8 Calibration and Adjustment
8.4.5 Adapting and creating calibration methods
The calibration methods supplied with the STAReSoftware en-able you to adjust your STARe module to a high degree of ac-curacy. If you want the best possible accuracy, you can adjust your STARe module with methods adapted from existing meth-ods or methmeth-ods that you create yourself.
The following shows you how to adapt existing calibration methods and to create new calibration methods.
To adapt an existing calibration method:
(1) Open a method window.
(2) Choose File/Open...
A list with all the methods stored appears.
display calibration methods (3) To find calibration methods more quickly: click the Filter button and then select the Only calibration methods func-tion. Click OK.
A list with all the calibration methods appears.
(4) Click the desired adjustment method.
The adjustment method selected is displayed in the Method Win-dow.
(5) Make the necessary changes to the method. Edit the ad-justment method just like a normal method and pay at-tention to the following instructions and notes:
heating and cooling rates in the
method Make sure that your module is able to achieve the de-fined heating and cooling rates. If need be, adapt the rates accordingly.
crucible type in the method If you are not using the standard crucibles, change the type of crucible in the method as appropriate.
crucibles of large thermal inertia When using crucibles of large mass and/or poor ther-mal conductivity, expand the temperature range of the heating and cooling segments to take the larger ther-mal inertia of such crucibles into account.
temperature range of your
measurement Choose reference substances whose melting points correspond to the temperature range of your mea-surement (otherwise the results would be less accu-rate due to extrapolation).
measurement accuracy
♣ To obtain the best possible accuracy, you should adjust the mod-ule for each of its specific measurement combinations before per-forming the measurement. If you do not perform an adjustment, the STAReSoftware calculates adjustment data for a non-adjust-ed measurement combination on the basis of the standard ad-justment data and factors stored in the database. You do not, however, achieve the same degree of measurement accuracy that you would if you performed specific adjustment beforehand.
method name
(6) Click File/Save as... and enter the name of the method with the following information in the Name box:
• Module type (DSC, TGA, TMA, DMA etc.)
• Type of calibration: tau lag, temperature, heat flow, sample holder or total
multiple / single
• Multiple (multiple) or single sample crucible (single)
• Calibration substance (e.g. In or Zn) (7) Click OK to store your method.
Example:
– The method name for a DSC method: DSC Heat Flow Single Sn
You have now adapted an calibration method to your requirements and stored it.
To create a new calibration method:
(1) Open a method window.
(2) Choose File/Open..., to open a new method.
A new empty method appears in the method window.
(3) Choose Miscellaneous/Calib/Adjust.
The Calibration dialog window appears.
temperature range of your measurement
(4) Mark the reference substance you want to use for your calibration so that their melting points cover the temper-ature range of your measurement (otherwise the results would be less accurate due to extrapolation).
selecting several substances at the same time
♣ You can select several reference substances at the same time by holding down the CTRL key and marking the desired substances with the mouse.
Type button
(5) Click the Type button to define the type of adjustment method.
A drop-down list with the types of calibration methods appears.
♣ The definition of the type results in macros being attached to your method. These macros automatically evaluate the measured val-ues and produce displays corresponding to the type of calibra-tion. It is only at this stage that the method becomes an actual calibration method. The None type corresponds to an ordinary method without any attached macros.
(6) Mark the desired type of calibration method and click OK.
(7) Define the temperature program for your calibration. Pay attention to the following instructions and notes:
start and end temperature
of the heating segment Set the start temperature of your heating segment to the expected value of the melting temperature of the substance less about five times the numerical value of the temperature in the heating rate (in K/min).
Set the end temperature of your heating segment to the expected value of the melting temperature plus about twice the numerical value of the temperature in the heating rate (in K/min).
reference points for the
calibration Use only first order transition points as reference points for the calibration. The melting peaks of high
Example:
– Gallium (29.8 °C): 25 °C to 32 °C at 1 K/min Benzoic acid (122.4 °C): 100 °C to 135 °C at 5 K/min
With a tau lag adjustment method: define an additional heating and cooling segment before the segments of the actual calibration. Use at least two different heat-ing rates for the calibration measurement (e.g. 2 and 5 K/min).
premelting the sample
♣ Heat transfer to the sample is usually greatly improved by melting and recrystallizing the sample beforehand. A slightly lower onset temperature is obtained.
heating and cooling rates in the method
Make sure that your module is able to achieve the de-fined heating and cooling rates. If need be, adapt the rates accordingly.
crucibles of high thermal inertia
When using crucibles of large mass and/or poor ther-mal conductivity, expand the temperature range of the heating and cooling segments to take the larger ther-mal inertia of such crucibles into account.
measurement accuracy
♣ To obtain the best possible accuracy, you should adjust the mod-ule for each of its specific measurement combinations before per-forming the measurement. If you do not perform an adjustment, the STAReSoftware calculates adjustment data for a non-adjust-ed measurement combination on the basis of the standard ad-justment data and factors stored in the database. You do not, however, achieve the same degree of measurement accuracy that you would if you performed specific adjustment beforehand.
method names
(8) Choose File/Save as... and enter the name of the method with the following information in the Name box:
• Type of module (DSC, TGA, TMA, DMA etc.)
• Type of calibration: tau lag, temperature, heat flow, sample holder or total
multiple / single
• Multiple (multiple) or single sample crucible (single)
• Calibration substance (e.g. In or Zn) (9) Click OK to store your method.
Example:
– The method name for a DSC method: DSC Heat Flow Single Sn You have now created and stored a new method.