The present invention is generally related to viscometers, and, more particularly, to a viscometer for heating a fluid and measuring temperature variation of the fluid to determine viscosity.
Oil viscosity is an important physical parameter in many lubricant applications. For example, the viscosity of lubricants used in vehicles, such as engine oils and transmission oil, is one of the key parameters to determine oil quality and establish replacement intervals. A variety of viscosity measurement means have been developed for this purpose.
One known method of measuring viscosity of a fluid is to measure changes of behavior of system damping due to changes in the tested fluid's viscosity. A mechanical dynamic system, typically a vibration system, is used in this method. The mechanical system is immersed in the fluid to be tested and the system damping effect caused by the fluid can be measured and used to calculate a viscosity of the system. While this method works well in a laboratory environment, it does not appear to be suited for vehicle applications because of the complexity of the system and potential maintenance and serviceability problems. Other known viscometers use quartz crystal oscillators to measure viscosity of a fluid. The viscosity of the fluid affects the resonant frequency of the crystal and also causes a phase delay between an input and an output signal. These parameters can be monitored and measured to determine a viscosity of the tested fluid. However, such a test system may be expensive and difficult to package. Yet another way to measure viscosity is to heat the test fluid and measure the temperature variation of the fluid as the fluid moves in response to the heating. For example, it is known that a comparatively lower viscosity fluid will flow faster than a comparatively higher viscosity fluid when heated.