Look for our answers to typical questions
Related to the use of the instrument
Q: How often should I calibrate the texture analyser?
A: Many people ask this question. The texture analyser does not need to be calibrated every time you use it. Normally, as a guideline we would suggest that you calibrate at least once a month, if the texture analyser is moved to a different position and if you cause an overload. However, as calibration only takes a matter of seconds you could calibrate every day if you prefer. Where the texture analyser is used by several people who may have optimised the calibration range that they have been testing within it is always advisable to recalibrate with your chosen calibration weight.
Q: What data acquisition rate should I choose for collecting test data?
A: When measuring crispness, brittleness or fracture the events occur very quickly. In order to obtain an accurate understanding of the fracture events one should try to obtain as many data points as possible. By using a data acquisition rate as low as e.g. 50pps you may indeed be missing the true picture of what is really happening in terms of fracture. For brittle products, therefore, a data acquisition rate of 400 or 500pps is recommended. When testing products that are not brittle and do not necessarily fracture (i.e. fast events need not be captured quickly) a data acquisition rate of 200pps is recommended. At 200pps data is still captured very quickly and accurately but at this speed the test will not take up as much space on your hard drive.
Q: The test does not start when the probe reaches the product. Why is this?
A: The trigger force may be too high and should therefore be lowered. Alternatively, there may be loose connections in which case all the connectors should be checked to ensure that they are plugged in correctly.
Q: Occasionally my texture analyser appears to start collecting data in mid-air, i.e. before it has reached the test sample. Why is this?
A: The trigger type may be set to 'Button' in which case it is instructed to collect data as soon as the test is commenced. If this is not required then Trigger Type 'Auto' should be selected in the the T.A. Settings window. However even when Trigger Type 'Auto' is selected you may experience this 'early triggering'.
The following is a list of reasons associated with the 'early triggering' problem which customers may encounter.
The texture analyser may trigger early if:
• The trigger force is set lower than 5g when a 30kg load cell is installed
• An open window or circulating fan is located near to the texture analyser
• Screws on the load cell plug are not tightened and therefore vibrate
• Probes are incorrectly fitted
• Inertia is present (i.e. heavy probes)
• There is vibration on the table on which the texture analyser is situated which may be from other equipment or e.g. drilling in a nearby room.
If the machine is subjected to vibration then small fluctuations in the force readings may be measured. The fluctuations will be amplified when using heavier probes etc. due to inertia.
In an extreme case the last calibration may have obtained false data or the environment and condition of the machine may have changed. Whatever the reason, it is possible that the sensitivity of the machine has become exaggerated and force re-calibration would be advised.
Q: I appear to get a lot of ‘noise’ on my curve (produced using a Kramer Shear Cell), even when the blades are not touching the sample. Why is this?
A: When setting up a fixture such as a:
• Blade Set
• Kramer Shear Cell
• Forward Extrusion Cell
• Ottawa Cell
it is important to avoid friction of the probe on other surfaces of the fixture which can contribute to a considerable amount of measured force which is not due to the testing of the sample itself. When the fixture is set up it is recommended that users perform a 'blank' test (i.e. a test should be run with no sample) so that the frictional force (if any) can be measured to see what contribution it will be making to the measurement. In the case of the forward extrusion a small frictional force of the piston against the cylinder interior cannot be avoided but can instead be substantially reduced by careful positioning.
Q: How can I check that the force calibration is correct?
A: Within the software, click on T.A. > Calibration > Check Force. Place known weights on the calibration platform to check the reading in this window. The weight value placed on the calibration platform should be that displayed in the box of this window.
Q: Can you give me further information to consider regarding the force calibration of the texture analyser?
A: Points that should be noted when performing force calibration: The calibration weight should not be lifted off the calibration platform too soon - wait for instructions from the software Do not use a calibration weight which is less than 10% of the force capacity you intend to go to Overload/Underload should not cause force calibration problems but in any event calibration is very quick to perform and is therefore recommended. However overload/underload does lose the probe height calibration which will then need to be performed again if required as part of your test procedure.
