Does it have an old percentage input timer? Or something more modern with a thermocouple that reads from the elements? Percentage input timers run on a cycle, I seem to remember 30 second cycles; if set at 50%, then it's on for 15 seconds, and off for 15 seconds. This can make for some temperature swings... A thermocouple sends it reading directly to the controller and your temperature remains constant, or should anyway. After you get that settles, then belt speed is next. The right belt speed and temperature is the combination you're looking for. I hope this helps a little.
Steve