DYNTTS - Individual System Components
- Diogo Teles (Deactivated)
Actuator Unit and Cell top
The actuator unit is the main cabinet which houses the axial actuator and on which the cell base is fixed.
The axial actuator unit consists of a brushless DC servo-motor which drives a ball screw via a toothed belt. The axial ram is attached to a thrust-cylinder and ball-nut which is driven by the ball screw. The thrust cylinder is prevented from turning by means of a linear guide connected to the centre plate. The thrust cylinder is connected to the axial ram which passes through the ‘balanced-ram’ arrangement and then through the base of the cell. The base pedestal is connected to the axial ram.
The cell base is fixed on the top of the actuator unit. The cell base houses all of the hydraulic connections to the cell, which include: back pressure, pore pressure, cell pressure and cell fill/empty connections.
The power supply and motor control unit which is contained within the main cabinet has the following items:
Transformer
DC power supply
Brushless DC servo-motor controller
In normal operation the power supply and the motor controller unit should have a green LED showing. If a red LED shows, shut the system down and re-start it. If a red LED is still showing refer to the power supply and motor controller documentation for a description of the problem.
When working in this area it is essential that the ground connectors are not disturbed - these are critical for the maintenance of low noise on the A/D system.
The cell top is removable to allow the test specimen to be put in place. The cell top also contains the exchangeable load-cell attached to the ram which passes through the top of the cell. This load cell can be of various sizes, depending on the tests needing to be performed and the machines specifications.
Typical MINIDyn apparatus
Hydraulic cell pressure controller
The cell pressure controller is either a Standard v2 200cc Pressure Controller (STDDPCv2) or Advanced v4 200cc Pressure Controller. These are specifically for pressure ranges 1 - 4MPa. A separate manual exists for the GDS Pressure/Volume controllers.
The MINIDyn system can be upgraded to include a Sig 3 Cell Pressure Controller which is attached to the side of the Actuator Unit. Sig 3 is a dynamic pump for the precise & rapid regulation and measurement of fluid pressure and volume change.
a)
b)
c)
a) STDDPCv2 b) ADVDPCv4 and c) Sig 3 controller controllers
Back pressure controller
The back pressure controller is often a Standard v2 200cc Pressure Controller (STDDPCv2) or Advanced v4 200cc Pressure Controller.
Balanced Ram
The cell is provided with a balanced ram. This compensates for the volumetric displacement of the loading ram into or out of the cell. Down the centre of the hollow ram, the cell fluid is hydraulically connected to a chamber through which the ram passes. In this chamber the ram has an annular piston attached to it. The annular area is exactly equal to the area of the ram. When the ram moves in the cell and causes a volume change, the annular piston causes an equal and opposite volume change. In this way the net volume change in the cell is zero. In addition, cell pressure acting on the annular ring automatically compensates for the effect of cell pressure acting on the ram. This means that the axial force capacity of the cell is independent of cell pressure.
Figure showing balanced ram arrangement
GDS Advanced Digital Control System v2 (ADVDCS v2)
The ADVDCS v2 unit is a combination of dynamic control processor and signal conditioning.
The analogue signal conditioning consists of one eight channel A/D board which supplies transducer excitation to each transducer and provides the correct zero and gain for each transducer input. All inputs are processed by the dynamic control processor for 24 bit analogue to digital conversion.
The transducers plug into the GDS AdvDCS v2 unit using Lemo connectors, which are individually colour coded.
ADVDCS v2 unit with 8 channel data acquisition
Each channel has a configurable gain value according to the type of transducer that will be connected, typically each colour represents a different transducer as follows:
Colour | Channel | Transducer Name |
Black | 0 | Loadcell |
Brown | 1 | Local Axial 1 |
Red | 2 | Local Axial 2 |
Orange | 3 | Local Radial |
Yellow | 4 | Pore Water Pressure |
Green | 5 | Pore Pressure 2 |
Grey | 6 | Spare 1 |
White | 7 | Spare 2 |
Channels on an ADVDCS have variable gain range which will be automatically set depending on the transducer full scale. The available gains for each channel are +-10V, +-5V, +-1V, +-200mV, +-100mV, +-30mV, +-20mV, +-10mV. The gain value will be set to the closest value which is greater or equal to the transducer full scale output in mV.