In this master’s thesis, we are faced with the problem of making an accurate and long-term stable dew point meter in a compressed air system. We present the design and production of two pilot dew point meter prototypes using an analog sensor element P14 2FW Thermo. It is currently the only element available on the market suitable for making such a meter. The element consists of a capacitive relative humidity sensor and a resistive (Pt-100) temperature sensor. The first prototype was intended to test the sensor element and observe its response to changing humidity. The results showed that the sensor element has a good response time to humidity changes, but poor repeatability. Consequently, the need for frequent calibration of the meter due to measurement creep emerged. Since the initial measurement system used to observe the performance of the first prototype was too sensitive, we built a new, more robust test environment to perform measurements. In the second prototype, the noise that was observed in the measurements of the first prototype was eliminated by more suitable structure of the meter. Further, by implementing an auto-calibration protocol that was patented in 1991 by a major manufacturer of similar devices, we tried to eliminate the creep. The selected protocol requires the sensor element to be heated to a high temperature (around 150 °C) for a short period of time during which it dries completely. Thus, the capacitance of the relative humidity sensor in a completely dry air can be defined. It turned out that such an implementation of the meter is not feasible with the selected sensor element since the sensor is not robust enough.
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