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The design of temperature‐compensated quartz crystal oscillators (TCXOs) in thick film hybrid technology is described. TCXOs controlled by varicap diodes are usually…
The design of temperature‐compensated quartz crystal oscillators (TCXOs) in thick film hybrid technology is described. TCXOs controlled by varicap diodes are usually realised with discrete NTC thermistors and resistors. Data obtained by precision measurements of voltages on varicap diodes for the same oscillator frequencies over the operating temperature range are used for calculating values of the NTC thermistors and resistors. In most cases these values cannot be found in the Renard scale, with the result that manipulation or ‘juggling’ of values is necessary. The realisation of temperature‐compensating circuits in thick film technology has certain advantages, such as miniaturisation, better characteristics at high frequencies and in particular the possibility to trim thick film resistors and NTC thermistors to values calculated for each oscillator. The method of realisation of TCXOs in thick film hybrid technology was developed and verified on prototypes. The compensation curves were obtained by measuring compensation voltages for each oscillator over the operating temperature range from — 20°C to 70°C. From these data the values of resistors and NTC thermistors were calculated. A computer program was used to minimise frequency instability error as a function of six parameters (resistance). The frequency stability (Δf/f) of TCXOs obtained was better than ±2 ppm.
This study shows the effects of aging on epoxy‐based rapid tooling materials. Two epoxy‐acrylate resins used for stereolithography and one aluminum powder‐filled epoxy…
This study shows the effects of aging on epoxy‐based rapid tooling materials. Two epoxy‐acrylate resins used for stereolithography and one aluminum powder‐filled epoxy used for the high‐speed machining of plastic injection molds were selected to investigate their aging behavior in different environments. Four different conditions, each characterized by a specific relative humidity, were used to perform a seven week long aging study. Temperature was kept a constant at 30°C. Both the stereolithographic resins showed a drop in mechanical properties and in their glass transition temperatures in wet environments, whereas aging time showed little influence on these properties after an initial induction phase. Moisture uptake is mainly responsible for this drop and the coefficients of water diffusion were determined in this process. On the other hand, the aluminum powder‐filled epoxy showed little humidity‐dependent drop in mechanical properties and in its glass transition temperature during aging. A simple empirical model that only takes into account the moisture uptake was developed.