improve dt unit handling

Author: kain88-de

package/MDAnalysis/coordinates/DCD.py

@@ -118,7 +118,8 @@ def __init__(self, filename, convert_units=True, **kwargs):
         self.n_atoms = self._file.n_atoms
 
 
-        dt = self._file.delta
+        delta = mdaunits.convert(self._file.delta, self.units['time'], 'ps')
+        dt = delta * self._file.nsavc
 
         self.ts = self._Timestep(self.n_atoms, **self._ts_kwargs)
         frame = self._file.read()
@@ -194,6 +195,10 @@ def _frame_to_ts(self, frame, ts):
 
         return ts
 
+    @property
+    def dt(self):
+        return self.ts.dt
+
 
 class DCDWriter(base.WriterBase):
     """Base class for libmdaxdr file formats xtc and trr"""