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May 2010

DROPimage Calibration and Measure Distance Commands Revisited
This month we will be taking a look at two commands in our DROPimage software which are powerful and important but frequently overlooked. The calibration command is critical to ensuring that all distance and angular measurements relate to a known dimension. The measure distance command allows the user to easily determine the distance between any two points in the image window.

All three editions of our DROPimage software include the calibration command and all of our systems ship with a Precision Combo Calibration Device (p/n 100-27-31-U). This device includes a 4mm sphere which is positioned and focused in the center of the image window. The one minute video below shows how easy it is to calibrate DROPimage Advanced. If your email does not support video playback, simply go to this page and play the first video at the top of the page: http://www.ramehart.com/goniometers/diadv.htm.

The steps involved in calibrating DROPimage as shown in the video include:

1. Placing the calibration device on the stage.

2. Centering and focusing the ball in the center of the image window.

3. Starting the calibration command using the sphere method.

4. Setting the cursor position (vertical line through the center of the circle; horizontal line under the circle).

5. And then calibrating. The results reported include the vertical and horizontal pixel dimensions in µm (microns) and the aspect ratio which should be very close to 1.0000.

For detailed step-by-step instructions, please consult the how to guides located on our support page here: http://www.ramehart.com/goniometers/support.htm

If you are using DROPimage and you require a certified calibration device, we offer p/n 100-27-31-U which is a device that has been measured and is certified with traceability to NIST and ANSI standards. All of our calibration tools can be purchased directly or on our spare parts web store www.ramehartstore.com.

Once your system is calibrated, we recommend you check your calibration on a daily basis. This will ensure that no changes have occurred that will affect the precision of your system.

Now that your instrument is calibrated, you are ready to begin taking measurements. While our tools are built to measure contact angle, surface and interfacial tension, surface energy, advancing and receding contact angle, roll-off angle, contact angle hysteresis, and even advanced rheological properties, we have a very useful command for measuring distance. Whether you wish to accurately determine the outside dimension of a needle, the thickness of your substrate, or specific drop dimensions, this command plays an important role.

The one minute video below walks through the sequences involved in measuring the diameter of a pendant drop at its widest point using the DROPimage Advanced measure distance command. If your email does not support video playback, simply go to the following page on our website and play the last video on that page: http://www.ramehart.com/goniometers/diadv.htm



Note that DROPimage Standard also has a measure distance command. It's located on the View pull-down menu. If you're interested in watching any of our additional videos which walk through various contact angle, surface tension, interfacial tension, and oscillatory measurements, you can access them here: http://www.youtube.com/ramehart.

If you are DROPimage user and have any questions regarding the calibration and measure distance commands or any other aspect of the software, don't hesitate to let us know how we can be of further assistance.



Last month's newsletter generated an unusual number of responses from our faithful readers. Some of the comments have led us to make a few clarifications and corrections. The updated version of the newsletter can be found in our newsletter archive here: http://www.ramehart.com/goniometers/newsletters.htm. Here is summary of clarifications and corrections:

1. The first diagram showing Young's Equation has a short vector for surface energy and a long one for interfacial energy. Our intention was to show the force and direction only, not relative amplitude.

2. In the original text we also did not talk about 'gamma sl'. This was on purpose in order to keep things at a easy-to-follow level. We updated the paragraph after the surface tension graphic to include interfacial free energy.

3. In our discussion of the structure of the solid, we said there atoms at the surface which have "no neighbors". We meant to say they have no neighbors on one side which means overall they have fewer neighbors than atoms not at the surface.

4. In our original text, we made a reference to surface energy and work of adhesion as being the same thing. We corrected that statement. Likewise surface tension is not the same as work of cohesion.

Thank you all for your valuable comments and feedback and I hope you enjoy the amended archive version. 


Carl Clegg
Director of Sales
Phone 973-448-0305
Contact us