fixes #86

hkl/diffract.py

@@ -200,6 +200,12 @@ def __init__(self, prefix, calc_kw=None, decision_fcn=None,
         self.energy.subscribe(
             self._energy_changed, event_type=Signal.SUB_VALUE)
 
+        self.energy_offset.subscribe(
+            self._energy_offset_changed, event_type=Signal.SUB_VALUE)
+
+        self.energy_units.subscribe(
+            self._energy_units_changed, event_type=Signal.SUB_VALUE)
+
     @property
     def _calc_energy_update_permitted(self):
         """return boolean `True` if permitted"""
@@ -223,9 +229,59 @@ def _energy_changed(self, value=None, **kwargs):
         if self._calc_energy_update_permitted:
             self._update_calc_energy(value)
 
+    def _energy_offset_changed(self, value=None, **kwargs):
+        """
+        Callback indicating that the energy offset signal was updated.
+
+        .. note::
+            The ``energy_offset`` signal is subscribed to this method
+            in the :meth:`Diffractometer.__init__()` method.
+        """
+        if not self.connected:
+            logger.warning(
+                (
+                    "%s not fully connected,"
+                    " '%s.calc.energy_offset' not updated"
+                ),
+                self.name, self.name)
+            return
+
+        # TODO: is there a loop back through _update_calc_energy?
+        # raise NotImplementedError(f"units = {self.energy_units.get()}")
+        try:
+            energy = pint.Quantity(
+                self.calc.energy, "keV"
+            ).to(
+                self.energy_units.get()
+            )
+        except Exception as exc:
+            raise NotImplementedError(f"units = {self.energy_units.get()}: {exc}")
+        self.energy.put(energy.magnitude - value)
+
+    def _energy_units_changed(self, value=None, **kwargs):
+        """
+        Callback indicating that the energy units signal was updated.
+
+        .. note::
+            The ``energy_units`` signal is subscribed to this method
+            in the :meth:`Diffractometer.__init__()` method.
+        """
+        if not self.connected:
+            logger.warning(
+                (
+                    "%s not fully connected,"
+                    " '%s.calc.energy_units' not updated"
+                ),
+                self.name, self.name)
+            return
+
+        # TODO: is there a loop back through _update_calc_energy?
+        energy = pint.Quantity(self.calc.energy, "keV").to(value)
+        self.energy.put(energy.magnitude - self.energy_offset.get())
+
     def _update_calc_energy(self, value=None, **kwargs):
         """
-        writes self.calc.energy from value or self.energy
+        writes ``self.calc.energy`` from ``value`` or ``self.energy``.
         """
         if not self.connected:
             logger.warning(
@@ -234,7 +290,7 @@ def _update_calc_energy(self, value=None, **kwargs):
             return
 
         # use either supplied value or get from signal
-        value = value or self.energy.get()
+        value = float(value or self.energy.get())
 
         # energy_offset has same units as energy
         value += self.energy_offset.get()

hkl/tests/test_diffract.py

@@ -142,3 +142,27 @@ def test_energy_units(fourc):
         .magnitude,
         fourc.energy.get(),
     )
+
+    fourc.energy_units.put("keV")
+    fourc.energy.put(8)
+    fourc.energy_offset.put(0.015)
+    assert fourc.calc.energy == 8.0
+    assert round(fourc.energy.get(), 6) == 7.985
+    fourc.energy.put(8)
+    assert fourc.calc.energy == 8.015
+    assert round(fourc.energy.get(), 6) == 8
+
+    # issue #86
+    # changing units or offset changes .energy, not .calc.energy
+    fourc.energy_units.put("eV")
+    assert fourc.calc.energy == 8.015
+    assert round(fourc.energy.get(), 1) == 8015
+    fourc.energy.put(8000)
+    assert round(fourc.calc.energy, 8) == 8.000015
+    assert round(fourc.energy.get(), 1) == 8000
+    fourc.energy_offset.put(15)
+    assert round(fourc.calc.energy, 8) == 8.000015
+    assert round(fourc.energy.get(), 1) == 7985
+    fourc.energy.put(8000)
+    assert round(fourc.calc.energy, 8) == 8.015
+    assert round(fourc.energy.get(), 1) == 8000