Torque transducers

Mechanical rheometry requires a measurement of both stress and strain (or strain rate) and is thus usually performed in a simple rotating geometry configuration. Typical examples are the cone-and-plate and cylindrical Couette devices [1,14]. In stress-controlled rheometric measurements one applies a known stress and measures the deformational response of the material. In strain-controlled rheometry one applies a deformation flow and measures the stress. Stress-controlled rheometry requires the use of specialized torque transducers in conjunction with low friction air-bearing drive in which the control of torque and the measurement of strain is integrated. By contrast, strain-controlled rheometry is generally performed with a motor drive to rotate one surface of the cell and a separate torque transducer to measure the resultant torque on the other surface. 

Power measurements require the measurement of the torque and the rotational speed. The torque can be measured using a torsion shaft with strain gauges, electrically with eddy-current torque transducers, or mechanically with a swiveling motor. The speed of rotation can be measured using mechanical, electrical (photocell), or optical (stroboscope) instruments. 

Rheological Experiments. Melt viscosity and low-strain oscillatory experiments were performed on a Rheometrics RDS-7700 dynamic spectrometer equipped with a 0.2-2.0-g-cm torque transducer. The samples were mounted on 25-mm-diameter parallel-plate fixtures with a gap of 0.5 mm. Prior to each scan, samples were heated to 50 °C and then cooled slowly to room temperature. Steady-shear... 

By the third law of Newton, for every force there is a counterforce, collinear, equal and opposite in direction. As the impeller shaft rotates, the motor tries to rotate in the opposite direction, but it does not because it is bolted in place. The tensions in the stationary motor base can be measured by a reaction torque transducer. 

The fibre-windup technique [Padmanabhan et al., 1996] can provide transient extensional-viscosity data using modified rotational shear rheometers. One end of the sample is clamped while the other end is wound around a drum at a constant rotational speed to achieve a given extension rate, with the rheometer s torque transducers being used to obtain the extensional viscosity. The technique is claimed to provide valuable extensional viscosity data for high viscosity liqmds. 

This is most commonly achieved with an electrical torque transducer in which an oscillatory current... 

The measuring apparatus consisting of a test wheel with a smooth tyre (ASTM E 1551 2008), force or torque transducers and a watering system is usually built into a vehicle or into a trailer towed by a vehicle. 

Fig. 6.71. Numerical transformation of step torque 1. measured torque-transducer signal 2. first estimate of ER clutch torque response 3. predicted torque-transducer response for first estimate 4. final estimate of ER clutch torque response. To + Tf are viscous and real friction torques, with Te due to application of step voltage V...

Torque transducer units are available that contain strain-gauged sections of shaft that can be fitted in line with the mixer shaft. They must be suitably isolated from any bending moments and axial loads (Figure 4-9). They are generally subject to the same calibration and care during use precautions as are sensitive strain gauges (Chappie et al., 2002). 

Meissner (1972) shows how this small transient deflection of the torque transducer can affect short time start-up data (see Figure 8.3.7). Gottlieb and Macosko give relations to correct G and G" for compliance. These corrections are made in the software in some rheometers. Corrections are reliable only if the spring constant K is known accurately, and then typically only when the measured strain is 10% or more of the commanded value. 

Schematic diagram of a torque transducer for a pressurized rheometer. The thin-walled tube twists slightly when torque is exerted by the sample on the inner cylinder. This twist is recorded by the rod and capacitance gage.

The rest of the test will be automatic. Every 30 seconds the control computer will translate each desired shear rate to an angular velocity set point for the circuit that controls the motor speed. The tachometer sends back the true velocity, which the software uses with eq.5.3.11 to calculate the shear rate. In some instruments the software may make corrections for wide gap using data from the preceding low shear rates (eq.S.3.24). The voltage from the torque transducer is typically averaged over several seconds, then converted to shear stress with eq 5.3.8. scosity is calculated and plotted versus shear rate as the test is running. 

In the stress relaxation test, the material is subjected to a step strain at time zero (inset. Figure 8.3.5), and the decay in the stress (or modulus) is monitored as a function of time (Figure 8.3.5). At short time, limitations due to electronic hardware can affect the data collection speed and the transducer inertia can affect the torque values, thereby affecting the quality of the data. At long time, the low torque signal and hysteresis of the torque transducer affects the data quality. 

Franck A (2003) Measuring structure of low viscosity fluids in oscillation using rheometers with and without a separate torque transducer. Ann Trans Nord Rheol Soc 11, RH090... 

Figure 1. Specially designed camshaft pulley torque transducer...

The two torque transducers, cylinder pressure transducer, liner absolute pressure transducer and two encoder signal were connected to a 12-bit high speed simultaneous sampling data acquisition system. Two National Instruments 6110E boards were used each having four analogue input channels and two 20 MHz timer/counter channels. Unlike most of the data acquisition boards the 6110E does not work in multiplex mode as each... 

Calibration of both the camshaft torque transducers was carried out to establish accurate transducers correlation between the torque and output voltage over the range expected in the Hydra engine and to ensure that external factors such as... 

Figure 4. Typical torque transducer output voltages, engine speed ISOOrpm.

Mackay, M. E., Halley, P. J. Angular comphance error in force rebalance torque transducers. /. Rheol. 

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