From b6551c6433f20dd7e0aad0132c35d61ab708e675 Mon Sep 17 00:00:00 2001
From: Jens Ahrensfeld <jens@jayfield.org>
Date: Fri, 19 Jun 2026 19:34:15 +0200
Subject: [PATCH] Derive Pot's M/C from pot/grain/water mass instead of
 hardcoding them

Add Sud.derive_plant_params(), which combines pot_mass/pot_material/
grain_mass/water_mass into a single lumped (mass, specific heat) pair
using approximate specific-heat constants for water, grain, and (by a
small material lookup table) the pot itself. demo_sud.py now builds
its plant_params from this instead of hardcoded C/M values, keeping
L/Td as the only manually-tuned plant parameters.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 components/sud.py             | 28 ++++++++++++++++++++++++++++
 scripts/demos/sud/demo_sud.py |  6 +++---
 sude/sud_0010.json            |  6 +++---
 3 files changed, 34 insertions(+), 6 deletions(-)

diff --git a/components/sud.py b/components/sud.py
index 6d99c9e..6dde2c2 100644
--- a/components/sud.py
+++ b/components/sud.py
@@ -2,6 +2,15 @@ import json
 from enum import Enum
 from utils.value import AttributeChange
 
+# Specific heat capacities [J/(kg*K)] used to derive a single lumped
+# (mass, specific heat) pair for the pot's contents from pot_mass/
+# grain_mass/water_mass. Approximate, typical values.
+SPECIFIC_HEAT_WATER = 4190
+SPECIFIC_HEAT_GRAIN = 1800
+SPECIFIC_HEAT_BY_MATERIAL = {
+	"Edelstahl 18/10": 500,
+}
+
 
 class SudState(Enum):
 	IDLE = 0
@@ -21,12 +30,31 @@ class Sud(AttributeChange):
 		self.description = data.get('Description', '')
 		self.schedule = data['schedule']
 
+		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
 		self.state = SudState.IDLE
 		self.step = None
 		self.user_message = None
 
+	def derive_plant_params(self):
+		"""Lumped (mass, specific heat) lifted from pot_mass/pot_material/
+		grain_mass/water_mass, for use as Pot's "M"/"C" params."""
+		c_pot = SPECIFIC_HEAT_BY_MATERIAL.get(self.pot_material, SPECIFIC_HEAT_WATER)
+		mass = self.water_mass + self.grain_mass + self.pot_mass
+		capacitance = (self.water_mass * SPECIFIC_HEAT_WATER
+			+ self.grain_mass * SPECIFIC_HEAT_GRAIN
+			+ self.pot_mass * c_pot)
+
+		return {
+			'M': mass,
+			'C': capacitance / mass if mass > 0 else SPECIFIC_HEAT_WATER,
+		}
+
 	def start(self):
 		if self.state != SudState.IDLE:
 			return
diff --git a/scripts/demos/sud/demo_sud.py b/scripts/demos/sud/demo_sud.py
index 802ce15..157a8c5 100644
--- a/scripts/demos/sud/demo_sud.py
+++ b/scripts/demos/sud/demo_sud.py
@@ -33,14 +33,14 @@ if __name__ == '__main__':
 		}
 	}
 
+	sud = Sud("sude/sud_0010.json")
+
 	plant_params = {
-		"C"			: 4190,
-		"M"			: 20,
+		**sud.derive_plant_params(),
 		"L"			: 0.2,
 		"Td"		: 30
 	}
 
-	sud = Sud("sude/sud_0010.json")
 	ctrl = TempController(dt, ctrl_params, plant_params, theta_amb)
 	plant = Pot(dt, plant_params, theta_amb)
 	stirrer = StirrerSim(dt)
diff --git a/sude/sud_0010.json b/sude/sud_0010.json
index fc3b0a6..7af1a18 100644
--- a/sude/sud_0010.json
+++ b/sude/sud_0010.json
@@ -1,10 +1,10 @@
 {
 	"Name" : "Sud-0010",
 	"Description"		: "Rotfraenkisch, Dunkles Lager",
-	"pot_weight_kg"		: 5.960,
+	"pot_mass"		 	: 5.960,
 	"pot_material"		: "Edelstahl 18/10",
-	"Schuettung_kg"		: 5.21,
-	"Wasser_kg"			: 22,
+	"grain_mass"		: 5.21,
+	"water_mass"		: 22,
 	"schedule":
 	[
 		{