diff --git a/slic/devices/general/detectors/pvdatastream.py b/slic/devices/general/detectors/pvdatastream.py
index 4e8e6ff6..b8939967 100644
--- a/slic/devices/general/detectors/pvdatastream.py
+++ b/slic/devices/general/detectors/pvdatastream.py
@@ -5,63 +5,89 @@ class PvDataStream:
         self._pv = PV(ID)
         self.name = name
 
-    def collect(self, seconds=None, samples=None):
-        if (not seconds) and (not samples):
-            raise Exception("Either a time interval or number of samples need to be defined.")
-        try:
-            self._pv.callbacks.pop(self._collection["ix_cb"])
-        except:
-            pass
-        self._collection = {"done": False}
-        self.data_collected = []
-        if seconds:
-            self._collection["start_time"] = time()
-            self._collection["seconds"] = seconds
-            stopcond = lambda: (time() - self._collection["start_time"]) > self._collection["seconds"]
 
-            def addData(**kw):
-                if not stopcond():
-                    self.data_collected.append(kw["value"])
-                else:
-                    self._pv.callbacks.pop(self._collection["ix_cb"])
-                    self._collection["done"] = True
-
-        elif samples:
-            self._collection["samples"] = samples
-            stopcond = lambda: len(self.data_collected) >= self._collection["samples"]
-
-            def addData(**kw):
-                self.data_collected.append(kw["value"])
-                if stopcond():
-                    self._pv.callbacks.pop(self._collection["ix_cb"])
-                    self._collection["done"] = True
-
-        self._collection["ix_cb"] = self._pv.add_callback(addData)
-        while not self._collection["done"]:
-            sleep(0.005)
-        return self.data_collected
 
     def acquire(self, hold=False, **kwargs):
         _acquire = lambda: self.collect(**kwargs)
         return Task(_acquire, hold=hold)
 
+
+
+    def collect(self, seconds=None, samples=None):
+        if seconds is None and samples is None:
+            raise ValueError("Either a time interval or number of samples need to be defined.")
+
+        if not hasattr(self, "_collection"):
+            self._accumulate = {"n_cb": None}
+
+        self._pv.callbacks.pop(self._collection["n_cb"], None)
+
+        self._collection = {"done": False}
+
+        self.data_collected = []
+
+        if seconds:
+            stopcond = mk_collect_seconds_stopcond(seconds)
+        elif samples:
+            stopcond = mk_collect_samples_stopcond(samples)
+
+        def addData(value=None, **kwargs):
+            self.data_collected.append(value)
+            if stopcond():
+                self._pv.callbacks.pop(self._collection["n_cb"])
+                self._collection["done"] = True
+
+        self._collection["n_cb"] = self._pv.add_callback(addData)
+
+        while not self._collection["done"]:
+            sleep(0.005)
+
+        return self.data_collected
+
+
+
+    def mk_collect_seconds_stopcond(self, seconds):
+        self._collection["start_time"] = time()
+        self._collection["seconds"] = seconds
+        return lambda: (time() - self._collection["start_time"]) > self._collection["seconds"]
+
+
+
+    def mk_collect_samples_stopcond(self, samples):
+        self._collection["samples"] = samples
+        return lambda: len(self.data_collected) >= self._collection["samples"]
+
+
+
     def accumulate(self, n_buffer):
         if not hasattr(self, "_accumulate"):
-            self._accumulate = {"n_buffer": n_buffer, "ix": 0, "n_cb": -1}
-        else:
-            self._accumulate["n_buffer"] = n_buffer
-            self._accumulate["ix"] = 0
-        self._pv.callbacks.pop(self._accumulate["n_cb"], None)
-        self._data = np.squeeze(np.zeros([n_buffer * 2, self._pv.count])) * np.nan
+            self._accumulate = {"n_cb": None}
 
-        def addData(**kw):
-            self._accumulate["ix"] = (self._accumulate["ix"] + 1) % self._accumulate["n_buffer"]
-            self._data[self._accumulate["ix"] :: self._accumulate["n_buffer"]] = kw["value"]
+        self._pv.callbacks.pop(self._accumulate["n_cb"], None)
+
+        self._accumulate["n_buffer"] = n_buffer
+        self._accumulate["ix"] = 0
+
+        shape = (n_buffer * 2, self._pv.count)
+        self._data = np.squeeze(np.zeros(shape)) * np.nan
+
+        def addData(value=None, **kwargs):
+            index = self._accumulate["ix"] + 1
+            n_buffer = self._accumulate["n_buffer"]
+            self._accumulate["ix"] = index % n_buffer
+
+            start = self._accumulate["ix"]
+            step = self._accumulate["n_buffer"]
+            self._data[start :: step] = value
 
         self._accumulate["n_cb"] = self._pv.add_callback(addData)
 
+
+
     def get_data(self):
-        return self._data[self._accumulate["ix"] + 1 : self._accumulate["ix"] + 1 + self._accumulate["n_buffer"]]
+        start = self._accumulate["ix"] + 1
+        stop  = start + self._accumulate["n_buffer"]
+        return self._data[start:stop]
 
     data = property(get_data)