Actofit tracker takes heart rate measurement at an interval of every 5 minutes. Generally heart rate measurements (continuous) are initiated when the user is on the Heart Rate screen and after a good quality signal is found. This typically takes 10-20 secs depending on the user. If you are not getting heart rate, try removing and wearing the band again. You need to wait for some time again (10-20 secs) for the heart rate sensor to pick up the heart rate signal.
If wrist is having sweat please remove band clean your wrist wear band again to get accurate Heart rate.