| | | Mechanical The vertical design and backward movement of the industrial furnace into parking position provide free access for changing the various sample holders (three-point bending, single/ dual cantilever bending, compression/penetration, shearing, tension). Compensation is made for dimensional changes occurring during the measurement (expansion, shrinkage, creep) by moving the oscillator and the displacement transducer against the sample holder using a stepper motor. In tension, compression, penetration and three-point bending the dynamic force is superimposed by a static preliminary force. Thus, even with great changes in the modulus, secure positioning of the sample is guaranteed. The static preliminary force is controlled according to the particular problem: | | I. constant value (tension or pressure) II. proportional (the initial stress on the sample is fit to the current modulus value) III. combination of I. and II. Of course, operation under constant static force is possible as well (TMA mode). Thermal The rectangular cross section of the furnace is fit to the sample geometry, such that the sample is heated constantly and homogeneously. The temperature gradient is minimized to ±1°C over a sample length of 60 mm. The sample temperature is registered by a sample thermocouple and precisely controlled via the STC function (Sample Temperature control). With controlled cooling using liquid nitrogen, temperatures to -170°C can be achieved with minimal consumption. | | |
| | | Dynamic The oscillator converts an electrical signal into a force, which is applied to the sample via the push rod. The broad oscillation frequency range of 0.01 Hz to 100 Hz is made possible by the high degree of inherent rigidity and the stability of the instrument. The position of the push rod registered by the displacement transducer shows the resulting deformation. The displacement transducer, which was specially developed for the DMA 242 C, measures the deformation with greatest sensitivity and, even at higher frequencies, with no distortion or time lag. The subsequent digital filtering, achieved by means of FOURIER Analysis, provides an excellent signal/ noise ratio. This makes it possible to resolve even the smallest tan 6 values. | | |