Single point calibration and investigations of thermosensitivity, thermal response time and long term stability of quartz temperature sensors

This paper presents the obtained results from the investigations of thermosensitivity; thermal response time and long-term stability of new miniaturized designs of thermosensitive quartz resonators with NLC-cut at fundamental frequency 29,3 MHz, used as high sensitive quartz temperature sensors (QTS). The comparison between thermal response time of the two types QTS01 (with plane parallel piezoelement) and QTS02 (with strip piezoelement) shows that QTS02 has shorter response time because of the smaller dimensions of the resonators. The frequency change does not exceed 3,5.10^-7 after the 40^th day of aging. This guarantees the reliable function of the sensor without additional recalibration in the next several years. Special attention is given to the methodology and equipment for single point calibration of QTS. The QTS are calibrated at ice point according to the requirements of ITS-90. Knowing the thermosensitivity the frequency-temperature dependence in the interval from minus 20°C to 120°C is approximated. Thermosensitivity in this range is calculated as 1125 Hz/°C. The expanded uncertainty, obtained by multiplying the standard uncertainty by a coverage factor k=2, in the temperature range from minus 20°C to 120°C is estimated as 0,24°C. This value could be in an order lower if a correction of the non-linearity is taken into account at every defined temperature point.