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Bubble pressure tensiometer:
Is there a specific immersion depth at which to measure surface tension? 		No, one advantage of the SITA bubble pressure tensiometer is the independence of measurements from the immersion depth. Also, switching between samples is much easier with this feature. The density of the liquid being measured (often unknown) does not have to be determined or entered prior to measuring.
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Do we need a computer for measuring?

No, the hand-held devices work independently. All measured quantities, such as surface tension, temperature, bubble lifetime (equals surface age) will be measured automatically and, depending on the type of device, it will also be stored within the device.
The available Windows Software additionally allows:
- comfortable adjusting and controlling with standard Windows elements,
- easy data analysis, editing and printing of all measurements, and
- saving of measurements in common file formats.

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Why do we need a bubble pressure tensiometer? The SITA bubble pressure tensiometers permit an uncomplicated measurement of the dynamic surface tension even from a small sample. A wide range of adjustable bubble lifetimes (surface age) allows a survey of the kinetic characteristics of surface active components in the liquid. The interface (air/sample), which is crucial for measuring, does not have to be cleaned after reading because with every new bubble the interface is freshly created.
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What experience do I need in order to use a SITA Tensiometer?

None. While developing the instruments we attached importance to easy operation. Special training is not necessary.
-Online measuring (permanent measurement at a constant surface age) and
-Auto-measuring (measurement with an automatically increasing surface age)
start with one key-press. Complicated parameter settings are not necessary. Naturally, as for every measurement, one needs a minimum of knowledge, experience and care for solving the measuring problem.

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How does one clean the capillary? To clean the capillary use the Clean-Mode which is activated by pressing the "clean" button. In this mode a maximum air flow goes through the capillary, thereby removing particles which may have attached to the capillary during use. For better cleaning results, we recommend immersing the tip of the capillary into an ultra-sonic cleaning bath. Please do avoid submerging the whole capillary. The time the capillary needs to remain in the cleaning bath depends on how dirty it is.
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Does the capillary data need to be given? No. After changing the capillary, simply calibrate it in water and the instrument is ready to measure.
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How long does one measurement take including the initialization? With the SITA pro line t15:
 
1. Measured Value (with initialization):
 ca. 25s
All following measured values: max. 2s (depending on the bubble lifetime)
With the SITA science line t60:  
1. Measured Value (with Initialization): ca. 1min
All following measured values: According to the bubble lifetime 0,5s (40ms bubble lifetime) up to 10min max. (60s bubble lifetime)
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What material is the capillary made from? The capillary consists of the material PEEK™, a heavy-duty polymer by Victrex plc. PEEK™ has a high level of thermo-resistance, as well as a good resistance against the effects of highly concentrated alkali and non-oxidized acids. PEEK™ has superb hydrolysis resistance against boiling water and its resistance against solvents is, as well, excellent.
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How does one set the bubble lifetime?

With the SITA pro line t15 the bubble lifetime is set as follows:
- In Online-Mode by pressing the left softkey, a menue opens and you can easy set the bubble lifetime with the arrow keys
- In Auto-Mode the instrument automatically sweeps through all bubble lifetimes from 15 ms up to 15 s.

With the SITA science line t60 the bubble lifetime is set as follows:
- In Online-Mode: under the menu item "tlife".
- In Auto-Mode: choose bubble lifetime as the driving variable by setting the "start" value "stop" value and the increase "factor". - In the Software "SITA-online": under the menu item "device" à Settings à the bubble lifetime can be set either in Online-Mode or Auto-Mode.

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Can the surface tension be plotted over the temperature or the bubble lifetime with the Software "SITA-online"? Yes. The surface tension can be plotted over the menu point x-Axis over temperature or over the bubble lifetime. Note: Likewise, the surface tension is plotted over the measured values, as well as over the bubble lifetime.
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Can liquids with a higher viscosity also be measured? Yes. However, after a specific level of viscosity the measurement results will be distorted due to the influence of viscosity. This effect is low for a long bubble lifetime. For short bubble lifetimes, however, the effect can result in a measurement. The influence of viscosity can be corrected manually with compensation tables.
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How long can the tensiometer work on batteries? SITA pro line t15: ca. 8 hours
SITA science line t60: ca. 2 hours
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Do all measured values get lost at the beginning of a new measurement? SITA pro line t15 and SITA science line t60: No. All measured values are permanently saved.
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How many measured values can the SITA science line t60 save? More than 2000 Measured values
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How is the tensiometer calibrated? To calibrate the tensiometer, immerse the capillary in fresh water (mineral water, distilled water or tap water) and press the "calibrate" button.
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Can I export the measured data in Excel? Yes. You can export measured data from the program "SITA-online" in the form of a TXT-file, and then import the file into Excel. Further work with the data can now be done in Excel.
Procedure:
"SITA-online":
a)Menu item file à export... or
b)automatically save TXT-files with options à Program...: click on automatic export (from these options the regular DAT-file is produced as well as an additional TXT-file).
Excel: file à open...à file type= choose and open a text file. Alternatively, you can also proceed as follows: Select the TXT-file in Windows Explorer and drop it onto the Excel icon using the left mouse button.
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Can the measurement diagrams be connected to a presentation program? Yes. In "SITA-online" you can copy the measurement diagrams to the Windows Clipboard by selecting the key combination ALT + Print. From here the copied diagram can be imported into presentation programs such as Winword, MS Power Point, Corel Draw, etc. by selecting the "Paste" (STR+V) command.
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Are the measurement results of the bubble pressure tensiometer comparable to the measurement results of the Du Noüy method of measurement? Actually, no. The Du Noüy method of measuring is a static method, whereas the bubble pressure method, owing to the finite bubble lifetimes, is a dynamic method of measuring. The longer the bubble lifetime is the more the measured value of the dynamic method approaches the value of the static method. For that reason, this is also called measuring in the semi-static range. The bubble lifetime at which the semi-static range is reached depends on the surfactant being tested and can go beyond a bubble lifetime of 60s.



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