| 摘要 |
<p>A thermally insulated substrate, e.g. a system of pipes, is maintained above a selected minimum temperature by means of one or more electrical heaters, preferably elongate self-regulating heaters. Each heater is successively switched on for a heat-up period and then off for a cool-down period. The durations of these periods are successively determined by reference to the ambient air temperature adjacent the substrate at an earlier time, e.g. at the end of the previous cool-down period. The method is particularly useful for temperature-maintenance systems in which a number of heaters are used to heat a complex system of pipes. The durations of the heat-up and cool-down periods for each heater (or for a group of two or more heaters) are separately determined by means of a single microprocessor. The microprocessor (a) is linked to an ambient air temperature sensor; (b) contains in its memory the relevant information about each heater, the pipes which it heats, and the thermal insulation surrounding the pipes; (c) is programmed to calculate the durations of the heat-up and cool-down periods; and (d) is linked to a number of switching means, one for each heater or group of heaters.</p> |