Q: Do I need to calibrate the Probe Height every time I use the TA?
A: No. In fact, Probe Height calibration is only necessary when wanting to test samples to a certain 'Strain' or if you wish to used a 'Button Trigger'. However, it is useful if you wish to set Pre-set positions on your texture analyser to speed up multiple sample testing. For example, you may wish to have a chosen position for sample loading and a chosen position just above the sample before you start the test to reduce test times.
Q: What test vessel size should I use?
A: As a general rule, a test vessel diameter of at least 10 times the probe diameter is advised to reduce 'wall effects'. Similarly a target distance for a test should be no more than 75% of the product fill level to reduce 'base effects'.
Q: How many samples should I test?
A: Whilst it is appreciated that time and sample availability are often limiting factors, it is necessary to test at least 3 and ideally 4 samples to differentiate between samples with some confidence. However, time permitting, it is recommended that 5 or more samples are tested expecially where low sample repeatability is expected from inherently variable samples, e.g. potato crisps.
Note: It is not statistically valid to apply a standard deviation or coefficient of variation calculation to a sample set fewer than 4 and ideally these statistical measures should be applied to a sample set of more than 5.
Related to the use of the software
Q: When should I use a ‘Button’ trigger type instead of an ‘Automatic’ trigger type?
A: First of all, a brief explanation of both trigger types:
Button: Measurement starts as soon as the Run command is given and the probe starts moving.
Auto: The Texture Analyser will move the probe up (Tension test) or down (Compression test) until it detects a force greater than the Trigger Force setting. Measurement starts once this force point is reached. This ensures that products of different sizes are accounted for. This facility also allows the Texture Analyser to measure the product height (particularly important when measuring in strain). Sometimes you can experience false triggering when using the Auto option. If this is the case then try increasing the Trigger Force setting.
Most products should be tested with an automatic trigger for detecting the surface of the sample and starting to collect the test data. The penetration, cutting or compression distances etc. are then identical for all automatic trigger tests without regard to the precise height and geometry of each sample tested.
The sensitivity of the automatic trigger can also be used to adjust for minor differences in sample geometry and sample preparation. For example, if you used a 3g trigger force for a product with an irregular surface you would almost certainly get relatively extreme differences in the depth of penetration, based on how deep the surface irregularities were. If the surface irregularities were from peaks like those on whipped cream, you could negate the surface irregularity impact by using e.g. a 25g trigger force, so the light surface peaks would be ignored, and the penetration distance would start at a more consistent product surface, i.e. when the probe and product surface have full contact.
The sensitivity of the automatic trigger can also adjust for differences in probes. For example, if you used a 3g trigger with a 3mm cylinder probe the texture analyser may not detect the surface of a very soft gel until the probe is 4-5mm into the gel. Perhaps much better consistency between hard, soft and very soft gels could be attained by using a much lighter trigger force, or even a button test where the probe can be more precisely positioned over the sample by eye (or preset positions). Of course, using a different probe would also be suggested for gels.
Button tests are particularly good for testing the Firmness of e.g. pastes, doughs and other products where geometry is difficult to control. We also highly recommend a Button trigger type when using the Kramer Shear Cell and Ottawa Cell. These attachments are often used when testing products of differing heights such as compressing a portion of cereal flakes. In these instances you can program the probe to travel a fixed distance so that the product, whatever its original shape or height, is deformed to a consistent height or cut to a constant distance above the base. For example, if you calibrate a probe to 10.0mm over the base, and then use a button trigger with a Return to Start test to travel 9.0mm, you will always deform or cut the product to a 1mm distance from the base.
Q: What minimum trigger forces do you recommend?
