diff --git a/src/fastcs/demo/controllers.py b/src/fastcs/demo/controllers.py
index 5926fc8ce..b39937eee 100755
--- a/src/fastcs/demo/controllers.py
+++ b/src/fastcs/demo/controllers.py
@@ -8,7 +8,7 @@
 
 from fastcs.attributes import AttributeIO, AttributeIORef, AttrR, AttrRW, AttrW
 from fastcs.connections import IPConnection, IPConnectionSettings
-from fastcs.controllers import Controller
+from fastcs.controllers import Controller, ControllerVector
 from fastcs.datatypes import Enum, Float, Int, Waveform
 from fastcs.logging import logger
 from fastcs.methods import command, scan
@@ -80,15 +80,16 @@ def __init__(self, settings: TemperatureControllerSettings) -> None:
 
         self._settings = settings
 
-        self._ramp_controllers: list[TemperatureRampController] = []
-        for index in range(1, settings.num_ramp_controllers + 1):
-            controller = TemperatureRampController(index, self.connection)
-            self._ramp_controllers.append(controller)
-            self.add_sub_controller(f"R{index}", controller)
+        self.ramps = ControllerVector(
+            {
+                index: TemperatureRampController(index, self.connection)
+                for index in range(1, settings.num_ramp_controllers + 1)
+            }
+        )
 
     @command()
     async def cancel_all(self) -> None:
-        for rc in self._ramp_controllers:
+        for rc in self.ramps.values():
             await rc.enabled.put(OnOffEnum.Off, sync_setpoint=True)
             # TODO: The requests all get concatenated and the sim doesn't handle it
             await asyncio.sleep(0.1)
@@ -118,14 +119,14 @@ async def update_voltages(self):
 
         await self.voltages.update(voltages)
 
-        for index, controller in enumerate(self._ramp_controllers):
+        for index, controller in self.ramps.items():
             self.log_event(
                 "Update voltages",
                 topic=controller.voltage,
                 query=query,
                 response=voltages,
             )
-            await controller.voltage.update(float(voltages[index]))
+            await controller.voltage.update(float(voltages[index - 1]))
 
 
 class TemperatureRampController(Controller):
diff --git a/tests/demo/test_controllers.py b/tests/demo/test_controllers.py
new file mode 100644
index 000000000..bd7775bdf
--- /dev/null
+++ b/tests/demo/test_controllers.py
@@ -0,0 +1,60 @@
+from unittest.mock import AsyncMock
+
+import numpy as np
+import pytest
+
+from fastcs.connections import IPConnectionSettings
+from fastcs.controllers import ControllerVector
+from fastcs.demo.controllers import (
+    OnOffEnum,
+    TemperatureController,
+    TemperatureControllerSettings,
+    TemperatureRampController,
+)
+
+
+@pytest.fixture
+def controller() -> TemperatureController:
+    settings = TemperatureControllerSettings(
+        num_ramp_controllers=4,
+        ip_settings=IPConnectionSettings(ip="localhost", port=25565),
+    )
+    controller = TemperatureController(settings)
+    controller.post_initialise()
+    return controller
+
+
+def test_ramps_is_controller_vector(controller: TemperatureController):
+    assert isinstance(controller.ramps, ControllerVector)
+    assert list(controller.ramps) == [1, 2, 3, 4]
+    for index, ramp in controller.ramps.items():
+        assert isinstance(ramp, TemperatureRampController)
+        assert controller.ramps[index] is ramp
+
+
+@pytest.mark.asyncio
+async def test_cancel_all_disables_every_ramp(controller: TemperatureController):
+    puts = {}
+    for index, ramp in controller.ramps.items():
+        puts[index] = AsyncMock()
+        ramp.enabled.put = puts[index]  # type: ignore[method-assign]
+
+    await controller.cancel_all()
+
+    for put in puts.values():
+        put.assert_awaited_once_with(OnOffEnum.Off, sync_setpoint=True)
+
+
+@pytest.mark.asyncio
+async def test_update_voltages_updates_waveform_and_each_ramp(
+    controller: TemperatureController,
+):
+    controller.connection.send_query = AsyncMock(return_value="[1, 2, 3, 4]\r\n")
+
+    await controller.update_voltages()
+
+    np.testing.assert_array_equal(
+        controller.voltages.get(), np.array([1, 2, 3, 4], dtype=np.int32)
+    )
+    for index, ramp in controller.ramps.items():
+        assert ramp.voltage.get() == pytest.approx(float(index))