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Tuesday, March 31, 2015

Color: Converting Lab to L*a*b*

Last week a customer asked a simple question, "How do you convert from Lab color space to L*a*b*?"

I simply solved the equations for L,a and b for X,Y and Z. Then I plugged these values in to the equations for L*a*b*.  Keep in mind I used the equations for Illuminant C and 2° Observer. The equations would be different for different Illuminant/Observer conditions.

Monday, March 16, 2015

From the Testing Lab: Size of Aperture

When making optical measurements, there are different apertures used for measurement of samples.



DIRECTIONAL
DIFFUSE
Geometry
45° illumination     0° viewing
diffuse illumination    0° viewing
Brightness
T 452
ISO 2469, T 525
Color
T 524
ISO 5631, T 527
Aperture (viewing)
9 mm diameter
30 mm diameter
Viewed Area
63.6 mm²
706.9 mm²


The viewed area of the diffuse geometry is over 11 times the viewed area of the directional geometry. Therefore, the directional geometry will be more sensitive to small variations in paper or a handsheet. Most grades of machine-made paper are relatively uniform and satisfactory results can be obtained by making a few measurements at various points across the sheet and averaging the results, however, significant variations in brightness readings can be expected when using the directional brightness tester to measure pulp and other non-uniform materials.  The smaller measuring area results in much larger variation from reading to reading.

The main advantage of the diffuse geometry is that it averages non-uniformities in the sample and is, therefore, excellent for measuring pulp. However, the larger viewing area will not detect smaller variations when they exist and when they are important. In this case, the larger aperture can mask the actual variation in the sample.

In order to get better agreement in the measurements, one could make 11 measurements on the directional geometry for every 1 measurement on the diffuse geometry.  However, this may mask any true variation. In that case, the standard deviation from each device could be useful. The biggest problem here is that at most roll turn-ups only 1 measurement is made. If this is the case, the diffuse geometry will likely show an average value for the sheet and the directional geometry may show a higher, lower or similar value depending on where the measurement is made on the sample.

Thursday, March 12, 2015

Local Support in the Southeast US

We are pleased to introduce, Travis Lemon, as our new Southeast Service Technician.

Travis will provide field service and Preventative Maintenance activities as well as assist in installations and demonstrations of new Technidyne products.  He lives in this area and will be able to respond more quickly to customers.

Prior to joining Technidyne, Travis worked as a maintenance specialist with hospice medical and also in lift stations. Some duties included installation, start up, trouble shooting, and maintenance.

Travis has 8 years (and counting) as a member of the South Carolina Guard as an automated logistics specialist. He was deployed to Afghanistan for one tour.  He has an associates degree from Aiken Technical College in Electronics Engineering.  He is continuing his education as he pursues a bachelor's degree from DeVry in Electronics Engineering.

Travis will be the primary service contact for Technidyne customers in: NC, SC, GA, FL.

Monday, March 9, 2015

From the Testing Lab: Brightness

A question recently came from a customer: When we talk about color we have to specify an Illuminant. Why don't we have to specify an Illuminant when we talk about brightness?

Think about the sequence of a color measurement using a spectrophotometer:
1) An emitter with a specified UV Level shines on the sample.
2) The reflected light is then split into its components across the spectrum.
3) This reflectance spectrum is then multiplied by appropriate CIE tristimulus functions (red, green and blue) corresponding to the desired Illuminant/Observer condition.
4) The resulting x, y. z values can be converted into any color system, typically L*a*b*.

Think about the sequence of a brightness measurement using a spectrophotometer:
1) An emitter with a specified UV Level shines on the sample.
2) The reflected light is then split into its components across the spectrum.
3) This reflectance spectrum is then multiplied by the brightness function from 400-500 nm.
In the brightness measurement sequence, the brightness function takes the place of the CIE tristimulus functions in the color sequence.  Brightness is the reflectance of blue light under a certain UV Level condition. Color is how does this sample looks under a certain UV Level condition compared to the average Observer in 1931 (2°) or 1964 (10°) as if it were under a certain Illuminant condition (C, D65, A, FL2, etc.)

Let me know if this explanation makes sense. Contact me, Todd Popson.

Thursday, March 5, 2015

Visiting New Zealand


February 12-15, 2015, Paul Crawford (Business Director - Asia) and I visited our agent in New Zealand, Contract Instrumentation Services Ltd.  CIS was established in 1997. It is a privately owned company, that can supply, install, service and calibrate a wide range of industrial instruments to measure and control most process parameters such as temperature, pressure , level flow, pH, conductivity and density along with many others.  They have many years of plant and process experience in industries as diverse as Food and Beverage, Brewing, Dairy, Pulp and Paper, Petrochem, Water and Waste and Power Generation.

Lance Miller and Ian Mercer of CIS
Partners Lance Miller and Ian Mercer met with us to discuss activities in the market.  We discussed Technidyne's new products the Color Touch X™ and TEST/Plus™.  Lance, Paul and I also made customer visits to several paper and packaging companies throughout New Zealand. The relationship allows customers in New Zealand to use the latest technology in the Paper Industry with extremely good, local technical support and service.

Thanks to the people of CIS for their continued good work, hospitality and professionalism.

Monday, March 2, 2015

Paper Roughness (Smoothness) and Formation

Formation:
There is an interrelationship among roughness, porosity, and optical formation measurements. Those regions that are calendered the heaviest will be smoother, denser, and will have lower opacity than the adjacent regions that are calendered lightly. Local variations in opacity will show up as having poor formation on optical formation testers. A rough surface will absorb more ink, and that same rough surface will be more porous, as it received less calendering action. The more porous region will also absorb more ink into its interstices. When printers correlate poor printing with poor formation, perhaps it is the roughness and porosity variations that are the culprits, and the formation tester is one additional piece of test equipment that verifies the root of the problem. These formation problems
occur on a small scale, smaller than what a basis weight process control system will discriminate. Formation problems are perhaps quite detectable by analyzing the standard deviation of porosity and roughness measurements within a small region. The roughness and porosity variations caused by fiber flocs are much smaller than the test area of either the roughness or porosity measuring heads. There can be other reasons for high standard deviations, such as non-uniform sizing, which may also be caused by the localized absorbency properties in the region of fiber flocs.

Related posts include information on the relationship between paper roughness (smoothness) and the following items:
  • Papermaking Process
  • Printing processes
  • Formation
  • Parker Print Surf Test
  • Sheffield Test
  • Applications