A: When using an automatic trigger type our guide as to minimum trigger forces is: 5kg load cell – 0.5g 25kg load cell – 5g 50kg load cell – 7g The trigger force is extremely sensitive and could result in a false surface detection in 'vibration noisy' environments such as production floors or high-traffic R&D labs. In such locations we recommend a trigger force of at least 5g for 5kg load cells, and perhaps as high as 20g for 30kg and 50kg load cells. Choosing an optimum trigger force is a balance between one high enough to avoid triggering in the air during the downstroke and low enough to be sensitive to the true surface of your product. A short period of experimentation will help you find the right trigger for your product. It is difficult to recommend a perfect trigger force for each test as there are several variables to consider, namely, trigger force will depend on the size of the probe and/or product for testing, the Hardness of the product and the irregularity of the product surface. Other trigger force considerations are explained in a previous question and answer.
Q: When I receive a software upgrade, how can I find out what has changed between the new and last version?
A: When you install the software you are asked if you would like to view the notes file. This file contains a list of the changes made to each version. The file is called "updateinfo.rtf" and is installed into the application directory so you can view this at any time using Notepad.
Q: Data appears backward when displayed in distance. What happened?
A: Either the Distance Relative setting or the Inverted Graph option is incorrect.
There are two ways to change these settings:
a) Right-click on the units displayed on the graph axis. The options appear at the bottom of the pop-up list that appears. Click on an option to toggle the status.
b) Open the Graph Preferences (File > Preferences > User > Graph menu item, or press the F3 key). Change the options for the required data type.
Q: So many choices show up in the pop-up boxes which do not apply to my work. How can I hide those elements I don't wish to see?
A: The Plug-in Manager can be used to hide Test Parameters such as Product Height, etc., Axis types such as Pressure, etc., and Calculations such as Area, etc.
To run the Plug-in Manager, select from the Windows taskbar Start > Programs > Texture Exponent 32 > Plug In Manager. The folders can be expanded to show more folder / items. The items in the list are active when the is an tick in front of them. Click on the the tick to toggle the status. Items with a [Graph picture] represent axis types. Items with a [Sum picture] represent calculations. Items with a [abc picture] represent parameters. Items with [Binoculars picture] represent goto functions. Click on OK to save the changes and close the Plug-in Manager. Changes will take effect when you next start Exponent.
Q: When I start up I want to see a graph window, but all windows are closed. How do I control the initial screens that boot up when I start the program?
A: Create a Workspace. Also note that you do not need a graph window open to run a test, as the T.A. commands are always available and a new Graph window is automatically created when the test starts.
Q: How do I clear calculations I have made on a curve?
A: Use the Graph window's menu item Results > Clear for Current Graph or Clear for All Graphs.
Q: My various windows are floating around the screen. How do I put them back in place?
A: Double click the title bar of the window to re-dock it or drag it to the edge of the parent window to dock it on a specific side.
Q: How do I modify my toolbars?
A: You can drag toolbars to any location within Exponent and change the buttons that are on the toolbars. Use the menu command Tools > Customise Toolbars. Use the Toolbars tab to create new toolbars and specify global properties. Use the Commands tab to view specific commands and drag them to a toolbar.
Q: How do I access a Macro to edit it?
A: This can be done in one of three ways:
a) If the macro appears in the toolbar list box, you can select it in the list (so that the background is blue) and then press the Enter key.
b) From the Project panel's Macro tab, click on the macro to select it, then right-click to display the pop-up menu and select Edit.
c) Open the file using the File > Open menu command.
Q: What is a Workspace and why do I need one?
A: Workspaces save the layout and content of windows within Exponent. They are not compulsory so you can use them if you wish or just ignore them.
If you have any questions which you would like to ask us, please send us an e-mail and we will get back to you or post the answer on this page. Alternatively, please use the Technical Support Request form (link above).
Questions about product testing methods should be sent to firstname.lastname@example.org
Questions about the Texture Analyser or software should be sent to email@example.com.
Don’t worry if you are not sure which address to use as your question will be answered by either; it might just take a little longer.