| 摘要 |
<p>In a LOW range of operation a heater element L1 is energised via an adjustable energy regulator and an element L2 is not energised, whereas in a HIGH range element L1 is energised continuously and element L2 is energised via the regulator. Elements L1, L2 may be of thick film material deposited on the underside of a ceramic hot plate, the resistance of L1 being twice that of L2. The control arrangement reduces inrush current problems associated with the high temperature coefficient of resistivity of such elements. A thermal relay may be provided to prevent energisation of element L2 before the hotplate has been warmed by element L1. The energy regulator may have a shaft carrying cams to operate switches S1 to S4 and a regulator adjustment cam, the cams being shaped so that the regulator progresses to full power energisation of element L1 over the first 180 DEG of rotation, then switches element L1 to full power and connects element L2 to the regulator whereby further rotation to 270 DEG increases energisation of element L2 from zero to full power. A stop on the cam shaft may prevent it being turned directly from OFF to the HIGH range. <IMAGE></p> |
