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GDS LF50
GDS LF50 50kN Load Frame v2 Handbook
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Introduction
What is it?
The GDS LF50 50kN load frame is an electromechanical loading frame designed for use in geotechnical testing laboratories. The load frame is primarily used for velocity based testing such as that used in traditional triaxial shearing or consolidation CRS (constant rate of strain) tests.
The load frame also allows direct closed loop control of load and/or external displacement by connecting a loadcell and/or displacement transducer via DigiRFM(s).
The load frame uses USB for quick and easy connection to a controlling computer, and it is selectable via serial number. This makes for more rapid setup and automatic reconnection should the communications be interrupted.
Overview of Functions
A summary of the features offered by the GDS LF50 50kN Load Frame are listed below.
Target displacement velocities from 0.00001 to 90 mm/min.
95mm nominal travel.
Large graphical OLED display clearly displays current velocity, position and status of load frame.
LED status indicator lights show at a glance platen direction, speed, limit proximity and status.
Protection against computer power failure – adjustable ‘dead man timer’ will stop the frame automatically after a preset interval.
Protection against operator misuse – frame is locked against operator inputs while a computer controlled test is running.
Protection against electronics damage from accidental overloading or complete power failure during testing by use of in-built shunt resistor.
USB computer control and acquisition by GDSLab software.
Upgrade path available for connection of external loadcell and/or displacement transducers by DigiRFM to allow direct closed loop control from the frame.
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Device Setup
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To use the load frame, first plug in the IEC mains cable to the onboard socket and switch the red power switch on. A red LED will light inside the switch to show the power is connected and the frame is turned on.
Note: If the power switch light does not show, first check that the mains supply is plugged in and switched on. If the light still does not show, check the built in fuses have not blown.
If a DigiRFM is to be used with the load frame, ensure the RFM is screwed in place to one of the marked positions as shown above (with the chamfered outer edge up), plug in the CAN connection lead between the load frame and either CAN port on the RFM, and connect the transducer before powering up the load frame.
To connect the load frame to a computer with GDSLab for control and acquisition, simply plug the supplied USB cable into the port on the load frame and a spare port on the computer.
Note: we strongly recommend connecting directly to a USB port on the back of your computer or via a high quality USB hub rather than via a screen or a port on the front of the computer. This is because screens, low quality hubs and PC front connections are more likely to disconnect during a test.
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Connecting to GDSLab
Once the frame is connected via USB, open GDSLab and select a relevant *.ini file. Navigate to the Object Display and left click on the picture of the load frame. The screenshots below show how to select the load frame by its serial number. Once the frame has been connected, GDSLab will remember the serial number and connect automatically when it is opened again, even if the load frame has been moved to a different USB port.
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User Interface
Front Panel
Manual interaction with the load frame is via the 21 key keypad and large OLED screen on the front panel as shown below.
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OLED Graphical Display
The graphical display shows the current velocity, position, status and last command or warning message from the load frame. Below is a photo showing the display after first powering up the load frame. Here it can be seen that the load frame is currently stopped with no errors, and the measured platen position is 0 mm.
The USB connected icon is also shown near the bottom right corner of the screen. This icon symbolises that the frame is connected to a USB port on a computer (note the frame does not have to be connected in GDSLab). When the USB is disconnected from the computer, the icon will change to show a cross through the USB symbol.
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Status Messages
Status messages are displayed below the position reading next to the “Status” label. Possible frame status messages and their meanings are as follows:
Extending = The platen is extending (moving upward) due to a velocity or displacement target.
Retracting = The platen is retracting (moving downward) due to a velocity or displacement target.
Stopped = The platen is stopped.
Extension limit = The platen has reached the extension (upper) limit and will back off 2mm automatically.
Retraction limit = The platen has reached the retraction (lower) limit and will back off 2mm automatically.
Note: When the load frame first discovers its physical extension and retraction travel limits, the platen will automatically back off by 2mm and stop, then create a virtual end stop to prevent the physical limit from being triggered again. We recommend leaving the load frame powered on so that the limit positions are recalled between tests.
Frame Status LED
The Frame status LED changes colour following an error status in the load frame. The status LED colours are as follows:
Blue = Frame powering up
Green = Frame is on and there are no errors
Flashing red/blue = Frame has encountered an error
If the frame encounters an error or travel limit, the status LED will flash until the warning is cleared by pressing the ‘Cancel’ button.
