Based On Quartz Digital Telemetric Temperature Sensor System Design

With the rapid development of industry, the temperature, which is one of the most important elements in industry, its measurement is strictly demanded. We hope that we could measure the temperature fleetly and accurately in the most situations. Especially there are some situations without human being entrance.Quartz crystal sensor is rapid developed for its high resolution. But up to now, there is no industrialization of high resolution sensor made by quartz crystal in our country yet. So, the research of digital and small quartz crystal sensor of temperature is more and more important.In this paper, we expounded the theory of temperature sensor which was made by the quartz crystal. With the Christoffel equation, we draw the F-T characteristics of the thickness mode of YXL+5°anisotropy quartz crystal. The result shows that its frequency is in direct proportion to temperature in a wide temperature range and its sensitivity is about 94×10^-6/℃. The simulation result shows the error is less then 2.8‰℃whenΔT =100℃. As high Q characteristic of quartz crystal, sensors made by these crystals are of high accuracy, high stability and high resolution. Moreover, since outputs of these sensors are frequency signals, it is convenient to process without A/D converter.Then, a digital telemetry thermometer is developed, which includes a sensor, a mixer, a sender and a receiver. The sensor is made of a YXL+5°anisotropy quartz crystal. It gets current ambiance temperature T and exports the frequency signal f (T ) to the mixer, which outputs a lower frequency. It is low enough for microprocessor AT89S52 to calculate its periods in sampling time. Then, the calculation result N will be converted to ambiance temperature T through serial calculations according to the mathematic model. T is written into the sender nRF401 and transmitted to the receiver. In receiver, T is shown on the LCD.The experimental result shows that the resolution reaches 0.001℃and their effective communication distance reaches 50 meters. It implies that this method is right and effective. And it realizes the telemetry of temperature. As description, this thermometer is useful for industrial detection as well as some special situations without human being entrance.