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

具有5mm直径和50mm长度的X切割石英晶体棒用作传感器。通过金的真空沉积在其圆周上制成四个电极。将该传感器连接到阻抗分析仪，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流体的粘度。实验在大气压下进行，以研究几个参数的影响，这似乎是重要的，当测量在高压下进行。应澄清的最重要的因素是可由该装置测量的最大粘度。因为润滑油的粘度随压力呈指数增加。虽然如果适用于该测量的最大粘度将增加，则应增加施加的电压，但是发现所使用的阻抗分析仪的最大电压过低。为此，提出了一种由频率合成器和数字信号处理器组成的新系统，利用谐振频率差和谐振频率下的等效电阻计算粘度。但晶体的阻抗太高，无法直接测量等效电阻，因此引入了双晶技术来测量粘度，使用阻抗分析仪测得的最大粘度约为1000 cP。当粘度超过100 cP时，流体呈现弹性行为，应按弹粘流体处理。此外，还发现高压下油的弛豫谱提供了油的弹粘性质的重要信息。

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.