Fix initialization

camrasdevices.py

@@ -4,27 +4,26 @@ from astropy.units import Quantity
 import hpib
 import serial.threaded
 
-command_thread = None
-
 
 class CamrasHpibDevice(object):
     """Wrapper around HPIB commands"""
 
+    command_thread = None
+
     def __init__(self, address):
-        if not command_thread.is_alive():
-            command_thread.start()
         self.hpib_address = address
 
-        if not command_thread:
+        if not CamrasHpibDevice.command_thread:
             serial_port = serial.Serial("/dev/ttyUSB0")
-            command_thread = serial.threaded.ReaderThread(serial_port, hpib.GPIBProtocol)
-            command_thread.protocol.init_hpib()
+            CamrasHpibDevice.command_thread = serial.threaded.ReaderThread(serial_port, hpib.GPIBProtocol)
+            CamrasHpibDevice.command_thread.start()
+            CamrasHpibDevice.command_thread.protocol.init_hpib()
 
     @property
     def frequency(self):
         """Returns the frequency of the device as an astropy Quantity.
         Throws a RuntimeError if no response"""
-        freq_str = command_thread.protocol.command("freq?", address=self.hpib_address)
+        freq_str = CamrasHpibDevice.command_thread.protocol.command("freq?", address=self.hpib_address)
         if len(freq_str)==0:
             raise RuntimeError("Camras device at address {} is not responding".format(self._hpib_address))
         return int(float(freq_str)) * u.Hz
@@ -38,7 +37,7 @@ class CamrasHpibDevice(object):
         """
         if isinstance(freq, Quantity):
             freq = freq.to(u.Hz).value
-        command_thread.protocol.command("freq {:d} Hz".format(int(freq)), address=self.hpib_address)
+        CamrasHpibDevice.command_thread.protocol.command("freq {:d} Hz".format(int(freq)), address=self.hpib_address)
         new_freq = self.frequency
         if new_freq.to(u.Hz).value != int(freq):
             raise RuntimeError("Setting frequency failed: tried to set to {}, it is now {}".format(