Make grain_mass/water_mass per-step and re-derive plant params on change

grain_mass and water_mass now live on each step (defaulted from
default.step) instead of being fixed for the whole brew, since both
change over a mash (malt going in, water boiling off).
Sud.derive_plant_params() takes them as arguments so it can be
recomputed per step; the demo re-applies the resulting M/C to both the
real plant and the controller's Smith-predictor model on every step
change via the new Pot.set_thermal_params()/
TempController.set_model_params().

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CgR9tPaSzFkAwRAUyeaaCD

README.md

@@ -129,10 +129,7 @@ environment (`$WORKON_HOME`/`$BREWPI_HOME`) on a Raspberry Pi-style deployment.
 ## Mash schedules
 
 Files under `sude/` describe a brew's mash schedule ("Sud"): `pot_mass`,
-`pot_material`, `grain_mass`, `water_mass` (used by `Sud.derive_plant_params()`
+`pot_material` (fixed for the whole brew), and a `steps` list, each either:
-to compute a lumped thermal mass/specific-heat pair for `Pot`'s `M`/`C`, e.g.
-in `scripts/demos/sud/demo_sud.py`, instead of hand-tuning them), and a
-`steps` list, each either:
 
 - a ramp — `"ramp": {"rate": ..., "temp": ...}` — ramp to `temp` at `rate`
   (°C/min), or
@@ -147,6 +144,16 @@ Both `ramp` and `hold` carry a `stirrer` block (`speed`, `interval_time`,
 the user with) to pause for confirmation once the step completes, e.g. to
 add malt or check gravity, instead of advancing immediately.
 
+Each step also has its own `grain_mass`/`water_mass` (defaulted like
+everything else from `default.step`), since both change over the course of
+a brew — e.g. malt going in partway through, or water boiling off. Pass a
+step's `grain_mass`/`water_mass` to `Sud.derive_plant_params()` (together
+with the brew-wide `pot_mass`/`pot_material`) to get that step's lumped
+`Pot` `M`/`C`; `scripts/demos/sud/demo_sud.py` recomputes and re-applies
+these (via `Pot.set_thermal_params()`/`TempController.set_model_params()`,
+on both the real plant and the controller's Smith-predictor model) every
+time the current step changes, instead of deriving them once at startup.
+
 The top-level `default.step` object gives every field above (including the
 nested `ramp`/`hold`/`stirrer` blocks) a default value; a step in `steps`
 only needs to specify the fields it overrides — anything it omits is filled

components/pid/temp_controller_smith.py

@@ -24,6 +24,10 @@ class TempController(TempControllerBase):
 		self.model.set_power(power)
 		self.model_delay.set_power(power)
 
+	def set_model_params(self, M, C):
+		self.model.set_thermal_params(M, C)
+		self.model_delay.set_thermal_params(M, C)
+
 	def on_state_entered(self, state):
 		if state == States.HEAT:
 			self.model.initial(self.theta_ist)

components/plant/pot.py

@@ -56,6 +56,10 @@ class Pot(APlant):
 	def set_ambient_temperature(self, theta_amb):
 		self.theta_amb = theta_amb
 
+	def set_thermal_params(self, M, C):
+		self.M = M
+		self.C = C
+
 	def set_power(self, power):
 		self.p_in = power
 

components/sud.py

@@ -37,7 +37,7 @@ def _build_step(number, defaults, raw_step):
 	ramp or a hold depending on which of those keys it specifies; the other
 	is left out rather than synthesized from defaults."""
 	step = {'number': number}
-	for key in ('descr', 'user_message', 'user_wait_for_continue'):
+	for key in ('descr', 'user_message', 'user_wait_for_continue', 'grain_mass', 'water_mass'):
 		step[key] = raw_step.get(key, defaults.get(key))
 	for key in ('ramp', 'hold'):
 		if key in raw_step:
@@ -59,8 +59,6 @@ class Sud(AttributeChange):
 
 		self.pot_mass = data.get('pot_mass', 0)
 		self.pot_material = data.get('pot_material')
-		self.grain_mass = data.get('grain_mass', 0)
-		self.water_mass = data.get('water_mass', 0)
 
 		self.index = -1
 		self.hold_remaining = 0.0
@@ -68,13 +66,16 @@ class Sud(AttributeChange):
 		self.step = None
 		self.user_message = None
 
