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| | Description of Thermal System | Heat a tank containing 2 kg of chemical solution from 20°C to 50°C in 10 minutes. The space available for mounting the heater is 4" x 5" (102 x 127 mm). Input voltage is 120 VAC. | Heat moving film in a thermal processor. A sheet of polyester film weighing 5 g must be brought from 25°C to 90°C every 2 seconds. The heater will measure 2" x 12" (51 x 305 mm) and will be mounted on a metal platen. Input voltage is 120 VAC. | An LCD heater must be capable of bringing the 6" x 8" (152 X 203 mm) display from-55°C to 0°C in 5 minutes and maintaining it there. Input voltage is 120 VDC. | |
| | Wattage requirements | From Thermal Calc*, we need 450 watts minimum for warmup plus losses. | From Thermal Calc*, we need 275 watts minimum for warmup plus losses. | From Thermal Calc*, we need 50 watts for warmup and 20 watts for maintenance of temperature. | |
| | Electrical parameters | R = E7W = 1207450 = 32 Q | R = E2/W = 1207275 = 52 Q | R = E2/W = 282/50 = 16 Q | |
| | Heater selection | Choosing polyimide for chemical resistance, the best choice is HK5490R27.7L12E | Specifying silicone rubber for lower cost, the best choice is HR5433R44.1L12A | From Minco's standard Thermal-Clear™ heaters we choose model H6709R14.8L12B | |
| | Actual wattage | Wattage is 120727.7 = 520 W | Wattage is 1202/44.1 = 32 7 W | Wattage is 282/14.8 = 53 W | |
| | Watt density | Watt density = W/effective area = 520/17.74 in2 = 29 W/in2 (4.5 W/cm2) | Watt density = W/effective area = 327/21.80 in2 = 15 W/in2 (2.3 W/crrf) | Watt density = W/effective area = 53/48 in2 = 1.1 W/in2 (0.2 W/crrf) | |
| | Installation | From watt density charts we specify Acrylic PSA with aluminum backing (E option). This is rated to 31 W/in2 (4.8 W/crrf) at 50°C. | Any type of heater mounting will handle the watt density. We will factory vulcanize the heater for lowest installed cost. | We choose Acrylic PSA backing for convenience (B option). The watt density is well within the rated maximum. | |
| | Leadwire current | AWG 24 leadwire current rating is 7.5 A. Actual current is: I = 120/27.7 = 4.3 A (OK). | AWG 24 leadwire current rating is 7.5 A. Actual current is: I = 120/44.1 = 2.7 A (OK). | AWG 30 leadwire current rating is 3 A. Actual current is: I = 28/14.8 = 1.9 A (OK). | |
| | Control | | The customer integrates a custom controller into other electronic circuits. | A CT198-1005 Heaterstat™ will control the heater. Its setpoint will be adjustable from 6 to 62°C. We have chosen a model with a higher range in order to ensure that the LCD itself reaches 0°C. We know the setpoint will have to be higher because it controls the heater element which runs hotter than the surface beneath it. | |
| | Sensor | An S665 Thermal-Tab™ RTD will be mounted to the side of the tank. | An S247 thin-film RTD will be potted into a hole in the platen. A thermostat with 100°C setpoint will provide overtemperature shutoff. | None: The heater acts as the sensor! | |
| | Custom options | An AP heater would provide a higher watt density for faster warmup (at higher cost). A rubber or mica heater would allow more watts for faster warmup, if acceptable in the application. | The sensor and thermostat could be integrated into the heater. | Placing the lead connections on an external tab would remove the lead bulge from the display area. Switching to a sensor and CT325 for control, instead of the Heaterstat, would allow higher wattage and finer control. | |
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