Usually the control system runs with a rather high frequency, that is, its period is low. If you want to log signals in the control system it is advisable to use a much lower frequency in order not to clog the output stream. This can be accomplished by defining a periodic function with the desired frequency and add it to the executor.

  Lambda l1 ([&] () { });
  Periodic periodic("per1", 1, l1);
  periodic.monitors.push_back([&](PeriodicCounter &pc, Logger &log){
    log.info() << controlSystem.myBlock.getOut().getSignal();
  });
 
  // and further down the code
  executor.add(periodic);

This will output the output of a chosen block once per second. The lambda function is necessary so that the periodic knows what to do, though it actually does nothing, as the function is empty.
For more complete examples see examples/controlsystem/BlockTest2 and examples/controlsystem/BlockTest3.