diff --git a/thorlabs_apt/core.py b/thorlabs_apt/core.py
index bf6c629..9d1332d 100644
--- a/thorlabs_apt/core.py
+++ b/thorlabs_apt/core.py
@@ -1343,10 +1343,16 @@ def set_dc_settled_current_loop_parameters(self, settled_proportional,
     """DC settled current loop: fast forward"""
 
 
-def _load_library():
+_lib = None
+
+def load_library():
     """
     Loads the APT.dll shared library. Calls APTInit.
     """
+    global _lib
+    if _lib is not None:
+        # The library has already been loaded
+        return
     # load library
     if (os.name != 'nt'):
         raise Exception("Your operating system is not supported. " \
@@ -1370,17 +1376,20 @@ def _load_library():
                         "%s" % _get_error_text(err_code))
     if (lib.EnableEventDlg(False) != 0):
         raise Exception("Couldn't disable event dialog.")
+    # Store the library globally
+    _lib = lib
     return lib
 
-_lib = None
-_lib = _load_library()
+load_library()
 
 import atexit
 @atexit.register
-def _cleanup():
+def cleanup():
     """
-    Calls APTCleanUp
+    Calls APTCleanUp.
     """
+    global _lib
     if (_lib is not None):
         _lib.APTCleanUp()
+        _lib = None