Shortening Thermal Balance Tests hy Heater Power Regulation

摘要

Equations are presented that give the optimum timing for changing the heater power during a transient cooling or heating phase, to minimize the duration of the subsequent steady-state phases. For these steady-state phases caloric mean equilibrium temperatures are calculated. The heater power is altered when these mean temperatures are measured during the transient phases. Predicted and measured temperature time gradients at the beginning of the first cooling phase are used to consider model uncertainties, which cause the measured equilibrium temperatures to differ from the predicted ones. Examples demonstrate that the test times can be reduced drastically. Power switching was performed when the .predicted steady-state temperature was reached and according to the new procedure. The total test tunes were reduced by a factor between 31 and 50. The same deviation of approximately 0.1 K between transient and steady-state temperatures was used comparing the two methods. For the HUYGENS probe the calculated test time was reduced from 306 to 120 h due to the new method, by which the power was switched on 3 h later than by the usually applied method. Proposals for the sequence of thermal balance tests and the content of work sheets are given.