-	def derive_plant_params(self):
+	def derive_plant_params(self, grain_mass, water_mass):
-		"""Lumped (mass, specific heat) lifted from pot_mass/pot_material/
+		"""Lumped (mass, specific heat) lifted from pot_mass/pot_material and
-		grain_mass/water_mass, for use as Pot's "M"/"C" params."""
+		the current step's grain_mass/water_mass, for use as Pot's "M"/"C"
+		params. grain_mass/water_mass vary per step (e.g. malt going in,
+		water boiling off), so this is recomputed on every step change
+		rather than once at startup."""
 		c_pot = SPECIFIC_HEAT_BY_MATERIAL.get(self.pot_material, SPECIFIC_HEAT_WATER)
-		mass = self.water_mass + self.grain_mass + self.pot_mass
+		mass = water_mass + grain_mass + self.pot_mass
-		capacitance = (self.water_mass * SPECIFIC_HEAT_WATER
+		capacitance = (water_mass * SPECIFIC_HEAT_WATER
-			+ self.grain_mass * SPECIFIC_HEAT_GRAIN
+			+ grain_mass * SPECIFIC_HEAT_GRAIN
 			+ self.pot_mass * c_pot)
 
 		return {

scripts/demos/sud/demo_sud.py

@@ -35,8 +35,9 @@ if __name__ == '__main__':
 
 	sud = Sud("sude/sud_0010.json")
 
+	first_step = sud.schedule[0]
 	plant_params = {
-		**sud.derive_plant_params(),
+		**sud.derive_plant_params(first_step['grain_mass'], first_step['water_mass']),
 		"L"			: 0.2,
 		"Td"		: 60
 	}
@@ -65,9 +66,15 @@ if __name__ == '__main__':
 			stirrer.set_duty_cycle(1.0 if speed > 0 else 0.0)
 		stirrer.set_speed(speed)
 
+	def apply_plant_params(step):
+		params = sud.derive_plant_params(step['grain_mass'], step['water_mass'])
+		plant.set_thermal_params(params['M'], params['C'])
+		ctrl.set_model_params(params['M'], params['C'])
+
 	def on_step_changed(step):
 		if step is not None:
 			print(f"Step {step['number']}: {step['descr']}")
+			apply_plant_params(step)
 			if 'ramp' in step:
 				ctrl.set_theta_soll(step['ramp']['temp'])
 				ctrl.set_heatrate_soll(step['ramp']['rate'])

sude/sud_0010.json

@@ -3,14 +3,14 @@
 	"Description"		: "Rotfraenkisch, Dunkles Lager",
 	"pot_mass"		 	: 5.960,
 	"pot_material"		: "Edelstahl 18/10",
-	"grain_mass"		: 5.21,
-	"water_mass"		: 22,
 	"default":
 	{
 		"step" : {
 			"descr": "Put description here",
 			"user_message": "Put user message here",
 			"user_wait_for_continue": false,
+			"grain_mass"		: 5.21,
+			"water_mass"		: 22,
 			"ramp": {
 				"rate": 1.0,
 				"temp": 0,
@@ -33,6 +33,7 @@
 	"steps":
 	[
 		{
+			"grain_mass"		: 0,
 			"descr": "Heizen für Einmaischen",
 			"ramp":	{
 				"rate": 1.8,
@@ -101,6 +102,7 @@
 			}
 		},
 		{
+			"water_mass"		: 21,
 			"descr": "Halten Abmaischen",
 			"user_message": "Quittieren zum Abmaischen",
 			"user_wait_for_continue": true,