Torque measurement transducers

FIG. 21-32 iShear rotary, full annulus split cell, illustrating normal load weight application, rotational base, and shear stress/torque measurement. Vertical displacement of lid is monitored by displacement transducer. (Courtesy E G Associates, Inc.)... 

In order to determine the viscoelastic properties of silicone gel materials, vibrational measurement techniques are used. The principle of vibrational measurement techniques involves determining die viscoelastic quantities by observing the responding mechanical behavior when cyclic deformation is applied repeatedly. Dynamic viscoelastic property measurements are performed with a dynamic mechanical spectrometer such as the RDA-II from Rheometrics. This instrument measures the complex modulus G and loss factor tan S from the torque measured by the transducer equipped at the upper portion of the sample chamber when shear deformation is applied to the sample at a specified shear strain and frequency from the actuator at the bottom of the sample chamber. 

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. 

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). 

The drive system of a rotational rheometer is likely to be optimized in one of two ways depending upon its preferred mode of operation. The most common form of rheometer is a controlled-rate (controlled-speed) device. This configuration is also used in most viscometers and has been around for decades. A shear rate is applied to a rotor by the motor controlling the viscometer s speed. The rotor is normally a flat plate or cylindrical cup. The stator is thus a cone or plate for the first two geometries or a cylindrical bob for the third (Figure HI. 1.1). The stator is linked to the rotor via the sample, which acts to couple the input signal like an automobile transmission. Thus, the torque on the stator when measured by a transducer is used to derive the shear stress in the sample. 

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 meat grinder technique for measuring meat tenderness was reported by Miyada and Tappel (1956) in this method, power consumption of the meat grinder motor was used as a measure of meat tenderness. The electronic recording food grinder described by Voisey and deMan (1970) measures the torque exerted on a strain gage transducer. This apparatus has been used successfully for measuring meat tenderness. 

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. 

Speed limits the ability to transduce applied force or torque for all measurement methods. Apart from electrical limits of filtering and signal conversion effects like material internal friction, skin effects and non-homogeneous material behavior will define speed limits. In most cases the rotational speed defines the principle of signal transmission. This is one of the reasons why torque sensors are still not used with automatic transmission. The input torque is calculated by the engine management [5],... 

The operating principle of the YR-1 Rheometer is to drive a spindle through a calibrated spiral spring connected to a motor drive shaft (see Fig. 3). The vane spindle is immersed in the test materiaJ. The resistance of the material to movement is measured by observing increasing torque values as the YR-1 motor rotates. The amount of shaft rotation is measured by the deflection of the calibrated spiral spring inside the instrument. Spring deflection is measured with a rotary transducer. 

Test and measurement sensors, pressure transducers, torque sensors, instrumentation, accelerometers, and displacement sensors An extensive array of instruments and systems for applications ranging from automotive R D, process and environmental monitoring, in vitro medical diagnostics Surface plasmon resonance biosensors for the determination of the affinity and kinetics of biomolecular interactions... 

In a rheometric dynamic spectrometer such as RDS7700 manufactured by Rheometrics, Inc., the torque and normal force generated in response to an imposed motion are measured by a transducer. A microcomputer determines stresses from these values with measured sample motion to calculate strains and viscoelastic functions such as G, G", and tan d [12]. 

Transducers for measuring force or torque usually contain an elastic member that converts the mechanical quantity to a linear or rotational deflection that can be measured by a set of strain gages, which give an electrical signal proportional to the quantity of force or torque. 

Fig. 14 Transducer for measuring both axial load and torque...

Thus G and G are obtained by measuring /o. 00, and 8. The difficult quantity to determine is 8. The best method is to convert 0 into a voltage using a rotational transducer. The phase difference 8 between this voltage and the torque current can then be obtained by one of a number of precise electrical methods. This forced-oscillation technique is used most efficiently at frequencies somewhat remote from the resonant frequency of the system. 

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. 

The panel was turned upside down and simply supported near the corner, as shown in Figure 8. The steel insert plate and its surrounding area were left completely free. To counterbalance the torque which was produced when the rod was pushing down on the bracket, dead weights were put on to the top side of the panel. The load was applied continuously and the load deflection curve was recorded autographically. One transducer measured the vertical displacement of the tip of the bracket. 

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...

During Rheometrics analysis, a torsional motion is imposed on the sample and the torque and normal forces resulting from the motion are measured by a transducer. From these values the storage modulus, G , the loss modulus, G" and the ratio of the latter to the former, the loss tangent (tan 6) can be calculated. 

In the study of hlling modihcation, a torque rheometer is a common piece of small test equipment. Because it is equipped with a corresponding internal mixer chamber, the material shows an opposite reaction on rotors in the process of mixing. The opposite reaction is measured by a force transducer and converted into torque value, and the torque value reflects... 

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