Torque measurement strain gauges

A.pparatus for torsion of bars with direct measurements of torque (by strain gauge transducers) and angle (by deflection of a light beam) has been described by Heydemann.2 By interfacing to a computer, the relative amplitudes and phase of torque and deflection can be obtained by a cross-correlation analysis which rejects noise and distortion.22... 

Power. There are two main ways to measure the power deUvered by the driver to the pump. The first method is to install a torque meter between the pump and the driver. A torque meter is a rotating bat having a strain gauge to measure shear deformation of a torqued shaft. Discussion of the principle of torque meter operation is available (16). The benefit of this method is direct and accurate measurements. The power deUveted to the pump from the driver is calculated from torque, T, and speed (tpm) in units of brake horsepower, ie, BHP (eq. 4a) when Tis in lbs-ft, and kW (eq. 4b) when T is N-m. 

Laboratory rotors have been used to evaluate the drag resistance of immersed surfaces as well. The rotational frequency of the innermost cylinder is adjusted to the relevant speed (monitored by a tachometer) and after about 30 minutes of flow stabilisation a 50 Nm strain gauge transducer picks up the torque, M,. All measurements are based on the average of three replicate tests. A sketch of the set-up is shown in Figure 13 details on the set-up and calculations are described in Weinell et al. (2003). 

Before a torsion shaft with strain gauges was employed to determine the torque on a rotating stirrer shaft, a swiveling motor had to be used and the torque measured by weighing. 

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. 

A second popular approach is measurement of the main impeller torque, which reflects the increasing cohesive force of the powders via addition of liquid and agglomerate tensile strength. This requires strain gauge installation on the impeller shaft, retrofit installation is more involved than power instrumentation, yet it has the distinct advantage of a direct link to the impeller load and thus the status of the granulating powders, and it is not impacted by mixer conditions. 

Force sensors are not used in general automotive applications. In agricultural machines a force sensor measures the load at the connection rod [1], Some force sensors are specially made for measuring forces during vehicle testing and validation. Often metal strain gauges are welded to the devices under test The data is sometimes needed for system development or to verify simulation results. The first and only mass production of torque sensors is in electrical steering systems [2]. 

The 3-D ground reaction force vector, the vertical ground reaction torque and the point of application of the ground reaction force vector (i.e., center of pressure) are measured with force platforms embedded in the walkway. Force plates with typical measurement surface dimensions of 0.5 x 0.5 m are comprised of several strain gauges or piezoelectric sensor arrays rigidly mounted together. 

An alternative to power consumption is torque measurement. A high-shear mixer was instrumented with a new capacitive sensor, a watt meter, and a strain-gauge torque sensor (50). Placebo formulations containing DCP, MCC 101, MCC 102, and lactose were granulated in the high-shear granulator. A similar map (profile of torque measurement or power consumption) of the granulation process was obtained for power consumption and torque measurement. 

Extremely careful calibration of the strain gauges is required. Known torques must be applied to the shaft and the response measured. Note that no bending loads should be applied during calibration. If a single strain gauge is to be mounted on the shaft, it should be placed toward the top of the shaft where it will not be submerged and above where any impellers are to be mounted. Where... 

Figure 4-8 Torque measurement using strain gauges and slip rings.

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