consider the following:

Qt Code: 
  1. void FuelSystem::DSLFL_DataReceive(QByteArray data)
  2. {
  3.     /* 4)Lower sensor  5)upper Sensor  6)water sensor */
  4.  
  5.     QByteArray command_SV15;
  6.     QByteArray command_HV14;
  7.     QByteArray command_FTWL_SV9;
  8.  
  9.     if(data.at(3) == FUEL_SYSTEM)
  10.     {
  11.         if(data.at(4) == 0x01)
  12.         {
  13.             FuelPump_start();
  14.  
  15.             command_SV15.append(FUEL_SYSTEM);
  16.             command_SV15.append(DSLFL_ST_SV_15);
  17.             command_SV15.append(0x01);
  18.  
  19.             emit DSLFL_SendToRS485(command_SV15);
  20.             delay(_DELAY_MSEC);
  21.         }
  22.         else if(data.at(5) == 0x01)
  23.         {
  24.             FuelPump_stop();
  25.  
  26.             command_HV14.append(FUEL_SYSTEM);
  27.             command_HV14.append(DSLFL_HT_SV_14);
  28.             command_HV14.append((char) 0x00);
  29.  
  30.             emit DSLFL_SendToRS485(command_HV14);
  31.             delay(_DELAY_MSEC);
  32.         }
  33.  
  34.         if((data.at(6) == 0x01) && (pumpStat == OFF))
  35.         {
  36.             command_FTWL_SV9.append(FUEL_SYSTEM);
  37.             command_FTWL_SV9.append(DSLFLWaterEvacuate_SV_9);
  38.             command_FTWL_SV9.append(0x01);
  39.  
  40.             emit DSLFL_SendToRS485(command_FTWL_SV9);
  41.             delay(_DELAY_MSEC);
  42.  
  43.             waterEvacuateTimer->start();
  44.         }
  45.     }
  46. }
  47.  
  48. void FuelSystem::delay(int msec){
  49.     QEventLoop loop;
  50.     QTimer::singleShot(msec, &loop, NULL);
  51.     loop.exec();
  52. }
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As I send a packet to PLC, I need to delay for some time, waiting for the result of PLC operations. Here, I cannot use sleep() as it is a system call and it will suspend all other
QTimers and the whole program. what I want is to only delay the current particular thread or object for 2 seconds everytime I connect to PLC.

I hope this is clear now. : )