Increasing the Strain Amplitude of Oscillatory Measurements by Using a Configuration with Two EC Drive Units in Counter Oscillation Mode

When performing oscillatory rheological tests at very high frequencies and strain amplitudes, the feasible strain amplitude becomes limited by the maximum angular acceleration that the motor of the device can impose. However, if the setup consists of two drive units revolving in counter-movement, so that both contribute to the deformation process, then the maximum strain amplitude may be significantly increased.


Rheometers with two individual EC motors, where oneis located in the rheometer head and the other sits atthe bottom of the device, have several advantagesover conventional “single drive” instruments. Theyoffer a variety of new applications and allow forimprovements to the already-existing measurementmethods with new features. More information isavailable in application reports and/or presentationssuch as[1][2].

One setup configuration can be chosen so the driveunits work independently in separate motor transducermode (SMT). In this case, only the lower drive isactuating the measurement system, while the upperone takes the role of a transducer, recording thesample’s response. Using this mode, a higher torquesensitivity can be obtained[1].

Alternatively, the device can be operated in combinedmotor transducer mode (CMT), where the lower driveis removed. In this case, both functions (setting thestrain and measuring/controlling the torque at thesample) are covered by the upper drive. This setupconfiguration is equivalent to any single driverheometer device.

In contrast, the counter-movement mode allowsmotion patterns where both drives revolve in oppositedirection, such as counter rotation or counteroscillation (CO). This mode is useful for microscopyfor example, where it helps to generate a stagnationplane[2].

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