马尔文常见问题介绍.docVIP

Alignment: Why does my instrument sometimes take a long time to align? The optical path of the instrument needs to be clear of contamination. If alignment is lengthy, this is usually due to dirt on the cells windows or the instrument lenses. The contamination diffuses the laser beam and makes it difficult for the alignment detectors to work properly. Therefore cleaning the cell windows, as described in the manual, will often cure this problem. Background: What is a good diffraction background? A good background should have a peak in detector 1 of less than 150 scattering units, and slope away in an exponential manner to less than 20 units at detector 20. Calibration: How do I calibrate a Malvern Instruments laser diffraction system? You don’t need to; laser diffraction is based upon fundamental scientific principles. Instrument performance however, can be verified using NIST traceable latex standards, or Malvern Instruments Quality Assurance Standards (QAS). Cell windows: Why are bubbles sticking to the windows of my wet cell? Dissolved air is gassing out of your dispersant due to thermal gradients between room and water. The water must attain room temperature by using a header tank, leaving the tank in the room before measurement or reducing the water pressure into the unit. Try cleaning the cell windows as bubbles may be adhering to dirt on the window surface. Ultrasonics can also be used to remove dissolved gas from the water. Data: What is the Span value? The Span value is a dimensionless number indicating the width of the particle size distribution, calculated by: Span= (D90-D10/D50), and is independent of the median size. Distribution: Will the distribution obtained from a Sedigraph, be different to that obtained from diffraction? As diffraction is based upon the volume of the equivalent sphere, then unless the particles are perfectly spherical, there will be differences dependent upon the shape of the particle. For example, disc shaped particles such as clay