title: OpenOPC tag activation?
body: <p>I'm trying to use OpenOPC as a client to connect to an OPC server generated thanks to Dymola.</p>
  
  <p>What I can't figure out is the way to read from a particular tag. </p>
  
  <p>Some tags are available ('SimControl') and others are not ('ModelVariables') whereas those tags should be available after server Initialization.</p>
  
  <p>Is there a way to activate tags in the same way that what is it done in Matrikon Explorer.</p>
  
  <p>Here is the code that I used :</p>
  
  <pre><code># -*- coding: utf-8 -*-
  """
  Created on Fri Feb 06 09:48:09 2015
  Simple test to connect to the Dymosim server generated with Dymola
  """
  
  import os,sys
  import time,OpenOPC
  
  #%% Connexion to server
  opcserv='Dymosim.OPCServer'
  
  opc = OpenOPC.client()
  opc.connect(opcserv)
  
  #%% Tags description in a dictionnary form
  
  # Following tags are for simulation control 
  # and are available as soon as the client is connected to the server
  root1='SimControl.'
  l1=['Realtime','tScale',
  'Initialize','Pause','Run','Stop',
  'Delay','Initialized','Time','Status']
  Sim={t:root1+t for t in l1}
  
  # Following tags are for variables display during simulation.
  # They should be available after the simulation was "Initialize"
  root2='ModelVariables.'  # Available once the model has been initialized
  v1=['heatCapacitor.port.T','heatCapacitor.port.Q_flow']
  l2=['T','Q']
  Var={k:root2+v for (k,v) in zip(l2,v1)}
  
  
  #%% Simulation
  # Initialization of the simulation
  opc.write((Sim['Initialize'],True))
  
  #%% Run the simulation
  opc.write((Sim['Run'],True))
  
  # Pause simulation after 2 s
  time.sleep(2)
  opc.write((Sim['Pause'],True)) 
  
  #%% Read variables
  opc.read(Sim['Time']) # OK
  opc.read(Var['T'])       # Seems not accessible. Quality is bad
  opc.list() # The 2 tags appear (SimControl and ModelVariables)
  
  #%% Run the simulation until the end
  opc.write((Sim['Run'],True))
  </code></pre>
  
  <p>Many thanks for any help.</p>