Introduction & Subsystems - RV

For my project, I reverse engineered an old oilfield viscometer. The goal of this machine is to measure the viscosity of an oil sample for processing processes. The viscometer used a gear train to rotate the oil sample at a constant angular velocity. A cylinder of known size was inserted into the sample and the viscosity of the sample caused the cylinder to rotate. The shear force that caused this motion was counteracted by a torsional spring in the display dial. By knowing the angular output of the sample and the angular displacement of the dial, we can calculate the viscosity of the fluid. 

A rotational viscometer consists of three subsystems: the mechatronic system, a varying gear train, and a dial system. 

Mechatronic System

The mechatronic system for this device is quite simple. The components are an AC motor and a switch which controls the frequency supplied to the  motor. The AC motor varies its speed from 900 rpm to 1800 rpm by employing a switch which varies from an open circuit, a low frequency circuit, and a high frequency circuit.

Varying Gear Train

The varying gear train in this viscometer makes it much more convenient to measure a wider range of viscosities. The varying gear train has three different gear trains: low, medium, and high. All gear trains start from the end of the mechatronic system. The output of the motor, Nin, rotates a gear train (N1 and N2) in the base of the viscometer that reduces the angular velocity of the motor by 3:10 and also transmits the angular velocity from the base of viscometer to the head of the viscometer via vertical shaft that runs through the support of the head. So, the angular velocity of N3 is equal to the angular velocity of N2.

Once the angular momentum of the base has been transmitted to the head, a compound gear (let's call it "Gear 3")  is interlocked with another compound gear (let's call it "Gear 5"). The high setting employs the top gear of Gear 3, N3a, interlocking with the top gear of Gear 5, N5a. The high setting has a gear ratio of 1:1 between N3a and N5a. The medium setting uses the middle gear of Gear 3, N3b, interlocking with the gear below the top gear of Gear 5, N5b. The medium setting has a gear ratio 1:3 between N3b and N5b.

The low setting employs a longer and more complex gear train. The bottom gear of Gear 3, N3c, rotates an axial gear, N4a. N4a and N4b share the same shaft, so they share the same angular velocity. This angular velocity is translated back to Gear 5 via another worm gear, N4b. This worm gear drastically reduces the angular velocity of the other interlocked gear, N5c. The worm gear ratio for this mechanism was 9:1, and, therefore, reduced the angular velocity of N5c by 1/9. 

After this point, all the gear trains align on the same shaft but rotate at different speeds. The gear shifter allows the lowest gear of Gear 5, N5d, to rotate at the same angular velocity as one of the other gears (N5a, N5b, or N5c). This angular velocity is transferred to the Gear Out by a ratio of 9:8. The fluid container will then rotate with that same angular velocity. The output angular velocity of the sample is important to know in order to calculate the dynamic viscosity. 

Dial System

The dial system consists of a dial that measures the angles between 0° and 300°, a torsional spring, and a cylindrical link. All three parts are connected so that they all rotate in the same manner. The torsional spring is grounded to the lid of the viscometer. The torsional spring can be switched out to measure a different range of viscosities, but, for this oilfield viscometer, only one spring is needed to cover the ranges of viscosities for crude oil.