C-VOR Digital Rheometer - Features

Torque Rebalance
First generation strain controlled rheometers were based on the principle of a lower driven plate together with a compliant torsion transducer attached to the upper plate. The inherently compliant nature of this design means that the command strain and the actual strain are different, the error depending on the torque. Resonance of the torsion element at the onset of a step strain test was another undesirable trait. Modifications to this design attempted to overcome this by using re-balanced transducers, at the expense of band-width
or dynamic range.

By incorporating both the measuring and driving components of the instrument within a single spindle assembly, Bohlin has overcome these problems to produce a perfectly re-balanced system without compromising dynamic range or bandwidth. This ensures that the actual stain perfectly tracks the command strain producing compliance free, true controlled strain data.

High Resolution Normal Force Sensing and Measurement
Malvern has incorporated a high resolution normal force sensor directly into the C-VOR mechanics which gives both extreme sensitivity and a wide range. With a measurement range down to just 0.1g, the C-VOR's sensor is suitable for generating data for the first normal stress difference at even low values of thrust. In oscillation mode the sensor can be used to compress or tension a sample with a pre-defined force using 'autotension' mode.

Wide Dynamic Range - For flexibility and ease of use
Malvern's C-VOR motor technology, combined with the air bearing system ensures that the C-VOR has a dynamic range in torque in excess of 1:1 million, without the need to change torsion elements or torsion heads. This dynamic range is greater than any other commercially available unit. Practically, this minimizes the need to change measuring sensors to cope with different sample viscosities giving flexibility and ease of use, it also means that large variations in modulus during material transitions can be properly followed.

At the low end of the torque range, the minimum torque is just 0.1 microNm which enables even the most weakly structured viscoelastic dispersions to be investigated fully.

Flexible Temperature Control - To suit all testing requirements
For maximum flexibility, the C-VOR can be quickly and easily configured with a wide range of temperature controls to suit all testing requirements. Available temperature control units include a range of fluids circulators, a Peltier device, electrically heated plates and a forced gas oven with a liquid nitrogen cooling option.

Practically, this means that the C-VOR test station can quickly be adapted as testing requirements change.

High Speed Measurement Capability
Using a completely revised high dynamic range position sensor technology, which is unique to Malvern, the C-VOR is unsurpassed in its ability to generate data at high shear rates, which are applicable to many coating applications. An upper speed of 600 rad/sec means that shear rates well in excess of 5x10 s-1 are achievable.

Sub Micro-Strain Position Sensing - For sensitive low strain measurement
Using Malvern's most advanced position sensor technology, the C-VOR is able to resolve position to less than any other comparable commercially available unit. This has obvious benefits in sensitivity and complements the C-VOR's low torque response, for example, it enables extremely sensitive creep and recovery measurements to be performed.

Flexible 32 bit Operating Software
The latest 32-bit MS-Windows based operating software is easy to use and allows user friendly programming of even the most complex test protocols. A built-in, context sensitive' help system features a rheology 'textbook' as well as a topic search feature. In addition to the basic measurement modes, software is available for Time-Temperature superposition (WLF), advanced viscoelastic analysis (VE data conversion) and molecular weight determination.

Fluids to Solids capability - Configurable for all sample types
Flexibility in both measuring sensors and temperature controls means that the C-VOR is equally as capable of measuring solid polymers in torsion as it is in generating viscosity data on low viscosity fluids.

Measurement Modes

• Creep and Creep recovery - programmable stress, creep and recovery times, and data sampling.
• Controlled stress viscometry - as a function of time, shear rate, or temperature.
• Controlled shear rate viscometry - as a function of time, shear rate or temperature.
• Yield Stress - programmable stress ramp in time.
• Oscillation and Multiwave - as a function of frequency, strain amplitude, stress amplitude, time or temperature. Can be superimposed on steady shear.
• Relaxation - programmable strain, strain rise time, and data sampling.
• Stress Growth - programmable growth time, data sampling, and shear rate. Can be followed by relaxation.