Warning/error messages
Warning/error messages are shown in the green box in the bottom left corner of the frame’s display. When there is a warning message the box will glow and fade. If there are no messages to display the box contains “LF50” and is a constant shade. The possible warning messages that can be shown, and their meanings, are as follows:
Extension limit = The platen has reached the extension (upper) limit and will back off 2mm automatically.
Soft extension limit = The platen is stopped on the virtual extension limit.
Retraction limit = The platen has reached the retraction (lower) limit and will back off 2mm automatically.
Soft retraction Limit = The platen is stopped on the virtual retraction limit.
When a warning is triggered the Frame Status LED will also flash. To clear a warning/error message from the frame’s display press the ‘Cancel’ button.
Note: when an error is encountered by the frame this message will also be passed to GDSLab. Test control will be paused and the same warning message will be displayed in the GDSLab Object Display status bar.
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Direction and Limit Status LEDs
The direction and limit status LEDs show how the platen is moving and how close it is to its end limits. Below is a set of drawings showing possible light combinations and their meanings.
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a) Frame stopped.
b) Frame stopped on extension limit.
c) Frame stopped on retraction limit.
Note: once the limits have been detected the red limit status lights fade between full brightness at the limit to off when 5mm from the limit to allow early detection that a limit is nearly reached.
d) Frame extending at 10mm/min.
e) Frame extending at 90mm/min.
Note: the green movement status lights fade up proportional to the frame speed selected.
f) Frame extending away from retraction limit.
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Quick rate buttons
The quick rate buttons allow the user to set a specified rate or quickly target predefined rates up or down. The button functions are as follows:
Button | Short press | Long press |
Fast up | Opens rate window with fast up speed entered. | Frame moves at fast up speed – note for safety this can only be performed when the frame is stopped. |
Up | Opens rate window with up speed entered. | Frame moves at predefined up speed. |
Rate | Opens target rate window. | Opens rate menu window where fast up, up, down, fast down and position targeting rates can be defined. |
Down | Opens target rate window with down speed entered. | Frame moves at down speed. |
Fast down | Opens target rate window with fast down speed entered. | Frame moves at fast down speed – note for safety this can only be performed when the frame is stopped. |
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Command menus
The command menus can be used to perform common functions using the load frame. Pressing the command menu button (“CMD”) will open the menu, with the internal frame controls displayed as shown below. Pressing “CMD” again will cycle through the control options for external displacement and load controls (Note: the second and third command menu options are only available where transducers are connected via a DigiRFM).
Functions can be chosen by pressing the number shown on the frame’s keypad. In the above example the current platen position reading can be set to 0mm by pressing “2”, then pressing the “↵” button to confirm.
Main menu
From the main menu, common functions and the system information window may be accessed. To navigate up and down through the list use the “8” and “2” keys on the keypad.
In the system information window details can be seen of the load frame’s hardware and firmware versions, as well as the system serial number.
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Manual Computer Control
Manual control of the load frame using a computer is possible using the GDSLab Object Display. For the standard load frame there will be an internal frame displacement read parameter, and control parameters for target velocities in mm/min or frame displacement in mm (using the in-built stepper motor for displacement measurement).
If RFM(s) with additional loadcell and/or displacement transducers are used there will be additional read and control parameters visible.
The platen can also be manually controlled using the window that pops up after clicking on the load frame in the Object Display. Open the window then select the control tab. From here the platen can be extended (i.e. the platen moved upward), retracted (platen moved downward) or stopped using the ‘Move Platen’ buttons.
This screen also allows you to set the load frame’s watchdog timer options. The watchdog timer is a new safety feature built into the load frame that will automatically stop the load frame if communications are broken with a controlling computer for a predefined time. Possible reasons for this could include a laptop running out of battery, accidental disconnection of the USB, a computer crash or a brief power cut in the lab. Note the units of the WatchDog Interval are seconds.
Automated Computer Control
Once the load frame has been powered on, the correct *.ini file selected in GDSLab and communications verified through the Object Display, test control will be automated according to the test stages defined by the user in GDSLab.
Manual user inputs are only required for setting up the test specimen in the frame before a test is started.
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