HEATER ELEMENT LIFE CURVE
Tutco SureHeat air heater element life is directly related to the filament wire temperature. The graph below illustrates that 5000 hours of air heater life is obtainable, if the filament temperature remains below 1900°F. PLEASE ALSO REALIZE THAT THE HEATER ELEMENT DOES NOT FAIL UNTIL IT REACHES MORE THAN 2200°F.
HEATER PERFORMANCE CURVE
The Tutco SureHeat air heater element’s temperature is controlled by the airflow and applied voltage. Click here to see the Threaded Inline Air Heater’s performance curve showing the safe operating airflow rates and voltages.
HOW TO PREVENT TEMPERATURES ABOVE 1900°F
Because the heater element has an extremely high watt density, a fast closed-loop controller and adequate voltage control are required for safe operation. Please note the following process recommendations from Tutco SureHeat/Osram Sylvania:
- Ensure airflow is always turned on BEFORE and AFTER the heater is powered on or off. Air pressure switches can be utilized for this purpose.
- Use a type K thermocouple with an exposed junction, and locate the thermocouple within 1″ of the heater’s air outlet.
- Using a temperature controller with a 100 ms or faster cycle time to ensure fast response to changing process conditions. Be sure the power controller and solid state relay are equally fast in regulating the AC voltage to the heater.
- Start the heater with a 70°F (Ambient) or 0°C Set-Point (SV) to ensure the output signal to the power controller starts off low (0% Output) before the contactor is engaged and immediately applies full power.
- Tutco SureHeat/Sylvania recommends using the following closed loop Proportional, Integral and Derivative (PID) settings as a starting point for stable temperature control. Some manual tuning may be required for even more precise process control:
- Include a controller ramp rate for starting up the air heater element. The slower the controller ramps up to the final set-point, the less likely the process will have temperature overshooting problems. It is recommended the Tutco SureHeat air heaters are ramped up to the desired set-point temperature over a period of several minutes. The following are basic ramp rate recommendations based on the final required set-point temperature, but Tutco SureHeat/Sylvania technical support can be contacted for custom temperature ramp rates:
|SET-POINT TEMPERATURE||DEGREES PER MINUTE|
|Up to 600°F (300°C)||360°F (150°C)|
|601-1000°F (301-500°C)||240°F (100°C)|
|1001-1400°F (501-760°C)||120°F (50°C)|
|Up to 1650°F (900°C)||60°F (25°C)|
- Reduce the high limit value output of the temperature controller. Usually the default high limit value is 100%, but this value can be reduced since most air heaters are oversized in wattage for the application. 100% power output normally isn’t necessary to achieve the desired process set-point temperature. The heater can be manually controlled to determine the approximate fixed output that is required from the power controller for achieving the desired set-point temperature. This determined value can then be set as the high limit output for the temperature controller.