Throw error if device is off

camrasdevices.py

@@ -11,12 +11,16 @@ class CamrasHpibDevice(HpibDevice):
 
     @property
     def frequency(self):
-        """Returns the frequency (in Hz) of the receiver"""
+        """Returns the frequency (in Hz) of the device. Throws a RuntimeError if no response"""
+        freq_str = self.query("freq?")
+        if len(freq_str)==0:
+            raise RuntimeError("Camras device at address {} is not responding".format(self._hpib_address))
         return int(float(self.query("freq?")))
 
     @frequency.setter
     def frequency(self, freq):
-        """Set the receiver to the specified frequency. Throws a RuntimeError if failed"""
+        """Set the device to the specified frequency. Throws a RuntimeError if failed"""
+        print("setting frequency to", freq)
         self.command("freq {:d} Hz".format(int(freq)))
         new_freq = self.frequency
         if new_freq != freq: