Thermal pollution is one of the most urgent issues in the fields of ultra-precision measurement and manufacturing, which presents the demand of producing ultra-precision circulating cooling water (CCW) with the temperature stability up to millikelvin level and response time at hundred-second level. In this paper, an ultra-precision CCW producing method based on model identification and fuzzy-PID control is proposed and illustrated. A structure of circulating water loop with ultra-precision temperature control is proposed. A cooling module using of thermoelectric cooling device arrays as refrigerator and a heating module using electrical heating-tubes as heater are employed. A control algorithm based on fuzzy-PID is designed, and a variety of model identification experiments has been carried out to extract key parameters of the modules. Experimental results show that a temperature stability up to ±3mK is achieved, the temperature control resolution is better than 5mK, and the adjusting time of 1K step is 128s, satisfying the urgent need of ultra-precision measurement and manufacturing.
During proposal and development of a new non-contact nano-probe based on tunneling effect, analysis of the bias electric field (BEF) distribution is a key step for modeling and characterization of the probe. However, the BEF between the spherical electrode serving as the probing ball and the surface to be measured has combined features of macro- and micro- dimensions, which makes the modeling of it a far tricky problem. In this paper, a modeling finite difference method (FDM) based on non-uniform grids generation according to the structural features of the BEF is proposed, and the field distribution is solved with high accuracy. The maximum relative calculation error is within 15% compared with calculation results for a bias electric field with regular boundary with analytical electric image method.
KEYWORDS: Sensors, Spherical lenses, Chemical elements, Algorithm development, Environmental sensing, Control systems, Thermal energy technology, Temperature metrology, Structural design, Fluctuations and noise
In order to solve the problem of thermal drift and further improve the performance for sensors with extreme demand for precision, based on analysis of shortcomings of existing compensation methods and characteristics of thermal drift, a novel active suppression technology against thermal drift is proposed. Considering the change of properties of reference elements in sensors caused by temperature variation is the most major factor that introduces thermal drift error, a special thermal structure is designed to provide a small environmental chamber with sub-structure design of high performance heat isolation, heat conduction and homogenization of temperature, and the temperature in the environmental chamber is controlled with high precision based on bilateral temperature adjusting with thermo electronic cooler (TEC) devices, and a compound control algorithm of Bang-Bang and anti-windup PID. Experimental results with an ultra-precision spherical capacitive sensor show thermal drift error is significantly eliminated and the precision of the sensor can reach the level of several resolutions.
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