState == ReflowState.REFLOW_STATE_ERROR):
# Exit the state machine loop
reflowCycleComplete = True
# PID computation and relay control
if (self.__reflowStatus == ReflowStatus.REFLOW_STATUS_ON):
now = datetime.now()
self.__reflowOvenPid.Compute()
if ((now - self.__windowStartTime) >
timedelta(milliseconds=self.__windowSize)):
# Time to shift the Relay Window
self.__windowStartTime += timedelta(
milliseconds=self.__windowSize)
if (timedelta(milliseconds=self.__reflowOvenPidContext.Params[
PIDContext.Output]) > (now - self.__windowStartTime)):
self.__relay.SwitchRelay(RelayInterface.ON)
else:
self.__relay.SwitchRelay(RelayInterface.OFF)
else:
self.__relay.SwitchRelay(RelayInterface.OFF)
#!/usr/bin/python
from pid import PID, PIDContext
from datetime import datetime, timedelta
SetPoint = 260.0
Input = 1.0
Output = 0.0
WindowSize = 3000.0
WindowSizeTimeDelta = timedelta(milliseconds=WindowSize)
WindowStartTime = datetime.now()
pidContext = PIDContext(Input, Output, SetPoint)
pid = PID(pidContext, 0.2, 0.5, 0.1, PID.DIRECT)
pid.SetOutputLimits(0.0, WindowSize)
pid.SetMode(PID.AUTOMATIC)
while pidContext.Params[PIDContext.Input] < SetPoint:
now = datetime.now()
pid.Compute()
print(pidContext.Params.__str__())
output = pidContext.Params[PIDContext.Output]
if (now - WindowStartTime > WindowSizeTimeDelta):
WindowStartTime += WindowSizeTimeDelta
pidContext.Params[PIDContext.Input] += 1
if (timedelta(milliseconds=output) > now - WindowStartTime):
print("Relay ON")