HEATER STARTS
BUT
DOES NOT MAINTAIN TEMPERATURE PROPERLY
There are many factors which affect the proper temperature control of your heater, these factors include but are not limited to:
Tuning constants in the temperature controller.
Proper operation of the air and fuel control valves.
The correct air and fuel ratio delivered to the burner.
Product flow conditions.
TUNING CONSTANTS - The control loop on a heater can be difficult to tune. These loops are generally much slower acting than flow control loops. If the difficulty you are experiencing is that the heater generates to much heat (overshoot) at some times and to little heat at other times (undershoot), this can be cleaned up by using the correct tuning constants. The slow acting temperature control loops which are common to these heaters typically require use of all three PID constants. The heater responds to firing rate changes in minutes not seconds therefore tuning these loops to get the best performance requires time and patience. If your controller has automatic tuning features they will provide you with the quickest way to get your system tuned. If your controller does not have self tune capabilities and you need a starting point to work from review your requirement and choose from the selections in the chart below.
| Faster Response to Change ß ß ß | à à à Tighter Temperature Control |
|||
| Proportional (Gain) | 4 |
5 |
10 |
20 |
| Integral (Reset) | 1.5 |
5 |
10 |
20 |
| Derivative (Rate) | 0.1 |
2.5 |
5 |
10 |
CONTROL VALVE OPERATION - The actuator on your heater must travel properly in response to the control signal from the temperature controller. On a heater which has an electric actuator the travel (as viewed from the power end of the actuator) should be 90 degrees of motion where a 4mA signal represents the furthest counterclockwise position and 20mA signal represents the furthest clockwise position. On a heater which has a pneumatic actuator, the actuator arm should be fully retracted when provided with a 3 PSI control signal and fully extended when provided with a 15 PSI control signal. If the actuator will not demonstrate full and proper travel the heater will not be able to properly control to the desired temperature. The actuator must be repaired or replaced before proper control can be achieved.
AIR FUEL RATIO - For the heater to achieve it’s peak performance it is critical that the right amount of fuel be delivered to the burner along with the proper amount of air. If the amount of fuel being delivered to the heater is to little or to great the heater may not be able to perform to the design specifications of that heater. Included in the operations and maintenance manual supplied with the heater is a section titled Final Heater Adjustment. This section should provide you with the information on how to perform the air/fuel ratio adjustments required to achieve peak performance from your heater. These procedures call for the use of equipment which you may not have available to you. Thermoflux does provide field services to perform these adjustments. Contact the service department at Thermoflux for specifics.
PRODUCT FLOW CONDITIONS - Each of our heaters is designed to meet specific demands with regard to flow rate and temperature as well as type of product to be heated. Specific listings for flow rate, heater inlet temperature, heater outlet temperature and the material to be heated can be found on the pages in the front of the operations and maintenance manual supplied with the heater. If your product type, temperatures, or flow rate conditions do not match those criteria the heater may not be able to perform the heating task that you require. If you need to deviate from the original specifications, contact one of our sales engineers and they should be able to advise you if the heater can or can not perform to your new specifications.
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