Development of High-pressure Viscometer for Lubricating Oils using Torsionally Oscillating Quartz Crystal.

传感器采用直径为5 mm、长度为50 mm的X切石英晶棒。用真空镀金的方法在其圆周上制作了四个电极。该传感器与阻抗分析仪相连，用于测量晶体的等效电路常数和谐振频率的变化。根据这些值可以计算出流体的粘度。实验是在常压下进行的，以考察几个参数的影响，当测量在高压下进行时，这些参数似乎是重要的。需要澄清的最重要的因素是仪器可以测量的最大粘度。因为，润滑油的粘度随压力呈指数增加。虽然如果要增加适用于此测量的最大粘度，则应增加施加电压，但所使用的阻抗分析仪的最大电压太低。为此，介绍了一种由频率合成器和数字万用表组成的新系统，并利用谐振频率差和谐振频率下的等效电阻来计算粘度。但由于晶体的阻抗较高，不能直接测量等效电阻值，因此引入了双晶技术来测量粘度，使用阻抗分析仪时，最大粘度在1000cP左右。研究发现，当粘度超过100cp左右时，流体表现出弹性行为，应将其视为弹粘性流体。在高压下工作时，应使装置更加紧凑。此外，还发现高压下油品的松弛谱给出了油品弹粘性的重要信息。

X-cut quartz crystal rod having a diameter of 5mm and a length of 50mm was used as a sensor. four electrodes were made on its circumference by vacuum deposition of gold. This sensor was connected to an impedance analyzer for measuring equivalent circuit constants and change in resonant frequency of the crystal. The viscosity of the fluids can be calculated based on these values.The experiments were carried out under atmospheric pressure for investigating effects of several parameters, which seemed to be important when the measurements were carried out under a high pressure. The most important factor which should be clarified was maximum viscosity which can be measured by the apparatus. Because, the viscosity of the lubricating oils increases exponentially with pressure. Though the applied voltage should be increased if the maximum viscosity applicable for this measurement would be increased, the maximum voltage of the impedance analyzer used was found to be too low. Therefore, a new system consists of a frequency systhesizer and a digital multimeter was introduced, and the viscosity was calculated using difference in resonant frequency and equivalent resistance at resonating frequency. However, the impedance of the crystal was too high to measure equivalent resistance directly, therefore, twin crystal technique was introduced to measure viscosity.The maximum viscosity when the impedance analyzer was used was around 1000 cP. It is found that if the viscosity exceeds around 100 cP an elastic behavior was appeared and the fluids should be treated as an elasto-viscous fluid. The apparatus should be made more compact when it works under the high pressure.In addition, it is also found that the relaxization spectrum of the oil under the high pressure gives important informations of elasto-viscous property of the oil.